As an important tectonic unit of Eastern Tethyan tectonic domain, Sanjiang orogenic belt started from the expansion, subduction, subtraction and closure of the Paleozoic Paleo-Tethys Ocean, went through the opening and closure of the Neo-Tethys Ocean and the subduction and collision process of the Indian continent and ended in the Himalayan comprehensive intracontinental convergence and uplift orogeny, forming a giant composite orogenic belt composed of several island arc collision orogenic belts and several stable blocks. With the wide range of orogeny, huge uplift amplitude, strong magmatic activity and intense mineralization, it ranks first in the global orogenic belt. The Sanjiang orogenic belt is also an important part of Tethys metallogenic domain, which is comparable to the Andean metallogenic belt in South America for its huge metal reserves, concentrated and large ore deposits, diverse ore deposit types, complex mineralization and huge prospective scale. There are not only a number of world-famous large and super-large ore deposits, such as Yulong copper deposit, Gacun polymetallic deposit, Jinding lead–zinc deposit, Ailaoshan gold deposit and Tengchong tin deposit, but also a number of new large and super-large ore deposits, such as Pulang copper deposit, Beiya gold deposit, Baiyangping silver polymetallic deposit, Xiasai silver deposit, Gala gold deposit, Yangla copper deposit, Dapingzhang copper polymetallic deposit, Nongduke gold-silver deposit, Duocaima lead–zinc deposit, Duri lead–zinc deposit, Hetaoping copper polymetallic deposit and Luziyuan lead–zinc polymetallic deposit.

The anatomy and metallogenic regularity of typical deposits in the Sanjiang orogenic belt have undergone several rounds of scientific and technological research, and important progress has been made. There are also multi-perspective studies on the summary of the metallogenic regularity of Sanjiang. Ye (1993) summarized the regional metallogenic regularity of the Sanjiang orogenic belt from the concept of metallogenic series and identified 19 metallogenic series of ore deposits; Li et al. (1999) extended the concept of metallogenic series, emphasizing that it is strictly controlled by the process of mountain-to-basin, basin-to-mountain and mountain-controlled basin in orogenic belt, and divided the Sanjiang mineralization into three structural metallogenic series and ten metallogenic series; Hou and Li (1999) systematically analyzed the mineralization of the Sanjiang orogenic belt from a new perspective of plume tectonics and proposed that the formation and evolution of the Sanjiang orogenic belt were restricted by plume tectonics, and the mineralization was composed of hot plume metallogenic giant system and cold plume metallogenic giant system. Based on the data obtained from multiple rounds of scientific and technological research, this chapter will explain the metallogenic characteristics of the Sanjiang orogenic belt and the temporal and spatial distribution of ore deposits under the guidance of the concepts of archipelagic arc-basin metallogenic theory and intracontinental tectonic transition metallogenic theory.

4.1 Metallogenic Event of Archipelagic Arc-Basin-Block System

It has been mentioned that the Sanjiang Tethys giant orogenic belt is an archipelagic arc-basin-(continent) block system formed by the shrinking and subduction of the Tethys Ocean in different periods of Phanerozoic and has been assembled through the combination of archipelagic arc collision orogeny. Along with the archipelagic arc-basin-block phylogeny from the Paleozoic to Triassic, multi-episodic metallogenic event sequence occurred, showing regular metallogenic spatial structure characteristics.

4.1.1 Paleozoic Metallogenic Events

The Paleozoic metallogenic events mainly occurred in two peak periods, namely, the intersection of early Paleozoic Є/O and Є/P. The former one developed in the interior and edge of the stable landmass at the initial stage of the formation of the MABT, while the latter one developed in the continental margin rift-ocean basin and the volcanic-magmatic arc formed by the subduction and closure of the MABT at its peak.

4.1.1.1 Early Paleozoic Є/O Metallogenic Period

The mineralization mainly develops on the passive margins of the Zhongza block and Baoshan block on the east and west sides of the Qamdo-Pu’er block, mainly forming exhalative sedimentary lead–zinc deposits, which occurred in the Early Paleozoic marine carbonate rocks. The metallogenic age ranges from 426 to 655 Ma (Liu et al. 1993a, b). Representative ore deposits include Luziyuan lead–zinc deposit (Є3), Mengxing lead–zinc deposit (O1), Hetaoping lead–zinc deposit on Baoshan Block and Najiao System lead–zinc deposit on Zhongza Block. Most of these deposits have undergone the transformation of tectonic–magmatic metallogenic events in the later period. The ore deposits in this metallogenic period are mainly lead–zinc mineralization and the superposition of copper and iron mineralization in the later period, so the ore deposits are large in scale. In recent years, new ore deposits have been discovered continuously in this area, showing great potential.

4.1.1.2 Late Paleozoic C/P Metallogenic Period

The mineralization mainly develops in three important metallogenic environments. The first is the Changning-Menglian ocean basin environment, in which Tongchangjie copper deposit related to Permian oceanic ridge basalt series (with Cyprus-type ore deposit characteristics) and Laochang Pb–Zn–Ag polymetallic deposit related to alkaline intermediate-basic volcanic rock are produced, showing the characteristics of volcanic-associated massive sulfide deposit (Yang et al. 1992). The second is the Late Permian volcanic arc environment generated by the eastward subduction of the Lancang River ocean basin, mainly producing massive sulfide copper deposits related to the Late Permian marine intermediate-acid volcanic rock series and volcanic-sedimentary iron deposits related to marine basic volcanic rock series. The former is represented by the Sandashan copper deposit, and the latter is represented by the Manyang Fe deposit. The third is the intra-oceanic arc environment produced by the westward subduction of Jinsha River ocean basin, in which volcanic-associated massive sulfide deposit related to Permian arc volcanic rock series is produced, represented by Yangla copper deposit. In general, the metallogenic period is dominated by Cu, Pb and Zn mineralization, followed by Fe mineralization. Volcanogenic massive sulfide deposits are the main types of deposits, which are large in overall scale and rich in prospects. The basic-ultrabasic rock masses of Jinggu Banpo, Jinghong Nanlin Mountain, etc., recently measured in the Lancang River volcanic-magmatic belt are formed in the middle and late Permian (258–292 Ma, Lehman 2007), which may also be related to the basic eruption of the mantle series at the same time as the Emeishan basalt eruption. Pyrite, pyrrhotite and other sulfide mineralization are widely developed in the rock mass, which is an important target area for finding copper-nickel-platinum-palladium deposits in Yunnan except the Jinsha River-Ailaoshan belt.

4.1.2 Late Triassic Metallogenic Events

The Late Triassic became one of the most important metallogenic periods in the Sanjiang orogenic belt. The deposits were mainly formed in the closed period of the development of MABT. During this period, some arc-basin systems continued to develop (such as the Yidun arc), and most arc-basin systems entered the post-collision and extension stage. Therefore, there are at least three types of metallogenic environments in the Late Triassic: arc-basin environment, superimposed volcano-rift basin environment, and rift basin environment inside the block.

4.1.2.1 Metallogenic Events in the Yidun Island Arc Orogenic Belt

The mineralization of the Yidun Island Arc Orogenic Belt occurred mainly with the Indosinian subduction orogeny, and the deposits were mainly produced in the volcanic-magmatic arc and back-arc extension basins of the island arc orogenic belt, respectively forming two important metallogenic belts with different deposit types and metal associations (Fig. 4.1).

Fig. 4.1
figure 1

Distribution of mineral deposits in the Yidun island arc orogenic belt

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The copper polymetallic metallogenesis related to arc volcanic rocks develops along the volcanic-magmatic arcs, starting from Zengke in the north and reaching Shangri-La in the south, and is divided into two metallogenic sub-belts in the north and south. The deposits in the north sub-belt are concentrated in the Changtai Arc and are mainly volcanic-associated massive sulfide deposit (VMS) related to submarine volcanic exhalation. The ore deposits in south sub-belt are concentrated in Shangri-La arc, mainly include porphyry and skarn deposits.

At present, a super-large ore deposit (Gacun), a medium-sized ore deposit (Gayiqiong) and a series of small ore deposits and ore occurrences have been discovered in the sub-belt of massive sulfide deposits.

They occurred in the Late Triassic intra-arc rift belt of Changtai arc, and their metallogenic tectonic environment is similar to that of the Okinawa Trough Back-arc-Basin (Letouzey and Kimura 1986) and Miocene back-arc-basin of Japan (Cathles et al. 1983). Among the intra-arc rift belts, the most typical rift basins are Changtai and Zengke fault basins, where typical bimodal rock assemblages and limited basin facies deposits are developed, with a water depth of about 800–1200 m (Hou et al. 2001a, b). Almost all massive sulfide deposits occur in confined or depressed basins within fault basins (Hou and Mo 1990; Xu an Fu 1993; Hou et al. 1995). The Re-Os age of the sulfide in the Gacun deposit is (217 ± 12) Ma (Hou et al. 2003a, b), and the K–Ar age of the altered surrounding rock of the Gayiqiong deposit is 210–221 Ma (Hou et al. 1995), that is, the mineralization time of the two deposits is basically the same.

In the porphyry-type polymetallic sub-belt, a super-large porphyry-type deposit, a large-scale porphyry-type deposit, a large-scale skarn polymetallic deposit and a series of small and medium-sized deposits have been discovered. The volcanic rocks in the belt belong to calc-alkalic basaltic andesite andesite-andesite-dacite series, the intrusive rocks are mainly a series of ultrahypabyssal porphyry and porphyrite homologous to volcanic rocks and the rock assemblage is diorite porphyrite-quartz dioritic porphyrite-monzonite porphyry-quartz monzonite porphyry-granite porphyry. Porphyry (porphyrite) occurs in groups of small stocks, bosses and dikes, controlled by NNW-striking fracture zone, intrudes into volcanic-sedimentary rock series and forms east–west belt. The diagenetic ages of the western belt are 235 Ma (Tan et al. 1991) and 249 Ma (Zeng et al. 2003, 2004); the diagenetic ages of the eastern belt range from 214 to 216 Ma (Zeng et al. 2000, 2003). The metallogenic age of the western belt is 224.6 Ma (Tan 1985), and the metallogenic age of the eastern belt is 213–216 Ma (Li et al. 2007). There are Xuejiping large porphyry copper deposit and Chundu porphyry copper deposit in the west, Pulang super-large porphyry copper deposit and Hongshan large porphyry-skarn copper deposit in the east. The deposit is located in a relatively concentrated porphyry (porphyrite) group complex and where several groups of structures are interlaced.

The epithermal Au–Ag–Hg metallogenic belt related to volcanic rocks is mainly developed in the back-arc-basin of Changtai arc. The mineralization is related to the “bimodal” (shoshonite-rhyolite) volcanic activity in the late Triassic back arc expansion period. The ore-bearing rock series is a high-potassium rhyolitic volcanic series, with an Rb–Sr isochron age of 213 Ma (Hu et al. 1992). The representative deposits are Kongma temple large mercury deposit and Nongduke medium gold-silver deposit. The deposit of Kongma temple is located at the northern end of volcanic zone in back-arc-basin. The volcanic rock belongs to the Miange Formation in Upper Triassic (T3m). The deposit is produced in the ultra-acidic rhyolite in the middle section of Miange Formation, with its mineralization controlled by shear fracture zone in near north–south direction. The surrounding rock alteration is dominated by strong silicification, followed by sericitization and clayization. The ore body consists of altered rhyolitic clastic rocks in the fracture zone. The mineralized rock is rhyolite with breccia-like and porous structure and strong silicification-sericitization. Its occurrence is consistent with the surrounding rock. The ore belt is 8–27 km long and consists of more than ten lenticular ore bodies. The metal minerals are mainly cinnabar, with a small amount of pyrite, galena, sphalerite, orpiment and livingstoneite. The Nongduke deposit is located in the middle of the volcanic rock belt in the back-arc-basin (Qu et al. 2001). The mineralized acid volcanic rock series of the Miange Formation in Upper Triassic is rich in tuff and is characterized by high silicon content. In addition to native gold, there are antimonite, ramdohrite, silver-tenantite and so on. The ore-forming process includes two stages: the pre-enrichment of ore-forming elements in volcanic rocks and post-enrichment of magmatic hydrothermal reformation (Qu et al. 2001).

4.1.2.2 Metallogenic Events of Jinsha River Arc-Basin System

In the Jiangda-Weixi continental margin arc, a volcano-rift basin was formed by the late Triassic collision and extension, which was superimposed on the Permian epicontinental arc terrain. The metallogenic events represented by the VMS deposit were mainly developed in the superimposed volcano-rift basin on the continental margin arc, becoming an important polymetallic ore belt (Fig. 4.2).

Fig. 4.2
figure 2

Schematic diagram of Jinsha River Arc-Basin System structure-magma-mineralization. 1—granite (γ4-5); 2—sandstone sedimentary area (J-K); 3—clastic rock sedimentary area (T3); 4—intermediate-acid volcanic rock belt in continental marginal arc (T1-2); 5—Jiangda-Deqin-Weixi volcanic rock belt of superimposed rift basin (T2-T3); 6—Adenge-Nanzuo continental marginal arc intermediate-basic volcanic rock belt (P1-P2); 7—Jubalong-Benzilan basic volcanic rock belt in the intra-oceanic arc (P12-P2); 8—Deqin-Shimianchang tectonic melange belt; 9—Jinsha River tectonic melange belt; 10—Qingnidong-Haitong thrust zone; 11—Qamdo-Lanping landmass; 12—Zhongza-Shangri-La landmass; 13—Ore deposit (occurrence) and its number

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In the volcano-rift basin in the southern segment of the continental marginal arc, the filled volcano sequence of sedimentary rock is composed of at least ten volcano-sedimentary cycles. The lower cycle is dominated by the basalt series, with thick basalt alternating with thin sand-slate and siliceous rocks; the middle cycle is composed of basalt in the lower part, calcareous siltstone in the middle part and limestone and thick rhyolite in the upper part; the upper cycle consists of siliceous slate and turbidite in the lower part and rhyolite series in the upper part. The volcanic activity shows a typical “bimodal” feature. At the top, it is a sequence of littoral-neritic clastic rock formations with molasse properties, intercalated with neutral-intermediate-acid volcanic rocks and pyroclastic rocks. In the Luchun deposit, its ore-bearing rock series can be divided into four volcanic-sedimentary rhythm units, with its lithofacies characteristics reflecting the development process of the extensional rift basin from tension fracture to fault depression to atrophy, as well as the evolution process of paleosedimentary environment of basin water body from shallow to deep and then to shallow again. In the “bimodal” volcanic rocks, subabyssal facies tuffaceous turbidite and sandy argillaceous flysch formations, there is volcanic-associated massive sulfide deposit. The Rb–Sr age of the ore-bearing rhyolite is 224–238.9 Ma (Wang et al. 1999), and the Rb–Sr age of the regional rhyolite with equivalent horizon is (235 ± 7) Ma (Mu et al. 2000). VMS deposits are controlled by horizon strictly, occur mostly in layered or stratoid form and coexist closely with lamellar siliceous rocks and ribbon limestone. Luchun copper polymetallic deposit is the most typical deposit (ore deposit ③ in Fig. 5.2). However, there is no essential difference between the submarine hydrothermal fluid activity and sulfide sedimentary environment and the intra-arc rift environment produced by black ore-type minerals. Both types of rift basins provide the following important mineralization conditions, including magma system driving convective circulation of submarine hydrothermal fluid, volcanic rock series producing ore-forming materials, fault system transporting fluid migration and drainage and fault depression environment accumulating fluid and ore-forming materials. The upper cycle is composed of clastic rocks, intermediate-acid volcanic rocks and gypsum-salt formation with littoral-neritic molasse, and the sedimentary facies characteristics reflect the evolution history of rift basin with gradual shrinkage and shallow-water body. Among them, the Chugezha silver-rich siderite deposit is produced in the intermediate-acid volcanic rock series. The ore bodies are disseminated, vein, reticulated and lenticular, which are strictly formed in stratiform-stratiform-like siderite beds and closely associated with barite siliceous rocks.

The sequence of sedimentary assemblages in the upper superimposed basin of the northern segment of the Jiangda-Weixi continental margin arc is generally consistent with that of the southern segment. The basin is filled with Upper Triassic sediments, with a sequence of red siliceous conglomerate molasses generally developed at its bottom, reflecting that the basin was formed in the extensional environment after the collision orogeny. The lower sequence is composed of fluvial-lacustrine facies clastic rocks and neritic limestone, which evolved into flysch turbidite formation composed of deep-water facies sand-slate series. Pillow-shaped basic lava and its clastic rocks are widely developed in some sections. Granite porphyry is commonly emplaced near the crater, showing a similar “bimodal” combination feature, which can be stratigraphically compared with the “bimodal” volcano-sedimentary sequence in the lower part of the Luchun-Hongpo basin; in this horizon, VMS deposit (Deposit ⑧ in Fig. 4.2) is typical of Zuna lead–zinc deposit. The ore-bearing rock series consists of carbonate rock, sandstone interbedded with barite layer and siliceous rock/hematite/barite interlayers with stripes or bands, showing the geological features of exhalative-sedimentary mineralization. The upper sequence consists of littoral-neritic red-gray clastic rock and thin-layered limestone, with intermediate-basic and intermediate-acid volcanic rocks widely distributed. The volcanic rock assemblage is mainly andesite-dacite-rhyolite of potassium calc-alkaline series, which can be compared with the ore-bearing horizon of the gold-bearing and silver-rich siderite deposit in Chugezha. In this horizon, there are VMS deposits represented by Zhaokalong and Dingqinnong silver polymetallic deposits. The ore-bearing rock series in Zhaokalong area is composed of thick stratiform microcrystalline limestone in the lower part, middle gray intermediate-acid pyroclastic rocks and gray sand-slate, upper dark purple neutral volcanic rocks and medium-thin sandstone and sand-slate. The direct host rocks mainly consist of clastic rock series composed of sandstone, siltstone, slate and tuff and exhalative sedimentary rock series composed of dolomite and siderite deposit. The metal sulfides are mainly veined, reticulated, densely disseminated and strictly produced in the siderite deposit. The ore-bearing rock series in the Dingqinnong mining area consists of lower gray intermediate-acid volcanic clastic rocks and strongly altered siliceous layers, middle gray-white giant thick marble and upper acidic volcanic tuff. The ore-hosting rocks are mainly strong silicified rocks and acidic volcanic rock, and the ore body is produced between the middle and lower parts in layered and stratoid form and folded in the same shape as the surrounding rock strata.

4.1.2.3 Metallogenic Events of the Southern Lancang River Arc-Basin System

In bimodal assemblage rock series of shoshonite-rhyolite in the superimposed basin of Zuogong-Jinghong continental margin arc, a large number of ore occurrences and mineralization sites have been discovered, especially Dapingzhang copper deposit, which was thought to have formed in Carboniferous. The recent ore-bearing rock series and metallogenic age dating results show that it may have formed earlier in the middle and late Silurian, which is a typical VMS deposit. See Fig. 4.3 for the distribution of main deposit deposits in this belt.

Fig. 4.3
figure 3

Main deposits’ (points) distribution map in the southern section of Jinggu-Jinghong metallogenic belt

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4.1.2.4 Lanping Basin

The late Triassic intracontinental rift evolution stage is one of the important metallogenic periods in Lanping Basin. Rift-rift basins and mineralization are constrained by the large-scale delamination of the lithosphere in the Late Triassic. At this stage, the lower crust was greatly delaminated, the hot mantle material upwelled in large quantities and the large basin extended, forming a central axis fault and a series of small contemporaneous faults. Driven by the upwelling source, the hydrothermal fluid migrated vertically along the contemporaneous fault, and intense hydrothermal activity occurred along the syngenetic fault zone, forming hydrothermal sedimentary siliceous rocks and hydrothermal sedimentary polymetallic ore bodies or mineralized bodies, which are scattered in the quantity of up to more than 100. Among them, there are two large-scale silver deposits and three medium-sized copper–silver polymetallic deposits, represented, respectively, by Heishan-Huishan silver lead–zinc deposit, Yanzidong silver–copper–lead–zinc deposit, Xiawu District-Dongzhiyan silver-copper deposit and Dongzhiyan-Hexi strontium deposit. The deposit is produced in the Upper Triassic Sanhedong Formation, and the ore-bearing rock series is mainly composed of siliceous rock, fine-grained layered crystalline dolomite and dolomitic limestone, showing the characteristics of hydrothermal sedimentation. Most of the ore bodies are layered-lens-like, controlled by specific stratigraphic horizons. The ore is in the shape of ribbon, breccia, mass and disseminated and is mainly composed of galena, sphalerite, chalcopyrite and freibergite. The ore-forming fluids mainly migrate vertically along contemporaneous faults, with a large content of Cl-, F-, Pb, Zn, Sb, Cu, Ag and other ore-forming material. Although these medium–low-temperature hydrothermal sedimentary polymetallic deposits have been strongly reformed in the Himalayan period, there are still a lot of hydrothermal sedimentary characteristics (Fig. 4.4).

Fig. 4.4
figure 4

Distribution of Cu and Ag polymetallic deposits in the Sanshan area, Lanping Basin

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In conclusion, with the development of the Sanjiang Tethys archipelagic arc-basin system from infancy, maturity to closure, three different episodes of metallogenic event have developed, which mainly occur in the inner margin of stable landmass, MABT and post-collision extensional rift basin. There are several important metallogenic belts and ore concentration areas in space, forming a metallogenic lineage dominated by base metals. The main metallogenic types consists of VMS-type, porphyry-type, exhalative-sedimentary-type and tectonic-hydrothermal deposits, and the metallogenic metal assemblage includes Pb–Zn, Pb–Zn–Cu–Ag, Cu and Sr-Ba assemblage, from simple to complex with the evolution of archipelagic arc-basin system.

4.2 Metallogenic Event of Intracontinental Conversion Orogeny

The intracontinental orogenic metallogenic event is the most significant metal metallogenic event in the Sanjiang orogenic belt and is typically represented by the Himalayan metallogenic event. The development of this metallogenic period is closely related to the strike-slip extension, nappe shear and associated porphyry system and basin fluid system produced in the Sanjiang orogenic belt by the collisional uplift of the Qinghai-Tibet Plateau. Many large and super-large deposits, such as Yulong porphyry copper deposit, Jinding lead–zinc deposit and Ailaoshan gold deposit, were formed during this metallogenic period.

4.2.1 Porphyry Copper–Gold Metallogenic Events

The porphyry copper–gold metallogenic events are mainly developed in the eastern margin of the Qinghai-Tibet Plateau formed by the collision of the India-Asian continent. Tectonically, this area is a tectonic transfer zone absorbing and adjusting the collision stress and strain of Indo-Asian continent and has successively experienced Paleozoic Paleo-Tethys orogeny and Himalayan large-scale intracontinental deformation. Its Paleozoic orogeny is mainly manifested in the subduction and reduction of the Paleo-Tethys ocean basin of the Jinsha River and the development of the Jiangda-Weixi arc. The Cenozoic deformation is mainly manifested as Eocene–Oligocene (40–24 Ma) transitional compression-torsional deformation, Early-Middle Miocene (24–17 Ma) transitional tension-torsional deformation and east–west extension since Neogene, with a series of strike-slip fault combinations in different directions developed successively. Among them, the western assemblage includes Jiali and Gaoligong Mountain strike-slip faults, developing around the eastern tectonic knot; the central assemblage includes the Batang-Lijiang fault in the northern section and the Ailaoshan-Red River fault in the southern section. The former is distributed in SN direction with right strike-slip, and the latter is extended in NW direction with left strike-slip. The two constitute the boundary fault zone between the Yangtze landmass on the east side and the Qiangtang terrane on the west side; the eastern assemblage includes the Longmen Mountain thrust zone and the Xianshuihe and Xiaojiang strike-slip faults. A series of derivative extensional basins are developed along the strike-slip fault, such as Gongjue, Jianchuan and Dali basins, among which Cenozoic alkali-rich intrusive rocks and potash volcanic rocks are developed, forming the famous Jinsha River-Red River alkali-rich magmatic rock belt. In this huge magma belt, there are two ore-bearing alkali-rich porphyry belts that are eye-catching. One is the Jiangda-Heqing-Dali alkali-rich porphyry belt, distributed along the suture between the two continental blocks, with the isotopic ages ranging from 48 to 27 Ma; another is the Shangri-La-Yanyuan-Yaoan alkali-rich porphyry belt, produced in the western margin of the Yangtze, with its isotopic age ranging from 48 to 31 Ma.

In the Jinsha River-Red River alkali-rich magmatic rock belt, there are two important porphyries copper–gold belt (Fig. 4.5) formed with the large-scale copper–gold mineralization occurred along with porphyry emplacement. Figure 4.5 shows the spatial distribution of important porphyry deposits in the tectonic transfer zone on the eastern margin of the plateau. It is roughly bounded by the Jinsha River ancient suture zone and is divided into two metallogenic belts in the east and west. The west belt starts from Jiangda in the north and reaches Xiangyun in the south, with a length of 750 km, including the Yulong porphyry Cu belt in the north; the east belt starts from Shangri-La in the north and stretches from the middle-south section to Beiya porphyry Au (Cu) deposit and Machangqing Cu–Mo–Au deposit in the south section, with a length of about 300 km. Generally, the western belt is produced on the suture zone between the Yangtze landmass and the Qiangtang terrane, controlled by a large-scale strike-slip fault zone; the eastern belt is produced on the western margin of the Yangtze block, with its northern section controlled by strike-slip faults, and its southern section is restricted by the inherited faults following the Panxi rift period. Porphyry metallogenic belts appearing in “pairs” have the following similar characteristics:

Fig. 4.5
figure 5

Distribution of porphyry deposits in eastern margin of the Qinghai-Tibet Plateau

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  1. (1)

    Metallogenic age: the metallogenic age of the porphyry deposit can be accurately dated by using the Re-Os of molybdenite, or it can be estimated indirectly based on the crystallization age of the ore-bearing porphyry. Generally speaking, porphyry mineralization usually occurs 1–3 Ma before the last intrusion of ore-bearing porphyry. In the western belt, the Re-Os age of molybdenite in the Yulong porphyry belt is 35.6–35.8 Ma. The metallogenic age of the Machangqing porphyry copper-molybdenum deposit has not been directly determined, but it is estimated to be around 36.0 Ma according to the Rb–Sr isochron age of the ore-bearing porphyry. The mineralization history and mineralization type of the Beiya porphyry deposit are relatively complex. According to the K–Ar age of the Beiya syenite porphyry (48 Ma), its main metallogenic age is estimated to be (45 ± 2) Ma. In the eastern belt, the 40Ar/39Ar plateau ages of Cu-bearing monzoporphyry amphibole in Xifanping is 47.52 Ma, with the isochron age of 46.8 Ma, and the estimated metallogenic age of 44 ± 2 Ma. The K–Ar age of the Yao’an syenite porphyry varies from 31 to 50 Ma, and its metallogenic age of the deposit is estimated to be 34 to 47 Ma. The above data are somewhat speculative, but the metallogenic ages of the two belts are consistent in sequence.

  2. (2)

    Ore-bearing porphyry. Similarities are shown as follows: ① The ore-bearing porphyry assemblages in the eastern and western belts are monzonitic granite porphyry, monzonitic porphyry and a small amount of syenite porphyry. From north to south in space, it changes from monzonitic granite porphyry to syenite porphyry. ② Ore-bearing porphyry bodies are mostly produced as small rock strains, and most of them are complex rock bodies with multiple intrusions. ③ In the complex rock bodies, the mineralization is mostly closely related to the meta-acidic porphyry intruded in the middle and late stages.

  3. (3)

    Surrounding rock alteration. Surrounding rock alteration is mainly centered on rock mass, developing in an annular shape. Silicification nuclei are frequently found in mineralized rock mass, which are potassium-silicate lithification zone, quartz sericitization zone and propylitization zone in turn outward, and skarn lithification zone, marble lithification zone and hornstone zone are developed in outer contact zone.

  4. (4)

    Metallogenic characteristics. Similarities are shown as follows: ① Although the production environments of the eastern Tibet porphyry deposits and the Pacific Rim porphyry deposits are different, the mineralization characteristics are basically consistent; ② similar mineralization assemblages appear in the eastern and western belts. The western ore belt is Cu, Cu–Mo and Au–Pb—Zn assemblages, and the eastern belt is Cu, Cu–Au and Au–Pb–Ag. ③ The mineralization types are similar, such as disseminated mineralization of veinlets in the porphyry body, sulfide-rich plate-like bodies in the contact zone and layer-like, lens-like and vein-like bodies in the surrounding rocks.

4.2.2 Metallogenic Events of Gold Deposits in Shear Zones

The shear zone-type gold mineralization events related to large-scale sinistral strike-slip and nappe shear have formed the famous Ailaoshan large-scale gold belt, which occurs in the strongly sheared Ailaoshan ophiolite melange belt (Hu et al. 1995). The metallogenic belt is 120 km long and 500–5000 m wide, consisting of four large Au deposits (Laowangzhai, Donggualin, Bifishan, Shangzhai, Jinchang, Daping), eight medium-sized gold deposits and over 30 small and ore occurrences. The main part is distributed along the Red River strike-slip fault zone and occurs in the ophiolitic melange tectonic slices near the three faults and distributed in the right-line oblique row (Fig. 4.6).

Fig. 4.6
figure 6

Geological map of Ailaoshan gold deposit belt

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Tectonically, Ailaoshan fault and the Jiujia-Mojiang fault control the distribution of the Ailaoshan gold belt, the intersection of NW-trending brittle shear zone and near EW-trending thrust fault zone, the distribution of gold field or gold deposit. Brittle-ductile shear zones of different lithological layers control the formation of single deposits or ore bodies (Hu et al. 1995). Horizontally, the gold belt is generally controlled by the Upper Paleozoic tectonic-stratigraphic unit. The gold deposits are developed in tectonic slices composed of basic volcanic tuff-sedimentary tuff-clastic rock-crystalline limestone and radiolarian siliceous rock of Upper Paleozoic. Its mineralization intensity is positively correlated with the development intensity of Carboniferous basic-ultrabasic rocks and Yanshanian-Himalayan lamprophyre and granodiorite porphyry, reflecting that the mineralization is closely related to Ailaoshan oceanic crust material (ore source) and late magmatic activity (heat source) (Huang et al. 1997). According to the output characteristics and ore types of gold deposits in the Ailaoshan gold belt, the deposits are mainly of tectonic altered rock type or shear zone type (Hu et al. 1995). At present, such deposits are widely accepted abroad as orogenic gold deposits. It can be divided into three types according to the gold-bearing formations and ore types: Laowangzhai type, Jinchang type and Kudumu type. Laowangzhai-(Donggualin) type ore deposit directly occurs in basic lava, breccia, breccia lava and sedimentary tuff, quartz complex sandstone and sericite with strong pyritization, dolomitization and sericitization in Lower Carboniferous. Kudumu ore deposit occurs in the bedding shear zone of pyritization and sericitization tuff and basic lava of Middle Carboniferous. The Jinchang deposit mainly occurs in the outer contact zone of ultrabasic rock mass, forming Au ore body of strong silicification and carbonation ultrabasic rock type and Au ore body of metasomatic siliceous rock type. These ore bodies are mostly vein-like, lens-like and layer-like. The veins fill the fracture zone to form gold-bearing quartz veins and lens bodies; hydrothermal metasomatism in the contact zone of mafic ultrabasic rocks forms the layered and lenticular gold-bearing quartzite ore bodies (Hu et al. 1995). The altered mineral dating results of the ore-bearing host rocks and altered surrounding rocks indirectly indicate that the metallogenic age of the gold belt varies from 180 to 28 Ma, but the main metallogenic period is the Himalayan period, with an estimated age of 35–43 Ma (Huang et al. 1997).

4.2.3 Metallogenic Events of Tectonic-Fluid Polymetallics

Structured with strong intracontinental convergence and compression during the Himalayan period, thrust nappe, detachment gliding nappe and strike-slip-shear are the main tectonic forms of the crust surface in the Sanjiang area. The mountain systems on both sides of the Qamdo and Lanping foreland basins respectively shift toward the basins on a large scale, and the medium and shallow crustal fluids controlled thereby migrate and converge from the orogenic belt to the basin, discharge and unload along the nappe belts or internal faults on both sides of the basin, resulting in metallogenic event of massive drainage-metal accumulation. The trans-unit tectonism in the process of intracontinental convergence, large-scale and multi-source fluid convergence and migration, as well as extensive material source fusion and massive metal accumulation have formed a medium-low-temperature hydrothermal polymetallic metallogenic belt with huge extension scale and a number of promising deposits.

4.2.3.1 Thrust Nappe Structure-Fluid Metallogenic Event

Regional fluid flow caused by tectonic compression during intracontinental convergence is the most important metallogenic factor. Driven by regional tectonic stress, massive fluids are discharged from the middle and upper crustal basins and orogenic belts and greatly converge and mix with metamorphic hydrothermal fluids from the deep crust, magmatic hydrothermal fluids, tectonic hydrothermal fluids formed by intracontinental subduction and even mantle fluids and possibly heated atmospheric precipitation. Under the tectonic compression, these fluids from different sources can migrate and move on a large scale across tectonic units, extract and transport ore-forming material from wider provenance areas and form a huge metallogenic-fluid system. The fluid-metallogenic system formed mainly acts in the middle upper part of the crust. It is a medium-low-temperature hydrothermal fluid, with fluid action appearing in scale, and controlled by regional fracture. The tectonic channel for fluid reservoir discharge is a favorable place for mineralization. Alteration and discoloration, mineralization and geochemical anomalies of hydrothermal ore-forming elements related to hydrothermal activities are widely developed in the Middle and Upper Triassic, Jurassic-Cretaceous, Paleogene-Neogene red beds in the thrust belts on both sides of the Qamdo Basin, which well records and reflects such tectono-fluidic interaction and its spatiotemporal scale. The North Lancang River belt in the west of the basin is the largest thrust nappe belt developed along the Qamdo-Markam foreland basin and the Leiwuqi-Dongda Mountain island arc orogenic belt in the west of the Qamdo block. In the process of intracontinental subduction of the former to the latter or thrust nappe of the latter to the front, on the one hand, a large amount of tectonic hydrothermal fluid may be formed in the subduction zone and rise along the subduction surface; on the other hand, the large-scale eastward tectonic nappe has strongly squeezed the Qamdo-Markam basin, resulting in a large amount of drainage. Then, it mixes with the tectonic hydrothermal fluid from the subduction zone, rises along the thrust front, releases and unloads and causes extensive medium-low-temperature hydrothermal alteration and mineralization in the region (Fig. 4.7). The main types of alteration include silicification, argillization, carbonation, baritization, etc., accompanied by asphalt and nappe faults along Huoyexiong, Erluo Bridge and other fronts. Cold and hot springs are developed in modern times, and the (medium) low-temperature hot brine fluid is very active. The metallogenic belt and geochemical anomaly belt controlled by this run through the north and south, with mineralized sites and geochemical anomalies scattered all over the place, forming a number of potential ore deposits including Oluoqiao large arsenic deposit, Zhaofayong lead–zinc deposit, Xigang lead–zinc deposit and Laruoma lead–zinc deposit, indicating a promising prospecting. The ore-forming element assemblages are mainly (copper), lead, zinc, silver, arsenic, antimony, mercury, etc., the typical medium and low temperature assemblage. The secondary fault structures in the thrust front belt are the main ore-bearing structures, and the ore-forming hydrothermal fluids are mainly formed by filling and metasomatism. Though the medium-low-temperature metallogenic belt is formed in the Qamdo Basin, the metallogenic-fluid system is the result of the joint action of two adjacent tectonic units, and the ore-forming fluids and ore-forming materials have multiple sources. The same fluid-metallogenic system also appears in the thrust belt on the east side of the basin. During the further pushing process of the Jinsha River orogenic belt during the Himalayan period, a group of faults represented by the Tuoba fault may have been active again, and a westward thrust occurs, causing the drainage of ore-forming fluid in the basin on the western front belt, forming a medium-low-temperature hydrothermal deposit represented by the Duri large lead-silver deposit. The scale of the eastern thrust belt is far less than that of the northern Lancang River belt in the west, so the scale of the metallogenic belt formed is also small. However, the eastern thrust belt is adjacent to the Yulong Himalayan porphyry belt.

Fig. 4.7
figure 7

Relationship between the Jiqu Basin and the Machala uplift nappe structure in the North Lancang River belt and the mineralization of medium- and low-temperature hydrothermal fluids. 1—Upper Triassic—Jurassic; 2—Upper Paleozoic Carboniferous—Permian; 3—Hot brine; 4—Stratabound reformed copper-silver deposit; 5—Filling metasomatic polymetallic deposit

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In addition to originating from the basin system itself, the ore-forming fluid and ore-forming material are likely to be joined by deep magmatic fluid or metamorphic fluid, which still have the conditions for forming large ores locally. The same orogenic belt-foreland basin thermal and dynamic fluid metallogenic system is also fully displayed in the Lanping Basin. The most prominent event in the intracontinental convergence process of the Lanping Basin is the large-scale nappe expansion of the orogenic belts on both sides of the basin, eventually forming a tectonic pattern of two large-scale thrust nappe tectonic belts symmetrical to the central axis of the basin. Along with the development and formation of hedging tectonic belts and strike-slip activities, the activity and migration of fluids in orogenic belts and basins were triggered, which generated a significant impact on the mineralization and metallogenic enrichment of the Cenozoic basin, and the basin entered a new era of large-scale mineralization since the Paleocene. In the Cretaceous period of unidirectional thrust nappe from the northeast to the southwest, the fluids mainly migrated and flowed laterally to the basin on a large scale. In the late Eocene–Oligocene, under the conditions of NE–SW offset compression and dextral strike slip, the fluid had undergone lateral-to-vertical migration-convection, and the overpressure fluid system in the deep basin mainly rose along the central axis fault zone with strike-slip properties in the basin and mixed with the basin fluid in the shallow red beds, providing a large amount of ore-forming materials. Then, it is metallized in the dome trap structure formed by extrusion thrust and nappe, forming the famous Jinding lead–zinc deposit and the Sanshan-Baiyangping large-super-large silver-copper polymetallic metallogenic prospect. Compared with the Qamdo Basin in the north, the fluid system of the intracontinental convergence basin in the Lanping Basin is mainly discharged through the central axis fault of the basin and the thrust fault on the east side of the basin. It is discharged through the front fault of the thrust belt on both sides of the basin.

4.2.3.2 Metallogenic Events of Strike-Slip Pull-Apart Basin

In the process of intracontinental convergence in the Cenozoic Sanjiang area, a series of Paleogene and Neogene tectonic basins of different sizes were formed, which were juxtaposed with nappe structure, strike-slip structure and gliding nappe structure, forming an important component of intracontinental convergence. The Cenozoic basins are mainly dominated by the regional deep and large faults in the foreland basins of Qamdo and Lanping and between them and the orogenic belts on both sides and are the strike-slip pull-apart products of these faults. The eastern Tibet area in the north is controlled by the dextral activity of the Chesuoxiang fault that divides the Qamdo Basin and the Jinsha River orogenic belt. The Paleogene Gongjue Basin formed by it extends for hundreds of kilometers from north to west, with a sedimentary thickness of more than 4000 m, and locally contains calc-alkaline intermediate base-intermediate-acid volcanic rocks. Controlled by the secondary fault on the east side of the North Lancang River giant thrust fault zone, the Nangqian Paleogene Basin and the Jiqu Paleogene-Neogene Basin were formed in the central and western parts of the basin, respectively. The Nangqian Paleogene Basin developed alkaline trachyandesite-trachyte volcanic rocks. The Cenozoic is related to the sinistral activity along the Red River fault. On both sides of the Lanping Mesozoic basin, the Qingkou-Mishajing-Qiaohou fault and the Bijiang River fault on the central axis of the basin are controlled to form strike-slip basins. The Lanping-Yunlong basin controlled by the latter is the largest, with a north–south length of 140 km and a east–west width of 5–10 km. These basins mentioned above are characterized by extensional or compressive strike-slip. Due to their connection with deep and large faults, some of them contain magma eruptions and become favorable places for deep fluid to rise and unload. Taking the famous Jinding lead–zinc deposit in Lanping-Yunlong basin as an example, the mineralization is mainly related to the discharge of deep fluid rising in the basin during strike-slip along Bijiang River fault (Fig. 4.8). In the Jiqu Basin of Qamdo, the Paleogene-Neogene red molasse clastic rocks have both sandstone-type copper mineralization and hydrothermal-type copper-silver-mercury polymetallic mineralization formed along basin-controlled faults, as well as discoloration and alteration of rocks, indicating that there is also the mechanism of deep fluid discharging to the basin along the fault structure.

Fig. 4.8
figure 8

Distribution map of fluid in the evolutionary stage of extensional strike-slip in the Lanping Basin

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4.2.3.3 Extensional Detachment Structure-Fluid Metallogenic Event

During the process of intracontinental convergence, the old orogenic belt further undergoes unidirectional or bidirectional outward thrust nappe, and extensional detachment structures appear to varying degrees at the trailing edge of the orogenic belt to control the activities from the orogenic belt and atmospheric precipitation. The basic model is that the fluid extracts minerals from the rocks of the orogenic belt with rich provenance and converges into the detachment and gliding nappe structures in the extensional environment. During the eastward thrust nappe of Jinsha River orogenic belt in the Himalayan period, the detachment and stripping structures occur along different tectonic layers in the extension and tension of the western rear edge, resulting in the filling and metasomatism of ore-forming hydrothermal fluids, forming the gold polymetallic deposits represented by Azhong (Fig. 4.9).

Fig. 4.9
figure 9

Relationship between himalayan detachment structure and gold (silver) polymetallic mineralization in Jinsha River Orogenic Belt. 1—The metallogenic pre-enrichment layer related to Indosinian volcanism; 2—The deposit transformed and enriched by the Himalayan detachment structure

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In the south, the Tuoding copper deposit, the Najiao system, the Gangriluo and other lead–zinc deposits and even the Xiasai super-large silver polymetallic deposits all have the obvious characteristics of such tectonic control or transformation. In the Lancang River orogenic belt, due to its large-scale thrust nappe to the Qamdo-Pu’er block, an extensional stripping zone developed in the Baoshan block at its trailing edge, forming the Shuangjiang extension basin, the Ximeng metamorphic core complex, and the Mengsheng extensional basin, accompanied by crustal molten granite and granite porphyry and related tin and lead–zinc deposits, such as Aying tin ore, Xinchang lead–zinc ore, and were simultaneously controlled by detachment faults (Li et al. 1999).

4.2.4 Metallogenic Events of Syn-Collision Granite Tin

The syn-collisional granite tin metallogenic event mainly occurred in Tengchong-Bomi granite belt, which constitutes an important tin and rare mineral and rare earth ore concentration area. Tectonically, the Tengchong-Bomi granite belt is produced on the Lhasa terrane between the Pangong Lake-Salween River suture (BNS) and the Yarlung Zangbo River suture (IYS) and belongs to the southeastern extension of the Gangdise granite base. Due to the strong wedging of the Indian continent to the northeast and the subsequent development of the Nanga Bawa tectonic knot, the Gangdise granite base dominated by the Yanshanian granite takes a strong turn, and the western section is distributed in the near EW direction and is separated from the Tethys Himalaya in the south by the IYS. The eastern section is generally distributed in an arc in the near SN direction, limited by the BNS in the east and separated by the Naga Hills suture zone (where IYS is located in Myanmar) in the west. The strike-slip fault system or large shear zone that regulates the strong collision strain between India and the Asian continent is distributed around the tectonic knot. The northwest section is the Jiali fault zone, and the southeast section is the Gaoligong fault zone (Yin and Harrison 2000), especially the large-scale strike-slip-shear action of the latter, which fundamentally controls the formation and development of the Tengchong-Bomi granite belt. The Chayu-Tengchong granite belt can be roughly divided into two sets of granites based on the time limit of the Indo-Asian continental collision: Yanshanian granites before collision and collision-period Cenozoic granites. The Yanshanian granites before collision are related to the subduction of the Neo-Tethys oceanic plate, with the emplacement age and rock assemblages consistent with those of the Gangdise granites in the western segment; the collision-period Cenozoic granites and Yanshanian granites are coherently distributed, but the early potassium-rich granites are mainly concentrated in the Tengchong-Lianghe area, while the late two-mica granites are concentrated in the Chayu-Bomi area (Lu et al. 1993). The exposed area of granite in Tengchong area accounts for more than 50% of the whole area, forming three granite belts of different ages, different genetic types, interdependent in time and space and distributed in parallel. From east to west, they are the Early Cretaceous-Late Jurassic Donghe granite belt, late Cretaceous Palaeoyong granite belt and Paleogene Binlang River granite belt. The Binlang River granite belt mainly exposes complex rock bodies such as Huashui, Xintang, Lailishan, Xinqi and Bingwai. The Xintang complex rock bodies are produced in the form of a rock base, with an area of more than 36 km2; the main body of the Lailishan complex rock mass is produced by rock strains, with an area of more than 7 km2; the plane distribution of the Xinqi rock mass is elliptical, with the rock plant area of about 40 km2. These Himalayan rock masses are clearly controlled by a series of strike-slip faults. Isotopic dating data show that (Chen et al. 1991; Lu et al. 1993) the Cenozoic granites during the Tengchong collision period have multi-stage emplacement characteristics. The Rb–Sr isochron age and K–Ar age of the earliest emplaced monzonitic granite limit the magma crystallization age to 58–60 Ma. The Rb–Sr isochron age and K–Ar age of the subsequently emplaced moyite are concentrated between 51 and 54 Ma, which limits the crystallization age of the second phase emplaced magma to about 52.5 ± 1.5 Ma. The Rb–Sr isochron age of the neoporphyritic granite or granite porphyry produced by the rock strain has a narrow range of 52.4–52.5 Ma. Although there are no direct dating data for muscovite granite and muscovite albite granite intruding into moyite in the form of bedrock intrusion, it is speculated that their formation age should be less than 51 Ma.

Rock geochemical studies show that the Al saturation index (ASI) of monzogranite and moyite is close to 1, which belongs to meta-aluminate to peraluminous granite. The ASI of muscovite (albite) granite varies from 1.02 to 2.63 and belongs to peraluminous to strong peraluminous granite. The w(K2O)/w(Na2O) ratio of these granites is greater than 1, and the w(K2O)/w(Na2O) ratio and SiO2 content increase in turn. The content of trace elements in the former is relatively high in Sr, Ba and low in Rb, while the latter is obviously high in Rb and abnormally low in Sr, Ba. The muscovite granite is characterized by an abnormally high Y, and the muscovite albite granite is characterized by an abnormally high Rb; the former has a right-dipping LREE enrichment type, with obvious negative Eu anomaly; the latter has a “swallow-type” REE distribution patterns, suggesting that different types have different magmatic source rocks or melting mechanisms. The analysis of the tectonic environment shows that although the Tengchong Cenozoic granites were produced in the continental collision zone, the monzonitic and moyite at 51–60 Ma were formed in the stress relaxation stage after the strong collision between the Indian and Asian continents, while the formation of muscovite granite was related to the activity of Gaoligong strike-slip fault zone.

Tengchong tin and rare mineral and rare earth mineralization are related to moyite and muscovite albite granite, respectively. The former is represented by the large-scale tin deposit in Lailishan, and the latter is characterized by the rare ore and rare earth ore of Baihuanao. Together with various tin mineralizations in the Yanshanian period before the collision in the area, they constitute part of the 800 km-long tin belt in Southeast Asia. The ore-bearing moyite is characterized by high K, F, S and high initial ratio of 87Sr/87Sr (0.7124 to 0.7138), with its w(Sn) varying from 150 to 200 µg/g, w(Mg)/w(Ti) varying from 1.5 to 3.0 and w(Zr)/w(Sn) varying from 10 to 416, showing the typical geochemical characteristics of Sn-bearing granites (Lehman et al. 1990). The tin ore body mainly occurs in the contact zone between the granite body and the surrounding rock and in the fracture zone of the surrounding rock. Tin ore is mainly of massive sulfide type, composed of cassiterite, a large amount of pyrite, pyrrhotite and a small amount of sphalerite and galena, with the grade of tin ore varying from 0.63 to 1.58% (Liu et al. 1993a, b). The Baihuanao muscovite albite granite is characterized by rich LILE (K, Rb, Cs and Li) and REE, and the mineralized granite has undergone a complex process from REE mineralized granite to Sn-W granite through Nb–Ta mineralized granite (Liu et al. 1993a, b). Disseminated and greisen type ores are the main types of mineralization, mainly produced in the inner and outer contact zones of granite. The mineralized metals are mainly of Cs, Li, Ta, Sc, Y, Sn and W, of which Rb resources account for about 1/3 of the global total Rb resources.

In conclusion, intracontinental orogeny and mineralization are mainly related to the large-scale collision process of Indo-Asian continent, and the main metallogenic events are related to four major geological processes: large-scale strike-slip (fault, pull-apart), large-scale strike-slip-shear action, large-scale nappe slippage and syn-collision magmatism. Four major metallogenic belts or ore concentration areas are mainly formed, namely porphyry Cu-Au ore belt, ductile shear (orogenic) Au ore belt, composite basin polymetallic ore concentration area and collision granite Sn ore concentration area.

4.3 Archipelagic Arc-Basin System and Collisional Orogenic Metallogenic System

The Sanjiang orogenic belt is an important tectonic-metallogenic unit of the East Tethys metallogenic domain. The metallogenic characteristics of the Paleozoic early Mesozoic and Tethys ocean continent transition process are attributed to the tectonic background of the archipelagic arc-basin system. After the opening and closing of the Neo-Tethys Ocean and the subduction and collision of the Indian continent, it ended in the Himalayan full intracontinental convergence and uplift orogeny, forming various metallogenic systems with specific metallogenic functions coupled by various elements controlling mineralization in a specific geological space–time structure. This section will describe the Sanjiang archipelagic arc-basin system and the collisional orogenic metallogenic system based on the data obtained from multiple rounds of scientific and technological research and from the ideological point of view of the metallogenic system.

4.3.1 Metallogenic System Types in the Sanjiang Orogenic Belt

4.3.1.1 Concept and Connotation of Metallogenic System and Metallogenic Series

Metallogenic series and metallogenic system are common modes of thinking and conceptual models adopted by the current ore deposit academia to study regional mineralization and explore the temporal and spatial evolution and distribution laws of ore deposits. The concepts of metallogenic system and metallogenic series are guided by the theory of metallogenic system, emphasizing the internal connection and overall function of metallogenic processes and environmental elements, and revealing the temporal and spatial evolution and distribution laws of metallogenic processes and their products. The metallogenic series refers to a group of ore deposit-type assemblages that are closely related in time, space and genesis, formed under the dominant metallogenic process in a certain geological period and geological environment (Chen 1999). However, since the formation of ore deposits often goes through a complex and long-term process of accumulation, transportation and deposition of ore-forming materials and is often subjected to the superimposition and transformation of the later geological process, resulting in repositioning, re-enrichment or redestruction, it is difficult to accurately demarcate the ore-forming age or grasp the internal relationship between the deposit and the environment. Therefore, the determination and division of the metallogenic series often have its limitations. Additionally, due to the characteristics of multi-source composite genesis of many deposits, it is difficult to identify their exact geological mineralization or determine their exact metallogenic series; some important metallogenic processes, such as crustal (submarine or intracontinental) hydrothermal mineralization, are still difficult to be classified into the existing metallogenic series. The metallogenic system is composed of all the geological elements that control the formation, change and preservation of deposits, the metallogenic process and the series of deposits and abnormal mineralization series formed in a certain geological time and space domain. It is a natural system with metallogenic function (Zhai 1998), emphasizing the organic connection between mineralization and environmental factors, processes and laws of material accumulation and dispersion, and regarding mineralization as the related product of coupling of various elements in the system. Therefore, the metallogenic system not only studies the mineralization products of deposits in the temporal and spatial structure of the geological environment, but also studies the four elements system of material, energy, time and mechanism that control the metallogenic process, so as to reveal and identify the mechanism and internal relations of various mineralizations on the whole. Although the thought of metallogenic system is in the process of research and exploration, its concept, connotation and extension are still vague and need to be determined, and some issues (such as the boundary and scale of metallogenic system, classification and naming) have not yet reached a consensus and need to be studied in depth. Nevertheless, the thinking mode and scientific connotation of the metallogenic system should undoubtedly become an important guiding ideology for the study of regional mineralization and the formation law of deposits.

4.3.1.2 Metallogenic System Types

4.3.1.2.1 Boundary Scale and Classification Level of Metallogenic System

The boundary scales of metallogenic systems are generally defined according to the temporal and spatial scales of their respective research objects, ranging from the global scale to a single deposit. No consensus has been reached so far. We believe that the global tectonic evolution usually goes through the evolution and transformation of the oceanic-continental tectonic system. Different stages of the oceanic-continental tectonic system evolution usually have different tectonic backgrounds, shaping different tectonic–magmatic–sedimentary formations, resulting in different metallogenic environments, and constraining different metallogenic systems. Based on this, we have determined four metallogenic giant systems according to the tectonic evolution and the development characteristics of the Sanjiang giant orogenic belt: continental marginal splitting metallogenic giant system, continental marginal convergent metallogenic giant system, intracontinental convergent metallogenic giant system and intracontinental rift metallogenetic giant system. The boundaries of metallogenic giant systems are usually discrete continental margins, island arcs or collision orogenic belts and intracontinental orogens or rifts. One or several metallogenic systems can be developed in the metallogenic giant system. The orogenic belt usually experiences the subduction orogenic stage and the collisional orogenic stage, in which the collisional orogenic stage also goes through the process of syn-collision orogeny, root demolition and subsidence and post-orogenic extension (Dong 1999), developing the subduction orogenic metallogenic system, the collisional orogenic metallogenic system and the post-orogenic extensional metallogenic system. The boundaries of metallogenic systems are defined as secondary tectonic units of large tectonic belts. In the metallogenic system, according to the dominant factors (such as stress, magma, fluid) that constrain the ore-forming material convergence and metallogenic process, metallogenic product assemblage and possible ore deposit genesis types, metallogenic subsystems can be further determined, such as arc magma-hydrothermal ore-forming subsystem, intra-arc rift hydrothermal fluid ore-forming subsystem, back-arc volcano-hydrothermal metallogenic subsystem.

4.3.1.2.2 Metallogenic System Classification

By comparing the evolution characteristics of the ocean-continental tectonic system, the types of metallogenic environments, the main controlling factors and processes of the system, the mineralization assemblages and the genetic types of the deposits, four metallogenic giant systems and 11 metallogenic systems are preliminarily divided.

  1. (1)

    Continental margin splitting metallogenic giant system

    • Rift metallogenic system.

    • Ocean basin metallogenic system.

  2. (2)

    Continental marginal convergent metallogenic giant system

    • Subduction orogenic metallogenic system, arc magma-hydrothermal metallogenic subsystem; intra-arc rift hydrothermal fluid metallogenic subsystem, back-arc volcanic hydrothermal metallogenic subsystem.

    • Collisional orogenic metallogenic system.

    • Syn-collisional magmatic metallogenic subsystem, syn-collisional volcanic metallogenic subsystem.

    • Post-orogenic extensional metallogenic system.

    • Magmatic hydrothermal metallogenic subsystem, tectonic-fluid metallogenic subsystem.

  3. (3)

    Intracontinental convergent metallogenic giant system

    • Intracontinental magmatic metallogenic system, intracontinental crustal magmatic metallogenic subsystem, intracontinental mantle-derived magmatic metallogenic subsystem.

    • Tectonic dynamic fluid metallogenic system.

    • Thrust nappe tectono-fluid metallogenic subsystem, shear detachment tectono-fluid metallogenic subsystem.

    • Foreland basin fluid metallogenic system.

    • Metallogenic system of strike-slip pull-apart basin.

  4. (4)

    Intracontinental rift metallogenetic giant system

    • Fault basin metallogenic system.

    • Extensional stripping metallogenic system.

4.3.2 The Continental Margin Splitting Metallogenic Giant System

In the Sanjiang giant orogenic belt, the continental margin splitting metallogenic giant system is mainly developed in the Yunxian-Jinghong rift volcanic zone and the Changning-Menglian rift-oceanic basin volcanic rock belt. The former develops the rift metallogenic system, while the latter develops the post-rift-ocean basin metallogenic system. There are other continental margin splitting metallogenic systems, such as the Jinsha River-Ailaoshan continental margin splitting metallogenic system.

4.3.2.1 The Background of Metallogenic System

The Proto-Tethys Ocean may have been formed in the Neoproterozoic. From the Sinian to the early Paleozoic, the oceanic crust plate began to subduct eastward, forming the Jitang-Jinghong ancient island chain and the Lancang River back-arc-basin. Entering the middle and late Paleozoic, it transformed from contraction and extrusion to extension and expansion. In addition, possibly due to the demolition and subsidence of the mountain roots of the orogenic belt and its induced mantle uplift and thinning of the continental crust, it rifted in the Yun County-Jinghong area on the east side of the Jitang-Jinghong ancient island chain and gradually expanded into a back-arc ocean basin, which lasted until the Middle and Late Triassic, and finally closed in the later period of the Late Triassic. The Yun County-Jinghong continental margin rift-type volcanic rock belt was formed due to the intense volcanic activity in rifts and ocean basins.

4.3.2.1.1 Yun County-Jinghong Rift Volcanic Rock Belt

As stated in the geophysical data, the gravitational field is similar to the characteristics of the Oslo rift zone, which is bounded by the Lancang River fault in the west and the Mengla fault in the east (Wang et al. 2001). Volcanic rocks can be divided into two periods: Late Paleozoic and Mesozoic.

Late Paleozoic volcanic rocks are mainly Carboniferous and Permian volcanic rocks. Carboniferous volcanic rocks refer to a set of lava assemblages dominated by quartz keratophyre and secondary spilites, with pyroclastic rocks developing here. Lava includes spilite, keratophyre, dacite and quartz keratophyre. As described in petrochemical, rare earth and trace element analysis, the primitive magma was mainly formed in the lower crust-upper mantle. According to the characteristics of the Dapingzhang geological section, the composition and strength of the magma and the types of volcanic eruptions, Yang (2001) divided it into an eruption cycle and three subcycles from early to late: ① The first subcycle is dominated by the overflow of sodium-rich lava on the seabed. It started from the quartz keratophyre magma eruption, and then the composition of the magma changed to kratophyre. At the same time, the eruption of basic spilite magma appeared in a short period of time, and finally, it ended with submarine volcanic deposits, forming massive sulfide ore bodies. ② The second subcycle is dominated by magma eruption, which has a certain explosive effect. In the early stage, rhyolite magma and intermediate-basic magma erupted mainly; in the middle stage, the eruption activity weakened, accompanied by eruption in the intermittent period, forming volcanic breccia and tuff; in the later stage, the eruption and outbreak activity weakened, forming the tuff and sedimentary pyroclastic rock far away from the crater. ③ The volcanic activity of the third subcycle comes to an end. In the early stage, it was neutral magma eruption, and after a short pause, it turned to be dominated by acid magma eruption; after that, it was mainly an eruption to form volcanic breccia; finally, it ended with the formation of tuff, tuffaceous-siliceous rock and normal sedimentary rock.

Permian volcanic rocks. The Early Permian is dominated by tuff, intercalated with basic lava; the Late Permian is composed of dacite, breccia lava, breccia tuff, tuff, tuff lava and other intermediate-acid rocks.

Triassic volcanic rocks mainly include Middle and Late Triassic volcanic rocks. The volcanic activity in this period shows a decreasing trend from north to south. From the Middle Triassic to the early period of Late Triassic and to the late period of Late Triassic, the eruption environment showed a change of marine facies—land–ocean interaction—terrestrial facies (Regional Geology of Yunnan Province 1990). The Middle Triassic volcanic rocks are distributed in the Yun County-Lincang Bangdong area in the north and Jinghong-Mengla area in the south. The northern volcanic rocks are a set of high-potassium rhyolite volcanic rocks, which are well-developed, with Jingdong Minle copper deposits produced here. The Upper Triassic volcanic rocks are all over the region, and the lower segment is dominated by neutral-basic volcanic rocks; the upper segment in the northern Yun County is potassium-rich trachyte basalt and potassium-rich rhyolite volcanic rock, forming a “bimodal” volcanic rock assemblages. The volcanic rocks in the central and southern parts do not show the “bimodal” feature and are trachyandesite-dacite-rhyolite volcanic rock assemblages. Special mention should be made of the volcanic rocks in the Sandashan mining area in Jinghong. When the Yunnan regional survey team made a Jinghong amplitude of 1:200,000 in 1979, the strata in the mining area were changed to the middle and lower sections of the Upper Triassic Xiaodingxi Formation (the No. 16 team of the original Yunnan Geological Bureau classified it as the Lower Paleozoic; Sanjiang Regional Mineral Records defined it as the Upper Permian). The Wenyu, Guanfang and Sandashan copper deposits occur in the Upper Triassic Xiaodingxi Formation (Yang 2001).

The research on the Lancang River belt is still at a low level, but the copper deposits discovered are all produced in the “bimodal” assemblage of volcanic rock series, revealing that the extension and expansion of the Lancang River belt, the “bimodal” volcanic activity and the formation of copper deposits provide superior metallogenic environment and conditions.

4.3.2.1.2 Changning-Menglian Rift-Ocean Basin Volcanic Rock Belt

There are two magma evolution series in the belt: tholeiitic magma series and alkaline magma series. Rock types of the tholeiitic magma series include tholeiitic basalt, basaltic andesite and its pyroclastic rocks; rock types of the alkaline magma series include alkaline picrite basalt, alkaline olivine basalt, trachybasalt, trachybasal andesite and its pyroclastics rocks. These two series obviously belong to two types of parent magma with different properties.

Spatially, the alkaline basalt is the most widely distributed, while the tholeiitic basalt is limited; in terms of time, alkaline basalt is distributed in the early and middle Carboniferous, and tholeiitic basalt is distributed in the late Carboniferous (Laochang area). According to the rock assemblage, lithochemistry and geochemistry characteristics of volcanic rocks, most of them belong to continental rift-type volcanic rocks, with a few of them typical of ocean ridge basalt (Tongchangjie tholeiitic series volcanic rocks).

The above-mentioned types of volcanic rocks represent different stages of rift development: alkaline basalts are developed in the early stage, reflecting continental rift stage, with Laochang (black ore type) polymetallic deposits produced; ocean ridge basalt of new oceanic crust is developed in the late stage, and ophiolite is developed in some areas (Mo et al. 1990), reflecting the development stage of small ocean basin, with Tongchangjie (Cyprus type) copper-zinc deposit produced.

We cooperated with Professor Lehman of Germany to conduct research on the Lancang River volcanic belt. Sporadic molybdenite was found in Dapingzhang copper ore, and two Re-Os isotope samples obtained well matched isochrons with ages of 428.8 ± 6.1 Ma and 442.4 ± 5.6 Ma, respectively. Therefore, the occurrence and development of the Lancang River ocean basin in the southern section of the Sanjiang seem to have new implications for the evolution from Proto-Tethys to Paleo-Tethys. We believe that the Lancang River Ocean has not been completely closed since it opened in the Early Paleozoic (i.e., the Proto-Tethys stage), and the Lancang River volcanic rock belt shows multiple periods of expulsive sedimentary mineralization from the late Early Paleozoic to the early period of the Early Mesozoic, such as Dapingzhang copper polymetallic deposit (late Silurian), Minle copper deposit (middle and late Triassic) and Sandashan copper deposit (late Triassic).

In the Late Permian, there may be basic-ultrabasic magmatic intrusion and eruption, Jinggu Banpo, Jinghong Damenglong and Nanlianshan basic (local ultrabasic) intrusions in this area, with good conditions for searching copper–nickel sulfide deposits.

4.3.2.2 Metallogenic System Types

The continental margin splitting metallogenic giant system is related to the tectonic–magmatic–sedimentary environment in different stages of the self-rifting-rift-ocean basin due to the extension and expansion of the continental margin crust, which correspondingly constitutes a rift metallogenic system and a rift-ocean basin metallogenic system of a continental margin splitting metallogenic giant system.

4.3.2.2.1 Rift Metallogenic System

The rift metallogenic system is developed in the Yun County-Jinghong rift belt. It is generally believed that during the Silurian-Carboniferous period, the volcanic eruption metallogenic subsystem was developed in the middle segment of the rift (Dapingzhang) in the eruption cycle of sodium-rich quartz keratophyre-keratophyre-spilite-pyroclastic rock deposits, forming Dapingzhang VMS copper deposit and the same type and ore-forming anomaly. However, from the analysis of the Re-Os age of the molybdenite in the Dapingzhang copper polymetallic deposit, the time of the Dapingzhang submarine volcanic exhalation and mineralization may be as early as the Silurian. The types of metallogenic systems in the Triassic were different in different stages of rifting evolution and in different regions. The metallogenic subsystems are further divided according to the factors that restrict the mineralization and the difference of ore deposits. In the Middle Triassic, epivolcanic dacite porphyries related to volcanic rocks developed, appearing the magmatic hydrothermal metallogenic subsystem. For deposits such as Minle copper deposit, some people regard it as a new type, that is, ash-flow type copper ore, which is closely related to the sodium-rich welded tuff flow (Yang 2001). In the Late Triassic, a volcanic hydrothermal metallogenic subsystem was developed in the basaltic andesite series in the northern section of the rift, forming the hydrothermal copper deposits represented by Guanfang and Wenyu; the volcanic-sedimentary metallogenic subsystem was developed in the neutral or moderately acidic tuff in the remote crater of the southern segment of the rift valley, forming the Sandashan CVHMS (Cyprus type) copper deposit.

The above-mentioned deposits related to Carboniferous and Triassic rift volcanism constitute the South Lancang River copper belt.

4.3.2.2.2 Ocean Basin Metallogenic System

The rift-ocean basin metallogenic system was developed in the early Carboniferous Changning-Menglian rift-ocean basin volcanic rock belt. Different stages of rift-ocean basin evolution have different types of metallogenic systems. In the early stage, the volcanic activity in the rift development stage formed rift basalts with a high degree of alkalinity, with the hydrothermal fluid metallogenic subsystem developed and forming the KVHMS deposit represented by Laochang; in the late stage, the volcanic activity in the ocean basin stage reduced the alkalinity of volcanic rocks, forming ocean ridge basalts, developing a volcanic-sedimentary metallogenic subsystem, as well as the CVHMS deposits represented by Tongchangjie.

4.3.2.3 The Spatiotemporal and Chemical Structure of the Metallogenic System

4.3.2.3.1 Rift Metallogenic System

The rift metallogenic system developed in the County-Jinghong rift belt is bounded by the Lancang River fault in the west and limited by the Mengla fault in the east. The system originated in the Silurian period (442.4 ± 5.6 Ma), and later in the Late Permian and the Middle and Late Triassic, large-scale volcanic-magmatic activities occurred again in this area. Although the mineralization is generally controlled by the rift zone, the ore deposits and ore fields are mainly distributed along the volcanic apparatus of Jiufang fault zone and volcanic depressions, and the types and chemical structures of the deposits in different sections of the rift are also different. Taking the Dapingzhang VMS deposit of the submarine volcanic eruption metallogenic system in the central and southern section as an example, the mineralized metals mainly contain Cu–Pb–Zn, associated with Au–Ag. The metal elements of the deposit show vertical zoning, that is, the upper basin facies massive ore bodies are Cu–Pb–Zn, associated with Au–Ag assemblages; for the lower pipeline facies veinlet disseminated ore body, the metal element is mainly Cu (Fig. 4.10); for the Minle porphyry copper deposit in the magmatic hydrothermal metallogenic subsystem in the middle and northern section, the metal element is mainly copper; for the Guanfang and Wenyu hydrothermal copper deposits in the volcanic hydrothermal metallogenic subsystem in the north section, the mineralized metal elements are mainly Cu-Pb; for the Sandashan VMS deposit (Cyprus type) of the volcanic-sedimentary metallogenic subsystem in the south, the mineralized metal element is mainly Cu (Fig. 4.11).

Fig. 4.10
figure 10

Metallogenic model of the dapingzhang copper polymetallic deposit. 1—rhyolite porphyry; 2—dacite; 3—Silurian-Carboniferous Daaozi Formation; 4—dacite; 5—sericitization and silicification alteration zone; 6—carbonation alteration zone; 7—tuffaceous-siliceous rock; 8—barite; 9—massive ore body (Cu, Pb, Zn, Au, Ag polymetallic ore body dominated by sphalerite); 10—reticulated vein—disseminated ore body; 11—movement direction of infiltration circulating seawater; 12—movement direction of magmatic water

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Fig. 4.11
figure 11

Sandashan copper deposit exploration line profile (in the scale of 1:200,000 Jinghong amplitude). 1—dense copper-bearing pyrite; 2—iron cap; 3—carbonaceous sericite schist; 4—off-white massive metamorphic volcanic tuff; 5—off-white sheet metamorphic volcanic tuff; 6—dark gray sheet metamorphic volcano tuff; 7—bean-green massive metamorphic volcanic tuff

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4.3.2.3.2 Ocean Basin Metallogenic System

The ocean basin metallogenic system is developed in the rift-ocean basin metallogenic system of the Changning-Menglian belt, bounded by the Kejie-Menglian fault in the west and limited by the Changning-Lancang fault in the east. The system was formed in the Early Carboniferous. Although the volcanic activity is generally controlled by rift-ocean basins, the deposits are obviously dominated by volcanic apparatus and fault structures. However, different stages of rift-ocean basin evolution have different types and chemical structures of metallogenic systems. In the early stage, the type of metallogenic system was the hydrothermal fluid metallogenic subsystem (Laochang), with the mineralized metal elements dominated by Ag–Pb–Zn, associated with S and Cu. A single ore body showed the characteristics of “black ore” in the upper part and “yellow ore” in the lower part, that is, the upper part was a massive silver–lead–zinc ore body, and the lower part was a copper-bearing pyrite ore body. Fine vein disseminated structure appeared in the lower part of the copper ore body, and there might be concealed porphyry in the deep part; in the late stage, the type of metallogenic system was the volcanic-sedimentary metallogenic subsystem (Tongchangjie), with the mineralized metal elements dominated by Cu–Zn assemblages.

4.3.2.4 Main Controlling Factors of Metallogenic System

4.3.2.4.1 The Main Controlling Factors of the Rift Metallogenic System
4.3.2.4.1.1 Magmatic Hydrothermal Metallogenic Subsystem

The system is represented by Minle copper deposit, and the main controlling factors include rock mass, rock mass emplacement strata and hydrothermal alteration.

  1. (1)

    Rock mass. The ore-forming rock mass is gray-purple dacite porphyry, with a mottled, rhyolitic, massive structure. The phenocrysts mainly include plagioclase and potassium feldspar, followed by biotite, amphibole (pyroxene) and accessory minerals such as apatite and magnetite. The matrix is felsic, with felsic and subgraphic texture (Li 1996). The rhyolitic structure of the rock is developed, the xenoliths often have a tendency of directional arrangement, and the dark minerals (biotite) often appear dark edges and other phenomena, which belong to the volcanic-subvolcanic facies rocks.

  2. (2)

    The stratum where the rock mass is emplaced. The main host stratum of the ore deposit is the Middle Triassic.

  3. (3)

    Hydrothermal alteration. Alterations mainly include potassium silicification, mudstone, propylitization, kaolin-sericitization, chlorite-epidedization (Ren 2000), etc., indicating that gas–liquid activities are superimposed in the later stage of magmatic activity.

4.3.2.4.1.2 Volcanic Hydrothermal Fluid Metallogenic Subsystem

The system is represented by the Dapingzhang copper deposit, and the main controlling factors include volcanic apparatus, hydrothermal alteration and regional fault structures.

  1. (1)

    Volcanic apparatus. Occurred in the volcanic dome structure, the deposit is controlled by the volcanic exhalative sedimentary rock system composed of spilite-keratophyre and other open tectonic systems such as various primary structures, secondary structures and cryptoexplosive breccia pipes of the intrusive body. Volcanic massive sulfide deposits are controlled by paleo-sea-floor topography and damaged by later nappe structures. The ore bodies at the volcanic eruption center and the eruption pipeline are thick (Yang 2001).

  2. (2)

    Hydrothermal alteration. The hydrothermal alteration is mainly developed in the veinlet disseminated ore bodies, with weak hydrothermal alteration of the massive ore bodies. The main types of hydrothermal alteration include silicification, chloritization, pyritization, sericitization, carbonation and baritization. The mineralized-altered rock pipe is formed with the cryptoexplosive breccia belt controlled by NW-trending fault as the center. The hydrothermal alteration of the rock pipe is characterized by lateral zoning, in the order from the center to the outside as follows: pyritization-chloritization-silicification zone → sericitization-silicification zone → sericitization-carbonation zone. Silicification, chloritization and pyritization are closely related to mineralization.

  3. (3)

    Regional fault structure. The NW-trending regional Jiufang and Liziqing faults control the distribution of the ore-bearing spilite keratophyric volcanic series rocks. The volcanic eruption takes Jiufang fault zone on the west side as the channel and erupts from west to east in a fissure style. The Jiufang fault plays a role in controlling the mineralization.

The volcanic hydrothermal metallogenic subsystem developed in the northern section of the rift is represented by the Guanfang copper deposit. The ore body occurs in the middle-basic volcanic lava of the Upper Triassic Xiaodingxi Formation, with its mineralization controlled by the combination of lithology, structural fissures and hydrothermal alteration.

4.3.2.4.1.3 Volcanic-Sedimentary Metallogenic Subsystem

The volcanic-sedimentary metallogenic subsystem is developed in the southern section of the rift, represented by the Sandashan copper deposit. The ore body occurs between the neutral or moderately acidic tuff (roof) and the carbonaceous sericite schist (floor) in the far crater of the Upper Triassic Xiaodingxi Formation. The ore body tends to pinch out with the pinching out of carbonaceous sericite schist, and there is a phenomenon that pyrite is more enriched with the increase of the carbonization degree of sericite schist. The roof and floor surrounding rocks undergo intense hydrothermal alteration, including pyritization, silicification, sericitization, chloritization and carbonation. The formation of copper-bearing pyrite is that the sulfur-bearing basic volcanic eruptive material supplements the iron and copper elements in seawater with the participation of organic matter. In a strong reducing environment, they combine and precipitate with each other. After hydrothermal alteration, copper, cobalt and other elements are further enriched and mineralized.

4.3.2.4.2 Main Controlling Factors of Ocean Basin Metallogenic System

In the Early Carboniferous, a fissure-type intermediate-basic volcanic eruption occurred in the Changning-Menglian rift-ocean basin. In the Lower Carboniferous, the northern segment is called the Pingzhang Formation, and the lower part is an alkalescent series of sodium-alkaline basalt-latite; the upper part is carbonate rock, with the thickness of 105–595 m. The volcano-sedimentary metallogenic subsystem is also developed. In the Lower Carboniferous, the southern segment is called the Yiliu Formation, which is almost entirely composed of volcanic rocks. The lower part is the alkalescent series sodium–potassium-alkaline basalt-latite; the upper part is dominated by pyroclastic rocks, with the thickness ranging from 530 to 1159 m. For the potassium-alkaline basalt-latite, the hydrothermal-fluid metallogenetic subsystem is developed.

4.3.2.4.2.1 Main Controlling Factors of Volcanic-Sedimentary Metallogenic Subsystem

The system is represented by the Tongchangjie Cu–Zn deposit. The metallogenic subsystem is mainly controlled by horizon and lithology. The host stratum is a marine sodium-alkaline basaltic volcanic-sedimentary rock series in the lower part of the Lower Carboniferous Pingzhang Formation (1/200,000 regional geological survey division), and the copper-bearing pyrite bodies are mainly produced in the lower part of the ore-bearing rock series. The volcanic-sedimentary rocks are dominated by basic tuffs and sedimentary tuffs, intercalated with unstable sodium basic lava, jasper rock, carbon-bearing tuff or tuffaceous mudstone. The ore bodies are layered, lentil-like and lenticular (Fig. 4.12), folded synchronously with the strata, indicating that the ore bodies are controlled by horizons and lithology. In addition, small vein body and high-grade tectonic metamorphic hydrothermal copper-bearing pyrite veins occasionally penetrate along the fault. The ore-forming material originates from the sodium-based volcanic gas–liquid and is adsorbed and deposited underwater by tuffaceous, argillaceous and organic matter to form CVHMS (Cyprus-type) deposits.

Fig. 4.12
figure 12

Schematic diagram of ore-bearing layers and their lithofacies change characteristics of Tongchangjie copper deposit in Yun County (Adapted from the Tongchangjie report). 1—The first ore-bearing layer of the Lower Carboniferous Pingzhang Formation; 2—The second ore-bearing layer of the Lower Carboniferous Pingzhang Formation; 3—The third ore-bearing layer of the Lower Carboniferous Pingzhang Formation; 4—The fourth ore-bearing layer of the Lower Carboniferous Pingzhang Formation; 5—Basalt; 6—Basaltic tuff, sedimentary tuff intercalated with tuffaceous sedimentary rock; 7—Ore body

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4.3.2.4.2.2 Main Controlling Factors of Hydrothermal Fluid Metallogenic Subsystem

The system is represented by Laochang Pb, Zn, Ag deposits. The main controlling factors include host strata and lithology, volcanic apparatus and fault structures and hydrothermal alteration.

  1. (1)

    Host strata and lithology. The host strata in the mining area include the marine volcanic-sedimentary rocks of the Lower Carboniferous Yiliu Formation and the Middle and Upper Carboniferous carbonate rocks. The volcanic-sedimentary rock series of the Yiliu Formation belongs to the calc-alkaline tholeiitic basalt series and the alkaline basalt series (dominant), which can be divided into three major volcanic eruption-sedimentary cycles with eight layers (Fig. 4.13). Each cycle begins with the overflow of basalt magma and ends with the eruption of andesite magma. The ore bodies mainly occur in the lower volcanic cycles composed of trachybasalt, trachyandesite lava, breccia tuff, sedimentary tuff, exhalite, tuffaceous siltstone, limestone, etc. The ore bodies are developed in the upper part of the rhythm, accompanied by sulfide siliceous exhalite (Yang 1989). In the Middle and Upper Carboniferous, there are dolomite and limestone intercalated with dolomitic limestone, with vein-like ore bodies.

    Fig. 4.13
    figure 13

    Comprehensive stratigraphic histogram of the Laochang Ag polymetallic ore district, Lancang

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  2. (2)

    Volcanic apparatus and fault structure. The ore body is obviously controlled by volcanic apparatus and fault structures. The volcanic apparatus consists of two volcanic domes and three volcanic depressions (Liu et al. 2000), which in order from west to east includes the Xiangshan volcanic depression (corresponding to the Xiangshan syncline), the Qinglongqing volcanic dome (corresponding to the Qinglongqing anticline), Xiongshishan volcanic depression (corresponding to the Xiongshishan syncline), Laochang dome (corresponding to the Laochang anticline), Shuishishan volcanic depression (corresponding to the Shuishishan anticline) (Fig. 4.14). Among them, the Laochang volcanic dome is distributed along the east side of the F1 fault in a nearly north–south direction, with a relatively large scale, and the Qinglongqing volcanic dome is distributed along the north side of the F4 fault in a northwest direction. The main ore bodies are distributed in volcanic depressions, and the volcanic domes are mostly vein-shaped and network-vein-shaped ore bodies. Granitic dykes and skarn copper mineralization have been found recently during deep drilling for construction, and it is speculated that there is a concealed rock mass or porphyry in the lower part.

    Fig. 4.14
    figure 14

    Outline map of Lancang Laochang silver polymetallic deposit

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  3. (3)

    Hydrothermal alteration. The ore deposit has strong hydrothermal alteration, complex types, multi-phase superposition and obvious zoning characteristics. The main alteration types include iron-manganese carbonatization, propylitization, carbonation, silicification, pyritization and skarnization. It is generally shown that iron-manganese carbonation is developed in the upper ore group (III ore group), propylitization and skarnization are developed in the lower ore group (II and I ore group), and carbonation, silicification and pyritization are all over the ore group.

4.3.3 The Continental Marginal Convergent Metallogenic Giant System

In the Sanjiang giant orogenic belt, the continental marginal convergent metallogenic giant system is mainly developed in four composite orogenic belts with the Qamdo-Pu’er microblock as the central axis of the opposite hedging collage, namely the Yidun Island arc orogenic belt, the Jinsha River orogenic belt, the Lancang River orogenic belt and the Salween River orogenic belt. Along with the formation and evolution of orogenic belts, three important metallogenic systems are usually developed: subduction orogenic metallogenic system, collisional orogenic metallogenic system and post-orogenic extensional metallogenic system. This section mainly systematically expounds the metallogenic systems of the Yidun island arc orogenic belt and the Jinsha River orogenic belt.

4.3.3.1 The Background of Metallogenic System

4.3.3.1.1 Yidun Island Arc Collision Orogenic Belt

The Yidun island arc collision orogenic belt is a composite orogenic belt in the Tethys giant orogenic belt, which began during the late Indosinian (Norian-Rhaetian) large-scale subduction orogeny (Hou 1993; Hou et al. 1995), experienced the collisional orogenic process in the Yanshanian period, including arc-continent collision and continental crust shrinkage and thickening, orogenic uplift and extension, and finally suffered from the superimposition and reconstruction of intracontinental convergence and large-scale shearing and translation during the Neo-Tethys period. The westward subduction of the Ganzi-Litang oceanic crust plate resulted in the development of the Yidun remnant arc (237–210 Ma). Given the nature of the thin continental crust underlying the island arc, as well as the inhomogeneity of the subduction angle of the oceanic crust plate, the north–south segment of the remnant arc is shaped. The Changtai arc in the northern section is characterized by tension, and four secondary tectonic units can be identified from east to west, namely outer arc (volcanic-magmatic arc), intra-arc rift, inner arc (residual arc) and back-arc spreading basin. The island arc is characterized by an intra-arc rift basin formed by inter-arc rifting and a back-arc-basin formed by back-arc expansion. The former is marked by the basalt-rhyolite bimodal rock assemblage and the deep-water fault basin (Hou 1993); the latter is characterized by a shoshonite—high-potassium rhyolite bimodal rock assemblage and deep-water black rock series deposits. The Shangri-La arc in the southern segment is characterized by compression, the island arc is dominated by simple volcanic-magmatic arcs and basically no back-arc expansion basins are developed. The volcanic-magmatic arc is characterized by andesite-dacite and super-hypabyssal emplaced intermediate-acid rock mass (Hou et al. 1995), and there is no corresponding volcanic activity in the back-arc area. The arc-continent collision occurred around 210 Ma, which not only led to the uplift of the remnant arc terrane, but induced the continental crust melting to form syn-collision granite, which was superimposed on the volcanic-magmatic arc. At about 189 Ma, the delamination of the lithosphere might have induced asthenosphere upwelling, and the crust began to appear extensional tension fracture, inducing crustal melting and felsic volcanic eruption, and forming the intraplate fissure-type acidic rhyolite series distributed along the high-potassium rhyolite belt in the back-arc-basin. Subsequently, the lithosphere of the orogenic belt was further stretched and even collapsed. At about 80 Ma, there was massive emplacement of A-type granite, forming intermittently distributed A-type granites belts extending for hundreds of kilometers in the NNW direction in the inner (west side) of the orogenic belt (Hou et al. 2001a, b).

4.3.3.1.2 Jinsha River Orogenic Belt

The Jinsha River orogenic belt is an important orogenic belt in the Tethys giant orogenic belt, which began in the large-scale subduction orogeny in the early period of Early Permian (Mo et al. 1993; Li et al. 1998; Wang et al. 1999), experienced the collisional orogenic process of the Early and Middle Triassic (including arc-continent collision and continental crust shrinkage and thickening, magmatic activity and orogenic uplift), as well as the post-orogenic extension in the early period of Late Triassic and finally went through the superimposition and reconstruction of intracontinental convergence and large-scale shearing and translation during the Neo-Tethys period. It is a composite orogenic belt formed by successively developed continental marginal arcs and collision orogenic belts affected by the collision and uplift of the Qinghai-Tibet Plateau. Since Devonian, the Jinsha River rift basin was developed between Qamdo landmass on the west side and Zhongza block on the east side. It has expanded strongly in Carboniferous and formed an initial ocean basin and received radiolarian siliceous rock-thick stratiform limestone-black mudstone low-density turbidite series. By the early Permian, the ocean basin expanded strongly and rapidly, forming a mature ocean basin, developing a new ocean crust marked by ophiolite complex and deep-sea sediments represented by siliceous argillaceous-sandy argillaceous flysch formation. At the end of the Early Permian, the oceanic crust plate of Jinsha River may be detached and subducted westward along the intra-oceanic fracture zone, resulting in the development of Zhubalong-Dongzhulin intra-oceanic arc and west canal river-Jiyi single arc back-arc-basin. Among them, a set of basalt-basaltic andesite-andesite island arc volcanic rock assemblages from tholeiite series to calc-alkaline series developed in intra-oceanic arc, while the oceanic crust volcanic rock assemblages marked by diabase sheet wall group and tholeiite and abyssal facies-subabyssal facies deposits represented by siliceous argillaceous-sandy argillaceous flysch formation developed in the back-arc-basin (Mo et al. 1993; Li et al. 1998; Wang et al. 1999). Around the late Permian, the expanding oceanic crust plate of Jinsha River subducted toward the Qamdo block on a large scale, resulting in the development of volcanic along the eastern edge of Qamdo block, forming the Permian continental margin arc of Jiangda-Deqin-Weixi (Mo et al. 1993; Li et al. 1998; Wang et al. 1999). The arc volcanic rocks evolved from tholeiite series through calc-alkali series to shoshonite series from morning till night, which marked the evolution process of volcanic arc’s occurrence, development and maturity. Volcanic facies of volcano-sedimentary rock series varied along the continental margin arc, with various kinds of sedimentary and large fluctuation terrain.

Since the early Triassic, the tectonic and sedimentary environment of the Jinsha River arc-basin system and its stable landmasses on the east and west sides have changed dramatically. At the end of the late Permian, the Jinsha River ocean basin subducted and closed and gradually turned into the arc-land collision stage. The main signs are as follows: the Jinsha River Ocean Basin forms a remnant ocean basin; the collision mountain arc is superimposed on the Jiangda-Deqin continental margin arc; the Zhongza landmass on the east side uplifts into land, without Middle Triassic; the P2/T1 shows unconformity; the Qamdo landmass becomes a foreland basin, without Middle and Lower Triassic. As a result of arc-land collision and land-land docking, collision or post-collision intermediate-acid volcanic rocks and their associated intrusions developed in Shusong-Tongyou area in the southern segment of the continental margin arc. Collision or post-collision basaltic andesite-andesite-dacite-rhyolite assemblage developed in Jiangda-Xu Zhong area in the northern segment of the continental margin arc, covering the purple-red conglomerate of the early Triassic foothills, and superimposed on the continental margin arc.

In the Late Triassic, crustal extension began to appear in the collision orogenic belt. The mountain root delamination of the orogenic belt and asthenosphere upwelling caused by this may lead to the thinning and strong extension of the continental crust of the orogenic belt, even the collapse of the orogenic belt, thus forming extensional basins and even extensional rift (Wang et al. 1999). In the southern part of Jinsha River orogenic belt, extensional basins were formed by post-collision extension, such as Luchun-Hongpo basin and Reshuitang-Cuiyibi basin, and basalt-rhyolite bimodal rock assemblage, subabyssal facies turbidite and sandy argillaceous flysch were developed. In the northern section of Jinsha River orogenic belt, the post-collision extension was obviously strengthened. Jiangda continental margin arc expanded strongly and formed a volcanic-sedimentary basin of the Late Triassic. Jiangda continental margin arc received a sequence of basic-neutral-acidic calc-alkaline volcanic rocks (Dongka Formation) dominated by marine. On the west side of Jiangda continental margin arc, the crust expanded strongly to form a rift basin, and a sequence of marine pillow basaltic lava and gabbro-diabase wall group developed along the Xiaxiula-Shengda line. By the end of Late Triassic, the extensional basin gradually shrank and destroyed, and a large number of gypsum-salt deposits composed of gypsum, barite and siderite developed.

4.3.3.2 Metallogenic System Types

The metallogenic system in orogenic belts is closely related to the formation and evolution of orogenic belts and the tectonic–magmatic–sedimentary environment in different evolution stages of orogenic belts. With the evolution of orogenic belts from oceanic crust subduction orogeny through arc-continental collision orogeny to post-orogenic crustal extension, due to mineralization, it constitutes a continental margin convergent giant metallogenic system and several important metallogenic systems in orogenic belt.

4.3.3.2.1 Subduction Orogenic Metallogenic System

In the Late Triassic ancient island arc belt of Yidun, a subduction orogenic metallogenic system developed. However, the development types of metallogenic systems are different in different sections of island arcs. In the intra-arc rift zone of the Changtai extensional arc in the northern part of the island arc, it developed the hydrothermal fluid metallogenic subsystem and formed large VHMS deposits represented by Gacun deposit and Gayiqiong deposit and a batch of same type deposits, occurrences, mineralized anomalies and ore-induced anomalies, which are strictly confined to the intra-arc rift zone and its internal fault basins and volcanic depressions. In Shangri-La compressive arc in the southern section of the island arc, it developed magmatic hydrothermal metallogenic subsystem and formed porphyry deposits and skarn deposits represented by Xuejiping deposit and Hongshan deposit, which constituted an important copper polymetallic ore concentration area in Shangri-La area. This was closely related to hypabyssal-super-hypabyssal intermediate-acid rock masses and rock stock. In the back-arc-basin of Changtai arc, it developed back-arc volcanic hydrothermal metallogenic subsystem and formed epithermal deposits represented by Kongmasi deposit and Nongduke deposit, which constituted a new silver-gold-mercury metallogenic belt. This is closely related to high-potassium rhyolite. In Jinsha River orogenic belt, the subduction orogenic metallogenic system is developed in early Permian when Jinsha River Ocean Basin subducted westward and intra-oceanic arc and continental margin arc have formed and evolved. In the Zhubalong-Dongzhulin intra-oceanic arc, an arc magma-hydrothermal metallogenic subsystem related to Permian intermediate-basic volcanic rocks (basaltic andesite-andesite) has developed, and VHMS deposit has formed, represented by Yangla copper deposit. In Jiangda-Deqin-Weixi Permian continental margin arc, arc volcanic hydrothermal Cu–Au–Pb–Zn mineralization and corresponding metallogenic subsystem related to arc volcanic rock series have developed, and polymetallic deposits have formed, represented by Nanren Cu–Au–Pb–Zn polymetallic deposit.

4.3.3.2.2 Post-orogenic Extensional Metallogenic System

After a short arc-continent collision, Yidun island arc collision orogenic belt immediately entered the post-orogenic lithospheric extension stage. With the linear eruption of acid rhyolitic volcanic rocks and the large-scale intrusion of A-type granite, the post-orogenic extensional metallogenic system developed. Among them, A-type granite belt controls the development of magmatic hydrothermal metallogenic subsystem, and a tin polymetallic deposit assemblage has formed, represented by Nianlong polymetallic deposit. These deposits constituted an important tin-silver polymetallic ore belt. The extensional zone controls the development of tectonic-fluid metallogenic subsystem, and hydrothermal silver deposits or silver-bearing polymetallic deposits’ assemblage has formed, represented by Xiasai deposit. These deposits constituted an important silver polymetallic ore concentration area.

In Jinsha River orogenic belt, the post-collision extensional metallogenic system developed in the late evolution stage of the orogenic belt when mountain root delaminated and crust extended. This is the most important metallogenic system in this orogenic belt. The metallogenic system consists of at least two metallogenic subsystems. One is the hydrothermal fluid metallogenic subsystem. In Deqin (the southern part of the orogenic belt), the submarine sedimentary exhalative VMS deposits, which are related to bimodal rock assemblage and occurred in acid rhyolitic volcanic rock series, were formed. The deposits are concentrated in deep-water volcanic-sedimentary basins caused by extensional fault, represented by Luchun deposit and Hongpo copper polymetallic deposit. In Zhaokalong-Dingqinnong area in the northern part of the orogenic belt, mineralization occurred in shallow-water facies or sea-land intersecting facies intermediate-acid volcanic rock belt, which is formed in the post-collision extensional environment. Then, the exhalative-sedimentary sulfide deposits were formed in shallow-water environment, such as Zhaokalong iron-silver polymetallic deposit and Dingqinnong silver-copper polymetallic deposit. In Xiaxiula-Shengda extensional rift basin in the northern part of the orogenic belt, mineralization is controlled by the activities of contemporaneous fault, rift basins and hydrothermal fluid in the post-collision extensional stage. The hydrothermal sedimentary sulfide deposits with hydrothermal sedimentary rocks as the main host rocks were formed, including Zuna silver-bearing lead–zinc deposit. Although each of the three types of deposits have its own characteristic, they constitute a unified metallogenic subsystem developed in the post-collision extensional environment. Luchun deposit represents the products of deep-water volcanic-sedimentary-hydrothermal mineralization in post-collision extensional environment. Zhaokalong deposit represents the products of volcanic-sedimentary-hydrothermal mineralization in shallow-water environment. Zuna deposit represents the products of hydrothermal sedimentary mineralization far away from volcanic environment in post-collision extensional rift basin. The second is magmatic metallogenic subsystem, which mainly develops in andesite-diorite porphyrite complex area in Jiangda area of the north-middle section of orogenic belt. Porphyrite iron ore is formed primarily, represented by Jiangda iron ore. This type of deposit may have formed in the early stage of post-collision crustal extension or the transformation stage from continental margin arc to extensional basin.

4.3.3.3 Metallogenic System Structure

The structure of metallogenic system should include temporal, spatial and chemical structure, that is, the temporal framework of metallogenic events in the metallogenic system, the boundary scale of metallogenic system and its mineralization and the metal assemblage, mineralization zoning and distribution of elements anomaly in the metallogenic system.

4.3.3.3.1 Subduction Orogenic Metallogenic System

In Yidun ancient island arc zone, the subduction orogenic metallogenic system takes this island arc zone as its boundary, covering secondary tectonic units such as main arc, intra-arc rift and back-arc spreading basin. The main body of the subduction orogenic metallogenic system developed in the Late Triassic, with its age ranged from 237 to 200 Ma. The hydrothermal fluid metallogenic subsystem is limited by the intra-arc rift zone of Changtai arc. Although the mineralization is generally controlled by the intra-arc rift zone, the deposits are mainly concentrated in volcanic depressions and fault basins in the intra-arc rift zone. The metallogenic age ranges from 238 to 210 Ma. Among them, the mineralization age of Gacun VHMS deposit is about 210–221 Ma and that of Gayiqiong VMS deposit is 200 Ma (Hou et al. 1995). Mineralized metal is mainly base metal Zn–Pb–Cu, accompanied by a small amount of precious metal Ag–Au. As far as metallogenic zone is concerned, no obvious metal spatial zoning is found. But single deposit shows clear vertical zoning, which is Cu–Zn → Zn–Pb–Cu → Pb–Zn–Ag → Ag–Pb–Zn → Pb–Ba from bottom to top.

The magmatic hydrothermal metallogenic subsystem is confined to Shangri-La magmatic arc and mainly distributed around some hypabyssal-super-hypabyssal intermediate-acid rock masses and rock stock. Its production is based on ore concentration areas. Mineralization also mainly occurred in Indosinian. Among them, the mineralized porphyry age of Xuejiping copper deposit is 224 Ma, and the metallogenic age of Hongshan copper-bearing polymetallic deposit is 214 Ma (Tan 1985). The deposit types of this subsystem are mainly porphyry and skarn. Among them, ore-bearing porphyry is more neutral than typical porphyry copper deposit, and it is the homologous and heterogeneous product of Shangri-La island arc andesite. Ore-bearing skarn is characterized by stratiform-stratiform-like skarn, which may be the associated product of porphyry copper deposits. Mineralized metal mainly includes base metal Cu, accompanied by a small amount of Zn–Pb–Fe (Yang et al. 2001). The metal spatial zoning in the ore concentration area is not obvious, but it generally shows the outline of Cu-rich metal zone in the middle section and Pb–Zn–Ag-rich metal zone in the edge.

The back-arc volcanic hydrothermal metallogenic subsystem is restricted to the back-arc-basin. The mineralization takes place in the back-arc acidic rhyolitic volcanic rock area. The epithermal deposit occurs in the high-potassium rhyolitic volcanic rock, forming an intermittently distributed Ag–Au–Hg ore belt. The metal zoning along the ore belt is obvious. Hg mineralization is mainly concentrated in the northern section of the metal zone along the ore belt, represented by Kongmasi large mercury deposit, which occurs in the contact zone between rhyolitic volcanic rocks and overlying limestone. Ag–Au mineralization is mainly concentrated in the middle section of the metal zone along the ore belt, represented by Nongduke medium-sized silver deposit, which occurs in high-potassium rhyolite volcanic rocks and their fracture zones. Au–Ag mineralization is mainly concentrated in the southern section of the metal zone along the ore belt. Because of the extremely low exploration degree, most of the metal zone in the southern section is some ore occurrences, mineralized spots and ore-induced anomalies at present. The post-orogenic extensional metallogenic system is superimposed on the island arc orogenic belt and mainly developed in the A-type granite belt and within 10 km of its two sides. The development age of the metallogenic system is about 138–70 Ma (Qu et al. 2001).

In Jinsha River orogenic belt, the subduction orogenic metallogenic system occurred in its early intra-oceanic arc and continental margin arc, and the main body of the system developed in Permian arc-forming period. In the Permian intra-oceanic arc, although the metallogenic subsystem related to marine intermediate-basic arc volcanic rock series constitutes the main body of Yangla deposit, the initial metal enrichment formed in Permian has suffered from the superposition and transformation of magma-hydrothermal liquid and further metal enrichment in late Indosinian. Therefore, although the main body of metallogenic system occurred in the Permian intra-oceanic arc period, the mineralization may extend to Indosinian and Yanshan. Despite main body of sulfide deposits occurring in specific horizons of arc volcanic rock series, the spatial position of ore-rich bodies is closely related to Indosinian granite porphyry. The mineralized metal assemblage is Cu–Zn, and the regional zoning of mineralized metals has not been found yet. On the Permian continental margin arc, although there are also metallogenic subsystems related to arc volcanic rock series developed, no large-scale VMS deposits have been found, and the mineralized metal assemblage is Pb–Zn.

4.3.3.3.2 Post-orogenic Extensional Metallogenic System

The post-orogenic extensional metallogenic system in Yidun collisional orogenic belt takes this collisional orogenic belt as its boundary. The system is mainly confined to the tectonic–magmatic–sedimentary formation formed in late post-orogenic collisional extensional stage. The main body of the system developed in the lithospheric extensional stage and the orogenic belt collapse stage, with the system age ranges from 100 to 70 Ma. Magmatic hydrothermal metallogenic subsystem is mainly confined to A-type granite and its inner and outer contact zones. The major mineralized metals are tin and tin-bearing polymetallic metal, and skarn-type deposit is principal deposit. From Gaogong in the north to Rongyicuo in the south, the emplacement age of ore-bearing rock mass is from 102 to 75 Ma, corresponding to which the main mineralized metals change gradually from tin to silver. The metallogenic subsystem of tectonic fluid is mainly limited within 2–10 km of the periphery of A-type granite belt. The system mineralization is mainly controlled by large fault zone or interbed detachment zone formed in crustal extension stage. The deposit type of the system is mainly fracture zone altered rock, represented by Xiasai deposit and Lianlong deposit. Ag is the main mineralized metal element, followed by Zn–Pb. The spatial zoning of metal seems to be related to the distance from the “heat source” (granite). If the metal zone is close to the rock mass, it is mainly composed of tin-bearing polymetallic ore, with the metal assemblage of Sn + Ag + Pb + Zn. If the metal zone is far away from the rock mass, it is mainly silver-bearing polymetallic ore, with the metal assemblage of Ag + Pb + Zn.

In Jinsha River orogenic belt, the post-collision extensional metallogenic system is distributed as a whole in extensional basins or extensional rift belt formed by mountain root delamination and crustal extension in orogenic belt. The system generally developed in the relatively short geological period of the early period of Late Triassic. Due to the north–south segmentation of collision orogenic belts and the development differences of extensional basins, several different metallogenic subsystems have been formed. The submarine hydrothermal metallogenic system was developed in the deep-water extensional rift basin filled with “bimodal” volcanic rock series in the middle part of the orogenic belt. VMS deposits under deep-water environment were formed, with the mineralized metal assemblage of Cu–Pb–Zn or copper polymetallic type. The hydrothermal-sedimentary metallogenic subsystem was developed in the shallow-water extensional rift basin of intermediate-acid volcanic-sedimentary rock series in the northern part of the orogenic belt. A shallow-water environmental exhalative-sedimentary sulfide deposit was formed, with the mineralized metal assemblage of iron-silver polymetallic type. The magmatic hydrothermal metallogenic subsystem was developed in the weak extensional area between the north and south extensional basins of the orogenic belt, accompanied by a large number of hypabyssal-super-hypabyssal emplacement of intermediate-acid magma. Porphyrite deposits were formed, with the mineralized metal assemblage of iron domination.

4.3.3.4 Main Controlling Factors of Metallogenic System

The main controlling factors of metallogenic system mainly refer to the background, environment, material and the restriction leading to the dispersion-enrichment-deposition of ore-forming materials in the system. The coupling action of various factors in the system leads to the development of metallogenic system and the formation of mineralization assemblage of deposits.

4.3.3.4.1 Main Controlling Factors of Subduction Orogenic Metallogenic System
4.3.3.4.1.1 Main Controlling Factors of Subduction Orogenic Metallogenic System in Yidun Orogenic Belt

The main controlling factors of subduction orogenic metallogenic system include island arc tectonic environment, super-hypabyssal emplacement magma or magma chamber, convection hydrothermal fluid, marine felsic rock series supplying ore-forming materials, relatively closed sag basins and caprock deposits.

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    Arc magma-hydrothermal metallogenic subsystem

In arc magma-hydrothermal metallogenic subsystem, relatively compressed magmatic arc environment, relatively closed caprock system and hypabyssal or super-hypabyssal emplacement of intermediate-acid that segregated hydrothermal fluid are the main controlling factors for the development and formation of porphyry copper deposits and skarn copper polymetallic deposits.

The biggest difference between compressional island arc and tensile island arc lies in the stress state of the main arc area and back arc area in the late subduction orogeny. As mentioned above, under the state of tensile stress, volcanic arcs crack to form intra-arc rift, accompanied by “bimodal” volcanic activities and basin fault. Submarine metallogenic hydrothermal systems were developed. In the compressive island arc environment, the volcanic arc is not tensile cracking, but compressive uplift under compressive stress. Under this background, arc magma will be strongly differentiated. Some arc magmas show arc volcanic eruptions, while some arc magmas show hypabyssal or super-hypabyssal emplacement. It eventually forms a series of porphyry, porphyrite, rock stock and rock bodies, constituting volcanic-intrusive complex with volcanic rocks. Acid porphyry will lay a material base for the formation of porphyry copper deposits, and the emplacement of intermediate-acid rock mass will provide conditions for the formation of skarn-type deposits. In Shangri-La compressive arc, volcanic-intrusion developed on a large scale with magma along the island arc. Among them, volcanic rocks are mainly andesite, which is difficult to form mineralized parent rocks. The super-hypabyssal emplacement of late product of magmatic evolution forms quartz monzonitic porphyry and monzonite granite porphyry, which become important metallogenic parent rocks of porphyry copper deposits and constitute an important basis of arc magma-hydrothermal metallogenic subsystem. For example, Pulang copper deposit and Xuejiping porphyry copper deposit were formed in the arc volcanic-intrusive complex belt and occurred in the inner and outer contact zones of quartz monzonitic porphyry and monzonitic granite porphyry. Diorite porphyrite and/or quartz dioritic porphyrite are formed by hypabyssal emplacement or bedding penetration of arc magma evolution products. Contact metasomatic skarn and/or remote melt-hydrothermal reformed skarn can be produced in the contact zone between them (diorite porphyrite and/or quartz dioritic porphyrite) and limestone, which becomes the main ore-bearing unit of skarn-type copper polymetallic deposits. For example, skarn-type polymetallic deposits in Hongshan, Hongniu and Gaochiping were formed by mineralized skarns in the Upper Triassic sand-slate series in Shangri-La arc wing.

In Shangri-La volcanic-magmatic arc, porphyry-type copper deposits and skarn-type polymetallic deposits constitute a unified arc magmatic hydrothermal metallogenic subsystem. Spatially, skarn-type polymetallic deposits have deep metallogenic position and low horizon and are generally located in the wing of the volcanic magma arc, with relatively low metallogenic temperature. The metallogenic metals are Cu–Pb–Zn type, associated with Mo and Au, etc. Porphyry-type copper deposits have shallow metallogenic position and high horizon and are generally located in the core of volcanic magma arc, with relatively high metallogenic temperature. The metallogenic metal is Cu type. In time, although skarn-type polymetallic deposits and porphyry-type copper deposits were generally formed in the island arc orogenic stage, skarn-type polymetallic deposits may have earlier mineralization, which is roughly in the same period to or later than the arc andesite activity period. Porphyry-type copper deposits are formed relatively late and represented the final stage product of Shangri-La volcanic magma arc. Therefore, the two types of deposits may represent the early and late metallogenic products of arc magma-hydrothermal metallogenic subsystem, respectively, and the formation of the deposits requires a relatively compressive and stable environment to make arc magma fully differentiate and emplacement. A relatively closed caprock is needed to avoid boiling diffusion of ore-forming fluid. A hypabyssal-super-hypabyssal emplacement of intermediate-acid magma is needed to segregate magmatic hydrothermal fluid rich in metal matter in a closed condition.

4.3.3.4.1.2 Main Controlling Factors of Hydrothermal Fluid Metallogenic Subsystem in Intra-arc Rift

In the hydrothermal fluid metallogenic subsystem of intra-arc rift, the key factors for the development of this metallogenic subsystem and VMS deposit are the extension fracture system which promotes the convection of hydrothermal fluid, the deep-water fault basin which prevents the boiling of hydrothermal fluid, the shallow magma chamber which drives the circulation of hydrothermal fluid and the complex rock series composed of extremely thick rhyolitic volcanic rocks and intrusive dikes (metal materials of extremely thick rhyolitic volcanic rocks and intrusive dikes are leached by hot water fluid).

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    Intra-arc rift and contemporaneous fault. The ancient and modern submarine hydrothermal mineralization studies show that although VMS deposits occur in island arcs, oceanic ridges, intraplate volcanic activity centers and post-collision extensional environments, mineralization occurs in different extension fracture environments. In ancient and modern island arc belts, VMS deposits do not occur on volcanic arcs, but in intra-arc rift or back-arc extensional basins. Mineralization does not develop in the stage of island arc orogeny, but in the stage of island arc cracking. This is true of Japanese black ore, Gacun deposit and Okinawa Trough black chimney sulfide deposit. The reasons are as follows: On the one hand, the extension fracture environment provides an important channel and transport system for long-term stable convection of hydrothermal fluid. On the other hand, the extension fracture environment also provides important conditions for strong water/rock reaction and sufficient leaching of ore-forming materials. In Gacun deposit, a group of contemporaneous basement and basin margin faults, which are distributed in NNW direction and formed in the stage of intra-arc extension fracture, have been identified and constituted the channel of fluid migration. At the same time, the intersection network between them (contemporaneous basement and basin margin faults mentioned above) and the fault system spreading close to EW direction become the discharge vent of hydrothermal fluid on the seabed (Hou et al. 2001).

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    Fault basins and volcanic depressions. VMS deposits and ore fields are concentrated in the sub-fault basins and volcanic depressions in the intra-arc rift zone. Three deep-water fault basins (800–1200 m) have been identified, namely Zengke Basin, Gacun Basin and Xiangcheng Basin. Zengke Basin is an area with concentration occurrence of three VMS deposits, including Gayiqiong deposit. In Gacun basin, Gacun deposit occurs in volcanic depressions in fault basins. High-precision magnetic survey data also clearly reveal that at least 2–3 similar volcanic lithostatic depressions and large-scale ore-induced anomalies are developed in the southern part of Gacun deposit. In Xiangcheng Basin, VMS deposits and occurrences already known are concentration occurrence in this basin. On the one hand, these fault basins and volcanic depressions provide necessary pressure for preventing hydrothermal fluid boiling. On the other hand, they provide important sedimentary space for hot brine storage and sulfide accumulation.

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    Bimodal assemblage and felsic rock series. Basalt-rhyolite bimodal rock assemblage is not only the regional volcanic rock symbol of intra-arc rift, but also an important source rock of ore-forming material. In Yidun Island Arc zone, basalt and rhyolite can occur interbedded and coexist in space. Basalt can occur in the lower part of ore-bearing rhyolite series (including Gacun deposit) or cover the top of ore-bearing rhyolite series (including Gayiqiong deposit). The relative scale of basalt and rhyolite series determines the ratio of w (Cu)/w (Pb + Zn) of VMS deposit. The larger the scale of basalt series is, the higher the Cu grade of the deposit will be, and vice versa. Rhyolitic volcanic rock series is not only the direct host surrounding rock of VMS deposit, but also the ore source of metal ore-forming materials dissolved by hydrothermal fluid. Therefore, its development scale directly controls the tonnage of VMS deposits. The larger the acid volcanic rocks are, the larger the deposit occurrence scale will be. As the main ore-bearing rocks, the lithology and lithofacies of rhyolitic volcanic rocks also have restriction on VMS deposits to some extent. It is possibly due to relatively large fluid migration pores, and pyroclastic facies often occur in vein-reticulated sulfide ore belts. Perhaps because rhyolitic magma provides some ore-forming materials, the highly differentiated out-phase of calc-alkaline acidic magma often has a close temporal and spatial relationship with VMS deposits.

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    Hypabyssal emplacement of magma chambers. The field detection and observation of the submarine metallogenic hydrothermal fluid system show that magma chambers of a certain scale often develop at a depth of 1–3 km below the ancient and modern submarine hydrothermal active areas. In the east of modern submarine active hydrothermal area, Pacific Ocean ultrafast expanding ridge (Urabe et al. 1995) and Okinawa Trough (Halbash et al. 1993; Hou et al. 1999) are the representatives. In typical ancient submarine hydrothermal area, black deposit in Japan and Gacun deposit (Skinner and Ohmoto 1983; Cathles et al. 1983) are the representatives. Modern magma chamber not only drives the convection of submarine hydrothermal fluid, but also injects some magmatic fluid (gas) and ore-forming materials into the hydrothermal system (Yang and Scott 1996). Ancient magma chamber has now been consolidated into intrusive rocks of different scales. The rock stock and dykes that intrude upward along the magma chamber front fracture zone often penetrate into the overlying volcanic rock series, forming a volcanic-intrusive complex, becoming an important ore-bearing rock series.

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    Convection Thermal Fluid System In the past, it was generally believed that the convection metallogenic hydrothermal fluid was mainly pore fluid (seawater) which flowed through rocks and had water/rock reaction (Ohmoto 1983). However, increasing evidence showed that the depressurization and degassing of felsic magma could produce magma fluid rich in metal chloride and contribute to the metallogenic hydrothermal fluid system (Urabe 1989–1992; Yang and Scott 1996; Hou et al. 1999). Oxygen isotope evidence and high-salinity fluid inclusion evidence from the Gacun deposit also show that the metal-rich fluid segregated by rhyolitic magma is injected into the submarine hydrothermal fluid system, forming metallogenic fluid rich in 18O and with high salinity (Hou et al. 1999).

Is the convection hydrothermal fluid system single-pass convection or double-diffusive convection? No agreement has been reached yet. Although the former is accepted by most scholars, the latter is supported by some new evidence. In the Gacun mining area, the quantitative calculation of the hydrothermal alteration system, the high-temperature and high-salinity data of the lower stratiform-like epidotization-silicification zone and the material change in the water/rock reaction confirmed that the submarine metallogenic hydrothermal fluid system is a double-diffusive convection system, and the deep hot brine or high-pressure fluid reservoir is formed in the upper part of the fracture zone at the top of felsic magma chamber. As an important heat medium and fluid source, it drives the convection of the upper cold seawater (Hou et al. 1995).

4.3.3.4.1.3 Back-Arc Volcanic Hydrothermal Metallogenic Subsystem

In back-arc volcanic hydrothermal metallogenic subsystem, the back-arc extensional tectonic environment, the shallow magma chamber that drives the fluid circulation, and the complex system formed by the extremely thick rhyolitic volcanic rocks-intrusive dikes (the metal material of the extremely thick rhyolitic volcanic rocks-intrusive dikes was leached by hydrothermal fluid) and the superimposition and transformation of fault tectonics are the key factors for the development of this metallogenic subsystem and volcanic rock-type epithermal Au–Ag-polymetallic deposits. Over the past decade, a number of super-large epithermal Au–Ag polymetallic deposits have been found in volcanic rock areas in the world. These deposits all occurred in the extensional tectonic environment of the back-arc rift in the active continental margin, and the ore-bearing rock series are all acid volcanic rocks formed in the late period of island arc evolution. The bimodal volcanic rock series in the Yidun Island arc back-arc-basin was developed on the continental crust basement by a strong extensional tectonic environment. It has the tectonic conditions for forming volcanic rock-type epithermal Au–Ag polymetallic deposits. At present, along this volcanic rock belt (Miange Formation), besides Nongduke middle-type Au–Ag polymetallic deposit and Kongmasi large mercury deposit, regional geochemical exploration and microwave remote sensing data also show a number of comprehensive mineralization anomalies such as Tage, Darike and Dulonggou, which show a good metallogenic prospect of this volcanic rock belt. Nongke mining area is dominated by Ag and Au, accompanied by As, Sb, Hg and other mineralizing elements. Mineralization is characterized by low-temperature hydrothermal solution. In the Kongsi mining area, a large mercury deposit has formed, and there are also high Ag, Cu, As, Sb and other ore-forming elements. It also shows the characteristics of low-temperature hydrothermal mineralization. Throughout the volcanic zone, the mineralization assemblage is dominated by Ag-Au-Hg, accompanied by metallic elements such as As, Sb, Cu and Zn.

The epithermal mineralization in Yidun Island arc back-arc-basin is related to highly acidic rhyolite rich in volatile matter. These rhyolites occurred in the source region of weakly enriched mantle, and the fluid components from subduction plates participated in the magma formation, accounting for about 50% of the fluid in the magmatism of the main arc zone. During the rising process, magma interacted strongly with crustal rocks before eruption, assimilating a large number of crustal materials. Ore-forming elements Hg, As, Sb may mainly come from these assimilated crustal rocks, and ore-forming elements such as Au and Ag may provide more from mantle source region.

4.3.3.4.2 Main Controlling Factors of Subduction Orogenic Metallogenic System in Jinsha River Orogenic Belt

The subduction orogenic metallogenic system of Jinsha River orogenic belt is characterized by submarine hydrothermal fluid mineralization and volcanic hydrothermal mineralization, and the submarine hydrothermal fluid metallogenic subsystem and volcanic hydrothermal metallogenic subsystem related to arc volcanic rocks are correspondingly formed and developed.

4.3.3.4.2.1 The Submarine Hydrothermal Fluid Metallogenic Subsystem in the Oceanic Arc Environment is Located in the Jinsha River Orogenic Belt

The submarine hydrothermal fluid metallogenic subsystem related to intra-oceanic arc volcanic rocks in the subduction orogenic metallogenic system developed in the westward subduction of Jinsha River ocean basin and the formation and evolution of intra-oceanic arc and continental margin arc in the early Permian. The intra-oceanic arc is built on the oceanic crust basement marked by an ophiolite melange belt, in which the basic volcanic rocks are typical oceanic ridge basalts. The zircon U–Pb ages range from 363 to 296 Ma (Chen et al. 1998), which proves that the Jinsha River oceanic basin developed from Carboniferous to Early Permian. The ore-bearing volcanic-sedimentary rock series is basalt-basaltic andesite-hornblende andesite assemblage with a thickness of more than 600 m and deep-water flysch formation. The hornblende of andesite has a K–Ar age of 257–268 Ma (Li et al. 1998), which indicates that the volcanic activity in the oceanic arc occurred from the late period of Early Permian to the late Permian. Intra-oceanic arc environment where submarine hot water system is developed, deep-water fault basin where hydrothermal fluid boiling is prevented, shallow magma chamber which drives fluid circulation, and a large number of intermediate-basic volcanic rocks, in which the metal was leached by hydrothermal fluid, and complex series composed of late intrusive dikes are the key elements for the development of this metallogenic system and Yangla deposit. The deposit was formed in the intra-oceanic arc environment formed during the detachment and subduction of Jinsha River oceanic crust, and volcanic activity provided heat source and related material sources. The ore-forming hydrothermal fluid is mainly the high-salinity fluid formed by the infiltration seawater and the interlayer water of volcanic-sedimentary rock series after fully extracting ore-forming minerals. The metal mainly comes from volcanic rocks, and the fluid is from a mixed source. Mineralization is in the high permeability intra-oceanic arc section, where the submarine hydrothermal solution upwells and accumulates on the spot. Then, a large number of colloidal and cryptocrystalline metal sulfide-bearing sediments and calcium-iron silicate deposits (primary skarn bed) are formed in the high-temperature hot water environment. After the deposit was formed, it experienced many times of tectonic-magmatism and was superimposed and reformed by the late metallogenic hydrothermal activities.

4.3.3.4.2.2 Volcanic Hydrothermal Metallogenic Subsystem in Continental Margin Arc Environment

Volcanic hydrothermal Cu–Au–Pb–Zn mineralization and corresponding metallogenic subsystems related to arc volcanic rock series developed in the Permian continental margin arc of Jinsha River-Deqin-Weixi. It developed in the westward subduction of Jinsha River oceanic basin and the formation and evolution of intra-oceanic arc and continental margin arc in the early Permian, forming polymetallic deposits such as Nanren Pb–Zn deposit and Cu–Au mineralization. The continental margin arc is formed on the continental crust basement marked by the continental margin volcanic arc zone, among which the intermediate-basic and intermediate-acidic volcanic rocks have typical island arc volcanic rock characteristics. The earliest arc volcanic activity occurred in the late period of Early Permian and lasted until the late Permian (Li et al. 1998), and the arc volcanic activity developed tholeiite series → calc-alkaline series → potassium basalt series volcanic rocks from early period till late period, which marked the complete process of island arc generation, development and maturity (Mo et al. 1993), and confirmed that the subduction of Jinsha River oceanic basin was reduced from early Permian to late Permian. The ore-bearing volcanic-sedimentary rock series is basaltic andesite-andesite with a thickness of 200 m and its corresponding subvolcanic rock (diorite porphyrite) assemblage and (tuffaceous) sandstone, siltstone, sandy mudstone, tuffaceous-siliceous rock and thick massive bioclastic limestone formation.

The key factors for the development of this metallogenic system and Nanzuo style deposit are the continental margin arc environment in which intermediate-acid volcanic rocks are developed, the shallow magma chamber that drives the volcanic hydrothermal cycle, a large number of metal material leached by hydrothermal fluid in intermediate-basic-intermediate-acid volcanic rock series and the superimposed transformation of the later fault tectonics. The deposit took shape in the continental margin arc environment formed during the subduction of Jinsha River oceanic crust, and volcanic activity provided heat source and related material sources. The ore-forming hydrothermal fluid is mainly high-salinity fluid formed by infiltration seawater and volcanic hydrothermal fluid, the metal mainly comes from volcanic rocks, and the fluid belongs to mixed sources. Mineralization is in the continental margin arc with high permeability, which is further enriched to form deposits by the superimposition and transformation of late fault tectonics.

4.3.3.4.2.3 Main Controlling Factors of Extensional Metallogenic System After Orogeny

Main Controlling Factors of Post-orogenic Extensional Metallogenic System in Yidun Orogenic Belt

The main controlling factors of post-orogenic extensional metallogenic system include crustal extensional environment, large-scale fracture and decollement structure, A-type granite emplacement and large-scale fluid migration. In different metallogenic subsystems, the types, configurations and coupling modes of these main controlling factors are different.

Magmatic Hydrothermal Metallogenic Subsystem

In the magmatic hydrothermal mineralization subsystem, A-type granite and its segregated magmatic fluid, limestone in granite contact zone and contact metasomatic skarn are the key factors of mineralization.

  1. (1)

    A-type granite. As a magmatic product in the collapse stage of the orogenic belt, the A-type granitic magma activity started at 100 Ma (Gaogong in the north) and ended at 75 Ma (Batang in the south) and reached the peak of magmatic activity at 80 Ma, forming more than ten rock bodies large and small, constituting the A-type granite belt with NNW direction. It was formed in the extension-collapse stage of the orogenic belt. According to rock assemblage, geochemical characteristics and strontium isotopic composition, granites can be divided into at least two types, namely A1 type and A2 type. The former type is represented by Zhalong, Gaogong, Rongyicuo, with an 87Sr/86Sr initial ratio of 0.74407. A1-type granite is a typical crust-derived molten product and formed in the early stage of orogenic belt extension-collapse. A2-type granite, represented by Lianlong rock mass, is small in number, with an 87Sr/86Sr initial ratio of 0.7095, which indicates that its magma was originated with the participation of some deep-seated basic materials and was formed in the late stage of the collapse of the orogenic belt (Hou et al. 2001). Nevertheless, both types of granites were originated from the argillaceous rock-rich crustal source area, the source rock of A1-type granite source area is relatively uniform and the composition of A2-type granite source area varies greatly. Both types of A-type granites produce accessory minerals-cassiterite, which reflect that magma is rich in tin. Tourmaline minerals often appear in rocks, suggesting that magma is rich in volatile components. Compared with ordinary granites, granites in this area are significantly enriched in elements Sn, Ag, Bi, Pb and W, with enrichment coefficients Sn and Ag reaching 8.14 and 4, respectively. In comparison with the tin-bearing granites in the world, the Sn content is fairly, but the w(Rb)/w(Sr) ratio is higher, which reflects the geochemical characteristics of tin-bearing granites in collision orogenic belt. Most rock bodies of A-type granite are tin-silver mineralized in different degrees, which proves that A-type granite is the first main controlling factor for the development of magma-hydrothermal metallogenic subsystem.

  2. (2)

    Contact metasomatic skarn. Contact metasomatic skarn is usually the main ore-bearing rock unit of tin-silver mineralization, although tin-silver mineralization also occurs in the inner contact zone of granite. According to the contact surrounding rock types, it can be divided into several skarn metasomatic types. In the contact zone between granite and calcareous limestone, diopside skarn and garnet skarn mainly occur, which constitute the most important metasomatism type in the area. In the contact zone between granite and argillaceous limestone, vesuvianite-diopside skarn and melilite skarn occurred. Both types of skarnization were accompanied by important tin-silver mineralization events, forming cassiterite-natural bismuth-polymetallic sulfide assemblages. The hydrothermal fluid after skarnization is transformed to be acidic, which leads to acidic leaching, accompanied by greisenization and sericitization, and corresponding cassiterite-polymetallic sulfide mineralization, superimposed on the mineralized skarn belt.

  3. (3)

    Tectonic-fluid metallogenic subsystem. In the tectonic-fluid metallogenic subsystem, granite which heats and drives fluid activity, fracture structure and interlayer decollement structure which transport fluid in large scale and structural intersection space suitable for fluid convergence are the main controlling factors of the system.

    1. (3.1)

      Extensional fracture and decollement structures. Extensional fracture and decollement structures are the main structural forms in the crustal extension and collapse stages of Yidun orogenic belt. The extensional fracture generally strikes NNW, which extends perpendicular to the main extensional stress direction. This extensional fracture may cut down the whole crust and spread along the eastern edge of rigid metamorphic basement blocks. Along the extensional fracture zone, structural breccia, regional linear zonal hydrothermal alteration and stratiform-like and ribbon-shape ore bodies controlled by fracture develop, which proves that extensional fracture zone is not only the main channel for large-scale fluid transportation and migration, but also the ore-holding space for metal deposition of ore-forming fluid. With the strong extension of the earth’s crust, a series of decollement structures have been formed. The detachment zone is generally NNW or/and near SN strike and mainly occurs in the extremely thick Upper Triassic sand-slate system. Similarly, these detachment zones are not only the active channel of hydrothermal fluid, but also the ore-holding space of ore bodies.

    2. (3.2)

      Granite and peripheral rock series. Altered rock-type silver polymetallic deposits, occurrences and ore-induced anomalies in the tectonic-fluid metallogenic subsystem are distributed along the eastern edge of the basement rigid block in the region and spatially occur in NNW extensional fracture and interlayer detachment zones, generally occurring within 1–10 km of the periphery of A-type granite block. In Xiasai mining area, five ore blocks occur in the Upper Triassic sand-slate series within 1.5–5.0 km of the periphery of Rongyicuo granite block. In Nanzhigou, Lianlong mining area, the silver polymetallic mineralization belt occurs in the upper Triassic sand-slate of the periphery of the Lianlong granite block. From the granite body to its periphery, it often evolves from skarnization to propylitization (chloritization + actinolization) to sericitization to silicification, and it is distributed in a linear belt along the NNW direction or/and SN direction fracture zone. This proves that the granite body may act as a “heat engine” to maintain the regional hydrothermal fluid activity, driving the large-scale migration of hydrothermal fluid along the extensional fracture zone, and moving in NNW direction and near S N direction to accumulate and unload at intersection part. The lead isotope data of the Xiasai deposit confirmed that metallic lead originated from volcanic-sedimentary rock series in the upper crust of the orogenic belt, and the sulfur isotope composition characteristics (δ 34S average—8.2 ‰) were far different from that of magma, which confirmed that the sulfur was not provided by granite. The large variation range of δ 34S value (−4.9‰ to −10.5‰) indicated that the sulfur in the deposit might be biological sulfur reduced by bacteria, or it may be that the hydrothermal fluid is metasomatism leached from the sedimentary rock series through which it flows, especially the upper Triassic neritic-shelf sand-slate series. The high element abundance of Ag, Pb, Zn, Sb, As, Bi and regional polymetallic register and geochemical anomalies in the Upper Triassic sand-slate series also indicate that the sedimentary rock series in the upper crust emplaced by A-type granite bodies have important potential to provide a large amount of ore-forming materials.

Main Controlling Factors of Post-orogenic Extensional Metallogenic System in Jinsha River Orogenic Belt

The post-orogenic extensional metallogenic system is constructed on the Jiangda-Deqin-Weixi Hercynian-Indosinian continental margin volcanic arc belt in the eastern margin of Changdu block. It is the product of mountain root delamination and crustal extension in the late evolution of the orogenic belt and is the most important metallogenic system in the Jinsha River orogenic belt. The metallogenic system consists of at least two metallogenic subsystems. One is a hydrothermal fluid metallogenic subsystem, and the other is a magmatic metallogenic subsystem. Among them, the hydrothermal fluid metallogenic subsystem is the most important metallogenic system in this belt, and the coupling of magmatism, sedimentation and fluid action in the superimposed volcano-sedimentary basin formed by the late extension mechanism of continental margin island arc collision orogenic belt is the main control factor of systematic mineralization.

  1. (1)

    Space–time range and constituent elements of the system. The spatial range of post-orogenic extensional metallogenic system is consistent with the Jiangda-Deqin-Weixi continental margin volcanic arc belt, and it evolves synchronously with the development stage of extensional (T3) structure in the late orogenic period. From the perspective of the source and evolution of ore-forming materials, the system composition should extend to the lower crust and upper mantle. The main metallogenic elements of the system include magmatic hydrothermal solution related to intermediate-acid intrusion, volcanic-jet hydrothermal solution related to volcanic eruption and underground circulating hot water possibly indirectly heated by deep magma, which are closely related to the formation of porphyrite iron ore, skarn iron-copper ore-magma metallogenic subsystem and jet polymetallic ore-hot water fluid metallogenic subsystem, respectively. Magmatism is responsible for the direct or indirect transport of ore-forming materials and energy to the system, which plays a decisive role in the metallogenic evolution of the system, especially the tectonic–magmatic mineralization in the late Triassic extensional basin stage.

  2. (2)

    Formation and evolution of the system. Because the host of the system is above the volcanic arc of the continental margin, after the collision and orogeny of the volcanic arc in the early and middle Triassic, the mountain root delamination and crustal extension in the late stage has resulted in the tensile collapse of the upper continental margin arc, which transformed the volcanic arc from a long-term compressive tectonic system to an extensional system, resulting in strong magmatism and the development of superimposed rift (depression) basins on it. At the initial stage of extensional detachment, it was composed of littoral facies-shelf facies clastic rocks mixed with volcanic rocks formation, and the sediments formed a combination sequence from coarse to fine, and the water body changed from shallow to deep, accompanied by strong homologous magma intrusion in the same period or later. In its early stage, it is neritic-sub-abyssal facies clastic rocks’ formation mixed with volcanic rocks. In the middle stage, it entered the peak of extension. The magma stored under the volcanic arc was injected into the basin on a large scale through volcanic eruption or magma intrusion, and the sub-abyssal facies-abyssal flysch and bimodal rock assemblage were formed in a short time. In the late period, it is sub-abyssal facies-neritic clastic rock formation mixed with volcanic rocks. At the end of the period, the basin changed from extensional and rifting to compressional, and the basin gradually shrank and died out, forming clastic rocks with molasse property and basic-intermediate-acid volcanic rocks and volcanic clastic rocks formation in littoral and neritic facies, and a large number of gypsum deposits and purple-red clastic rocks have accumulated.

    At the same time, the peak of tectonic–magmatic activity is also the time when the metallogenic system matures and enters the main metallogenic evolution stage, forming the hydrothermal fluid metallogenic subsystem. Mineralization is controlled by the syngenetic faults, rift basins and hydrothermal fluid activities in the post-collision extension stage, resulting in sedimentary exhalative deposit in the deep-water environment, such as Zuna silver-bearing lead–zinc deposit in the northern section, Luchun deposit in the middle section and Hongpo copper polymetallic deposit in the southern section of Laojunshan lead–zinc deposit. Mineralization took place in the shallow-water facies or the intermediate-acid volcanic zone in the land-sea interaction facies formed in the post-collision extensional environment, forming the sedimentary exhalative deposits in the shallow-water environment, such as Zhaokalong Fe–Ag polymetallic deposit and Dingqinnong Ag–Cu polymetallic deposit in the north section, Chugezha Fe–Ag polymetallic deposit in the middle section. Magmatic metallogenic subsystem mainly develops in andesite-diorite porphyrite complex area in the northern part of the orogenic belt from Jiaduoling to Jiangda, forming porphyrite-type iron deposits, represented by Jiangda iron deposit, which may have been formed in the early stage of crustal extension after collision, or in the stage of transition from continental margin arc to extensional basin. At the end of the middle period of the Late Triassic, the extensional activity tended to weaken, the magmatic activity stopped, and the metallogenic system shrank.

  3. (3)

    Main metallogenic elements

    1. (3.1)

      Magma properties and ore-controlling effect. Magma provides ore-forming energy and main ore-forming materials for the system. As an important space channel, magma eruption or intrusion apparatus controls the evolution of ore-forming fluid system derived from magma, which is the final positioning space of ore-forming materials-deposits of the system. As the extension and rifting occurred on the “basement” background of volcanic arc, its magmatic rocks generally showed high-potassium calc-alkaline series. The main rock types were basalt, rhyolite and intermediate-acid andesite-rhyolite, with a small amount of basic basaltic andesite or andesitic basalt. The properties of magmatic rocks in the orogenic belt control mineralization obviously, and the minerals related to acidic endmember volcanic rocks (rhyolite) are lead–zinc–copper–silver polymetallic deposits (such as Luchun zinc–copper–lead–silver polymetallic deposit and Laojunshan lead–zinc deposit). Minerals related to intermediate-acid endmember volcanic rocks (dacite rhyolite) are iron-copper-silver polymetallic deposits (such as Zhaokalong iron–silver polymetallic deposit, Dingqinnong silver–copper polymetallic deposit, Chugezha iron–silver polymetallic deposit). Minerals related to basic endmember volcanic rocks (basalt) are Ag–Pb–Zn polymetallic deposits (such as Zuna Ag–Pb–Zn polymetallic deposit). Iron-copper polymetallic deposits (such as Jiangda iron–copper deposit) are related to intermediate (acid) andesite volcanic eruption and diorite intrusion.

    2. (3.2)

      Ore control by volcanic/intrusion apparatus. The magmatic activity in the Late Triassic volcanic-sedimentary basin was controlled by NW–SN fault structure, and it was a fissure-type multi-center eruption, forming a series of volcanic eruptions of different sizes or intrusion apparatus distributed in belt. On the Zhaokalong-Dingqinnong belt, it is preliminarily recognized that volcanic apparatus may exist in the northwest side of Zhaokalong, Shengjie, Zhenama of northeast of Dingqinnong as well as Gemma and Ba Long between them, which have become important ore-controlling conditions for the formation of volcanic exhalative deposits in the Late Triassic. Jiaduoling area is another big volcanic-intrusive center, which controls the formation of large porphyry iron deposits and skarn deposits in peripheral areas. There is a long-term relationship between the volcanic eruption or intrusion apparatus and the deep magma chamber. During and after the magma activity, it is the channel and spout for the deep ore-forming fluid system to discharge outward. The ore-forming fluid forms a circulation mechanism with this as the center, and ore-forming materials are continuously extracted from the deep and surrounding volcanic rocks, and it was carried to favorable structural parts near the volcanic/intrusion apparatus and unloaded to form ore bodies. Therefore, large volcanic activity centers are often important conditions for the formation of large deposits or ore concentration areas and have the function of accumulating ore-forming materials in the metallogenic system.

    3. (3.3)

      The ore-controlling function of the basin. Ore-controlling basins are mainly confined depressions between volcanic uplifts and rift in rift basins. The confined depression mainly develops in the marginal zone of volcanic-sedimentary basin, which is located between volcanic highlands at that time. It is closely related to the late volcanic activity and receives volcanic material deposits from volcanic uplift, and a large number of volcanic lava, volcanic breccia/agglomerate and other volcanic eruption rocks are developed. The transition relationship between volcanic rocks and normal sedimentary rocks is crisscrossed vertically and horizontally, and edging carbonate rocks can be developed around the volcanic uplift. A large number of volcanic falling objects are found in edging carbonate rocks. Such confined depression is closely related to volcanic apparatus and formed relatively closed environment in a certain scope, becoming the favorable place for unloading of ore-forming fluid of volcanic apparatus. After entering the basin, the ore-forming fluid is mainly formed minerals through normal sedimentation. The hydrothermal sedimentary rock with its characteristic, namely Sedimentary exhalative (SEDEX) deposits, both Zhaokalong polymetallic deposit and Dingqinnong silver (copper) polymetallic deposit, show this mineralization feature. The rift developed in median axis of volcanic-sedimentary basin (rift basin) mainly grew a set of extremely thick abysmal-bathyal clastic rock, carbonate rock deposition in its extension process. Constrained by the extension fracture at the same period, it grew a set of volcanic lava with bimodal volcanic rock assemblage as the main part. Mineralization occurred in the main extension period (extension rift period) of the basin, featuring the development of slump breccia, calcite turbidite, silicious turbidite, tuffaceous turbidite and convolution structure. The formation of metallogenic thermal fluid system is related to volcanic-sub-volcanic magmatism. Then, the fluid was discharged to the basin through volcanic channel or syngenetic fracture. The mineralization is realized by hydrothermal deposit, accompanied with a set of hydrothermal sedimentary rock assemblage, namely VHMS or SEDEX deposit, represented by Zuna (sliver)–lead–zinc deposit, Luchun zinc–copper–lead–silver polymetallic deposit, Laojunshan lead–zinc deposit.

      The ore controlling of the basin is mainly manifested as the metallogenic-fluid system provides favorable space for discharging and unloading. The coupling of hydrothermal system, discharging channel and relatively closed basin is the key factor determined volcanic eruption deposit and hydrothermal sediment deposit in hydrothermal fluid metallogenic subsystem under extension system in Late Triassic.

4.3.4 Intracontinental Convergent Giant Metallogenic System

4.3.4.1 The Background of Intracontinental Convergent Metallogenic System

4.3.4.1.1 The Profound Transformation of Intracontinental Convergence to Physical Structure of Sanjiang Orogenic Belt Is the Most Important Constraint Condition for Mineralization

Since the Late Cretaceous, with the successive closure and died out of Middle-Tethyan Ocean and Neo-Tethyan Ocean, micro and small microblocks have dispersed at the margin of Eurasia and Gondwana has finally welded and combined with the parent landmass through multiple orogenies. Eurasia and Gondwana and Yangtze continent combined to form a new continent. However, the interaction and movement among landmasses did not stop, but entered an overall period of intracontinental convergence and plateau uplift. The Sanjiang area in Southwest China restricted by the Indian plate, Eurasian plate and Yangtze plate constitutes the earth dynamic environment of crust deformation in the area. The extrusion and jacking occurred continuously in Indian plate in NNE is the main power causing convergence and deformation in the area. Influenced by Paleo-Tethys and Meso-Tethys archipelagic arc-basin orogenic system, the physical structure of Cenozoic Sanjiang crust shows extreme nonhomogeneity, block segmentation, soft-hard interbeddings. It went through complex tectonic deformation in intracontinental convergence. It generally showed large-scale shortened horizontal thickness in NE-NEE, forming Hengduan Mountains in nearly NS direction and Sanjiang stream sediment. After strongly extrusion, it formed tectonic wasp-waist near north latitude line 28°. Qamdo block in NW direction and Lanping-Pu’er block have extruded and skidded off toward two sides, respectively, forming huge “X’’ shape structure knot in Sanjiang area. With the extrusion and shortening of the crust and the skid-off of the block, taking the Qamdo-Lanping block as the central axis, a large-scale tectonic collision took place between the mountain systems on both sides. At the same time, a large-scale strike-slip activity has occurred between the blocks and the orogenic belts on both sides. These huge deformation structures have formed during the intracontinental convergence process not only deeply reformed the upper crust, but also led to the extensive development of thrust nappe, strike-slip pull-apart and extensional gliding nappe structures in the Sanjiang area. The intense intracontinental convergence even affected the lower crust and upper mantle, causing crust-derived and mantle-derived magma activities, which had an extremely important impact on regional mineralization and became an important constraint condition of intracontinental convergent giant metallogenic system.

4.3.4.1.2 Intracontinental Convergence Mineralization

Intracontinental convergence is a large-scale transformation, adjustment, recombination and integration of crust tectonic and physical composition after the evolution of Tethys MABT, resulting in widely activization of mantle matter. Two major structural system transformations in Paleo (Meso)-Tethys have laid an important geological structural background and material foundation for intracontinental convergence mineralization. From the successive cracking and stretching to subduction collision of Lancang River, Jinsha River, Ganzi-Litang Ocean Basin and Nujiang Ocean Basin, the tectonic-magmatism in the crust-mantle conversion process has profoundly influenced the physical structure of the Sanjiang crust, including the injection of multiple molten magmas from the upper mantle, lower crust, subduction ocean crust and the crust itself into the upper crust, and the distribution and location of ore-forming materials in the crust due to the fluid action in the magma evolution process, especially in volcanic island arc orogenic belt, where there are not only deposits formed by metal accumulation, but also caused relatively enrichment of metallogenic elements in stratum rock. Subsequently, the foreland basins (such as Qamdo basin and Lanping basin) developed on the block adjacent to the orogenic belt received a large amount of erosion materials from the volcanic arc orogenic belts on both sides. The materials in the orogenic belt were further differentiated through supergene weathering and sedimentation, and some ore-forming materials were transferred and deposited in the extremely thick stratum sedimentary rocks of the basin. Then, the ore-forming material was distributed again and was enriched in some rocks, such as sandstone-type copper mineralization widely occurring in the Upper Triassic, Jurassic-Cretaceous and Paleogene in Qamdo basin and Lanping basin which is related to this to a certain extent. Taking Lanping Basin as an example, hydrothermal sedimentary mineralization has occurred in the T3-J1 intracontinental rift metallogenic stage, followed by sedimentary copper mineralization in the depression basin metallogenic stage (J2-3) and foreland basin metallogenic stage (K), and copper, lead, zinc and other ore-forming materials were initially enriched in the extremely thick Jurassic-Cretaceous red beds. These material conditions influence and restrict the occurrence of Himalayan mineralization to some extent. On the basis of long-term tectonic-metallogenic evolution, sedimentation, accumulation, intracontinental convergence created more favorable conditions and opportunities for mineralization, causing large-scale mitigation, enrichment and mineralization of ore-forming material, forming a batch of large and super-large deposit such as Yulong copper deposit, Jinding lead–zinc deposit, Ailaoshan gold deposit. Some deposits formed before intracontinental convergence were transformed and enriched. It has become a consensus that Cenozoic is the most important metallogenic period of Tethys in Sanjiang.

Himalayan mineralization is not a simple repetition on the basis of early mineralization, but an inherited development and advance of mineralization in a wider three-dimension structure, featuring in metallogenic tectonic environment, metallogenic mechanism, mineralization, intensity and scale, etc. In the process of intracontinental convergence, due to the cross-tectonic unit action of tectonic, magma and fluid, various geochemical domains with constraints on mineralization, which were established based on blocks and sutures (suture zone) in the early days, became open systems. There were extensive material and energy exchanges between blocks and orogenic belts, and ore-forming materials and energy have not only covered the upper crust, but also extended to the lower crust-upper mantle vertically. The multiple sources of ore-forming fluids and ore-forming materials and the complex assemblage of ore-forming elements are important characteristics of Cenozoic intracontinental covergence and mineralization.

4.3.4.1.3 Two Tectonic Mechanisms Controlling the Intracontinental Convergent Metallogenic System

In Cenozoic, there were two types of tectonic ore-controlling mechanisms, namely, extension and extrusion. A large-scale and deep-seated extensional tectonic ore-controlling mechanism has mainly occurred in the north–south sector of the giant “X”-shaped structure knot of the Sanjiang River in Cenozoic. This was mainly related to the strike-slip and pull-apart activities in the process of block extrusion and mutual collision and rotation. In the Paleogene Eocene, influenced by the regional extrusion stress field in the northeast, a strong right-hand strike-slip pull-apart has occurred along the Qamdo block in the Jinsha River orogenic belt in the north of Sanjiang River, and salt-bearing pull-apart basins represented by Gongjue and Nangqian were formed on the earth surface. Crustal decompression resulted in partial melting of the lower crust and upper mantle, forming alkaline to alkaline-rich magma, which controlled the mantle-derived magma metallogenic system. In the south of Sanjiang area, the strike-slip pull-apart mechanism of the central axis fault in Lanping-Pu’er basin controls the formation of Lanping super-large lead–zinc deposit. The right strike-slip of Ailaoshan-Honghe Paleogene is not only closely related to the formation of Ailaoshan large-scale gold deposit, but also forms alkali-rich porphyry belt at the margin of Yangtze plate on the northeast side. Superficial extensional activities occur in large numbers in the front and rear edges of the strong nappe orogenic belt, represented by gliding nappe faults, whose extensional decollement structure interface is a favorable place for metallogenic hydrothermal activities. It controls the formation of many tectonic altered rock-type polymetallic deposits related to low-temperature hydrothermal solutions in the late orogenic belt.

The Cenozoic “Sanjiang” area tectonic movement is dominated by intracontinental convergence and extrusion, which has the strongest effect on the transformation of the crustal structure. Long-term regional lateral extrusion leads to the vertical superposition and thickening of the crust, and large-scale intracontinental subduction and overthrust nappe are the main ways of crustal thickening and stress absorption. As a result of the convergence and extrusion, some crustal materials melted again in some old orogenic belts, forming S-type granite series, and consituting metallogenic systems related to crust-derived granites, such as W, Sn, Mo and W metallogenic belts, respectively, formed in Leiwuqi-Dongda Mountain in eastern Tibet and two island arc orogenic belts in Yindun in the late Yanshan period. On both sides of the foreland basin, the convergence has caused the mountain belts on both sides to advance further to the basin, and a series of low-angle thrust structures are developed in the shallow parts of the crust on both sides of the foreland basin. With the material of the orogenic belt moving to the foreland, the tectonic compression drives the water in the rocks of the orogenic belt and the pressed foreland basin to be discharged. This water is mixed with the meteoric water, magma water from deep sources and metamorphic water, and then, they migrate to the front of nappe structure. A large number of ore-forming materials are extracted from the passing rocks, especially from the early ore-forming pre-rich beds. Particularly, when the sedimentary strata of the foreland basin are rich in gypsum and salt, they are easily dissolved into the fluid, forming a hot brine fluid system for mineralization, which greatly improves the extraction and transportation of minerals in the rocks. Because of the trap effect of overthrust nappe on fluid system, leakage mineralization and unloading mineralization may occur by the fluid at the front of the system. The middle-low-temperature polymetallic mineralization and extensive geochemical anomalies commonly developed in the east–west thrust fault zones of Qamdo and Lanping-Pu’er basins are mainly controlled by this tectonic-metallogenic mechanism.

4.3.4.2 Intracontinental Magmatic Metallogenic System

4.3.4.2.1 Intracontinental Crust-Derived Magmatic Metallogenic Subsystem

This metallogenic system is related to the continental crust remelting granite of the orogenic belt in the early stage of the late Yanshanian intracontinental convergence, which mainly occurs in the Leiwuqi-Dongda mountain composite island arc orogenic belt and Yidun island arc orogenic belt to the west of the northern Lancang River, respectively, forming a regional extension Tin-bearing granite belts with a length of 200–300 km, which controls two tin (tungsten) and silver polymetallic metallogenic belts, including Changmaoling-Xiaya-Larong-Suoda and Gaogong-Cuomolong.

Leiwuqi-Dongda mountain composite island arc belt is an island arc orogenic belt formed by the subduction and closure of the North Lancang River at the end of the Late Paleozoic. During the Indosinian, there was a further collision orogeny between the North Lancang River fault and the Qamdo block, which led to a large-scale remelting and transformation of the upper crust material, resulting in a strong continental crust collision magmatism. During the Middle and Late Triassic, high silicon and high-potassium (intermediate) acid andesite-rhyolite volcanic belt in the North Lancang River belt and granite belt in Jitang-Dongda mountain on the west side were formed, respectively. The abundance of mineralization and associated elements such as Sn, W, Ag, Sb, As, Bi, Pb in old metamorphic rocks such as Neijitang Group is several times higher than the average value of the crust, and they are important ore source rocks. In the process of continental crust remelting, the continental crust material has undergone a great degree of transformation and differentiation, and the crustal material has experienced the actions of heating and drainage, magma melting, crystallization differentiation, etc. All kinds of fluids overflew and dispersed outward, carrying the ore-forming materials activated and extracted from the crust to the low-temperature and low-compressive stress parts together. Since the late Triassic, the orogenic belt has been dominated by the overthrust nappe in the northeast direction, and its western rear edge is relatively in an extensional environment. Therefore, the hydrothermal solution tends to migrate and converge to this part, forming the pre-enrichment of minerals. In the middle and late Yanshanian period, with the closure and collision of the Nujiang ocean basin, an intracontinental subduction and collision occurred from west to east, which triggered the melting of the continental crust again. A series of small intrusions were formed along the west side of the Jitang-Dongda mountain plutonic belt in Indosinian. The rock bodies mainly intruded into sandy argillaceous clastic rocks of the Lower Carboniferous and Upper Triassic, with isotopic ages of 87.7–63.7 Ma. The hydrothermal activity after the magmatic period was related to tin (tungsten), (Nb–Ta), heavy rare earth.

Tin (tungsten)-bearing granites are mainly hornblende-biotite monzogranite, biotite (or two-mica) monzogranite, biotite granite and muscovite granite. From the center to the outside, the lithofacies of a single rock mass changes obviously; mineral crystal grains change from coarse to fine; and dark minerals gradually decrease, which is obviously a product of multi-stage full differentiation and evolution. According to the research on this belt of Yong et al. (1991), the lithochemical composition of tin-bearing granite is characterized by high silicon and high alkali, with the average w(SiO2) of 71.88%, w(K2O + Na2O) of 7.95%, and w(K2O) > w(Na2O). Low MgO and TiO2, with average values of 0.64% and 0.36%, indicate that there is a typical cause of continental crust reformation. The total rare earth content of tin-bearing granite is high, and it is of light rare earth enrichment type. (w(La)/w(Yb))N is 5.15–30.94, and the Eu is strongly deficient (δ EU 0.29–0.55), which indicates that magma is originated from partial melting of the upper crust and experienced good crystallization differentiation. Mineralization is related to the light granite formed by the high separation crystallization of magma. This kind of granite has a gentle rare earth pattern, the total amount of rare earth decreases and the contents of light and heavy rare earths are similar. (w(La)/w(Yb))N is 1.54–9.9, and the Eu is strongly deficient (δ EU 0.21–0.57). Tin-bearing granite generally has higher contents of ore-forming or mineralized elements such as Sn, W, Ag, Cu, Mo, B, F, Be, Rb, Bi than similar rocks. These elements may have inherited the early pre-enrichment material source. The above characteristics are similar to those of tin-bearing granites in Southeast Asia, South China and Western Yunnan.

Ore-bearing rock mass is mainly controlled by NW–SE strike fault structure, mostly presenting as small rock mass and rock strain. Mineralization is closely related to post-magmatic period hydrothermal activity, belongs to high-middle temperature hydrothermal filling metasomatism genesis and occurs in the contact zone inside and outside the rock mass. There are three main metallogenic types in Changmaoling-Xiaya-Larong-Suoda belt. The north section is mainly cassiterite (wolframite)-tourmaline-quartz type and greisen type. The former includes Saibeilong-Mabuguo tin deposit and many mineralized occurrences in the Changmaoling area of Leiwuqi County. Mineralization mainly develops in hornfelsic surrounding rock in granite’s outer contact zone. Mineralization is controlled by fracture zone and structural fissure, with cassiterite (wolframite)-tourmaline-quartz as the main combination, mainly in single vein and compound vein or reticulated vein. Ore-forming temperature is mainly between 380 and 240 °C, and the ore-forming fluid δ18OH2O is +6.83‰ ~ +8.56‰, indicating that the ore-forming hydrothermal solution mainly comes from magmatic water. The latter is represented by the Xiaya ore occurrence in Basu County, where mineralization occurs in the contact zone of granite or the altered zone of greisenization altered zone at the top of the granite.

The mineral assemblage is mainly cassiterite-tourmaline-fluorite-quartz, cassiterite-muscovite-quartz and fluorite-topaz-cassiterite-quartz. In the early stage, cassiterite and other minerals are distributed in greisen in a dispersed and stellate manner. In the late stage, vein mineralization is mainly formed, with mineralization temperature ranged from 300 to 220 °C, and the fluid δ \(^{{{18}}} {\text{O}}_{{{\text{H}}_{{2}} {\text{O}}}}\) of +7.45‰ (Yong 1991). A series of small acidic rock bodies are developed along the east and west sides of Indosinian-Yanshanian complex granite base in the southern section of Dongda mountain, and the corresponding tin (tungsten) geochemistry or cassiterite (wolframite) heavy sand anomalies are obvious. The main metallogenic types are greisen type or cassiterite-sulfide type, represented by some occurrences such as Larong and Qudeng.

Gaogong-Cuomolong tin-bearing granite belt is located on the inner side (west side) of Yidun Island arc zone, sandwiched between Keludong-Xiangcheng fault and Aila-Riyu fault. Most of the rock bodies are complex, mainly invading the Tumugou Formation of the Upper Triassic, with the isotopic age of the rock bodies of 115.8–76.8 Ma, and the duration of magmatic activity of 8–29 Ma. The early porphyritic moyite as well as the late porphyritic biotite monzogranite and moyite have the characteristics of crust-derived granite. The content of Sn, Ag, Bi and other ore-forming elements in granite is generally high, and the ore-forming materials are mainly provided by rock mass. Tumugou Formation of Upper Triassic invaded by rock mass also has a high background of ore-forming elements. Controlled by post-magmatic period hydrothermal and circulating meteoric water activities, the mineralization is carried out by filling metasomatism. When the rock mass intrudes into limestone with active chemical properties, it forms skarn-type tin polymetallic deposits after metasomatism, represented by Cuomolong and Lianlong deposits. When there are large structural channels around the rock mass, such as nappe and gliding nappe interface, magmatic fluid and meteoric water are mixed and filled along these channels to form a structurally altered rock deposit, represented by the large silver deposit in Xiasai.

In recent years, a lot of new progress has been made in molybdenum polymetallic prospecting in the southern section of this belt. The Tongchanggou Cu–Mo(W) ore, Xiuwacu Mo–W ore and Donglufang Cu–Mo ore have great resource potential. Our team studied the Cu–Mo(W) deposit in Tongchanggou and obtained that the zircon U–Pb age of mineralized molybdenite granodiorite diorite porphyry (TCG-16) is 79.1.2 ± 1.9 Ma and that of weakly mineralized granodiorite diorite porphyry (TCG-21) is 83.6 ± 1.1 Ma. The formation age of Xiuwacu monzonitic granite porphyry is 83.3 ± 1.7 Ma (MSWD = 2.6). For the mineralization age of molybdenite, according to the mineralization types and the spatial distribution of porphyry, the mineralization types of Cu–Mo–W deposits in late Yanshanian are porphyry-type Mo–Cu–W mineralization → skarn-type Cu–Mo mineralization → hydrothermal-type Cu–Pb–Zn–Ag mineralization from the porphyry to outward direction. The mineralized body is mainly controlled by the structural fissure system in porphyry, and the structural fissure mainly develops at the top or edge of the rock mass, but there is no obvious development in the center of the rock mass. Ore-bearing fractures are mostly distributed in vein and reticulated vein, and the more developed and mineralized the fissures are, the more enriched they are. For example, rich molybdenite mineralization is distributed in the structural fissures developed in the edge of Tongchanggou ore-bearing porphyry, and the ore bodies controlled by the structural fissures are mostly lenticular or stratiform-like. The development of molybdenite in Xiuwacu Cu–Mo deposits is closely related to the initial stage of quartz vein, and molybdenite, chalcopyrite and scheelite are all produced at the edge of wide quartz vein or veinlet-like quartz vein. At the same time, Cu–Mo–W mineralization also indicates the characteristics that porphyry body itself is an ore body.

In a word, the Yanshanian post-collision extension is the main tectonic mechanism of the terrigenous granite metallogenic system, and the magma formed by the remelting of crustal materials is the most important ore-controlling factor of the metallogenic system. Tin (tungsten) and silver polymetallic ore-forming materials mainly come from crust-derived magma. Multi-stage remelting and magma crystallization differentiation lead to mineral migration and enrichment. Hydrothermal driving after magmatic stage leads to the joining of groundwater in different degrees, and some ore-forming materials are brought in by surrounding rocks. Hydrothermal filling metasomatism is the main metallogenic mode.

4.3.4.2.2 Intracontinental Mantle-Derived Magmatic Metallogenic Subsystem

The intracontinental mantle-derived magmatic metallogenic system occupies an extremely important position in the intracontinental convergence mineralization of the Sanjiang River. The mineralization is related to the Yulong-Jinsha River-Honghe Cretaceous-Paleogene Eocene porphyry belt, which runs through the north–south tectonic units. The famous porphyry copper (molybdenum) deposit represented by Yulong was formed in the northern Qamdo area, and the porphyry-explosive breccia-type gold-silver (polymetallic) deposit was transited to the south. Extensional tectonic mechanism, deep source magmatism and hydrothermal convection system controlled by hypabyssal porphyry are the three important metallogenic elements of this system.

4.3.4.2.2.1 The Tectonic Environment of Porphyry Formation and Magma Source Area

According to the study of Yulong porphyry belt, the area of Xiariduo-Haitong, where Yulong porphyry belt is located, is the inner side of the ancient continental margin arc formed by the westward subduction of Jinsha River Ocean during Hercynian-Indosinian, rather than the long-term stable intraplate environment. The direct provenance of Himalayan porphyries is the upper mantle or lower crust which was subducted and transformed from the oceanic crust of Jinsha River to the lower part of Qamdo block. The age of 200–240 Ma Sm–Nd isotope model of porphyries (Wang 1995) indicates that the original magma of porphyries left the mantle in the late Indosinian. Therefore, it can be considered that the porphyry was formed in the island arc environment of the ancient continental margin. The magma source area is either the residual ancient oceanic crust of Jinsha River or the island arc mantle modified for it. This porphyry is not significantly different from the porphyry generally formed on the active continental margin of the Mesozoic and Cenozoic convergent plates and the porphyry directly originated from the melting of subducted oceanic crust. In addition, tourmaline-quartz explosive breccia is widely developed in ore-bearing porphyry. The porphyry magma is extremely rich in boron. As the porphyry magma is not contaminated by crustal materials on a large scale, one possible explanation is that boron from the ancient oceanic crust is rich in sediments.

4.3.4.2.2.2 Extensional Tectonics and Deep-Seated Magmatism

The isotopic ages of Himalayan ore-forming porphyry and homologous volcanic rocks in Qamdo area range from 52 to 30 Ma (it is mainly K–Ar age), equivalent to Paleogene Eocene. During the NE jacking of the Indian plate, dextral strike-slip occurred in the Jinsha River orogenic belt, which led to crustal decompression, partial melting of lower crust and upper mantle, forming deep-seated magma upwelling. The coupling between strike-slip pull-apart and magma plays an important role in the formation of porphyry deposits. Chesuo fault, which divides the Qamdo block from the Hercynian-Indosinian Jiangda-Mangling continental margin arc orogenic belt, is a regional super-deep crust fault. The Paleogene strike-slip pull-apart activity is very strong and controls the Gongjue half graben strike-slip extension basin, which stretches for hundreds of kilometers, and is an important rock-guiding structure of deep-seated magma. In the early stage, the right strike-slip-shear was the main activity, and a series of NW–NNW strike folds and compressional-torsional fault structures which presented in a left-hand geese line obliquely crossed with Chesuo fault developed on one side of Xipan fault, which constituted the main rock-bearing structure. Then, the left lateral relaxation accompanied with westward extension activity has occurred, and the secondary structure changed from compressional-torsional to tensional-torsional, thus becoming the most favorable place for the final location of ore-bearing porphyries. The extensional tectonic environment is not only conducive to the rapid and smooth upward migration of magma and ore-forming materials, but also can keep the metallogenic system in contact with the deep-seated magma chamber for a relatively long period of time, so that ore-forming materials can be continuously and fully supplied to the system, which provides an important condition for the system to form metal piles with great commercial value.

4.3.4.2.2.3 Magmatic Mineralization

Magmatic rock, as ore-forming parent rock, not only provides ore-forming fluid and ore-forming materials directly to the system, but also provides essential heat energy for the metallogenic system. It has the function of “heat engine” and drives hydrothermal fluid to circulate, so that mineralization can be fully realized under this mechanism. Porphyry plays a direct and decisive role in mineralization. Himalayan ore-bearing porphyries are mainly composed of calcium-alkaline to alkaline monzonitic granite porphyries, quartz monzonitic porphyry and orthophyre, which are mainly alkaline ones. These two kinds of porphyry control porphyry copper (molybdenum) deposits and gold-silver polymetallic mineralization series or assemblage, respectively. Porphyry magma formed in the lower crust or upper mantle is rich in ore-forming materials and directly enters the upper crust along active deep-seated faults. The transformation of crust-mantle material is an important constraint for mineralization. Ore-forming materials originating from the lower crust or upper mantle reservoir take magma and its derived geological fluids as carriers. From magma generation to mineralization, the main ore-forming materials basically follow a relatively simple unipolar evolution track of extraction from source area → magma migration → fluid differentiation → cyclic unloading.

The seating environment and output state of magma play an important role in controlling mineralization. Most of the ore-bearing porphyries invaded the anticline dome structure or the intersection of faults with near-surface structural expansion at that time, which was favorable to the accumulation of hydrothermal solution after magmatic stage, and made the ore-forming fluid system have a good ore-gathering function. Most ore-bearing porphyries contain explosive breccia, mainly tourmaline-quartz breccia, the formation of which is related to an extremely boron-rich magma melt mass differentiated from the magma, indicating that the magma has extremely high energy and volatile components during its upwelling. This is conducive to the separation of ore-forming materials from the magma. Porphyry rich in volatile matter can provide abundant ore-forming fluid, and its hydrothermal action is the key factor to form the circulation mechanism of ore-forming fluid centered on porphyry. As the main carrier, magma brings heat and ore-forming minerals from the mantle. Many research showed that the mantle-friendly elements such as Cu, Fe, Pt, Pd, Cr, Ni, Co, Au and Ag in porphyry copper deposits mainly come from the mantle, while the crust-friendly elements such as Mo, Pb, Zn, W, Sn, Sb and Bi mainly come from the crust. They are generally high in the upper crust strata of Qamdo block and are mainly brought in by fluid circulation. Porphyry emplacement is found near the edge of the basin or the fault zone in the basin, which are the active channel of the basin’s contemporaneous tectonic displacement fluid. The fluid is abundant, and it is mainly hot brine formed by flowing through gypsum-salt-rich strata such as the Upper Triassic, which has strong ability to extract and transport ore-forming materials. This is in favor of more ore-forming materials to enter the porphyry hydrothermal metallogenic circulation system.

4.3.4.2.2.4 Ore-Gathering Mechanism of Porphyry System. Predecessors Have Established Generally Applicable Genetic Models and Descriptive Models for Porphyry Deposits

It is widely believed that mineralization is related to hydrothermal convection system centered on porphyry, and hydrothermal convection system is the key factor to determine mineralization, alteration structure and the final positioning and shaping of ore bodies. For the porphyry copper deposits and porphyry-explosive breccia gold-silver (polymetallic) deposits, the spatial allocation of mineralization and alteration is summarized in Fig. 4.15. The hydrothermal system of the ore-gathering is composed of three different parts from bottom to top or from inside to outside with porphyry as the center. The depth of the lower part of the system is about 500–1000 m. In and around the porphyry, the hydrothermal solution mainly comes from the magmatic fluid with a temperature between 300 and 500 °C, which is in a relatively closed supercritical temperature state. The fluid is rich in mineralizing elements such as silicon, potassium and boron, fluorine, chlorine and sulfur. In the depth range of about 500 m in the middle of the system, the hydrothermal rising dominated by magmatic water suddenly changed from a closed supercritical state to a depressurized and open environment, which caused the hydrothermal boiling and depressurization at the top of porphyry or cryptoexplosive breccia, and the fluid volume expanded and the density decreased. This might cause pumping and made the peripheral meteoric water with lower temperature and higher density move to the rock mass. They quickly replenished, mixed and neutralized with magmatic water and was quickly heated to move further upward or outward, resulting in the formation of the hydrothermal circulation system. During the repeated circulation of hydrothermal solution, a large amount of quartz, potash feldspar and tourmaline are precipitated in the system, and copper, molybdenum and some minerals such as gold, silver, lead and zinc are mainly deposited in the vicinity of inside and outside of the rock mass of the lower part of the system (such as the contact zone of the rock mass) at first. The main components such as gold, silver, lead and zinc are further migrated outward by the fluid. With the decrease of temperature, these components are mainly deposited in the favorable tectonic channels around the porphyry body. The upper part of the system is located at the place from below the original earth surface to the top of the explosive breccia body, with a depth ranging from 0 to 500 m. It belongs to the discharge outlet of the geothermal pool convection system. The fluid is mainly discharged through the rising steep fault tectonic fissures in the same tectonic period. The rising deep-seated magma water is fully mixed with the surrounding groundwater, and the temperature is further reduced to 50–100 °C. Hot springs or large geothermal springs (fields) were formed on the earth surface. Epithermal mineralization can occur in the upper part of the system. There are still such hot spring activities in Yulong porphyry belt. The sinter contains typical low-temperature hydrothermal elements such as As, Sb, Mn, Hg, (Au), (Ag), forming a mineral assemblage such as natural sulfur, cinnabar, barite, stibnite and male (female) sulfur. From the system structure of the above circulating fluid, the upper part is epithermal mineralization, the middle part is related to the formation of explosive breccia-type gold-silver (polymetallic) deposits and the lower part mainly forms porphyry-type copper (molybdenum) deposits, which may constitute a complete metallogenic assemblage model. To some extent, porphyry copper (molybdenum) deposits seem to be equivalent to the deep system of explosive breccia or epithermal gold-silver (polymetallic) deposits. The fluid from the magma and the groundwater are in a transitional relationship with complete mutual solubility, without any interface. Therefore, the mineralization and alteration from the rock mass to the surrounding rock are also a continuous transitional relationship, and there is no strict boundary between the above-mentioned mineralization. As far as a certain deposit is concerned, due to the difference in the degree of development of the fluid system, as well as the differences in structural elements, surrounding rock conditions, current hydrogeological conditions, fluid temperature and pressure, properties, active stages, ore-forming material supply, etc., the development of its metallogenic assemblages is significantly different from each other, and only a part of them may be relatively developed and valuable deposits are formed.

Fig. 4.15
figure 15

Metallogenic model of porphyry copper deposit and explosive Breccia gold–silver (polymetallic) deposits’ fluid system. 1—porphyry; 2—cryptoexplosive breccia; 3—fine vein disseminated mineralization; 4—hydrothermal contact metasomatism; 5—reticulated vein fracture zone; 6—magmatic hydrothermal migration direction; 7—groundwater migration direction; 8—mixed hydrothermal fluid; 9—boiling surface. pro ± Ar—propylitization (argillization); Q + Tour + Ser—silicification, tourmalinization, sericitization; H–S—hornification, skarnization; Pota—potassization; K–Si—nucleus

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4.3.4.3 Metallogenic System of Tectonic Dynamic Fluid

The metallogenic system is characterized by a kind of metallogenic mechanism and mineralization, which is a large-scale drainage activity between the orogenic belt and the foreland basin driven by the thermodynamic and tectonic dynamics in the crust during the process of intracontinental convergence. The fluid extracts the ore-forming elements flowing through the stratum rocks and brings them into the overthrust zone or detachment gliding nappe structure at the junction of basin and mountain to unload. Under the tectonic background of intense intracontinental convergence and compression in the late Yanshanian-Himalayan period, thrust nappe, detachment gliding nappe and strike-slip-shear are the most important tectonic forms of the crustal surface in the Sanjiang area. The mountain systems on both sides of the Qamdo and Lanping foreland basins undergo a large-scale hedging to the basin, and the fluids in the middle and shallow layers of the crust controlled by this have migrated and converged from the orogenic belt to the basin and are discharged and unloaded along the nappe belts or internal faults on both sides of the basin, controlling the mid-low-temperature hydrothermal polymetallic metallogenic belts extending on a large-scale or comprehensive geochemical anomalous zones, and forming a number of promising deposits. Inside the orogenic belt, reverse extensional gliding nappe of different scales often appears on the trailing edge of the intense thrust nappe structure, causing fluids in the orogenic belt to move along these extensional faults for mineralization. To this end, the Tuoding in Jinsha River orogenic belt and medium-low-temperature polymetallic deposits are related to this.

This metallogenic system occupies an extremely important position in Sanjiang Cenozoic mineralization, which truly reflects the conditions and opportunities of trans-unit tectonism in the process of intracontinental convergence, large-scale and multi-source fluid convergence and migration, as well as extensive material source fusion and massive metal accumulation. The structural elements of metallogenic system mainly include thermodynamic and tectonic dynamic conditions formed by intracontinental convergence, fluid migration and discharge guided by nappe compression or extension strike-slip structural mechanism, abundant provenance bases in stratum rocks of orogenic belts and basins, ability to extract and transport metallogenic elements determined by fluid properties (such as hot brine formed by dissolving gypsum-salts) and ore-forming traps favorable for fluid unloading (such as dome structures, strike-slip basins, extension fractures).

4.3.4.3.1 Thrust Nappe Structure-Fluid Metallogenic Subsystem

Regional fluid flow caused by tectonic compression during intracontinental convergence is obviously the most important metallogenic factor of the metallogenic subsystem. In the Sanjiang area, especially in the middle-south section of Sanjiang, during collision, compression and shrinkage, thrust nappe structure-fluid metallogenic events were generally developed, and structure-fluid metallogenic subsystems were formed in many zones. Different orogenic belts have formed different metallogenic subsystems due to their different tectonic evolution backgrounds and differences in the composition of rock series strata. For example, in Ganzi-Litang and Jinsha River-Ailaoshan orogenic belts, accompanied by strike-slip-shear-nappe tectonic action, altered rock gold deposit metallogenic system was formed; on the east side of Qamdo-Lanping-Pu’er basin, Pb, Zn and Ag polymetallic hydrothermal metallogenic subsystems were formed under the participation of mantle fluids, and on the west side, Cu polymetallic hydrothermal metallogenic subsystems were formed. In Pangong Lake-Salween River-Changning-Menglian orogenic belt, Pb, Zn and Ag polymetallic hydrothermal metallogenic subsystems were formed during compression and nappe. The Qamdo-Lanping-Pu’er basin was strongly compressed, and a large amount of water was drained and mixed with the tectonic hydrothermal solution from the subduction zone, rose, released and unloaded along the thrust front belt, causing extensive medium-low-temperature hydrothermal alteration and mineralization in the region (Fig. 4.16), forming a medium-low-temperature hydrothermal mineralization and sedimentary-hydrothermal reworked metallization subsystems.

Fig. 4.16
figure 16

Relationship between the nappe structure in the middle segment of the Qamdo basin and the hot brine mineralization. 1—Upper Triassic-Jurassic; 2—Paleozoic; 3—Pre-Devonian Jitang Group; 4—Hot brine migration direction; 5—Arsenic, silver and lead polymetallic deposit

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4.3.4.3.2 Extensional Detachment Structure-Fluid Metallogenic Subsystem

During the process of intracontinental convergence, the old orogenic belt further undergoes unidirectional or bidirectional outward thrust nappe, and extensional detachment structures appear to varying degrees at the trailing edge of the orogenic belt to control the activities from the orogenic belt and atmospheric precipitation. The basic model of the metallogenic subsystem is that the fluid extracts minerals from the rocks of the orogenic belt with rich provenance and converges into the detachment and gliding nappe structures in the extensional environment. Many examples of such deposits have been found in the Jinsha River orogenic belt. During the further eastward thrust nappe of the Jinsha River orogenic belt in the Himalayan period, the detachment and stripping structures occur along different tectonic layers in the extension and tension of the western rear edge, resulting in the filling and metasomatism of ore-forming hydrothermal fluids, forming the gold polymetallic deposits represented by Azhong. In the south, the Tuoding copper deposit, the Najiao system, the Gangriluo and other lead–zinc deposits and even the Xiasai super-large silver polymetallic deposits all have the obvious characteristics of such structural ore control or reworked metallization.

4.3.4.3.3 Metallogenic System of Strike-Slip Pull-Apart Basin

This metallogenic subsystem refers to the metallogenic mechanism and mineralization that occur in the basin due to deep hydrothermal activity or sedimentary diagenesis, respectively, with the Cenozoic strike-slip basin as the main control element, and the basin is mainly acting as a mineralization carrier or reservoir.

The strike-slip pull-apart basins in the Sanjiang area are widely developed. For example, a series of pull-apart basins have formed in the Qamdo-Lanping-Pu’er basin. They are the products of the strike-slip pull-apart process of regional deep fractures between the two sides and internal orogenic belts of the basin. The eastern Tibet area in the north is controlled by the dextral activity of the Chesuoxiang fault that divides the Qamdo Basin and the Jinsha River orogenic belt. The Paleogene Gongjue Basin formed by it extends for hundreds of kilometers from north to west. These basins mentioned above are characterized by extensional or compressive strike-slip. Due to their connection with deep and large faults, some of them contain magma eruptions and become favorable places for deep fluid to rise and unload. For example, the mineralization in the famous Jinding lead–zinc deposit located in the Lanping-Yunlong Basin is mainly related to the discharge of deep fluid rise in the basin during the strike-slip process along the Bijiang River fault.

4.4 Analysis of Key Metallogenic Geological Process

The Sanjiang giant metallogenic belt, as an important part of Tethys giant metallogenic domain, one of the three giant metallogenic domains in the world, is famous for its unique forming environment, intense metallic mineralization, complex metallogenic types and huge prospective scale. There are not only a number of world-famous large and super-large ore deposits, such as Yulong copper deposit, Gacun polymetallic deposit, Jinding lead–zinc deposit, Ailaoshan gold deposit and Tengchong tin deposit, but also a number of new large and super-large ore deposits, such as Pulang copper deposit, Beiya gold deposit, Baiyangping silver polymetallic deposit, Xiasai silver deposit, Gala gold deposit, Yangla copper deposit, Dapingzhang copper deposit, Luziyuan lead–zinc polymetallic deposit, Chang’an gold deposit, Hetaoping lead–zinc polymetallic deposit, which have entered a scale development stage. Hou et al. (1999) summarized six characteristics of the mineralization in the Sanjiang area; Li et al. (1999) vividly described it as “a late bloomer surpassing the former, deep-seated source, collision and nappe mineralization”. Based on the long-term research on the Sanjiang metallogenic belt, and taking the mineralization geodynamic analysis as the main method, the section determines its main metal metallogenic periods and main metallogenic types, focuses on the dynamic background and metallogenic geological environment of its formation and development and reveals the key geological processes controlling mineralization.

4.4.1 Evolution of Mineralization

With the evolution of the Sanjiang giant orogenic belt experiencing subduction orogeny → collision orogeny → intracontinental orogeny, the evolution of the regional mineralization has the following apparent laws.

4.4.1.1 Evolution of Metallogenic Environment

The metallogenic geological environment of the Sanjiang orogenic belt has undergone three fundamental changes and transformations, corresponding to three important metallogenic peaks. During the Late Paleozoic metallogenic period, the paleo-ocean basins opened in Carboniferous-Early Permian underwent closure and subduction orogeny one after another, resulting in an MABT, which became an important metallogenic background for VMS deposits, porphyry copper deposits and epithermal deposits. During the Late Triassic metallogenic period, lithospheric delamination is occurred in the orogenic belt which had experienced the arc-continent collision in the Early and Middle Triassic, forming the superimposed volcano-rift basin, and developing basin fluid mineralization and submarine deep-water/shallow-water hydrothermal mineralization. In the Himalayan metallogenic period, the collision between the Indian and Asian continents, which started at 60 Ma, caused collision uplift of the Qinghai-Tibet Plateau in the hinterland of Tibet, and large strike-slip faulting in the eastern margin of the plateau, which has not only led to the development of large granite porphyry and alkali-rich porphyry belts becoming the main ore-bearing rock of porphyry Cu–Mo deposits and porphyry Cu–Au deposits, but also formed a series of strike-slip pull-apart basins and a series of large nappe shear zones, which controlled the fluid activity and hydrothermal deposit formation in the strike-slip pull-apart basins, and became an important ore-hosting space and ore-controlling structure for some large deposits (Jinding lead–zinc deposit and Ailaoshan gold deposit).

4.4.1.2 Evolution of Metallogenic Types

Different metallogenic environments are formed in different tectonic evolution stages, accompanied by different metallogenic types. In the Early Paleozoic period, the separation of landmasses and the opening of ocean basins usually occurred only at the boundary of discrete blocks, and hydrothermal sedimentary deposits were developed. In the Late Paleozoic MABT, porphyry copper deposits related to arc magmatic porphyry, VMS deposits and epithermal deposits related to arc volcanic rocks were mainly developed. Three types of submarine hydrothermal mineralization were mainly developed in the volcanic-rift basins formed by extension after collision orogeny in Late Triassic: ① VMS deposits related to marine acid volcanic rocks, mineralization occurred in deep-water and shallow-water environments; ② exhalative-sedimentary deposits related to marine rift basins and contemporaneous faults; ③ hydrothermal sedimentary deposits related to hot brine in silled basins, such as barite and gypsum deposits. In the Himalayan period, mineralization has tended to be complex with various metallogenic types. Among them, at least four types are particularly important: ① porphyry copper–molybdenum and copper–gold deposits closely related to large strike-slip faults; ② hydrothermal deposits related to the dual action of strike-slip pull-apart basin and strike-slip nappe structure; ③ shear zone type deposits related to large strike-slip and nappe shear zone; ④ hydrothermal deposits related to extensional detachment structure or nappe slippage structure.

4.4.1.3 Evolution of Metallogenic Metal Assemblages

The evolution of metallogenic metal assemblages has simple-to-complex and single source-to-multi-source composite features. During the Early Paleozoic metallogenic period, the metallogenic metallic assemblages were mainly Pb–Zn or Fe assemblages. During the Late Paleozoic metallogenic period, the metal assemblages were characterized by the presence of a large amount of Cu and the development of Cu–Zn, Cu–Pb–Zn and Fe–Cu assemblages. During the Late Triassic metallogenic period, the metal assemblages were characterized by the presence of large amounts of Ag, Au and Hg and the development of Zn–Pb–Cu, Cu–Zn-Pb, Zn–Pb–Ag and Ag–Au–Hg assemblages. In the Himalayan period, the metallogenic metal assemblages were extremely complex, which is mainly manifested as follows: ① rare and rare earth elements were enriched and mineralized; ② single elements were mineralized on a large-scale, such as extra-large Au deposit, large Sr deposit and extra-large Cu deposit; ③ multi-source elements coexist, and crust-source elements (Pb, Zn, Ag, Sr, etc.) and mantle source elements (Co, Ni, Au, Cu, etc.) coexist in time and space for enrichment and mineralization.

4.4.1.4 Evolution of Metallogenic Intensity

Although mineralization runs through the evolution of the Sanjiang orogenic belt, large-scale mineralization was mainly occurred in the Late Triassic and Himalayan periods, and the mineralization of many large and super-large deposits in the Sanjiang area was concentrated in the two periods. In the Late Triassic metallogenic period, the scale of submarine hydrothermal mineralization was the largest; in the Himalayan metallogenic period, the scale of hydrothermal fluid mineralization in porphyry copper deposits, shear zone-type gold deposits and strike-slip pull-apart basins was the largest, showing a triple balance of forces.

4.4.2 Analysis of Key Metallogenic Geological Process

As mentioned earlier, although the mineralization in the Sanjiang area runs through the evolution of the giant orogenic belt, the important mineralization was mainly developed in three different evolution stages of the giant orogenic belt and three important metallogenic geological environments resulted therefrom. The large-scale mineralization occurred in ① the arc-basin system related to subduction orogeny, ② the post-collisional orogenic extensional system related to lithospheric delamination (break-off), ③ the large-scale strike-slip fault system related to collisional uplift of Qinghai-Tibet Plateau. This section will conduct a deep analysis of the formation and evolution processes of the three important metallogenic backgrounds and geological environments, as well as the three key metallogenic geological processes.

4.4.2.1 Subduction Orogeny and Arc-Basin System

The evolution of the Paleo-Tethys in the Sanjiang area is a subduction orogeny and a development process of island arc orogenic belt. Since the island arc orogenic belts and their mineralization in the Sanjiang area have been discussed and understood deeply, only their basic characteristics are summarized here.

Before collision orogeny, the Sanjiang giant orogenic belt was formed by the collage of several (island) arc orogenic belts and microblocks sandwiched between them. These arc orogenic belts mainly include Yidun island arc orogenic belt, Jinsha River continental margin arc orogenic belt and Lancang River continental margin arc orogenic belt. Although they have different development histories, they all have formed their own arc-basin systems.

4.4.2.1.1 Yidun Island Arc Orogenic Belt

Yidun orogenic belt is a composite orogenic belt in the Sanjiang giant orogenic belt, which started from large-scale subduction orogenesis during the late Indosinian (Rhaetian–Norian) (Hou 1993; Hou et al. 1995), experienced the collisional orogenic process in the Yanshanian period, including arc-continent collision and continental crust shrinkage and thickening, orogenic uplift and extension, and finally suffered from the superimposition and reconstruction of intracontinental convergence and large-scale strike-slip and shearing during the Neo-Tethys period. Its subduction orogeny is originated from the westward subduction of the Ganzi-Litang oceanic crust slab in the early Late Triassic, which has led to the development of Yidun volcanic-magmatic arc (237–210 Ma) and the formation of a complete trench-arc-basin system. Given the nature of the thin continental crust underlying the island arc, as well as the inhomogeneity of the subduction angle of the oceanic crust plate, the north–south segment of the remnant arc is shaped. The Changtai arc in the northern segment is characterized by the development of intra-arc rift basins and active back-arc spreading basins, with extensional arc properties; the Shangri-La arc in the southern segment is characterized by the development of intermediate-acid volcanic-intrusive rock magmatic arcs and inactive back-arc-basins, with compressional arc properties; the Xiangcheng arc in the middle segment lies between extensional arc and compressional, with the development of intra-oceanic arcs marked by high-magnesium andesite (Hou et al. 1995). Four secondary tectonic units can be identified from east to west in the Changtai arc, namely outer arc (volcanic-magmatic arc), intra-arc rift, inner arc (residual arc) and back-arc spreading basin. The intra-arc rift is marked by the development of basalt-rhyolite bimodal rock assemblage and deep-water faulted basin (Hou 1993), while the back-arc spreading basin is characterized by the development of a shoshonite-high-potassium rhyolite bimodal rock assemblage and deep-water black rock series deposits. The Shangri-La arc is mainly a volcanic-magmatic arc, characterized by development of calc-alkaline magma series andesite-dacite and super-hypabyssal emplaced intermediate-acid rock mass (Hou et al. 1995), and there is no corresponding volcanic activity in the back-arc area. The Xiangcheng arc has developed earliest, which is composed of early intra-oceanic arc and late volcanic arc.

The trench-arc-basin system of the Yidun island arc orogenic belt is an important metallogenic environment for the Late Triassic mineralization and development in the Sanjiang area. The intra-arc rift zone in the Changtai arc provides an important ore-accumulating basin environment, magma “heat engine” driving fluid circulation and source rocks supplying ore-forming materials for submarine hydrothermal fluid mineralization. A large number of super-hypabyssal emplacement porphyry systems in the Shangri-La arc control the formation of porphyry copper deposits and skarn polymetallic deposits. The development of epithermal deposits (Ag–Au–Hg) is controlled by the back-arc spreading basin of the Changtai arc and high-potassium rhyolite series.

4.4.2.1.2 Jinsha River Orogenic Belt

The Jinsha River orogenic belt was formed and developed from the oceanic crust subduction in Early Permian, experiencing collision orogeny during Early and Middle Triassic and post-orogenic extension during Late Triassic, and suffering superimposed reformation by intracontinental convergence and large-scale shear translation in the Neo-Tethys, which is a composite orogenic belt consisting of successively developed continental marginal arcs and collision orogenic belts influenced by the collision and uplift of the Qinghai-Tibet Plateau. The oceanic crust remains marked by Carboniferous-Permian ophiolite complex, and the intermittent spreading and melange accumulation of deep-sea sediments along the Jinsha River fault zone represented by siliceous argillaceous-arenaceous flysch construction indicate that the insha River melange zone was once a closed ocean basin. On the west side of the Jinsha River fault zone, the Early Permian Jubalong-Dongzhulin intra-oceanic arc and Xiquhe-Jiyidu back-arc-basin are developed, indicating that the Jinsha River oceanic crust plate might have detached and subducted westward along the intra-oceanic fracture zone in Early Permian, forming a sequence of calc-alkaline magma series intra-oceanic arc volcanic rock assemblages of basalt-basaltic andesite-andesite-dacite. In the eastern margin of the Qamdo block, the Jiangda-Deqin-Weixi Late Permian continental marginal arc is developed, showing that the Jinsha River oceanic crust plate subducted to the Qamdo block on a large scale at the end of Early Permian, and formed arc volcanic rock series evolving from tholeiitic basalt series to shoshonite series through calc-alkaline magma series.

The arc-basin system of the Jinsha River orogenic belt is an important metallogenic environment for the Late Triassic mineralization and development in the Sanjiang area. Although the Ailaoshan gold mineralization belt was mainly formed in Himalayan Period, the host rock-ophiolitic melange undoubtedly provided an important source of ore-forming materials. The Yangla large copper deposit was produced in the Jubalong-Dongzhulin intra-oceanic arc environment and located in calc-alkaline andesitic arc volcanic rock series, indicating that intra-oceanic arc is also an important metallogenic environment for submarine hydrothermal fluid mineralization.

4.4.2.1.3 Lancang River Orogenic Belt

The arc-basin system of Lancang River Orogenic Belt is generally similar to that of Jinsha River Orogenic Belt. Although the ancient suture zone of Lancang River may have been covered by a large nappe in the later period, it was subducted eastward at the end of Early Permian, which has been proved by the development of the volcanic arc in Zuogong-Jinghong on its east side in Late Permian (Mo et al. 1993). It is not clear whether a back-arc spreading basin was formed in Lancang River Orogenic Belt in the subduction orogenic stage. However, since the volcanic arc formed in Late Permian was developed in the western margin of Qamdo-Pu’er Block and had characteristics of continental marginal arc, it is estimated that the back-arc-basin would be inactive even if it was developed. At present, only a few small polymetallic ore deposits and numerous ore occurrences have been found in the Lancang River continental marginal arc orogenic belt, but their metallogenic potential is still unclear.

4.4.2.2 Lithospheric Delamination (Detachment) and Post-collisional Orogenic Extensional System

The collisional orogeny was originally formed by continental crust subduction (A-type subduction) and often went through the following processes: shortening of continental crust and thickening of double crusts, mountain root delamination, and asthenosphere upwelling, post-orogenic extension and tectonic regime transformation. The collisional orogeny can be described with the P Tt trajectory, showing extrusion and increasing temperature in early stage, decompression, stretching and increasing temperature in the middle stage and stretching and decreasing temperature in the late stage (Jamieson 1991). In Sanjiang area, several (island) arc orogenic belts formed by oceanic crust subduction were developed and entered into the collision orogenic stage successively in Triassic and went through the following processes of arc-land collision, shortening and thickening of continental crust and lithosphere extension, during which Sanjiang and “countertrust orogenic belt being transversely blocked by mountains” were formed in Yanshanian and large-scale mineralization was formed and developed in Late Triassic.

4.4.2.2.1 Collisional Orogeny and Collision Orogenic Belt
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    Jinsha River arc-land Collision Orogenic Belt. The main body of Jinsha River Orogenic Belt is a composite mountain system formed in Early and Middle Permian by collating Zhubalong-Pantiange intra-oceanic arc in Early Permian and Jiangda-Weixi continental marginal arc in Late Permian. An arc-land collision mountain system was formed in the middle-south member of Jinsha River Zone due to the closure of ocean basin and collision between the intra-oceanic arc and Zhongza Block, and another arc-land collision mountain system was formed due to collision between the intra-oceanic arc and the continental marginal arc on the west side. The collisional volcanic rocks formed in the Early Triassic are intermittently outcropped along the collision mountain system. A land-land collision mountain system was formed in the northern member of Jinsha River due to collision between Zhongza Block and Qamdo Landmass, causing that Pushuiqiao Formation of Lower Triassic unconformably overlays on Jiangda collision crustal melting granite body. Qamdo Block lacks the sediments formed in Early and Middle Triassic due to the overall uplift. Collision occurred in Early-Middle Triassic not only leads to the continuous westward subduction of the substances in Zhongza Block, but also causes the overthrust of volcanic-sedimentary substances on the subduction plate toward Qamdo Landmass in turn, forming a “snake swallowing frog (smaller on both ends and bigger in the middle)” collision tectonics.

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    Lancang River Collision Orogenic Belt. The orogenic pattern of Lancang River Collision Orogenic Belt is similar to that of Jinsha River Orogenic Belt. The main body was formed by the collision and collage of Zuogong-Jinghong Continental Marginal Arc formed in Late Permian, Dongda Mountain-Lancang River Magmatic Arc and Qamdo-Pu’er Block in Early and Middle Triassic. With the overall eastward collision and thrust of the orogenic belt, the upper crust of the subduction plate trusted eastward on Qamdo Landmass and the rear margin was spread and split, forming extensional basins and metamorphic core complexes. The collision orogeny in Early and Middle Triassic has not only formed the intrusion of syn-collision granite for constituting the main body of Lancang River granite base, but also developed syn-collisional volcanic rock assemblage for superimposing on Zuogong-Jinghong Volcanic Arc.

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    Yidun Collision Orogenic Belt. Collision orogeny in Yidun Orogenic Belt has occurred relatively late and mainly occurred in the late stage of Late Triassic (206–200 Ma). During this period, Ganzi-Litang Ocean Basin was closed, Yangtze Landmass collided with Yidun Island Arc, and Zhongza Block thrust eastward as a tectonic slice, forming an asymmetric collisional mountain zone with non-coaxial shear. The typical product of collision is syn-collision granite, which is superimposed in the magmatic arc zone. The remnant arc lacks J-K sediments due to its overall uplift.

4.4.2.2.2 Post-collision Extension and Volcanic-Rift Basin

The main body was originally formed by the extension of post-collision orogeny in Late Triassic and was characterized by different tectonic responses and rock records in different collision orogenic belts, forming different metallogenic conditions with different mineralization.

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    Jinsha River Orogenic Belt. The gravity field of Jinsha River Collision Orogenic Belt changed significantly in Late Triassic after the arc-land collision in Early and Middle Triassic. The significant extension after the collision has not only led to “bimodal” volcanic activity, but also formed a volcanic-rift basin, which was superimposed on Jiangda-Weixi Continental Marginal Arc formed in Late Permian. At present, three important post-collision extension basins formed in the Late Triassic have been discovered, which are Shengda-Chesuo Volcanic-Sedimentary Basin, Xuzhong-Luchun-Hongpo Volcanic-Sedimentary Basin and Reshuitang-Cuiyibi-Shanglan Volcanic-Sedimentary Basin from north to south. Semi-pelagic volcanic turbidite, tuffaceous turbidite, tuffaceous-siliceous turbidite and arenaceous flysch were developed in the basin. The volcanic rocks in the northern basin are dominated by marine pillow basalt series, accompanied by the development of gabbro-diabase dykes, while the basalt-rhyolite “bimodal” volcanic rocks were developed in the southern basin.

The Rb–Sr isochron age of rhyolite in bimodal magma assemblage is 235–239 Ma (Wang et al. 1999; Mou et al. 2000), indicating that the bimodal rock assemblage was developed in the early stage of Late Triassic. The basalt of bimodal assemblage belongs to tholeiitic basalt, which can be divided into two groups according to the content of TiO2, namely group with high content of TiO2 (1.25–1.85%) and group with low content of TiO2 (0.25–1.08%). The former is represented by basalts in the Jijiading area, which are significantly different from basalts in the island arc or back-arc-basin due to the high content of TiO2, showing the geochemistry affinity of ocean ridge basalts (Wang et al. 1999). The latter is represented by basalts in Renzhixueshan and Cuiyibi area, showing the geochemistry affinity of basalts in island arc or back-arc-basin. The successive development of these two sequences of basalts may reflect the development process of volcanic-rift basins in the Late Triassic from intense stretching to gradual shrinkage.

Volcanic-sedimentary sequence of volcanic-rift basin: The lower bed is composed of semi-pelagic basaltic volcanic rocks-diabase complex and flysch sediments, the middle bed is composed of abyssal interbedded basalt-rhyolite bimodal assemblage and argillaceous rock series, the upper bed is composed of neritic rhyolitic volcanic rock series and sandy mudstone series and the top bed is littoral-neritic molasse clastic rock series mixed with intermediate-acid pyroclastic rocks, accompanied by gypsum-salt sediments containing barite, gypsum and siderite assemblage, which records the developmental history of volcanic rifted basin, namely, intense stretching and rifting in the early and middle stage and gradual shrinkage and destruction in the late stage. It is estimated that the three volcanic-sedimentary basins are different in the rifting speed and rifting distance. Among them, Xuzhong-Luchun-Jiangpo Basin has the highest rifting speed (0.43 cm/a) and the longest rifting distance (140 km); Shengda-Chesuo Basin has the lowest rifting speed (0.27 cm/a) and the shortest rifting distance (63 km), while the rifting speed and rifting distance of Reshuitang-Cuiyibi-Shanglan Basin are between the highest rifting speed and the lowest rifting speed and between the longest rifting distance and the shortest rifting distance, respectively.

These post-collision extension basins are important metallogenic basins in copper polymetallic ore deposits in Jinsha River Zone. The hydrothermal activity system with submarine eruption was formed by volcanic activity in the basin; in addition, the “brine pool” under semi-closed and closed conditions was formed in the secondary depression zone of the rift basin to further forming the exhalaive sedimentary VMS deposit by sedimentation. Mineralization was formed in the middle stage of basin extension and splitting, such as, Zuna lead–zinc ore deposit in Chesuo Basin, in which the ore-bearing rock series is composed of carbonate rock-clastic rock-barite formation; Luchun copper-lead–zinc ore deposit in Jijiading Basin, Hongpo copper–gold polymetallic ore deposit and Laojunshan lead–zinc ore deposit in Cuiyibi Basin, in which the ore-bearing rock series is composed of acid volcanic tuff-sedimentary rock-siliceous rock formation. The volcanic-subvolcanic hydrothermal-sedimentary siderite-type gold-silver polymetallic ore deposits related to intermediate-acid volcanic rocks were formed based on extrusion tectonics at the end of the basin development, such as Zhaokalong siderite-type silver-rich polymetallic ore deposit and Dingqinnong copper–gold ore deposit in Chesuo Basin and Chugezha Siderite ore deposit in Cuiyibi Basin, in which the ore-bearing rock series was formed by intermediate-acid pyroclastic rock-sedimentary rock-siderite formation; the gypsum ore deposit was formed in the Yulirenka area of Luchun Basin.

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    Development history of Lancang River Collision Orogenic Belt is similar to that of Jinsha River Orogenic Belt. Its post-collision extension also occurred in the Late Triassic, and the typical product is the potassic trachybasalt-rhyolite bimodal rock assemblage of Manghuihe Formation, which was overlaid on the shoshonite-latite series of Xiaodixing Formation. This sequence of bimodal rock assemblage is mainly distributed on Zuogong-Jinghong Volcanic Arc formed in Permian in Lancang River Orogenic Belt, but mainly outcropped in the middle-south member. Acid volcanic rock series with a thickness of 3000–4000 m were mainly developed in Northern Lancang River Zone (Eastern Tibet), which are in conformable contact with the underlying strata. The Rb–Sr age is 238.9 Ma. With high content of silicon (w(SiO2) 67–79%) and high content of alkali (w(K2O + Na2O) 6–8.6%), the rocks belong to the high-potassium calc-alkaline series. Its geochemistry characteristics are similar to those of the volcanic rocks of Xiaodixing Formation in the Southern Lancang River Zone (Western Yunnan), belonging to the collisional volcanic rock series (Mo et al. 1993). The bimodal rock assemblage of Manghuihe Formation is mainly distributed in the area north of Minle in Jinggu and the potassic trachybasalt and high-potassium rhyolite series are outcropped in interbeded way in the Southern Lancang River Zone (Western Yunnan), with seven rhythmic cycles at most. The rock belongs to the high-potassium calc-alkaline series-potassium basalt series. With the decrease of potassium content, the volcanic rocks are developed into a medium-potassium calc-alkaline series in the area south of Jinggu. Potassic volcanic rocks are moderately enriched in LREE, that is, (w(La)/w(Sm))N = 5.32–15.13, relatively scarce in high-field strength element (HFSE), such as Nb, Ta, Zr, Hf, Ti, and relatively enriched in K, Rb, Ba, Th, indicating the geochemistry affinity of volcanic arc shoshonite. In view of the above, Mo et al. (1993) defined it as a lagging arc volcanic rock. However, its temporal and spatial distribution and tectonic environment for outcropping show that this sequence of bimodal volcanic rock series may be originated from the “island-type” mantle source area but was formed in the lithosphere extension stage after collision orogeny and outcropped in the tectonic condition with crust stretching and rifting.

    Although the extent of geological study for Lancang River Zone is relatively low, the discovered VMS deposits were outcropped in this sequence of bimodal volcanic rock series, such as Wenyu copper ore deposit in Jingdong occurs in potassic trachybasalt, Minle copper ore deposit in Jinggu occurs in high-potassium rhyolite rock series and the recently discovered Dapingzhang copper deposit also occurs in bimodal rhyolite volcanic rock series, which reveals that the extension of Lancang River Orogenic Belt and “bimodal” volcanic activity provide a favorable metallogenic condition for the VMS formation.

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    Yidun Collision Orogenic Belt. The post-orogeny extension of Yidun Collision Orogenic Belt occurred later, and the typical magma product is composed of extensional acid volcanic rock series formed in Early Yanshanian and A-type granite formed in Late Yanshanian. Although no volcanic-rift basin superimposed on the collision orogenic belt was developed, two important volcanic-magmatic rock zones were formed.

    The extensional acid volcanic rock series is closely associated with the high-potassium rhyolite zone in the back-arc area in Yidun Island Arc Zone in space and erupted from Triassic to Jurassic, with Rb–Sr isochron age of (189.2 ± 5) Ma (Hou et al. 2001a, b). Being characterized by high alkali content (w(K2O + Na2O) = 5.58–10.16%) and w(K2O) (4.46–8.76%) > w(Na2O) (0.12–1.40%), the acid rhyolitic volcanic rocks belong to the shoshonite series. It is rich in K, Rb, Zr, Ta but poor in CaO, Sr and Eu as for its geochemistry characteristics, showing the geochemistry affinity of intraplate volcanic rocks (Qu et al. 2001). Compared with the rhyolite with high-k content (213 Ma) in the back-arc spreading basin (Hou et al. 1995), this sequence of alkaline rhyolite has a typical “swallow-shaped” REE distribution pattern, with the initial strontium ratio of 0.714578, showing that its magma is originated from the typical continental crust melting. Its development indicates a short period of intense collision (206–200 Ma) occurred in Yidun Collision Orogenic Belt, causing the change of regional stress field, that is, the stress field changed from the extrusion system to extension system since (189.2 ± 5) Ma.

    A-type granite was outcropped on the west side of the extensional acid volcanic zone in space and then intruded into the sand-slate series formed in the Upper Triassic, constituting an important granite zone in this area. It was formed in Late Yanshanian, with isotope ages of 102–75 Ma and the peak age of magmatic activity of 80 Ma (Hou et al. 2001a, b). The rock assemblage is moyite, granodiorite and monzogranite and mainly composed of potash feldspar (microcline), plagioclase, quartz and lepidomelane, accompanied with accessory mineral assemblage of allanite + apatite + zircon + tourmaline + magnetite + cassiterite. Rich in alkali (w (Na2O + K2O) = 6.13–8.68%) and AR = 1.9–3.0, the rock belongs to the alkaline series. Being characterized by its relatively high ratio of w(FeO*)/w(MgO) and w(Na2O + K2O)/w(CaO), relatively abundant HFSE (Zr, Hf, Nb, Ta, Ce, Y, etc.) and relatively large ratio variation in trace elements (w(Rb)/w(Ba): 0.52–39.3; w(Rb)/w(Sr): 8.0–39.8), the rock shows the geochemistry affinity of A-type granite and can be compared with A2-type granite (Eby 1992; Hou et al. 2001a, b). With a typical “swallow-shaped” REE distribution pattern and significant negative Eu anomaly, the 87Sr/86Sr ratio of granite with w(La)/w(Yb) = 2.46–5.99 is 0.7441. These geochemistry characteristics indicate that the granitic magma is originated from the partial melting of typical continental crust characterized by argillaceous rock series.

    Therefore, the large-scale development of A-type granite in this area indicates that the lithosphere extension reached its peak at about 80 Ma after collision orogeny. On the one hand, this type of significant extension promotes the significant upwelling and thermal erosion of asthenosphere substances and significantly changes the status of the thermal structure in the lower bed of the orogenic belt, resulting in large-scale melting of the crust and the formation of granite magma; on the other hand, it leads to significant extension of crust and even collapse of the orogenic belt (Hou et al. 2001a, b).

    The significant extension and volcanic-magmatic activity of Yidun Collision Orogenic Belt in Yanshanian led to large-scale silver-tin polymetallic mineralization. A series of skarn or granite-type tin polymetallic deposits, occurrences and mineralization points were developed intermittently in the inner and outer contact zone of A-type granite zone, forming an important tin polymetallic mineralization zone. The hydrothermal fluid driven by granite intrusions migrated and converged along the large-scale detachment zone and fault zone formed by extension within 1–10 km around the A-type granite zone, forming a large-scale silver polymetallic ore concentration area represented by Xiasai silver deposit. Although no gold ore deposits for industrial purpose have been found in the acid rhyolite series of 189 Ma at present, the significant whole-rock pyritization and excellent Au geochemistry anomaly reflect that this sequence of alkali-rich rhyolite has a certain metallogenic potential.

4.4.2.2.3 Lithospheric Delamination and Plate (Detachment)

The evolution history of Sanjiang giant orogenic belt shows that the regional gravity field experienced a major turning in the Late Triassic, and its tectonic response, rock record and mineralization are quite different from those of MABT. By taking Qamdo-Pu’er Block as the central axis, the arc-land collision has occurred in Early and Middle Triassic and then large-scale extension has occurred in Late Triassic in Jinsha River Orogenic Belt thrusting westward, accompanied by the development of bimodal rock assemblage with basalt-high-potassium rhyolite, forming a series of NW-trending extension basins. The significant extension has also occurred in the Late Triassic in Lancang River Orogenic Belt overthrusting eastward, with the distinctive potassium basaltic magmatic activity and the development of potassic trachybasalt-high-potassium rhyolite bimodal rock assemblage. Although the collision orogeny has occurred late in Yidun Orogenic Belt in the east, it was quickly developed and entered the extension stage at the end of Late Triassic or Early Jurassic. The high-potassium rhyolitic volcanic rocks (189 Ma) were formed in the early stage of extension, and A-type granite zone (102–75 Ma) was formed in the peak stage of extension and even the collapse stage of the orogenic belt. Major turning of regional gravity field and large-scale mineralization have occurred in the Late Triassic. VMS deposit related to hydrothermal activities of seawater, the exhalaive sedimentary copper–niobium polymetallic deposit related to fluid activities in the basin and the silver polymetallic deposit related to large-scale fluid migration-convergence process were mainly developed.

Extension, high-potassium volcanic rocks, bimodal rock assemblages and large-scale mineralization events occurred in Sanjiang Giant Orogenic Belt in Late Triassic are not accidental but are restricted by a unified deep orogeny mechanism. Lithospheric delamination and detachment of subducted continental crust plates may be two possible deep orogeny mechanisms.

High-density mineral assemblages (eclogite facies) were formed in the collision orogenic belt due to crust thickening and rock metamorphism in the lower crust, and the crust and lithosphere were thickened due to shortening of continental crust, resulting in the temperature of mountain root being relatively lower than that of asthenosphere (Dong et al. 1999). This thermal-substance structure will cause potential gravity instability, leading to de-rooting or lower crust delamination. As the direct result of delamination, the hot asthenosphere with low density rises to the crust-mantle boundary and overlays the cold lithospheric mantle, resulting in thickening of lithosphere and rapid heating of the lower crust, so that the crust uplifts rapidly and extends subsequently. The basaltic magma invades the lower crust due to the decompression melting caused by asthenosphere rising, and the lower crust being heated will be further melted to drive granite magma invading into the upper crust. Therefore, large-scale basaltic magma underplating and shoshonite magma exhalation are often considered as petrological evidence of lithospheric delamination (Key 1994; Key and Key 1994; Dong 1999). Sacks and Secor (1990) and Davies and Blanckenburg (1995) considered that the subducted lithosphere plates will be detached under the combined action of the uplift force of the subducted continental crust and the downward force of the subducted oceanic crust, which directly leads to the large-scale upwelling of asthenosphere and partial melting at the bottom of the crust, resulting in large-scale magmatism and the formation of a large amount of syn-collision granite. Obviously, both the delamination of the lower crust and the detachment of the subducted continental crust led to the large-scale upwelling of the asthenosphere and heat the crust, providing necessary thermal melting conditions for large-scale magmatism and a huge “heat source” for regional large-scale fluid activities.

The global seismic tomography data from Fukao (1995) show that the substances in Tethyan subduction plate have been detached, subsided and returned to the mantle on a large scale and are currently located 1200 km underground. The seismic tomography data of Sanjiang area from Zhong Dalai et al. show that the subduction plate was also detached and returned deep to the mantle. The lithosphere extension of Sanjiang Orogenic Belt occurred on a large scale in Late Triassic, and the significant development of high-potassium volcanic rock, basalt-rhyolite “bimodal” volcanic activity and volcanic-rift basins in the volcanic continental marginal arc indicated that the lithospheric delamination or subduction plate detachment began to develop in Late Triassic, while the large-scale intrusion of A-type granite indicated that the delamination or detachment reached its peak at 80 Ma.

The large-scale upwelling of asthenosphere induced by lithospheric delamination or subduction plate detachment is not only led to mantle-derived and crust-derived magmatic activity, but also brought large amounts of deep ore-forming materials. This is also led to crustal tension and faulting activities and developed important ore-forming basins while creating huge regional thermal anomalies that drove large-scale convective fluid circulations along tension-induced fracture zones as well as long-distance migrations and accumulations, thus inducing large-scale mineralizations in the Late Triassic.

4.4.2.3 Collision Uplifts and Large-Scale Strike-Slip Fault Systems of Qinghai-Tibet Plateau

After experiencing a subduction orogeny, a collision orogeny, and a lithospheric extension successively, the huge Sanjiang Orogenic Belt entered a new stage, i.e., the overall intracontinental convergence orogeny, in the Early Paleogene. With the collision uplifts of Qinghai-Tibet Plateau, large-scale strike-slip extensions and nappe shears successively took place in Sanjiang Orogenic Belt mainly under large-scale strike-slip faulting actions, thus developing a series of strike-slip basins (pull-apart ones), Jinshajiang-Honghe Porphyry Belt and large nappe shear belts therein and controlling the developments of large and huge deposits therein during the Himalayan Period.

4.4.2.3.1 Collision of Indian and Asian Continents and Large-Scale Strike-Slip Faulting

Intercontinental convergence might be tolerated through crustal thickening and lateral detachment (McKenzie 1972; Molnar and Tapponnier 1975; Tapponnier and Molnar 1977). The strains of the Qinghai-Tibet Plateau caused by the convergence and collision of India and Asian continents were represented by double crustal thickening and large-scale strike-slip faulting (Tapponnier and Molnar 1976; Peltzer and Taponnier 1988; England and Molnar 1990). The convergence and collision of Indian and Asian continents that started in the Paleocene were manifested as a forward compression from south to north, which led to the occurrence of the Himalayan orogenic belt and caused the crust in the middle of the plateau to shorten dramatically and thicken twofold, and which was accompanied by the generation of the large-scale syn-collision Gangdise Granite Belt about 55 Ma ago. As the Indian continent moved northward in its entirety, its northeast corner wedged forcefully into the east of Tibet and collided with the southwest edge of the Yangtze continent, causing the crust in Sanjiang Orogenic Belt to shorten drastically.

When the Indian continent collided strongly with the Asian continent and continued to move northward in the Eocene, large-scale strike-slip fault systems, such as the nearly EW Sanjiang Fault System (north section) and nearly SN Sagaing Fault Zone (south section), started to develop on the east edge of Qinghai-Tibet Plateau as right lateral strike-slip ones (Fig. 4.17). A series of large-scale NW strike-slip faults were developed in an extensive area east of the plateau, including Kunlun Fault, Xianshuihe Fault, and Honghe Fault successively from north to south (Fig. 4.17; England and Molnar 1990; Taponnier et al. 1990). The land block between the left lateral Kunlun and Xianshuihe faults rotated clockwise (1°–2°/Ma) and shortened (10–20 m/Ma) in the east–west direction under the nearly NW right lateral strike-slip-shear (England and Molnar 1990). The left lateral strike-slip of Xianshuihe Fault created the Zheduoshan-Gonggashan translational granite (10–15 Ma; Luo 1998). The 1000 km-long Ailaoshan-Diancangshan Metamorphic Rock Belt was developed under the left lateral Honghe strike-slip faulting, leading to partial melting of the enriched mantle (Huang and Wang 1996; Zhang and Xie 1997; Zhong et al. 2001) and controlling the development of Jinshajiang-Honghe Alkali-rich Porphyry Belt (41–26 Ma; Zhong et al. 2000). About 23 Ma ago, a large-scale strike-slip movement was occurred along the strike-slip-shear zone, and the Indosinian Block was extruded southward and slipped more than 500 km southeastward relative to South China (Taponnier et al. 1990).

Fig. 4.17
figure 17

Tectonic framework of Tibet Plateau’s East Edge

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4.4.2.3.2 Coupled Strike-Slip and Extension and Generation of Ore-Bearing Porphyry Belts

The convergence and collision of the Indian and Asian continents and the northward thrust of the former put the east part of Tibet in a huge strike-slip-shear system, thus developing a series of small-scale right lateral strike-slip faults, such as Chesuo-Deqin Right Lateral Strike-Slip Fault and Wenquan Right Lateral Strike-Slip Fault, accompanied by a series of en echelon left lateral NW–NNW folds and alternating fault structures (Fig. 4.18). These NNW–NW anticline and fault structures, as important rock-controlling structures, provided ultrashallow emplacement space for Yulong Porphyry Belt. The porphyry magma migrated upward along the Wenquan Right Lateral Strike-Slip Fault and was finally located in a series of dilatation spaces on the west side of the strike-slip fault, thus developing Yulong Ore-bearing Porphyry Belt (33–52 Ma).

Fig. 4.18
figure 18

Tectonic framework and spatial distribution of Yulong Porphyry Belt on Eastern Edge of Qamdo Block (Wang et al. 2000). I—Volcanic Rock Belt in Gongjue Basin; II—Yulong Granite Porphyry Belt; III—Ritong-Mamupu Syenite Porphyry Belt; IV—Volcanic Rock Belt in Nangqian-Lawu Basin. ① Chesuo-Deqin Fault; ② Wenquan Fault; ③ Tuoba Fault; ④ North Lancang River Fault; 1—asalt; 2—Andesite; 3—Rhyolite; 4—Trachyte; 5—Monzonite granite porphyry; 6—Syenite; 7—Age

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4.4.2.3.3 Coupled Strike-Slip and Torsional Thrust and Generation of Strike-Slip Pull-Apart Basins

Because the Indian continent forcefully wedged northeast and contacted and collided with the Yangtze continent, strong eastward and westward compressive stress components arose and a huge X-shaped structural knot centered on Deqin (Fig. 4.19) was developed in Sanjiang Orogenic Belt. The Pu’er Block at the southern end of the structural knot slipped southward on a large scale along the Honghe Left Lateral Strike-slip Fault about 23 Ma ago (Taponnier et al. 1990); the northern end of the structural knot saw a retreat and slipped northward along the left lateral strike-slip fault.

Fig. 4.19
figure 19

Relaxation rebound and violent extension of Qamdo Block during Northward Slip. 1—Cenozoic strike-slip pull-apart basin; 2—strike-slip fault; 3—anticline Axis. ① Chesuoxiang Fault; ② Qingnidong-Gongjue Fault; ③ Jiezha-Chaya Fault; ④ Honghe Fault; ⑤ Ailaoshan Fault; ⑥ Bijiang River-Zhenyuan Fault; ⑦ Lancangjiang Fault

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During the northward slip, Qamdo Block underwent relaxation rebound and strong extension, thus developing a series of strike-slip extension basins, such as Gongjue Basin east of Yulong Porphyry Belt and Nangqian Basin west of Alkali-rich Porphyry Belt (Fig. 4.19). With Chesuo Fault as its eastern margin, Gongjue Basin is a half graben basin. Nangqian Basin is controlled by Tuoba strike-slip fault, with characteristics of strike-slip pull-apart basins. Both of the basins received very thick Paleogene and Neogene fluvial-lacustrine red clastic rock series with latitic-trachytic volcanic rock series sandwiched. It was inferred according to the intrusion ages of these alkaline-slightly alkaline volcanic rocks that the strike-slip extensions and extension pull-apart basins were developed 42–37 Ma ago, when the middle-period magmatic emplacement peak of Yulong Porphyry Belt almost occurred (40 ± 2.3 Ma). The temporal and spatial paragenetic relations between the two K2O-rich volcanic rock series and the two porphyry rock series show that these strike-slip tensile actions might be key to inducing crust/mantle material meltings and controlling magma uprise emplacements.

When Pu’er Block thrusted and slipped southeast, a series of strike-slip pull-apart basins, such as Lanping-Yulong Basin and Jiangcheng-Mengla Basin, were developed as important mineralizing basins. Lanping-Yunlong Basin, which is controlled by the Bijiang Strike-slip Fault and spreads in the north–south direction, might be a pull-apart fault basin developed under both a right lateral strike-slip pull-apart action and a torsional thrust. The basin is filled with very thick continental salt-bearing formations, with slump deposits and fluviolacustrine alluvial fan deposits in its top and alkali-rich porphyry emplacement in its south extension. In the Jinding Mining Area, there are ore deposits on the side where the Bijiang Strike-slip Fault is located, which are at the bottom of the decollement zone of the thrust nappe’s footwall. In Sanshan Mining Area, ore deposits are located exactly in the overthrust zone and its hanging wall’s fault zone (Fig. 4.20). Jiangcheng-Mengla Basin, which is composed of a series of fault block uplifts and depressions, might be developed under both a strike-slip pull-apart action and a thrust depression (Liu et al. 1993a, b).

Fig. 4.20
figure 20

Nappe Thrust structure of Lanping Basin and its deposit-controlling form (Li et al. 1999). 1—Cenozoic; 2—Mesozoic; 3—glutenite; 4—argillaceous rock; 5—limestone; 6—ore body; 7—nappe structure; 8—ore-forming fluid

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4.4.2.3.4 Strike-Slip Faulting and Shearing Napping

With the continuous northward advancement of the Indian continent, a great strike-slip-shear is occurred in the Sanjiang area, thus developing complex nappe structural belts along some large strike-slip faults in addition to composite basins induced by strike-slip pull-apart actions and torsional nappings in Pu’er Microcontinental Block. Ailaoshan Mineralization Belt is a nappe structural belt under strike-slip-shear, which consists of three thrust fault zones, i.e., Honghe Fault Zone, Ailaoshan Fault Zone and Jiujia-Mojiang Fault Zone, with several nappes or tectonic rock slices sandwiched between them, such as Ailaoshan Front Nappe, Yushan Yakou Nappe, Sanmeng Nappe, Lvchun Nappe and Jinping Slip Body. The nappes are bounded by thrust faults, which are distributed in the right lateral en echelon pattern (Fig. 4.6). Nappes are the main ore-bearing rock series of Ailaoshan Gold deposit, and the interlayer slip planes within them provide important ore-bearing space. Research shows that intersections of strike-slip faults might be main migration channels for deep fluids, thrust faults between nappes might be migration channels for shallow fluids, and interlayer slip zones might provide storage and deposition space for fluids.

4.4.3 Analysis of Important Ore-Forming Environments and Mineralizations

In the huge Sanjiang Orogenic Belt, main mineralizations are mainly occurred in three important environments. One is a trench-arc-basin system formed under subduction orogeny, which mainly involved seabed hydrothermal mineralization and epithermal mineralization; the second is the extension system formed after the collision orogeny, which mainly involved seabed hydrothermal fluid mineralization in deep and/or shallow-water environments and fluid mineralization in extensional fault basins; the third is a system formed by intracontinental convergences and large-scale strike-slip faults caused by collision uplifts of Qinghai-Tibet Plateau, which mainly involved porphyry mineralization, strike-slip pull-apart basin mineralization, and shear nappe fluid mineralization. Here, three important mineralization environments are selected for further elaboration and analysis.

4.4.3.1 Mineralizing Porphyry System

In the huge Sanjiang Orogenic Belt, the intracontinental deep-rooted epithermal porphyries played a decisive role in the Himalayan intracontinental convergence mineralization system. They have unique structural setting, large output scale and huge mineralization potential and are comparable to those of the porphyry copper ore belt in the Andes continental margin arc in these aspects.

4.4.3.1.1 Temporal and Spatial Distributions of Ore-Bearing Porphyries

More than 100 Himalayan porphyry bodies have been found at the eastern margin of Qamdo Microcontinental Block in Sanjiang Orogenic Belt, and they are mainly distributed in the microcontinental block’s internal uplift area and uplift-depression junctions formed in the Cenozoic Era. On both sides of the uplift area are strike-slip pull-apart basins. On its east side is Gongjue Half Graben Slip Extension Basin and on its west side is Nangqian Strike-Slip Pull-apart Basin. In the basins, there are 4000 m thick gypsum salt-bearing red molasse sediments, accompanied by alkaline volcanic rock series that are sandwiched between Paleogene red beds.

Here, Himalayan porphyries can be divided into at least two belts. One is the eastern belt, i.e., Yulong Ore-bearing Porphyry Belt at the western margin of Gongjue Basin, which extends from Narigongma in Qinghai Province in the north through Ridanguo, Xiariduo, Yulong and Malasongduo into Mamupu in the south. It is 200 km long and 15–30 km wide, with more than 20 monzonitic granite porphyry bodies (Fig. 4.18). The other is the western belt, i.e., Alkali-rich porphyry belt consisting mainly of syenite porphyry. As a huge alkali-rich porphyry belt, it extends southward from Ritong and Xiangdui in the north through Mangkang, Shangri-La, Dali, and Jinping into the north part of Vietnam, with a length of more than 1000 km (Zhang et al. 1997). Yulong porphyry belt is characterized by typical porphyry copper/molybdenum deposits (Rui et al. 1984; Ma 1990). In the alkali-rich porphyry belt, there are porphyry-type and cryptoexplosive breccia-type gold-silver polymetallic deposits (Wang et al. 2000). Although the age data of Yulong Porphyry Belt were obtained from different laboratories by using different dating methods, the statistical law based on K–Ar age data clearly shows that the porphyry belt has at least three emplacement age ranges: 48.2–55 Ma, 38–41.5 Ma and 30.9–34.6 Ma, which correspond to three peaks, respectively: 52 ± 2.8 Ma, 40 ± 2.3 Ma, and 33 ± 3.3 Ma, respectively. The whole-rock-mineral Rb–Sr isochron ages of the Yulong monzonite granite porphyry are 52 ± 0.2 Ma and 41 Ma, respectively, and its biotite 40Ar/39Ar age is 52.84 ± 1.68 Ma (Ma 1990); the Rb–Sr isochron age of the Duoxiasongduo monzonite granite porphyry is 52 Ma, and its zircon U–Pb age is 41 Ma (Shen 1995). Besides, two zircon U–Pb ages of the Angkenong monzonite granite porphyry are respectively 40.9 Ma and 33.7 Ma (Ma 1990). These age data confirm that Yulong porphyry belt ever saw at least three magma emplacement periods: early, middle and late periods, and the magmatic activity peak periods are 52 Ma, 41 Ma and 33 Ma, respectively.

The magma emplacement ages of alkali-rich porphyry belt are relatively young. The Rb–Sr age of the lamprophyre in the Ailaoshan area is 28.8–49.0 Ma, and its fission track age is 22.7–27.2 Ma (Bi et al. 1996; Zhang and Xie 1997); the age of the alkali-rich porphyry in the Jianchuan area is 26.5–37.6 Ma (Deng et al. 1998) and that of the Jinping area is 27.0–41.0 Ma (Zhong et al. 2000).

The K–Ar age of the neutral volcanic rock in Gongjue Basin on the east side is 37.5 Ma and that of the trachyte in Nangqian Basin on the west side is 38.7–42.4 Ma (Wang et al. 2000), both of which are generally equivalent to the middle-period magmatic intrusion age of Yulong porphyry belt.

4.4.3.1.2 Lithogeochemical Characteristics

Monzonite granite porphyry and syenite granite porphyry are the main rock types in Yulong porphyry belt, but alkali feldspar granite porphyry is also contained therein. The rock masses often contain small amounts of dark granodiorite inclusions. The phenocryst assemblage is as follows: calcareous hornblende + magnesian biotite + andesite/oligoclase + sanidine potassium feldspar + quartz. The accessory mineral assemblage is as follows: magnetite + zircon + apatite + titanolite. The rocks here feature the accessory mineral assemblage characteristics typical of I-type granite and magnetite-bearing granite series. The ALK value range of the rocks in Yulong porphyry belt is 7.46–8.85, and their δ range is 2.10–3.04, with the characteristics of the typical calcic-alkalic series. The A/NKC values of the porphyry rocks are mostly lower than 1.1 and are equivalent to those of I-type granite (Hine et al. 1978; Griffiths 1983). Compared with the copper-bearing porphyritic rocks in Cordillera orogenic belts, the rocks in Yulong Porphyry Belt generally show the chemical characteristics as follows: lower SiO2 and Fe2O3 contents and higher Al2O3, MgO, K2O (K/Na > 1) and K2O + Na2O contents. Large-ion lithophile elements (LILE): compared with ocean ridge granite (ORG) and within-plate granite (WPG) (Pearce 1984), Yulong Porphyry Belt is typically rich in K, Rb, Ba and Sr (Fig. 4.21). The Rb, Ba and K2O content ranges of these rocks are respectively 168–315 μg/g, 95–380 μg/g and 4.15–8.06%, which are respectively 30–50, 10–30 and 10–20 times those of ORG and are respectively equivalent to those of arc granite and syn-collision granite (Fig. 4.22). These geochemical characteristics indicate that either the porphyry magma source area was strongly enriched with LILEs relative to the ORG-type mantle, or the porphyry magma was contaminated with a large amount of crustal materials during the uprise emplacement process.

Fig. 4.21
figure 21

Trace element distribution of Yulong Porphyry Belt. 1—Yulong rock mass; 2—Malasongduo rock mass; 3—Duoxiasongduo rock mass; 4—Mangzong rock mass; 5—Mamupu rock mass; 6—Zhalaga rock mass

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Fig. 4.22
figure 22

Trace element discrimination diagram for Yulong Porphyry Belt. ORG—Ocean Ridge Granite; VAG—Volcanic Arc Granite; WPG—Within-plate Granite; SYN-COLG—Syn-collision Granite

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High-field strength elements (HFSE): the HFSE (Zr, Hf, Nb, Ta, Ti, U, Th) contents of the rocks in Yulong Porphyry Belt are close to or lower than those of ORG (Fig. 4.22). Their Zr and Hf content ranges are respectively 90–148 µg/g and 5–19 µg/g, slightly lower than those of ORG, respectively, while their Nb and Ta content ranges 6–18 µg/g, which are largely equivalent to those of ORG respectively. Their Ti content range of (0.21–0.52%) is significantly lower than that of ORG, while their Th content range (24–54 μg/g) is significantly higher than that of ORG (Fig. 4.21). The Zr, Hf, Nb and Ta abundance characteristics of Yulong porphyritic rocks show that their magma source area was depleted to different degrees in terms of these elements relative to the ORG mantle, esp. Zr and Hf. Their Ti and Th abundance anomalies relative to ORG might be related to the fluid metasomatism in the magma source area.

All the porphyritic rocks in Yulong Porphyry Belt show the distribution characteristic of strong LREE enrichment (w(Ce)/w(Yb) = 54.1–109.1). Different from crustal remelting granites, they have a distribution pattern with no obvious negative Eu anomaly, indicating that the porphyry magma did not undergo any intensive fractional crystallization. The YbN and LaN ranges of Yulong porphyritic rocks are respectively 3–7 and 60–180, which are respectively lower and higher than those of Jiangda-Weixi Arc’s volcanic rock and dioritic porphyrite (3–4 and 30–40). Compared with ORG, Yulong porphyritic rocks are very poor in Yb and Y. The content ranges of the two elements therein are respectively 0.94–1.92 μg/g and 9.33–19.31 μg/g, only 1/100 and 1/10 times those of ORG, respectively. Since Y is a relatively stable trace element that did not participate in mantle metasomatism, its content therein being lower than that of ORG indicates that the porphyritic magma source area had lower HREE, Y, Zr, Hf, Nb and Ta contents relative to the ORG-type mantle, esp. Y, Yb, Zr and Hf. Yulong porphyritic rocks being rich in LREEs reveal that their LREE behavior was similar to their LILE behavior, i.e., either there was a secondary enrichment in the depleted mantle because of mantle metasomatism or the magma was enriched with LREEs and LILEs because of massive crustal material melting.

The 87Sr/86Sr values of Yulong, Duoxiasongduo and Malasongdo porphyry bodies in Yulong Porphyry Belt are respectively 0.70663, 0.70654 and 0.7077 (Ma 1990; Wang et al. 1995), which are equivalent to that (<0.707) of Berrida I-type granite in Australia (Chappel and White 1974) and are within the 87Sr/86Sr range of the typical I-type granites across the world (mostly ranging from 0.706 to 0.708). The εNd values of Yulong and Duoxiasongduo porphyritic rocks in Yulong Porphyry Belt are respectively −3.686798 and −2.828496 (Wang et al. 1995). As shown in Fig. 4.23, they are located near the joint between the depleted mantle and upper crust (Wang et al. 1995) and are within the εNd(t)-εSr(t) range of Australian I-type granite, clearly indicating that the magma forming the porphyritic rocks in Yulong Porphyry Belt consisted of both melted crust and mantle materials, the latter of which prevailed (Faure et al. 1978).

Fig. 4.23
figure 23

A εNd(t)-εSr(t) correlation diagram of ore-bearing porphyry of porphyry belt in Eastern Tibet (Wang et al. 1995). I—Australian I-type granite; II—Australian S-type granite; III—I-type granite in eastern Tibet; IV—S-type granite in eastern Tibet; V M-type granite in eastern Tibet; UC—Upper Crust; YC—Young Crust; PC—Paleocrust; 1—Granite in Jiangda rock belt; 2—granite in Yulong rock belt; 3—Dongdashan-Leiwuqi rock belt; 4—Nujiang rock belt; 5—Basu-Chayu rock belt

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4.4.3.1.3 Mineralization Characteristics of Ore-Bearing Porphyries

Yulong porphyry copper deposit belt is the largest porphyry copper deposit belt in China, in which one super-large copper deposit, two large copper deposits and three medium- and small-sized copper deposits have been discovered. All the ore-bearing porphyritic rocks are located in the Triassic volcanic-sedimentary rock series and their mineralizations feature small scale (<1 km2 outcrop area), shallow emplacement (mostly <1.5 km) and steep inclination. Although they were developed in an intracontinental environment, their mineralization characteristics are very similar to those of the porphyry copper deposits in Andes copper deposit belt. Their mineralizations are summarized as follows.

  1. (1)

    Mineralization Characteristics. They have three mineralization forms in space: (a) whole or partial mineralization in porphyry; (b) steeply inclined or vertical ore body in contact zone between porphyry and wall rock; (c) stratoid or lenticular ore body in altered wall rock strata. In most cases, the three mineralizations are closely accompanied by each other and show clear mineralization zoning and annular distribution centered on the porphyry mass. Except a small ore-free core in the center, the whole-rock mass has mostly been mineralized to different degrees into Cu/Mo ores that exist in the disseminated or veinlet disseminated pattern; there is a Cu–Fe polymetallic mineralization in the contact zone, in which ore bodies are vein-like or lenticular and ores are massive or veinlet-like; there is a Pb/Zn/Ag/Au mineralization assemblage in the altered wall rock, which contains vein-like, stratoid, and lenticular ores that constitute a mineralization zone of a certain scale.

  2. (2)

    Wall Rock Alteration with the Ore-Bearing Porphyry as the Center, Hydrothermal alteration zones featuring extensive coverage, high intensity and obvious zoning exist here, including potassium silicification zone, quartz-sericite zone and propylitization zone successively from porphyrite to outskirts. The main part of the potassium silicification zone was developed in the porphyry and is characterized by having large quantities of secondary potassium feldspar and quartz; the quartz-sericite zone was developed around the porphyry, within the contact zone, and above the potassium silicification zone, and is characterized by feldspar sericitization and large quantities of chlorite, epidote, and tourmaline; propylitization occurs extensively in the strata around the porphyry and around the quartz-sericite zone. Although hydrothermal alterations at medium and low temperatures took place, the characteristics of the original rocks are kept.

  3. (3)

    Mineralization Stages According to Li (1981) and Rui et al. (1984), there are three mineralization stages here: ① pneumatolytic stage at high temperatures ranging from 400 to 700 °C, at which the porphyry mostly underwent potash alternation and silification and the wall rocks in the contact zone saw skarnization, which was accompanied by Cu-Mo mineralizations; ② high-medium-temperature stage involving temperatures ranging from 200 to 500 °C, at which there occurred sericitization accompanied by Cu–Mo–Fe mineralizations; ③ mesothermal and epithermal stages, at which mineralization temperatures were lower than 230 °C and in the contact zone and peripheral strata there occurred argillation and propylitization accompanied by Au–Ag polymetallic mineralizations.

  4. (4)

    Mineral Assemblages Mineral assemblage varies with ore body location and ore type. The main metallic mineral assemblage of the veinlet disseminated ore in the porphyry is pyrite + chalcopyrite + molybdenite; the main metallic mineral assemblage of the massive sulfide ore in the contact zone is pyrite + chalcopyrite + magnetite, with small amounts of molybdenite, bismuthite, ilmenite, galena and sphalerite; the main metallic mineral assemblage of the sulfide ore in the altered wall rock is pyrite + chalcopyrite + galena + sphalerite. In addition, small amounts of bornite, chalcopyrite, native gold, gold-silver ore, antimony-gold ore, etc. have been found in the porphyry copper deposits.

4.4.3.1.4 Formation Environment and Diagenetic Mode of Porphyry

Generally, each porphyry copper–molybdenum or copper–gold deposit across the world was developed in an active continental margin arc or island arc environment at a Mesozoic or Cenozoic convergence plate boundary, e.g., the porphyry copper belt around the Pacific Ocean, the mineralizing porphyry in which originated from a molten or island arc mantle source area of the subducting oceanic crust and the mineralization involved in which was closely related to subduction orogeny. However, the Himalayan deep-rooted epithermal porphyry and its porphyry-type copper–molybdenum deposits and explosive breccia-type gold–silver deposits in the Sanjiang area were developed in an intracontinental environment, and the diagenesis and mineralization involved are not necessarily related to a plate subduction mechanism or a continental margin arc environment. Although the ore-bearing porphyry occurred in the intracontinental convergence environment, it was related to large-scale strike-slip faults; although it has nothing to do with subduction orogeny, it has geochemical affinity to island arc volcanic rocks. Thus, in order to reasonably explain the development, evolution and dynamic background of the Sanjiang ore-bearing porphyry belt, it is necessary to deeply understand the magmatic source rock characteristics of the ore-bearing porphyry and analyze in detail the strike-slip faults that restricted its distribution.

4.4.3.1.4.1 Large-Scale Strike-Slip Fault System Under Intercontinental Collision-Occurrence Background of Ore-Bearing Porphyries

Researches on the tectonic evolution history of the huge Sanjiang Orogenic Belt show that the Jinsha and Lancang River oceanic crust plates respectively east and west of Qamdo Microblock that was separated from the western margin of Yangtze Continent, ever subducted into each other at the P1/P2 intersection, and the orogenic belts on the east and west sides were pushed against each other from the Yanshan Movement Period on, thus causing Qamdo Microblock and its adjacent areas to enter the intracontinental convergence stage in its entirety in Paleogene.

The convergence and collision of the Indian and Asian continents, the northward thrust of the former and the southward movement of Yangtze Continent, which started around 65 Ma ago, caused the eastern Tibet region to be in a huge strike-slip-shear system, thus developing a series of small-scale right lateral strike-slip faults, such as Chesuo-Deqin right lateral strike-slip fault and Wenquan right lateral strike-slip fault. These faults, which were accompanied by a series of en echelon left lateral NW–NNW folds and alternating fault structures, are important parts of the Sanjiang Right Lateral Strike-Slip Fault System. The strikes of these structures intersect with Chesuo Fault and Wenquan Fault at acute angles. These NNW–NW anticline and fault structures, as important rock-controlling structures, have provided ultrashallow emplacement space for Yulong Porphyry Belt. In correspondence with the Gangdise syn-collision granite belt (55–36 Ma) formed by the India-Asia intercontinental collision in Paleocene, the porphyry magma in the eastern Tibet region migrated upward along the Wenquan Right Lateral Strike-Slip Fault and finally settled in a series of dilatation spaces west of the strike-slip fault, thus developing Yulong ore-bearing porphyry belt (52–33 Ma). The two granitic rock belts that occurred at different tectonic positions with different spreading directions were developed in the same period (55–52 Ma), showing that the developments of the porphyry belts were controlled by the right lateral strike-slip faulting derived from the northward convergence and collision of the Indian continent.

4.4.3.1.4.2 Subduction-Related Mixed Crust/Mantle Source—Possible Source of Ore-Bearing Porphyries

In eastern Tibet, the strike-slip faults generated through large-scale strike-slips cut the lithosphere as deep as the upper mantle, thus providing the necessary dynamic conditions for the formation of the ore-bearing porphyry magma. However, the Paleozoic Jinsha River oceanic crust plate subducted to Qamdo Microblock and stayed in the upper mantle for a long time, resulting in crust/mantle material exchange, which may form island arc-type mantle source rocks as magmatic source rocks of ore-bearing porphyries. This conclusion is strongly supported by the following evidence.

  1. (1)

    Geological Evidence. The oceanic crust fragments represented by ophiolitic melange are distributed in an intermittent way along Jinshajiang-Ailaoshan Fault Zone, indicating that the fault zone was once an ancient suture zone separating Qamdo Microblock on the west side from Zhongza Microblock on the east side. The plagiogranite in the ophiolitic melange was determined to have one of two U–Pb ages, respectively, 340 ± 3 Ma and 294 ± 3 Ma (Wang 1999), and the ocean ridge basalt has similar U–Pb ages, respectively, 362 ± 9 Ma and 296 ± 7 Ma (Zhan 1998), showing that Jinshajiang-Ailaoshan Ancient Ocean Basin was developed during Carboniferous and Early Permian. The calcic-alkalic moderately acidic volcanic rock system and Jiangda-Weixi Continental Margin Arc of Late Permian were developed on the eastern margin of Qamdo Microblock, showing that Jinshajiang Ancient Ocean Crust Plate began to subduct westward on a large scale at the end of Early Permian. The Rb–Sr isochron age of the syn-collision granite developed along the eastern margin of the continental margin arc is 227–255 Ma (Wang et al. 1999), showing that Jinshajiang Ocean Basin was closed and an arc-continent collision occurred during the early and middle Triassic Period. The main oceanic crust plate, even together with the arc volcanic-sedimentary materials, subducted obliquely and plunged beneath the Qamdo Microblock. The velocity disturbance profile of Sanjiang Orogenic Belt reveals that a subduction plate obliquely plunged beneath Qadom Microblock from east to west at an angle of about 45°. The subduction plate currently stays at a depth of 100–300 km underground, and its subduction front is beyond the west part of Qamdo Microblock and west of Tengchong (Zhong et al. 2001). Thus, it is inferred that the subduction plate might be at a shallower location on the eastern margin of Qamdo Microblock in the Paleocene. A relatively gentle high-speed (7.8–8.1 km/s) interlayer with the thickness of about 20 km is shown at the depth of 50–60 km in Dali (Zhong et al. 2001). It is probably a local remnant of subducting mantle slices. The magma origin depth of Yulong porphyries is estimated to be greater than 38 km (Ma 1990); the formation depths of the other alkali-rich porphyries and lamprophyres are estimated to be about 60 km (Zhong et al. 2001). It is obvious that the depth of the magma source area of Yulong Porphyry Belt is roughly equivalent to that of the remnant parts of the subducting rock slices.

  2. (2)

    Geochemical Evidence The Sr–Nd isotopic geochemical characteristics of the granite porphyry in Yulong Porphyry Belt show that the porphyry magma is originated from a mixed crust/mantle source in which mantle materials prevailed, and its crust/mantle ratio was estimated to be about 2/3–1/4 (Ma 1990; Wang et al. 1995). The following evidence shows that this mixed crust/mantle source might be a product of the metasomatic contamination of the overlying wedge-shaped mantle by the fluids from the subducting oceanic crust plate slices that were rich in LILEs, LREEs and Th. Boron is a light and easily soluble trace element that mainly occurs in seawater, ocean sediments and seabed altered rocks. However, in Yulong Porphyry Belt, boron occurs in large quantities in cryptoexplosive breccia and hydrothermal vein groups inside and outside the porphyry. The cryptoexplosive breccia is a product of the powerful explosion of the late-period magma and gas–liquid fluid in a lower-pressure environment (Rui et al. 1984; Wang et al. 2000). Its breccia is mainly composed of magma fragments, and the cementing matters mainly include tourmaline (up to 20–50%) and quartz. The hydrothermal veins are also mainly composed of tourmaline and quartz and are typically connected to the tourmaline-quartz breccia, showing that gas–liquid fluids extremely rich in boron were segregated from the calcic-alkalic porphyry magma at the late stage. Although the possibility of boron extraction from wall rocks by the uprising and invading porphyry magma can not be ruled out, the contribution of boron from oceanic sediments in the subduction zone to the porphyry magma may be a more reasonable explanation. Figure 4.24 Further Determine Composition of Magma Source Area of Yulong Porphyry Belt by Using Ratios of Main Elements Experimental studies in recent years show that the ratios w(CaO)/w(Na2O) and w(Al2O3)/w(TiO2) of a molten mass produced from a source rock mass consisting of different components can reflect the relative proportions of argillaceous rocks (clays) in the source rock (Douce and Johnston 1991; Holtz and Johannes 1995; Skjerlie and Johnston 1996). The monzonitic granite porphyry in Yulong Porphyry Belt is generally between mantle-derived basalt and argillaceous rock melt, near their joint (Fig. 4.24). This shows that argillaceous rock materials might contribute to the formation of the porphyry magma. It seems that the 50–60 km-deep argillaceous rock materials participating in magmatic melting might be sediments from the boron-rich oceanic crust that plunged into the mantle through subduction. Compared with ocean ridge granites derived from the mantle, the rocks in Yulong Porphyry Belt are very rich in LILEs (Rb, Sr, Ba and K), LREEs and Th, are very poor in HREEs and Y and have largely equivalent high-field strength element contents (Nb, Ta, Zr, Hf, and Ti), which are represented by relatively flat curves in the NAP diagram. Strong Rb and K enrichments in the porphyry and their positive correlation imply that K-bearing minerals might exist in its magmatic source rocks. The porphyry is relatively poor in Ti, Y and HREEs, showing that its magmatic source rocks were relatively rich in water so that Ti-bearing minerals and Y- and HREE-rich minerals could be stable to become residual facies during the melting process of the magma. Potassium-rich lamprophyre and phlogopite harzburgite xenoliths have been found in the alkali-rich porphyry belt that was formed together with Yulong porphyry belt on the eastern margin of Tibet Plateau (Huang et al. 1997; Wang et al. 2000). This also shows that the magma source rocks of Yulon Porphyry Belt might contain water-bearing and K mineral-rich phlogopite. Its generation might be related to fluid metasomatism (Huang et al. 1996, 1997). In addition, due to the instability of LILEs (Rb, Sr, Ba, K), LREEs and Th during the water–rock reaction process, they often enriched this fluid during the dehydration process of the water-bearing subduction zone (Gill 1981; Tatsumi 1983), and this fluid participated in the metasomatic reactions with the materials in the mantle in the wedge-shaped zone, thus developing a water-bearing mantle portion rich in LILEs, LREEs and Th, i.e., island arc-type source rock (Tatsumi 1983, 1986). Since HFSEs are stable in water/rock reactions and hot water alterations, there was no HFSE enrichment in the island arc-type source rocks. Accordingly, we believe that the magma of Yulong porphyry belt is originated from a kind of island arc-type source rock related to subduction. Therefore, although it is occurred in an intracontinental environment, it has the same geochemical affinity as arc granite.

    Fig. 4.24
    figure 24

    Correlation between w(CaO)/w(Na2O) and w(Al2O3)/w(TiO) of ore-bearing Porphyry in Eastern Tibet

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  3. (3)

    Island Arc-type Source Rock + Lithospheric Strike-slip Fault—A New Diagenetic Mode of Ore-bearing Porphyry

    Uyeda and Kanamori (1977) classified arcs into two extreme types: Mariana type and Chile type by subduction angle, stress state and characteristics of arc volcanic-magmatic products at the interface of convergence plates. The former features steep oceanic plate subduction angle, deep oceanic trench, volcanic island arc and back-arc spreading basin, and Kuroko-type deposits were often developed in the marine calcic-alkalic arc volcanic rock (Urabe and Sato 1978; Ohmoto 1983); the latter features gentle oceanic plate subduction angle, magmatic arc developed in the arc area due to strong compression and no back-arc spreading basins magmatic arcs, and porphyry copper deposits were often developed in the magmatic arc porphyrite (Sillitoe 1972). In eastern Tibet, the continental margin arc is a volcanic arc consisting mainly of calcic-alkalic island arc volcanic rock rather than a magmatic arc consisting mainly of granitic porphyry. Maybe, this is because the westward subduction angle of Jinsha River Oceanic Crust Plate is between the above two extreme types. In the Jiangda-Weixi Permian continental margin arc that extends hundreds of kilometers, neither typical Kuroko deposits nor typical Porphyry deposits have been found (Liu et al. 1993a, b; Hou 1993; Yang et al. 1993; Hou and Li 1999). However, the westward-subducting Jinsha River Oceanic Crust Plate provides a necessary island arc source area for the formation of the magma of Yulong porphyry belt through material and energy exchanges with the overlying wedge-shaped mantle, esp. the mantle metasomatism enrichment by the LILE-rich fluid from the subduction zone.

The convergence and collision of the Indian and Asian continents that started 65 Ma ago (Zhong 2001) developed the Himalayan Orogenic Belt and Gangdise syn-collision granite belt (55–36 Ma) in central Tibet, both of which are parallel to the collision zone. In the east of Tibet with an oblique or vertical collision zone, the northward movement of the Indian Continent and the lateral containment of Yangtze Continent led to great nearly SN shear strains, thus developing nearly SN right lateral strike-slip faults such as Sanjiang Fault System and Sagaing Fault Zone and a series of NW left lateral strike-slip faults such as Xianshuihe Fault and Honghe Fault. In western Yunnan, the left lateral strike-slip activities of the huge Honghe Fault controlled the development of the Red River alkali-rich porphyry belt and the development of the Ailaoshan metamorphic belt. In eastern Tibet, Chesuo Fault and Wenquan Fault, which constitute the Sanjiang Fault Zone, generated a series of NW folds and faults through early right lateral strike-slips and controlled the emplacement space and distribution characteristics of Yulong porphyry belt. The late-period stress relaxation and extension formed a tectonic framework of cutting and barrier alternating in the eastern margin of Qamdo Microblock. These strike-slip faults are not only basin margin faults of extensional and pull-apart basins but also crust-penetrating faults that induced partial melting in the mantle source area. Strike-slip faulting that cut lithosphere deeply led to pressure release and melting in the mantle source area and allowed the magma melt to move upward for emplacement. The partial melting in the mixed crust/mantle area, i.e., the island arc-type source area, developed Yulong Porphyry Belt, while the partial melting in the enrichment-type mantle source area developed the alkali-rich porphyry and high-potassium volcanic rock series (Huang and Wang 1996; Zhong et al. 2001). Due to the limited distribution of the island arc source area under subduction, Yulong porphyry belt is located only in eastern Tibet and parallel to the Late Permian arc volcanic belt. To sum up, we regard the diagenetic mode of Yulong porphyry belt as the coupled effects of the island arc source rock and lithospheric delamination strike-slip faulting (Fig. 4.25).

Fig. 4.25
figure 25

Diagenetic mode of Yulong ore-bearing Porphyry

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4.4.3.2 Large Basin System

In the huge Sanjiang Orogenic Belt, large basins have been located in tectonically active areas for a long time. Complex and changeable basin properties, rapid multi-source sediment accumulations, tectonic hydrothermal fluids in orogenic belts on both sides and their lateral migrations, complexly coupled basin and mountain and massive mixing of multi-source fluids finally led to large-scale mineralizations, various complex mineralization types and multi-source diplogene of metal assemblages in the basin system. Among these basins and large-scale mineralizations, Lanping Basin is the most typical.

A comprehensive analysis of the tectonic-sedimentary-fluid mineralization system in the large-scale Lanping Basin system and its basin evolution process reconstruction study show that the basin mainly experienced intracontinental rift-depression basin evolution (T2-3-J2-3), foreland basin evolution (K) and strike-slip pull-apart basin evolution (Cenozoic). Although mineralizations were developed to different degrees at every important evolution stage of Lanping Basin, they mainly occurred in the intracontinental rift-depression basin formed under large-scale lithosphere delamination and the strike-slip basin formed by the Himalayan intracontinental orogeny and ended with episodic drainage depositions and explosive mineralizations of Himalayan fluids.

4.4.3.2.1 Evolution and Mineralizations of Intracontinental Rift-Depression Basin

The intracontinental rift evolution stage is one of the important mineralization periods of Lanping Basin. The rift-depression basin and its mineralizations were controlled by the large-scale lithospheric delamination in the Late Triassic. At this stage, the lower crust was greatly delaminated, the hot mantle material upwelled in large quantities and the large basin extended, forming a central axis fault and a series of small contemporaneous faults. Driven by the upper uplift source, the hydrothermal fluid migrated vertically along the contemporaneous fault and brought about strong hydrothermal activities along the contemporaneous fault zone, thus developing hot water-deposited siliceous rocks and more than one hundred hot water-deposited alkali metal ore bodies that are widely scattered. Among them, there are two large-sized silver deposits and three medium-sized copper-silver polymetallic deposits, which are represented by Heishan-Huishan silver–lead–zinc deposit, Yanzidong silver–copper–lead–zinc deposit, Xiawuqu-Dongzhiyan silver–copper deposit and Dongzhiyan-Hexi Strontium deposit. The developments of the deposits were controlled by specific strata. The ore-forming fluids mainly migrate vertically along the contemporaneous faults and are rich in Cl-, F-, Pb, Zn, Sb, Cu, Ag and other ore-forming materials. Although these medium–low-temperature hydrothermal sedimentary polymetallic deposits have been strongly reformed in the Himalayan period, there are still a lot of hydrothermal sedimentary characteristics (Fig. 4.26).

Fig. 4.26
figure 26

Schematic diagram of rift basin and fluid mineralization (Wang et al. 2000, Scientific Research Report)

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As the rift basin disappeared and the Lanping Basin entered the depression basin evolution stage in the Middle Jurassic, it received a large amount of high-porosity red bed deposits, and favorable thermal fluid migration channels were developed therein during late tectonic activities, thus locally forming structural traps conducive to mineralization enrichment.

4.4.3.2.2 Evolution and Mineralization of Foreland Basin

Lanping Basin, which entered the foreland basin development stage in Late Cretaceous, received large amounts of terrigenous coarse clastic materials from the orogenic belts under the great uplift and napping actions of the orogenic belts on the east and west sides. Although the lenticular and nodular Cu–Fe polymetallic stockwork ore bodies developed in the interstices of these coarse terrigenous materials were not of commercial significance, these high-porosity accumulation layers provided a main activity place for ultrahigh-pressure fluids when tectonic changes occurred later and their initial mineralization provided an important material source for large-scale mineralizations in the Himalayan Period.

Figure 4.27 shows the fluid activity course within the orogenic belt and foreland basin system. Oliver (1986) first proposed the viewpoint that hydrothermal fluids migrate laterally in a foreland basin’s orogenic belt structure. This explains the spatial distribution pattern of various minerals in foreland basins. Luo and Du (1999) also believe that the deposits in Lanping Basin such as Jinding lead–zinc deposit exactly follow this mineralization mode. Although Jinding deposit was formed in the Himalayan Period and hosted in a strike-slip basin, massive amounts of data prove that this type of lateral migration did exist at the foreland basin stage. A lead isotope study of some lead–zinc deposits in Lanping Basin by Mo et al. (2000) also confirmed that the ore-forming materials are originated not only from Jinshajiang Orogenic Belt on the east side but also from Lancangjiang Orogenic Belt on the west and that fluids in the basin might migrate from the orogenic belts on both sides of the basin to its center. Due to the counterthrust nappings of the orogenic belts on both sides, the fluid pressure in the basin was equal to or slightly larger than the vertical pressure (Dominigne Granls 1997), thus resulting in lateral fluid migration under high-pressure stress without the opportunity of vertical upwelling. Because of the coarse sediment particles in the foreland basin, the porosity increased and fluids were preserved in the strata in the form of formation water, which provided large amounts of material reserves for Himalayan mineralization. Therefore, sedimentary sandstone-type copper deposits were formed only in some areas at this stage, such as the primary sedimentary deposit in Baiyangchang.

Fig. 4.27
figure 27

Intrabasinal fluids might move from orogenic belts on both sides to center

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4.4.3.2.3 Evolution and Mineralization of Strike-Slip Basin

The tensional and compressional strike-slip basin evolution period, which started from Paleocene, is the most important large-scale metallogenic period of Lanping Basin. The fluid evolution in the basin was more intense and active. Given the influence of the orogenic belts on both sides of the basin and the intensification of deep crustal tectonic activities, deep active ore-forming materials entered basin fluids through deep overpressure hydraulic or pneumatic fragmentation, which led to explosive mineralization.

At the Paleocene tensional strike-slip stage, the further delamination of lower crustal materials has led to large-scale and universal tensional strike-slips in Lanping Basin, and a hot uplift area was developed in the lower part of the basin, which acted as a “heat engine” to drive fluid activities in the basin (see Fig. 4.8). When the uplift area was cut due to a contemporaneous fault activity, the fluid rich in ore-forming materials in the area became part of the basin fluid, and a large-scale mixing of deep brine and shallow formation water occurred.

4.4.3.2.4 Summary of Basin Fluidization and Mineralization

In Lanping Basin that experienced complex property changes, there are superimposed basins of various properties. Since the Middle Jurassic, the very thick red bed deposits have served as a superior reservoir for the basin fluids. However, due to frequent tectonic activities and continuous activities of the contemporaneous inherited faults, good large-scale reservoir space was formed in the basin in the Eocene Epoch, such as Lanping Jinding Dome and Sanshan-Baiyangping fault traps. Thus, although the basin had good space for oil and gas generation, it had no good oil and gas storage space. Large quantities of oil and gas served as the transportation medium of metallatic minerals, and their residues were dispersed in various fissures and between rock-mineral grains, such as a large quantity of asphaltene found along fissures and beddings in Jinman copper deposit, through whose shrinkage a large number of chalcopyrite emulsion droplets were bled out, crude oil inclusions in Jinding lead–zinc deposit, etc.

The Himalayan ore-forming fluids are large-scale mixtures of deep fluids (rich in Co, Ni, Sb, As, Hg, Ba, Sr, Au, Ag, Cu, Pb, Zn, etc. and CO2) and shallow fluids (rich in CH4, SO42−, Cl−, Ca2+, H2S), etc. A distribution and metallogenic mechanism analysis of the extensive alkali metal deposits and Cu–Ag–Co polymetallic deposits in the basin show that the metallic matter and a large amount of CO2 in the ore-forming fluids were mainly from deep fluids, while CH4, SO42−, Cl−, Ca2+, H2S, etc. were mainly from shallow fluids. In the setting process of ore-forming fluids, basinal fluids ubiquitously involved degassing. The fact that H2S gas is settled in place first is very important to the mineralization of alkali metal deposits (such as Jinding Pb–Zn deposit). H2S gas first settled in structural traps and occupied mineralization space, thus causing a series of strong activities to change the trap structure, such as triggering fracturing and mechanical slumping of brittle rocks in the napping dome (many such events are found in Jinding Mining Area), cryptoburst and fracture in fault traps (Sanshan-Baiyangping area). In addition, the setting of CO2 gas is more important for Cu–Ag polymetallic deposits. It not only leads to cryptoburst and fracture in mineralization space, but also changes the physical and chemical properties of fluids, such as changing the pH value of the fluid to neutral-weakly alkaline. Under this condition, many silver-bearing tetrahedrites or silver tetrahedrites have been developed as the main copper-silver hosted minerals.

Given various structural types and multiple evolution stages of Lanping Basin, the ore-forming fluids of the basin have four characteristics: multi-level, multi-direction, multi-source and multi-migration mode. Specifically, they are represented by four fluid migration models: ① vertical migration model of moderately deep and deep fluids during tension and subsidence (T3-J); ② extensive and large-scale lateral fluid migration and convection model under the Cretaceous single thrust condition; ③ fluid passive setting, accumulation and zonal migration model in the order of solubility and sedimentation under Paleocene-Early Eocene tensional strike-slip conditions; ④ lateral and vertical fluid migration-convection model under the counterthrust compression strike-slip conditions in Late Eocene and Oligocene, in which intrabasinal overpressure fluids were set in the uplift storage or fault trap (Fig. 4.28).

Fig. 4.28
figure 28

Uplift storage or fault trap mineralization model of intrabasinal overpressure fluids

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Large amounts of deep elements participating in mineralization show the existence of deep brine. With regard to sources of ore-forming fluids, there are the following views: ① the intrabasinal formation water became chemically very active through fluid/solid interactions; ② the fluids from the orogenic belts were partially migrated through huge pores of old red beds and were mixed into the deposits water in the basin under counterthrusts or a single thrust, forming a unique mixture rich in CH4 and saturated NaCl/CaCl2 hot brine; ③ high-temperature and high-pressure fluids were upwelled due to the flow removal of the mantle or crust and were mixed with the moderately deep and shallow fluids in the red beds in the basin into ore-forming fluids, which were rich in CO2 gas.

4.5 Preliminary Discussion of Archipelagic Arc-Basin Metallogenic Theory

There are four huge metallogenic systems and 11 metallogenic systems in the Sanjiang Tethys mineralization domain, which were mainly controlled by two major tectonic processes, i.e., MABT evolution and collision orogeny.

The basic framework and structural evolution of the MABT developed in Paleozoic and Early Mesozoic have led to three important metallogenic events in the Sanjiang area, i.e., early Paleozoic, late Paleozoic and late Triassic metallogenic events. The early Paleozoic mineralization episode is mainly occurred in a tensional environment at the edge of the block and within it at the early development stage of the MABT and is characterized by SEDEX Pb–Zn mineralization; the late Paleozoic mineralization episode is mainly occurred at the main development stage of the MABT and is characterized by seabed VMS mineralization; the late Triassic mineralization episode is mainly occurred in environments such as volcanic-magmatic arc, inter-arc rift basin, back arc-basin and superposed rift extension basin developed at the late development stage of the MABT, and is characterized by porphyry Cu deposits, VMS, and SEDEX polymetallic deposits.

The basic framework and tectonic evolution of the MABT mainly resulted in two major metallogenic systems, i.e., continental margin split and convergence ones. There are two main mineralization modes: seabed SEDEX Pb–Zn mineralization and porphyry-type Cu–Au mineralization. As the island arcs evolved from immature ones (oceanic arcs) into mature ones, VMS mineralization evolved along the following route: Cu → Cu–Zn → Cu–Pb–Zn → Zn–Pb–Cu → Pb–Zn. Because of the change of the subduction plate angle, different sections of the island arcs have different stress states. VMS-type deposits occur in a tensile arc, while porphyry-type copper deposits occur in a compressive arc. In the Sanjiang area, multiple tectonic mineralizations could often occur in the same mineralization belt or even in the same deposit. Late porphyry Cu(–Mo–Au) deposits were developed under many early VMS-type deposits. For example, in Lancang Old Plant Lead Deposit in Changning-Menglian Belt, a porphyry Mo(–Cu) deposit has been found under an early Carboniferous (the volcanic tuff zircon SHRIMP age is 323 Ma, Huang 2009) VMS-type Cu(–Pb–Zn) deposit; in Yangla copper deposit in Jinshajiang Belt, Indosinian porphyry/skarn Cu(–Mo) mineralization is superimposed on the SEDEX Cu(–Pb–Zn) deposit formed from Late Devonian to Early Carboniferous, thus forming a composite deposit.

Given the volcanic-magnatic island arcs generated by the plate subduction in the late development period of the MABT, VMS-type Cu, Pb and Zn deposits and porphyry-type Cu(–Mo–Au) deposits were widely developed therein. The arc-continent and arc-arc collisions at the late stage (T3) led to no obvious mineralization, but the plate break-off, remelting, and crustal extension after the collisions resulted in strong A-type granite magma emplacement and rift basin development in the Sanjiang area, thus inducing magmatic Sn deposits and hydrothermal Pb–Zn–Ag mineralization.

Based on previous research findings, we systematically dissected four ophiolitic melange belts, five island arc or continental-margin-arc volcanic-magmatic rock belts and the blocks between them through several rounds of scientific and technological research and prospecting action plans. It is found that the framework of the Sanjiang Tethys orogenic belt is not a simple trench-arc-basin assemblage (one trench, one arc and one basin) formed by a Tethys Ocean subduction. Rather, it was completed mainly by subductions and closures of a series of small ocean basins formed by the previous continental margin break-off and realized by archipelagic arc-basin orogenic processes induced by ocean basin subductions (including those of back arc-basins), such as ocean crust subduction or obduction, arc-arc collision, arc-microblock collision and continent–continent collision. Different genetic types of deposits were formed in different island arc or continental-margin-arc belts, blocks (microblocks) or basins, joint belts or ophiolitic melange belts. Thus, the archipelagic arc-basin metallogenic theory was put forward.

4.5.1 Temporal and Spatial Structure and Mineralization Pattern of Multi-Arc-Basin-Terrane (MABT)

In Chap. 3, we discussed in detail the basic characteristics and evolution of the Sanjiang MABT as well as its temporal and spatial structure. Here, the mineralizations of the arc and basin systems are further summarized.

The original plate tectonics theory and the global Tethyan tectonic framework believe that the Tethyan Orogenic Belt was formed mainly by the subduction of the Tethyan Ocean, it has the typical structural framework consisting of one trench (ocean trench), one arc (island arc) and one basin (back arc-basin) that were developed in sequence from ocean to continent, Cyprus-type VMS deposits were developed in trenches, and volcanogenic massive sulfide (VMS) deposits, porphyry copper deposits and epithermal Au deposits were developed in the island arc or continental margin arc (Fig. 4.29a).

Fig. 4.29
figure 29

Mineralization model comparison of traditional plate subduction “Trench-arc-basin” system and Sanjiang MABT

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The systematic dissection of several ophiolitic melange belts and various types of island arcs and basin systems in the Sanjiang Tethys orogenic belt shows that Sanjiang Tethys has gone through a long, continuous and complex process involving occurrence, development, shrinkage and extinction at least from Paleozoic to Mesozoic. Paleo-Tethys is not the inheritance and development of the original Tethys and Mesozoic Tethys is not Paleo-Tethys reopened after extinction. Some Tethys Ocean crusts can be merged with the subsequent Indian Ocean. According to a study of the ophiolitic melange belts and arc-basin system in the Sanjiang area and their evolutions, the basic tectonic framework of Sanjiang Orogenic Belt consists of four main arc-land collision zones (Ganzi-Litang, Jinshajiang-Ailaoshan, Lancangjiang and Nujiang-Changning-Menglian), five island or continental margin arc volcanic-magmatic rock belts (Dege-Xiangcheng, Jiangda-Weixi-Lvchun, Zaduo-Jinggu-Jinghong, Leiwuqi-Lincang-Menghai and Bomi-Tengchong) and five blocks in between (Zhongza-Shangri-La, Qamdo-Lanping, Leiwuqi-Zuogong, Baoshan-Zhenkang and Chayu-Gaoligong) and is similar to the spatial configuration of a series of island countries in Southeast Asia today. The Sanjiang Tethys orogenic belt was not formed by a simple Tethys Ocean subduction. It was completed mainly by subductions and closures of a series of small ocean basins and was realized by archipelagic arc-basin orogenic processes induced by ocean basin subductions (including those of back arc-basins), such as ocean crust subduction or obduction, arc-arc collision, arc-microblock (block) collision, and continent-continent collision; different genetic types of deposits were formed in different island arc or continental margin arc belts, blocks (microblocks) or basins, joint belts, or ophiolitic melange belts (Fig. 4.29b). The tectonic framework of the complex MABT developed from late Paleozoic to early Mesozoic in the Sanjiang area controls the temporal and spatial distribution and mineralization zoning of deposits therein.

4.5.1.1 Yidun Arc-Basin System and Mineralizations

The Yidun Arc-basin System is mainly composed of Ganzi-Litang Ophiolitic Melange Belt and Yidun Volcanic-magmatic Island Arc Belt on the west side. The existing data show that on the continental crust that had extended and thinned for a long time, Ganzi-Litang Back Arc Ocean Basin opened in early Permian or earlier and began to subduct westward under Zhongza-Shangri-La Block in late Triassic. On the west side there occurred a typical spatial configuration framework consisting of Yidun island arcs (inner and outer arcs), inter-arc rift basin and back arc-basin system, in which bimodal volcanic rocks, subduction island arc volcanic rocks and intrusive rocks were developed. The ocean basin closure and arc-continent collision at the end of Late Triassic and the post-collision extension from Jurassic to Early Cretaceous led to the occurrence of a series of intrusive rocks in the collision and post-collision extension environment. At different stages and locations of the arc-basin system during its generation and evolution, VMS Pb–Zn–Ag deposits, porphyry/skarn-type Cu(–Mo–Au) deposits, epithermal polymetallic deposits and magmatic hydrothermal W–Sn–Bi–Mo polymetallic deposits were developed.

4.5.1.2 Jinshajiang Arc-Basin System and Mineralizations

The Jinshajiang Arc-basin System is mainly composed of the Jinshajiang-Ailaoshan ophiolitic melange belt and the Jiangda-Weixi-Lvchun continental margin arc volcanic rock belt on the west side. According to the available research findings, Jinshajiang-Ailaoshan Back Arc Ocean Basin opened in the Carboniferous Period and began to subduct westward in the late Middle Permian after the Early Devonian above the Early Paleozoic metamorphic soft basement began to rift and subside; the subduction between ocean plates developed the Zhubalong-Yangla-Dongzhulin intra-oceanic volcanic arc at the central axis of the back arc ocean basin from the late Middle Permian to Late Permian as well as the Xiquhe-Xueyayangkou-Jiyidu-Gongnong back arc-basin (ocean crust basement) on its west side; the ocean crust on the west side of the back arc ocean basin subducted westward under Qamdo-Lanping Block and a typical spatial configuration framework consisting of the Jiangda-Deqin-Weixi-Lvchun continental margin arc and its back arc-basin (continental crust basement) was developed from the late Middle Permian to the Late Permian, thus forming subduction-type intra-oceanic arc volcanic rocks, island arc volcanic rocks and intrusive rocks. The ocean basin closure, arc-continent collision and post-collision extension in Late Triassic developed arc volcanic rocks, bimodal volcanic rocks, and intrusive rocks in a collision and post-collision extension environment. At different stages and different locations of the arc-basin system during its generation and evolution, VMS Cu–Pb–Zn deposits, SEDEX massive sulfide Fe–Ag deposits and skarn-type Fe–Cu deposits were developed.

4.5.1.3 Taniantaweng Arc-Basin System and Mineralizations

With the Jitang-Chongshan-Lancang remnant arc as the frontal arc, Taniantaweng Arc-basin System is composed of Changning-Menglian Ophiolitic Melange Belt, Lincang-Menghai Island Arc Volcanic Rock Belt on its east side, Lancangjiang Ophiolitic Melange Belt, and Zaduo-Zhuka-Yunxian-Jinghong Continental Margin Arc Volcanic Rock Belt on its east side. According to the available research findings, Lancangjiang Back Arc Ocean Basin opened in the Carboniferous Period after the Early Devonian above the Early Paleozoic metamorphic soft basement began to rift and subside, and Changning-Menglian Ocean was the inheritance and development of the original Tethys ocean; from the late Middle Permian on, the main body subducted eastward under Lancang Remnant Arc Block and Qamdo-Lanping Block, thus developing a spatial configuration framework from late Middle Permian to Late Permian which consisted of Lincang-Menghai Island Arc, Zaduo-Zhuka-Yunxian-Jinghong Continental Margin Arc and its back arc-basin (arc basement) and in which subduction-type continental margin arc volcanic rocks and intrusive rocks were developed. The ocean basin closure and arc-arc collision in Early and Middle Triassic and the post-collision extension in Late Triassic have developed arc volcanic rocks, bimodal volcanic rocks, and intrusive rocks in a collision and post-collision extension environment. At different stages and different locations of the arc-basin system during its generation and evolution, VMS Cu–Pb–Zn deposits, skarn-type Fe–Cu deposits, etc. were developed.

4.5.1.4 Boshulaling-Gaoligong Arc-Basin System and Mineralizations

The arc-basin system is mainly composed of Luxi-Santaishan Ophiolitic Melange Belt and Boshulaling-Gaoligong Magmatic Arc and Bomi-Polongzangbu Ophiolitic Melange Belt on its west side. The available research findings reveal that Tethys Ocean above the Proterozoic metamorphic basement and the Early Paleozoic passive marginal basin, which is represented by the Luxi-Santaishan ophiolite melange, subducted southwestward under Tengchong-Lianghe Block from Carboniferous to Permian, thus developing Boshulaling-Gaoligong Magmatic Arc and its back arc-basin (continental crust basement). The ocean’s further subduction in the Mesozoic Era developed a spatial arc-basin system configuration framework consisting of Boshulaling-Gaoligong Magmatic Arc, Polongzangbo (Jiali) Inter-arc Ocean Basin and Chayu (South Gangdise) Magmatic Arc, respectively, from east to west. The ocean basin closure and arc-arc or arc-continent collision at the end of Late Triassic (possibly to Early Jurassic) developed a series of island arc intrusive rocks and volcanic rocks in multi-collision environment, esp. the superimposed transformations of the Boshulaling-Gaoligong arc-basin system by the subduction of the Yarlung Zangbo Back Arc Ocean Basin from Middle Jurassic to Late Cretaceous and the arc-continent collision in the Paleogene Period resulted in large-scale magmatic hydrothermal vein-skarn Sn–W, Fe, Pb–Zn and rare metal mineralizations.

4.5.1.5 Edges of Stable Blocks and Mineralizations

The main bodies of the split blocks embedded in the MABT such as Zhongza-Shangri-La, Qamdo-Lanping-Pu’er, Leiwuqi-Zuogong, Baoshan-Zhenkang and Chayu-Gaoligongshan ones, which were above the Proterozoic metamorphic basement and the Early Paleozoic fold basement, experienced an evolution or transformation process consisting of relatively stable Devonian-Early Permian neritic shelf plateau, Middle and Late Permian back arc-basin and Middle and Late Triassic back arc foreland basin. In addition to VMS and SEDEX deposits in passive continental margin rift basins, the counterthrust structure framework developed along the nearly north-south back arc foreland basin’s central axis in the Middle and Late Triassic after the Early Triassic ocean basin extinction and arc-continent or arc-arc collision, along with the drainage and convergence of hydrothermal fluids toward the center of the basin, provided a strong materials foundation for the later large-scale mineralizations of the intracontinental basin in the Cenozoic Era.

4.5.2 Evolution and Metallogenic Mechanism of Multi-Arc-Basin-Terrane (MABT)

Through dissecting and studying several ophiolitic melange belts and various arc-basin systems in the Sanjiang Tethys orogenic belt, it is found that the southwest margin of the unified Pan-Cathaysian Continent Group was formed due to the restriction of the eastward subduction of Tethys Ocean at the end of Early Paleozoic, Tanggula-Taniantaweng Remnant Arc split off like the Japanese Archipelago from Kangdian Continental Margin Arc constituted the Late Paleozoic–Mesozoic frontal arc at the southwest margin of Pan-Cathaysian Continent; according to records, an extensive area behind the frontal arc covering Yidun Arc-basin System (P-T3), Zhongza-Shangri-La Block, Jinshajiang Arc-basin System (D-T3), Qamdo-Lanping-Pu’er Block, Taniantaweng Arc-basin System (D-T3), Leiwuqi-Zuogong Block and Early Paleozoic Lancang-Chongshan Remnant Arc Block saw a geological evolution history involving MABT development, back arc spreading and arc-arc or arc-continent collision from Late Paleozoic to Mesozoic; the island arc orogeny in Triassic finalized the main body of the Pan-Cathaysian Continent and caused it to become an integral part of Eurasia, and in some areas of the Pan-Cathaysian Continent, rift basins were developed against the post-collision crustal extension background in Late Triassic.

Running through the whole process of the Tethys lithosphere evolution from Late Paleozoic to Mesozoic, the archipelagic arc-basin mineralizations in the Sanjiang area occurred in the Southeast Asia-like continental margin system characterized by Late Paleozoic–Mesozoic archipelagic arc-basin tectonic systems and were closely associated with a series of alternating processes including island or continental margin arc evolutions, back arc rift valley and ocean basin spreadings and extinctions, and activations and transformations of split blocks sandwiched between them, i.e., the complex structural-paleogeographic framework consisting of MABT in Late Paleozoic–Mesozoic in the Sanjiang area controls the temporal and spatial distribution of the deposits therein, and they feature obvious zoning, segmentation, diversity, and superposition. According to the evolution-mineralization relationship of the Sanjiang Tethys MABT, the mineralization or evolution process can be further divided into five stages: continental margin split period, ocean basin spreading period, ocean crust subduction period, arc-arc/continent collision period and post-collision extension period (Figs. 4.30 and 4.31).

Fig. 4.30
figure 30

Evolution stages and mineralizations of Sanjiang Tethys MABT. GD—Gangdise; LS—Lhasa; YL—Yarlung Zangbo; BG—Bange-Jiali Belt; QT—Qiangtang; JS—Jinshajiang; ZZ—Zhongza; GL—Ganzi-Litang; YZ (SC)—Yangtze (Sichuan)

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Fig. 4.31
figure 31

Spatiotemporal evolution and metallogenesis of the Paleo-Tethys in Sanjiang, SW China

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4.5.2.1 Metallogenic Mechanism During Continental Margin Split Period

At the end of Early Paleozoic, the South China Ocean Basin was destroyed, and the folds turned into mountains, and multiple back arc ocean basins such as the Qilian Ocean Basin, Northern Qaidam Margin Ocean Basin and east and west Kunlun ocean basins disappeared one after another, thus developing a subduction collision orogenic system. So far, Yangtze was connected with Cathaysia, Sino-Korea Block, Qaidam, Tarim, Indosinian Continent, etc. to form the unified Pan-Cathaysian Continent Group. Between the southwest margin of Pan-Cathaysian Continent Group and the northern margin of Gondwana Continent was the vast Tethys Ocean. The Sanjiang Tethys tectonic belt occurred and evolved exactly against this global tectonic background. It is located at the junction of Pan-Cathaysian Continent Group and Gondwana Continent Group and originated from the continental margin arc active zone at the southwest margin of Pan-Cathaysian Continent Group.

The southwest margin of the unified Pan-Cathaysian Continent Group was formed at the end of the Paleozoic Era due to the restriction of the eastward subduction of Tethys Ocean from Early Paleozoic to Middle Devonian. Tanggula-Taniantaweng Remnant Arc split off like the Japanese Archipelago from Kunlun Frontal Arc and Kangdian Continental Margin Arc constituted the Late Paleozoic-Mesozoic frontal arc including Sanjianga at the southwest margin of Pan-Cathaysian Continent. The basin extension behind the frontal arc developed a series of back arc rift basins, including Ganzi-Litang Rift Basin at the east margin of Zhongza-Shangri-La Block, Jinshajiang-Ailaoshan Rift Basin between the west margin of Zhongza-Shangri-La Block and the east margin of Qamdo-Lanping-Pu’er Block and Langcangjiang Rift Basin between the west margin of Qamdo-Lanping-Pu’er Block and the frontal arc. The existing data show that the strong, rapid and short-duration back arc spreading was unfavorable for the formation of industrial grade deposits in the back arc rift basins but was favorable for the initial enrichment and formation of source beds or source rocks, thus providing an important material source for later mineralizations (including the Cenozoic intracontinental convergence and transformation process), such as Tuoding Cu deposit in Devonian might be related to this. The important mineralizations in this period, which are characterized by the occurrence of large-scale SEDEX Pb-Zn deposits, mainly occurred in the passive continental margin rift basins far away from the back arc spreading area, thus developing products enriched with crust-derived Pb and Zn materials by the hydrothermal fluid circulation system in the continental margin extension environment, such as the huge Huize Pb–Zn deposit in Devonian at the western and northwestern margins of Yangzi Continent, the large-sized Bafangshan-Erlihe Pb–Zn deposit in Fengxian County and Fengshu-Zhaojiazhuang Pb–Zn Ore Belt in Xunbei.

4.5.2.2 Metallogenic Mechanism During Ocean Basin Spreading Period

From Late Devonian to Early Permian, a series of back arc rift basins behind Jitang-Chongshan-Lancang Front Arc expanded into back arc ocean basins due to the restriction of the further eastward subduction of Tethys Ocean. The continuous spreading and eastward subduction of Tethys Ocean represented by Nujiang-Changning-Menglian Ocean caused Leiwuqi-Zuogong Block, Qamdo-Lanping-Pu’er Block and Zhongza-Shangri-La Block behind the frontal arc to split off from Yangtze Continent, thus developing Lancangjiang back arc spreading Ocean Basin, Jinshajiang-Ailaoshan back arc spreading Ocean Basin and Ganzi-Litang back arc spreading Ocean Basin successively from west to east, which constituted the basic framework of the Sanjiang Tethys MABT.

It is found through a systematic dissection of the mineralization environments and deposit types of the important metallogenic belts in the Sanjiang area that although there are three important back arc spreading ocean basins of different scales in the region, such as Lancangjiang Ocean Basin, Jinshajiang-Ailaoshan Ocean Basin and Ganzi-Litang Ocean Basin, the mafic-ultramafic rocks constituting the ocean crust are mostly quasi-oceanic ridge ones because the limited ocean basins formed by back arc spreading feature short-duration development and low ocean crust maturity (Mo et al. 1993). This is the fundamental reason why it has no large-scale Cyprus-type VMS Cu and Cu–Ni deposits. Relatively speaking, the new ocean crust and large-scale quasi-oceanic ridge volcanic activities caused by back arc seabed spreading only occasionally developed small-scale magmatic liquation-type Cr–Pt sulfide deposits, such as Xumai Chromite–platinum group deposit in Jinshajiang ophiolite; deep ore-forming materials such as Au–Cr–Cu materials in the back arc ocean basins were more favorable for initial enrichment and formation of source beds or source rocks, which were kept and involved in ophiolitic melange belts, thus providing important material sources for later mineralizations (including the Cenozoic intracontinental convergence and transformation process), such as large or super-large deposits in the Jinshajiang-Ailaoshan ophiolitic melange belt including Laowangzhai Au deposit, Donggualin Au deposit, Jinchang Au deposit and Daping Au deposit and large deposits in the Ganzi-Litang ophiolitic melange belt including Cuo’a Au deposit and Shala Au deposit. The important mineralizations during this period mainly occurred in the oceanic island volcanic basins and their passive continental margin rift basins that were related to spreading ocean basins and are characterized by the occurrence of VMS deposits. The former were developed in the oceanic island basic-moderately basic volcanic rocks of expanding ocean basins by the hydrothermal fluid circulation system in a spreading ocean basin ridge environment, such as Cu–Pb–Zn deposits in the Changning-Menglian oceanic island ophiolitic melange; the latter were developed in passive continental margin rift basins related to spreading ocean basins by the hydrothermal fluid system in a continental margin extension environment, such as the large-sized Dapingzhang Cu polymetallic deposit in Carboniferous in the Jinggu-Jinghong continental margin arc zone on the western margin of Pu’er Block.

Only one Cyprus-type VMS Cu deposit, i.e., Tongchangjie Cu deposit, is known to exist in the Sanjiang Tethys orogenic belt. It was developed in the picrite with a large amount of olivine accumulation crystals that erupted out of the seabed due to magma chamber rupture under the Changning-Menglian spreading ridge. This zone, which is the Paleo-Tethys Ocean represented by Nujiang-Changning-Menglian Ocean, has very mature accumulations of ocean crust and mantle materials, so it provided the conditions for developing Cyprus-type VMS deposits. This is exactly the reason why no Cyprus-type VMS deposits exist in small back arc spreading-induced ocean basins.

4.5.2.3 Metallogenic Mechanism During Ocean Crust Subduction Period

From Middle Permian to Late Permian, the tectonic geological setting of the Sanjiang Tethys orogenic belt changed greatly on the basis of its early tectonic framework consisting of a series of small back arc ocean basins and microblocks arranged alternately, except that the main body of Ganzi-Litang Back Arc Ocean Basin was still in a spreading environment. Driven by the subductions of a series of back arc ocean basins behind the Jitang-Chongshan-Lancang frontal arc, the formation and evolution process of the MABT in the Sanjiang Tethys orogenic belt started when the alternating subducting island arcs, continental margin arcs and back arc-basins were formed. Among them, Ganzi-Litang Back Arc Ocean Basin began to subduct in early and middle Late Triassic.

Because of being generally restricted by the continuous eastward subduction of Tethys Ocean, Wulanwula-Lancangjiang Back Arc Ocean Basin subducted westward under Jitang-Lancang Remnant Arc Block so as to develop the Leiwuqi-Lincang-Mengdao island arc and subducted eastward under Qamdo-Lanping-Pu’er Block to form the Zaduo-Zhuka-Yunxian-Jinghong continental margin arc and the back arc-basin (continental crust basement) on its east side, thus developing the Taniantaweng continental margin arc-back arc ocean basin-back arc-basin system. The subduction between ocean crusts at the central axis of Jinshajiang-Ailaoshan Back Arc Ocean Basin developed the Zhubalong-Yangla-Dongzhulin intra-oceanic arc and the Xiquhe-Xueyayangkou-Jiyidu-Gongnong back arc-basin (ocean crust basement) on its west side; its westward subduction under Qamdo-Lanping-Pu’er Block developed the Jiangda-Deqin-Weixi-Lvchun continental margin arc and the back arc-basin (continental crust basement) on its west side, thus developing the Jinshajiang intra-oceanic arc-back arc ocean basin-continental margin arc-back arc-basin system. Due to the long-distance effect of the eastward subduction of Tethys Ocean and the restriction of the Jinshajiang back arc spreading ocean basin, the formation and spreading periods (mainly from Permian to Early and Middle Triassic) of the Ganzi-Litang back arc ocean basin, which is adjacent to Yangtze Continent on the easternmost side of Sanjiang Tethys, is obviously later than those of Jinshajiang and Lancangjiang back arc ocean basins on the west side (mainly from Late Devonian to Permian). The Ganzi-Litang back arc ocean basin subducted westward under Zhongza-Shangri-La Block in the early and middle Late Triassic, thus developing Yidun island arcs (inner and outer arcs), inter-arc rift basin and back arc-basin successively from east to west, which constituted the Yidun island arc (inner arc)-inter-arc rift basin-island arc (inner arc)-back arc-basin system.

As the main parts of the MABT of the Sanjiang Tethys orogenic belt, the island arc or continental margin arc volcanic-magmatic rock belts were products of the subductions of a series of small back arc ocean basins; the formation and development of the belts is also a process of great adjustments, great exchanges and recombinations of crust-mantle material components in the orogenic belt and also a process of enrichment of Cu–Au–Ag–Pb–Zn polymetallic ore-forming materials into deposits. In the traditional plate structure pattern and the framework of its trench-arc-basin metallogenic theory, it is established that its main mineralization types and tectonic environments are porphyry copper deposits in island arc zones and VMS deposits in back-arc-basins. However, during the evolution process of the MABT of the Sanjiang Tethys orogenic belt, there are multiple island or continental margin arc belts, together with more complex volcanic-magmatic arc types including intra-oceanic arc (equivalent to Mariana Arc), island arc (equivalent to Ryukyu Islands) and continental margin volcanic arc (Andean-type). All of the subduction-type volcanic-magmatic arc belts are important metallogenic belts in the Sanjiang area.

By tectonic environment and mineralization type, the volcanic-magmatic arc belts of the Sanjiang Tethys orogenic belt can be divided into five types: ① VMS deposit in an intra-oceanic arc volcanic basin, such as the large-sized Yangla Cu deposit in the Jinshajiang ophiolitic melange belt, which was developed in basic-moderately basic volcanic rocks by the hydrothermal fluid circulation system formed by mutual subductions of ocean crusts; ② VMS deposit in an intra-arc rift basin, such as the super-large Gacun Ag–Pb–Zn deposit and the large-sized Gayiqiong Ag–Pb–Zn deposit in the northern section of the Yidun island arc belt, which were developed in moderately basic and moderately acid bimodal volcanic rocks by the hydrothermal fluid circulation system in a tectonic environment of rift basin extension between volcanic arcs (inner and outer arcs); ③ Epithermal Au–Ag–Hg polymetallic deposit in a back arc-basin, such as the medium-sized Nongduke Au–Ag polymetallic deposit and the large-sized Kongmasi Hg deposit in the Yidun island arc belt, which were developed in moderately acid volcanic rock series by the volcanic hydrothermal cryogenic fluid circulation system formed under extensional rifting on the side of the volcanic arc adjacent to the continent; ④ Porphyry copper deposits, such as the large-sized Pulangte Cu deposit and the large-sized Xuejiping Cu deposit in the southern section of the Yidun island arc belt, which were developed in the island arc-type epithermal-ultraepithermal intrusive rock complex (porphyry) by the magmatic hydrothermal fluid circulation system in the compressive island arc tectonic environment; ⑤ Skarn-type Fe–Cu or Cu–Pb–Zn deposit, such as Hongshan Fe–Cu deposit in the southern section of the Yidun island arc belt and medium- and large-sized Cu–Pb–Zn deposits in the Bomi-Tengchong continental margin arc belt, such as Diantan deposit, Dadongchang deposit and Dakuangshan deposit, which were developed in an island arc-type mesogenic-hypogenic intrusive rock complex by the magmatic hydrothermal fluid circulation system in a compressive island arc tectonic environment.

The island arc or continental margin arc zones in the Sanjiang area have different types and scales of mineralization, but compared with the huge porphyry copper metallogenic belts in the Pacific Rim island arc belt and the large-scale Au metallogenic belts in its back arc-basins, none of the Leiwuqi-Lincang-Menghai island arc, Zaduo-Yunxian-Jinghong continental margin arc and Jiangda-Weixi-Lvchun continental margin arc has had any large-scale porphyry copper deposit or epithermal Au mineralization. Fundamentally, this is because the rapid subductions of a series of small back arc ocean basins led to the fast-paced development and formation of the multiple alternating immature island arcs or continental margin arcs and their back arc-basins; even though there are VMS deposits and porphyry copper deposits in the Yidun island arc belt, they are obviously segmented in space. The former occurred in the extensional volcanic arc in the northern part of the island arc belt, while the latter occurred in the compressive magmatic arc in the southern part of the island arc. A comprehensive analysis shows that the vertical tearing and differential subduction actions of the ocean crust plates of the small back arc ocean basins are the main reason for the segmented occurrence of VMS sulfide deposits and porphyry copper deposits in the same island arc belt.

4.5.2.4 Metallogenic Mechanism During Arc-Arc/continent Collision Period

During the Early and Middle Triassic, Sanjiang Tethys entered the arc-arc/continent collision stage after a series of small back arc ocean basins behind the frontal arc subducted and closed and the ocean crust destroyed except that the main body of the Ganzi-Litang back arc ocean basin was still in a spreading environment. The beginning of the stage is marked by the development of multiple alternating collision-type island arcs and the formation of the foreland basin (peripheral or back-arc). Among them, the Ganzi-Litang back arc ocean basin entered the arc-continent collision stage after its subduction and closure in the late Triassic.

Because of being generally restricted by the continuous eastward subduction of Tethys Ocean, Wulanwula-Lancangjiang Back Arc Ocean Basin extincted and the Leiwuqi-Lincang-Mengdao island arc collided with the Zaduo-Zhuka-Yunxian-Jinghong continental margin arc in Early and Middle Triassic, with the result that an ophiolic melange belt and the Qamdo-Lanping-Pu’er back arc foreland basin on its east side were developed. The Jinshajiang-Ailaoshan back arc ocean basin extincted and the Jiangda-Deqin-Weixi-Lvchun continental margin arc collided with Zhongza-Shangri-La Block, thus developing an ophiolitic melange belt and the Qamdo-Lanping-Pu’er back arc foreland basin on its west side. In the late Late Triassic, the Ganzi-Litang back arc ocean basin extincted and the Yidun island arc collided with Yangtze Plate, thus developing an ophiolitic melange belt and the marginal foreland basin on its east margin. To sum up, the Sanjiang Tethys orogenic belt was not the result of the eastward subduction of Tethys Ocean, but was formed through an island arc orogeny consisting of subductions and extinctions of a series of multiple alternating back arc ocean basins and arc-arc or arc-continent collisions at the southwest margin of Pan-Cathaysian Continent.

The series of collision orogenies involving arc-arc, arc-continent and continent-continent collisions after the Sanjiang Tethys back arc ocean basin subducted and destroyed, as fallouts of the subduction of the back-arc ocean crust, are not only a formation process of the ophiolitic melange belts and collision-type volcanic-magmatic arc belts, but also a process of great adjustments and recombinations of material components. These collision-type arc volcanic-magmatic belts are also important metallogenic belts in the Sanjiang area. They developed many and various minerals and deposits of complex types. By tectonic environment and mineralization type, the deposits of the Sanjiang Tethys orogenic belt can be classified into three types: ① Skarn-type Fe–Cu and Cu–Pb–Zn deposits, such as Hongshan Fe–Cu deposit and Dongzhongda Cu polymetallic deposit in the Yidun island arc belt, Jiaduoling Fe–Cu deposit and Renda Cu–Fe deposit in the Jiangda-Weixi continental margin arc belt, the large-sized Narigongma Cu–Au–Ag polymetallic deposit in the Kaixinling-Zaduo continental margin arc belt, Changdonghe Cu–Pb–Zn deposit in the Lincang-Mengdao island arc belt, etc., each of which was developed in an island arc-type mesogenic-hypogenic intrusive rock complex by the magmatic hydrothermal fluid circulation system under a compressive island arc tectonic environment; ② magmatic hydrothermal vein-type (greisen-Shi Ying vein type) Sn–W polymetallic deposits, such as Bulangshan Sn deposit and Mengsong Sn deposit in the Zaduo-Jinggu-Jinghong continental margin arc belt, each of which was developed in an island arc-type mesogenic-hypogenic intrusive rock complex by the post-magmatic stage hydrothermal fluid circulation system in a compressive island arc tectonic environment; ③ sedimentary Sr or Cu deposit in a foreland basin, such as the large-sized Hexi Sr deposit and a sandstone-type Cu deposit in the Upper Triassic, which were developed through convergence of large quantities of ore-forming materials into Qamdo-Pu’er Basin as a typical back arc foreland basin because of being restricted by the counterthrust framework of the collision-type continental margin arcs on both sides; in addition, the convergence process provided important source beds or rocks for later mineralizations (including the Cenozoic intracontinental convergence and transformation process), such as the Hexi-Lanping-Sanshan-Baiyangping Pb–Zn–Ag–Cu polymetallic enrichment area and the Yunlong-Weishan Sb–Hg–Au–As polymetallic enrichment area.

4.5.2.5 Metallogenic Mechanism During Post-collision Extension Period

After a series of arc-arc or arc-continent collision orogenies in the Sanjiang Tethys orogenic belt, post-collision crust extension environments were developed in the island arc belts or continental margin arc belts and their edge zones in the tectonic background of continuous collisions and convergences generally at the continental margin probably because of inversions or disconnections of subducting back-arc oceanic crust plates. In these environments there occurred mineralizations and corresponding deposit types that were induced by dominant factors such as the influence of the superimposed rift basin, activities of the potassic magma from the crust or from both the crust and mantle and the related hydrothermal fluid system, thus constituting the important Cu–Pb–Zn–Au and W–Sn–Bi–Mo polymetallic deposit belts in the Sanjiang area. This is also a special mineralization process different from the traditional plate tectonic pattern and the trench-arc-basin metallogenic theory.

In the Jiangda-Deqin-Weixi continental margin arc belt and the Yunxian-Jinghong continental margin arc belt respectively on the east and west sides of the Qamdo-Lanping-Pu’er back-arc foreland basin, there occurred a series of nearly NS superimposed graben-type rift basins under post-collision extensions in the Late Triassic, in which bimodal volcanic rock series and potassic intermediate-acid volcanic rock series composed of high-potassium basic rocks and intermediate-acid rocks were developed. By mineralization environment and deposit type, deposits in the two belts can be divided into two types: ① VMS-type Cu–Pb–Zn polymetallic deposits related to the bimodal volcanic rock series, such as Luchun Cu–Pb–Zn polymetallic deposit, Laojunshan Cu–Pb–Zn polymetallic deposit, Hongpo Niuchang Cu–Au deposit, Zuna Ag–Pb–Zn deposit, etc. in the Jiangda-Deqin-Weixi continental margin arc belt and Sandashan Cu deposit, Minle Cu deposit, etc. in the Yunxian-Jinghong continental margin arc belt, which were developed due to activities of the sea-floor potassic volcanoes derived from both crust and mantle materials and their hydrothermal fluid systems. ② exhalative-sedimentary Ag-rich siderite deposits related to the intermediate-acid volcanic rock series, such as Zhaokalong Ag-rich Siderite deposit, Chugezha Ag-rich Siderite deposit, etc. in the Jiangda-Deqin-Weixi continental margin arc belt, whose minerals occur in high-potassium intermediate-acidity tuff rich in siderite and which were developed as a result of the activities of the sea-floor potassic volcanoes derived from crust materials and their hydrothermal fluid systems.

In the Yidun island arc belt on the eastern margin of Zhongza-Shangri-La Block and the Lincang-Menghai island arc belt on the west side of the South Lancangjiang ophiolitic melange belt, there occurred a series of potassic intermediate-acidity intrusive complexes in the form of stock or batholith under post-collision extensions from Late Triassic to Early Jurassic, in which there occurred a series of mineralizations and numerous magmatic hydrothermal vein-type (greisen-quartz vein) W–Sn–Bi–Mo polymetallic deposits and epithermal vein-type Ag–Au deposits due to dominant factors including activities of potassic intrusive magmas derived from crust materials or both crust and mantle materials and their hydrothermal fluid systems formed after the magmatic stage. Such deposits include Lianlong Greisen-quartz Vein-type W–Sn–Ag polymetallic deposit, Xiuwacu Greisen-quartz Vein-type W–Mo deposit, Xiasai Hydrothermal Vein-type Super-large Ag–Pb–Zn polymetallic deposit, etc. in the Yidun island arc belt, Tiechang Greisen-quartz Vein-type Sn–W polymetallic deposit, Haobadi Greisen-quartz Vein-type Sn–W polymetallic deposit, etc. in the Lincang-Menghai island arc belt and Lailishan Greisen-quartz Vein-type Large Sn–W deposit, large Baihuanao greisen-quartz vein-type Sn–W and rare metal (Nb–Ta–Rb) deposits, etc. in the Bomi-Tengchong continental margin arc belt.

4.5.3 Preliminary Discussion on Archipelagic Arc-Basin Metallogenic Theory

4.5.3.1 Foundation of Archipelagic Arc-Basin Metallogenic Theory

In the Sanjiang Tethys tectonic-mineralization domain in the east of Qinghai-Tibet Plateau, which is the epitome of the complex evolution of geological processes and mineralizations in Chinese mainland and has experienced superpositions and transformations imposed by the Late Paleozoic-Mesozoic Tethys accretionary orogeny and the Cenozoic continental collision orogeny, there occurred large-scale multi-phase mineralizations and huge metallic mineral accumulations leading to the occurrence of economic deposits so that it is one of China’s most important polymetallic mineralization provinces or enriched areas that is composed mainly of nonferrous and precious metal deposits. According to the traditional trench-arc-basin metallogenic theory, Cyprus-type VMS deposits were developed in trenches marked by ophiolitic melange and VMS, porphyry copper deposits and epithermal gold deposits were developed in island arcs or continental margin arcs. In the Sanjiang area, however, there are up to four ophiolitic melange belts with shear zone gold deposits rather than Cyprus-type copper deposits, and neither porphyry copper deposits nor epithermal gold deposits have been formed in the Jinshajiang and Lancangjiang arcs so far. Though there are VMS and porphyry copper deposits in the Yidun Island arc, they have obvious zoning. The former occurred in the northern tensional arc, and the latter in the southern compressive arc. Therefore, the traditional trench-arc-basin metallogenic theory cannot explain the mineralization pattern of Sanjiang Paleo-Tethys. A systematic dissection of the important metallogenic belts in the Sanjiang area shows that the Paleozoic-Mesozoic mineralization characteristics in this area result from the archipelagic arc-basin tectonic background and the important constraints of the mineralization environment created by it. The short-duration development of the limited ocean basin formed by the back arc expansion is the fundamental reason for the absence of Cyprus-type copper deposits; the subtraction orogeny of the back-arc-basins and the fast-paced formation and immature development of the multiple island arcs are the inherent reasons why some arcs lack porphyry copper deposits or epithermal gold deposits; the vertical tearing and differential subduction of the oceanic crust plate during its subduction are the main reasons for the zoned occurrence of VMS and porphyry copper deposits in the same island arc belt. Especially, the VMS or SEDEX deposits developed in large quantities in the post-collision extension environments in the volcanic arc belts cannot be explained by using the single trench-arc-basin metallogenic theory according to the traditional plate tectonic model. In this archipelagic arc-basin tectonic setting, VHMS is the most important mineralization type, with a Dapingzhang-type deposit in a marginal basin (D-C), a Yangla-type deposit in an oceanic arc (P1-2), a Gacun-type deposit in an inter-arc rift basin (T3) and a Luchun-type VMS deposit in a post-collision extension basin (T3); porphyry copper deposits are the second important mineralization type, which was mainly developed in fast-paced and immature volcanic-magmatic arcs while VHMS was mainly developed in mature magmatic arcs with long-term stable development; SEDEX polymetallic mineralizations mainly occurred in the basins (such as Lanping-Pu’er Mesozoic Basin) developed on stable blocks under the post-collision extension (T3) in the MABT and mainly served as important protores for Himalayan mineralizations and the materials foundation for the superimposed mineralizations.

Many regional geological surveys and mineral exploration evaluations show that the complex MABT tectonic-paleogeographic framework of the Sanjiang area controls the temporal and spatial distributions of the deposits therein. The mineralization processes of its large and super-large deposits feature obvious zoning, segmentation, diversity and superposition. The main deposit types here include VMS type, porphyry type, SEDEX type, tectonic hydrothermal type, etc. The metal assemblages involved include Pb–Zn, Pb–Zn–Cu–Ag, Cu and Sr–Ba. As the MABT evolved, the framework became complex. These new findings have greatly deepened the understanding of the archipelagic arc-basin tectonic model, providing an important foundation for establishing the archipelagic arc-basin metallogenic theory.

4.5.3.2 Definition of Archipelagic Arc-Basin Metallogenic Theory

Sanjiang is one of the most complex orogenic belts in the world. It has experienced not only the tectonic evolution of Tethys but also the strong transformations of the Indian-Eurasian plate collisions and plateau uplifts, featuring complex geological structures, strong magmatic activities, active ore-forming fluids and various complex mineralizations. With the tectonic evolution, different metallogenic systems developed here. A systematic dissection of multiple ophiolitic melange belts and multiple arc-basin systems and a comparison with the arc-basin tectonic systems in Southeast Asia showed that most of the basin prototypes represented by these ophiolitic melange belts only had the characteristics of small ocean basins, back arc-basins and island arc marginal seas, with short-duration developments. However, these arc-basin systems have different origins and evolution processes, so the archipelagic arc-basin tectonic model was put forward. The Archipelagic arc-basin tectonic system refers to a complex tectonic system consisting of the frontal arc and the behind-frontal arc island arcs, volcanic arcs, sea ridges, island chains, seamounts, microblocks, back-arc oceanic basins, inter-arc-basins and marginal sea basins. The model emphasizes that the orogenies involved were mainly realized by the oceanic crust subduction or uplift, arc-arc collision, arc-microblock collision and continent-continent collision caused by the back-arc-basin subduction.

Archipelagic Arc-basin Metallogenic Theory refers to a deposit development pattern formed in a specific structural, tectonic and time evolution sequence during the continent convergence accompanied by the tectonic evolution of the MABT at the edge of the continent. Its main points are as follows: Sanjiang Paleo-Tethys was not a simple trench-arc-basin system, but a complex tectonic system composed of a series of multiple alternating arcs, small blocks and small ocean basins; during the evolution, new arcs were constantly born and small ocean basins constantly became extinct; the joining together orogeny of blocks was inherently not caused by the subduction of Tethys Ocean, but by the subductions and closures of a series of small ocean basins; different metal deposits were developed in different ocean basins, arcs and microblocks. The archipelagic arc-basin metallogenic theory reveals the genetic mechanisms of the deposits in the various metallogenic belts during this mineralization period, involving metallogenic mechanisms, patterns, systems and types.

4.5.3.3 In-Depth Study of Archipelagic Arc-Basin Metallogenic Theory

A tectonic analysis of the MABT can further deepen the understanding of the ore-forming geological background and mineralization pattern of the orogenic system. Based on the MABT’s tectonic pattern, a summary of the archipelagic arc-basin metallogenic theory was given; a comprehensive evaluation model (Fig. 4.32) for different tectonic environments and metallogenic systems was put forward by combining the MABT’s pattern with the metallogenic system theory, process theory and transformation theory (Pan et al. 2003), e.g., the Dapingzhang-type VMS deposit in the continental marginal rift basin, the Yangla-type VMS deposit in the oceanic arc, the Xiacun-type deposit in the inter-arc rift basin, the Pulang-type porphyry Cu deposit in the compressive arc and the Jiaduoling-type skarn-type Fe–Cu deposit in the continental margin arc, These theoretical models have achieved good results in the study of mineralization regularity, mineral exploration and prediction and evaluation of the Sanjiang Tethys orogenic belt.

Fig. 4.32
figure 32

Temporal and spatial structure evolution and mineralization evaluation model of Sanjiang Tethys MABT

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Then, an in-depth study on the coupled evolution and mineralization processes of the marginal MABT in the early Paleozoic MABT of Qinling, Qilian Mountains and Kunlun Mountains, the Mesozoic MABT of Gangdise in Tibet, and even those of the continental margins on both sides of the ancient Asian Ocean might enrich and improve the archipelagic arc-basin metallogenic theory and be of great significance to the study of the ore-forming geological background of the orogenic system. The following aspects need to be further studied: ① determine the ocean basin attributes represented by each ophiolitic melange belt (back-arc ocean basin, inter-arc-basin or marginal sea basin, etc.) and restore the spatial-temporal structure and evolution of the formations, subductions and closures of these ocean basins; ② the basement properties (oceanic crust, continental crust, accretion wedge, etc.), mechanical properties (tensile arc, neutral arc, compressive arc) and arc-making evolution (initial arc to mature arc) of volcanic-magmatic arcs; ③ deepen geostructure background studies on metallogenic processes of accretionary orogeny belts (deep crust-mantle processes during the arc-arc, arc-continent and arc oceanic island (seamount) collage collision orogenies, esp. collage collision orogenies that made ore-forming materials of magmatic and volcanic arcs reactivate and migrate again are favorable for large-scale mineralizations).

4.6 Preliminary Discussion on Intracontinental Tectonic Transition Metallogenic Theory

A deposit is essentially a product of metallic ore-forming material supernormal enrichment via a magmatic system, magmatic hydrothermal system and hydrothermal system. A mineralization system generally requires a specific tectonic setting and a specific geological environment. In essence, its being driven by abnormal heat energy and/or tectonic stresses from lithosphere scale to crustal scale is related to processes caused by continental lithosphere convergence, splice, delamination, spreading, etc., such as compression, extension, strike-slip and shear. Thus, a complete metallogenic theory needs to clarify three key scientific problems: ① dynamic background and driving mechanism of mineralizations; ② basic types and development mechanisms of metallogenic systems; ③ huge metal accumulation processes and metallogenic mechanisms of metallogenic systems.

Fine dating of the important mineralization events and a study of the temporal and spatial distribution of the important metallogenic belts in the Sanjiang area show that distinctive metallogenic systems and large deposits were developed in the tectonic transition environments therein. Through a detailed dissection and a comprehensive study of its main metallogenic systems, an intracontinental tectonic transition metallogenic theory was put forward. According to the theory, the metallogenic systems in the Sanjiang area mainly including the crust-mantle magmatic hydrothermal metallogenic system, metamorphic fluid metallogenic system and basin fluid metallogenic system, against an intracontinental tectonic transition background, were driven by the abnormal thermal energy from the upwelling deep aesthenosphere materials and the shallow strike-slip, shear and compression tectonic stresses. The core of the intracontinental tectonic transition metallogenic theory is elaborated below.

4.6.1 Tectonic Transition and Mineralization Driving

4.6.1.1 Tectonic Transition Environment for Mineralizations

According to the intracontinental tectonic transition metallogenic theory, the mineralizations were developed in an intracontinental environment and the metallogenic systems were developed in a tectonic transition environment. In the Sanjiang area, the intracontinental tectonic transition environment is manifested as different scales, different main types and different forms. On the lithosphere scale, the Paleozoic-Mesozoic MABT realized the time-space tectonic transition from oceanic lithosphere to continental lithosphere in the Sanjiang area through back-arc-basin shrinkage, arc-arc collision and arc-continent collision in Paleozoic and Mesozoic and continental collision and intracontinental convergence in Cenozoic; on a large regional scale, along with the large-scale collisions between Indian and Asian continents since 65 Ma ago, large-scale tectonic transition systems were developed in the Sanjiang area, thus leading to wide-angle rotations and short slips of spliced blocks (Wang et al. 2006, 2008) and crustal shortening (Wang et al. 2001; Wang and Buchifel 1997; Liu 2006; He et al. 2009) and realizing the adjustment and transformation of the stresses and strains caused by large-scale collisions (Dewey et al. 1988; Wang et al. 2001); on the mineralization belt scale, the tectonic transition marked a large-scale thrust-napping system, a strike-slip fault system and a ductile-brittle shear system induced the extremely strong regional magma-fluid mineralization process (Hou et al. 2006). For example, the activities of the potassic mantle-derived magma controlled by a large-scale strike-slip fault system resulted in the formation of the 1000 km-long alkali-rich porphyry belt (Chung et al. 1998; Guo et al. 2005); during the compressive-to-tensile torsion transition period (40–30 Ma), pulsating epithermal emplacements of the ore-bearing porphyry at three stages resulted in three porphyry magmatic hydrothermal metallogenic systems (40 Ma, 36 Ma and 32 Ma) (Hou et al. 2006a). In Lanping Basin, the convergence collision and crustal shortening that began 65 Ma ago led to large-scale thrust-napping structures and a large number of structural traps and migration and convergence of regional basin fluids. The compressive-to-tensile torsion transformation 40–30 Ma ago generated a large number of strike-slip fault systems and strike-slip pull-apart basins as well as large quantities of regional fluid drainage and metal deposits, thus developing basin fluid metallogenic systems (Hou et al. 2008a). In the Ailaoshan Belt, large-scale strike-slip-shear actions (23–38 Ma) developed the Ailaoshan giant shear zone, and the ductile shear zone and the brittle-ductile transition portion controlled the development of the gold fields and deposits.

4.6.1.2 Drive of Abnormal Thermal Energy for Mineralizations

A comprehensive analysis of the intracontinental transition mineralizations in the Sanjiang area shows that they have four important characteristics: ① they were mainly developed in the discontinuous potassic igneous province with a peak age of 35 ± 5 Ma and were closely related to mantle-derived or crust/mantle-derived magmatic activities; ② the ultimate sources of the ore-forming materials (metals, fluids and gases) were closely related to deep materials, esp. mantle-derived magma; ③ the formations of the alkali-rich porphyry related to Cu–Mo–Au mineralization, the alkaline rock-carbonatite related to REE and the lamprophyre related to Au deposits in the shear zone were closely related to the deep asthenosphere activities; ④ the mineralizations mainly occurred 40–21 Ma ago, and among them, the porphyry Cu–Mo–Au mineralization, REE mineralization, hot brine Pb–Zn–Ag–Cu mineralization and partial shear zone Au mineralization mostly occurred 35 ± 5Ma ago. These characteristics imply that the magma-hydrothermal-mineralization process in the intracontinental transition environment in the Sanjiang area was controlled by the unified deep process, and the abnormal thermal energy caused by asthenosphere upwelling might be the dynamic mechanism driving the formation and development of the metallogenic system.

Seismic tomography shows that in the lower part of the intracontinental transition orogenic belt (97°–99° E) at the eastern margin of the plateau there occurred an obviously low-velocity asthenosphere upwelling body from the depth of 450 km, which was necked at 200–250 km and continued to flow upward, causing the overlying lithosphere thin to 70–80 km (Liu et al. 2000). In the lower part of the Tengchong modern volcanic area, the underplating asthenosphere materials even thermally eroded the lithospheric mantle locally (Zhong et al. 2001). Spatially, the asthenosphere upwelling body is not in the shape of a large mushroom, but in the shape of a zonal vertical tile plate, which spreads along the NNW intracontinental transition orogenic belt (Zhong et al. 2001).

The formation of the asthenosphere upwelling body might be related to opposite block subductions. Of course, the NE intracontinental subduction of Lhasa Block (Wang et al. 2001) might also function as a subduction plate of the Indian continent when the Indian continent thrusted northeastward and subducted and converged obliquely. Its convergence with Yangtze Block and its intracontinental subduction also might induce the development of the asthenosphere upwelling body.

The asthenosphere upwelling provides a reasonable explanation not only for the formation of the alkali-rich porphyry (Zhong et al. 2001), but also for the development of the whole discontinuous potassic igneous province (Guo et al. 2005; Hou et al. 2006b). Under the asthenosphere tectonic thermal erosion and the injection of small melts, partial melting occurred in the crust-mantle transition zone that was once subjected to the strong metasomatism of the pristine oceanic crust plate fluid. The melting of the phlogopite peridotite in the lower part of the transition zone created Au-bearing syenite magma while the melting of the amphibolite eclogite in the lower crust created Cu-bearing adakitic-like magma (Hou et al. 2005). The emplacements of these porphyry magmas along the strike-slip faults and their intersections with the basement faults and the magmatic fluids segregated in the local tension and stress release environment developed a porphyry magma-hydrothermal metallogenic system (Hou et al. 2003a, b). The asthenosphere upwelling also caused the enriched mantle containing deep crustal cycle materials to melt into the CO2-rich silicate melt mass, which formed into syenite-carbonatite due to unmixing (Hou et al. 2006b) and derived an REE-rich ore-forming fluid, thus developing a carbonatite magma-hydrothermal REE metallogenic system (Hou et al. 2009).

4.6.1.3 Drive of Tectonic Stresses for Mineralizations

In the Sanjiang intracontinental tectonic transition environment, there were at least three different tectonic deformations delivering tectonic stresses driving the formation and development of the metallogenic systems.

  1. (1)

    Thrust nappe structural system, which, as a thin-skinned structure caused by collision orogeny and crustal shortening, was developed mainly in Lanping and Yushu’s Tuotuohe Area. Through a series of thrust faults, the Mesozoic strata were cut into tectonic slices stacked in turn and were pushed over the sedimentary strata of the foreland basin. In the Lanping area, the thrust nappes advanced from both sides of the basin to the center, forming a counterthrust nappe structural system covering the main body of Lanping Basin. In the Yushu area, the Carboniferous thrust rock plate thrusted northward to form an uplift belt, and a front fold-thrust belt was formed due to the strong compression by Cenozoic in the Jiezha-Xialaxiu Triassic back-arc foreland basin (Hou et al. 2008a). The large-scale thrust nappe structure is characterized by episodic thrusts. The early and late episodes occurred respectively 55–50 Ma and 40–37 Ma ago (Li et al. 2006) and correspond to the main collision period (65–41 Ma) and late collision period (40–26 Ma) of Qinghai-Tibet Plateau, respectively (Hou et al. 2006a, b).

    Controlled by a series of large thrust nappe structural systems, an MVT-like Pb–Zn polymetallic mineralization belt with a length of more than 1000 km has begun to appear (Hou et al. 2008a). Its representative deposits include Chaqupacha Pb–Zn deposit in the Tuotuohe area, Dongmozhazhao and Mohailaheng Pb–Zn deposits in the Yushu area and Jinding Super-large Pb–Zn deposit and Baiyangping Large Ag–Pb–Zn deposit in the Lanping area. These thrust nappe tectonic systems, as the main driving mechanism of the basin fluid metallogenic system, played three important roles: ① regional compression and thrust processes drove long-distance lateral migration and convergence of basin fluids (Oliver 1992; Deming 1992; Garven 1993); ② the deep detachment and decollement belt of the thrust nappe structure provided the optimal channel for large-scale basin fluid migration (Hou et al. 2008a); ③ the main thrust faults provided the communication means for vertical fluid migration in the basin, while various shallow thrust structures provided main places for fluid convergence (He et al. 2009).

  2. (2)

    Large-scale Strike-slip Fault System The large-scale strike-slip fault system in the Sanjiang area is composed of multiple faults, including Jiali-Gaoligong Fault, Gongjue-Mangkang Fault Batang-Lijiang Fault (north section), Honghe Fault (south section), Kunlun Fault, Xianshuihe Fault and Xiaojiang Fault (from west to east and from north to south). They controlled not only the distributions of the Cenozoic alkali-rich intrusive rock belt and carbonate-syenite complex belt (Chung et al. 1998; Wang et al. 2001; Hou et al. 2003a, b, 2006a, b), but also the development of a series of strike-slip pull-apart basins (Liu et al. 1993a, b).

    An analysis of the regional stress field shows that the Sanjiang area was in a compressive torsion state 40 Ma ago and changed into a tensile stress state in the Miocene (17–24 Ma) (Wang et al. 2001). The strike-slip fault system occurred 42 Ma ago and was highly active 30–40 Ma ago (Liang et al. 2008). The large-scale strike-slip fault system developed in the compressive-to-tensile torsion transformation period (40–30 Ma), as the tectonic driving mechanism of the magmatic hydrothermal metallogenic system, played three roles: ① the deep crust shear strains induced by the strike-slip faults would cause the crust- and mantle-derived melt to accumulate in the shear zone and rise along the diapir in the vertical shear zone (Sawyer 1994), with the vertical tensile torsion in the upper crusta providing an important channel for upward magma intrusion; ② The stress relaxation during the compressive-to-tensile torsion transformation period led to the pulsating emplacement of the lower magma, thus forming a large-scale, chronically active and continuously replenished magma chamber, so as to provide enough metals and fluids for the metallogenic system; ③ the stress relaxation and strike-slip pull-apart in the shallow crust led to pulsating segregation, massive exsolution and episodic drainage of the ore-forming fluids in the magmatic chamber, thus inducing the magmatic hydrothermal metallogenic system (Hou et al. 2003a, b).

  3. (3)

    Large-scale Shear System This system was developed in its entirety along the Ailaoshan-Honghe fault zone, thus forming the famous large-scale Honghe Shear Zone. This shear zone might be developed at the tectonic boundary between Yangtze Block and the Sanjiang orogenic belt as the deep system of the large-scale strike-slip fault zone and experienced an early left lateral strike-slip and a late right lateral strike-slip (Tapponnier et al. 1990). The left lateral strike-slip-shear process started 42 Ma ago and continued until 23 Ma ago (Liang et al. 2008). Along the large shear zone, not only lamprophyre aged 35 ± 5 Ma was developed in large quantities and large-scale gold mineralizations occurred simultaneously to form the Ailaoshan gold deposit belt (Hu 1995).

    The large-scale shear system, as the tectonic stress-based driving mechanism of the Au metallogenic system, had three functions: ① as a translithospheric fault zone with a history of multiple activities and reactivations, the large-scale shear system is a wide-angle inversion fault system and a thrust nappe shear zone (Li et al. 1999). It not only has the basic characteristics of large scale, deep cutting and good structural network connectivity, but also caused the Paleozoic Au-bearing ophiolite melange to suffer from intense metamorphism and transformation. In addition, it featured a high heat flow state due to the mantle-derived magma emplacement and provided the conditions of strong fluid activities and sufficient mineral supplies required by the orogenic-type gold metallogenic system (Barley and Groves 1992; Goldfarb et al. 2005; Groves et al. 2005); ② metamorphic fluids with rich CO2 and low salinity (<6%) were often generated through metamorphism by large-scale shears (Kerrich et al. 2000), thus providing enough ore-forming fluids for the orogenic-type gold metallogenic system; ③ the secondary structures in the large-scale shear system, esp. the transformation portion or intersection zone between the ductile shear zone and brittle inversed fault, provided important space for ore-forming fluid convergence and gold mineral accumulation (Hu 1995; Sun et al. 2009).

4.6.2 Metallogenic Systems and Typical Deposits

The activities of the crust- and mantle-derived magma in the intracontinental tectonic transition environment, large-scale strike-slip, shear, thrust and nappe structures and fluid activities induced by them developed at least three important metallogenic systems: ① the magmatic hydrothermal Cu–Mo–Au metallogenic system (Rui et al. 1984; Tang et al. 1995; Hou et al. 2003a, b, 2009); ② the orogenic-type Au metallogenic system related to the shear zone (Hu 1995; Xiong et al. 2006; Hou et al. 2007a); ③ the Pb–Zn–Ag–Cu brine fluid metallogenic system controlled by the thrust nappe structure (Hou et al. 2008a) (Table 4.1).

Table 4.1 Environments and deposit types of late collision transition mineralizations
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4.6.2.1 Magmatic Hydrothermal Cu–Mo–Au Metallogenic System

The magmatic hydrothermal Cu–Mo–Au metallogenic system developed in the intracontinental tectonic transition environment is strictly controlled by the large-scale strike-slip fault system. The acidic granitic porphyry developed Cu or Cu–Mo deposits, such as the Yulong porphyry Cu deposit belt (Hou et al. 2003a, b); the syenite porphyry or monzonitic porphyry developed Au or Au–Cu deposits, such as Beiya Au deposit (Xu et al. 2007). Cu-bearing porphyry is geochemically similar to adakite (Hou et al. 2003a, b; Jiang et al. 2006) and Au-bearing porphyry is characterized by high potassium and rich alkali. Both of the two magmatic systems are characterized by high fO2 (Liang et al. 2006) and originated from the rich mantle or crust/mantle transition zone (Chung et al. 1998; Hou et al. 2003a, b, 2005; Jiang et al. 2006). The molybdenite Re–Os dating data show that the porphyry Cu–Mo and Cu–Au metallogenic systems had three mineralization peaks (40 Ma, 36 Ma and 32 Ma; Hou et al. 2006a), equivalent to the diagenetic ages (41–27 Ma). These porphyry copper deposits in the intracontinental environment are very similar to the typical porphyry copper deposits in the magmatic arc environment in terms of alteration zoning, mineralization characteristics, mineral assemblage and fluid system (Rui et al. 1984; Tang et al. 1995; Hou et al. 2003a, b, 2007b), indicating that both of them have similar mineralization processes.

4.6.2.2 Orogenic-Type Au Metallogenic System

The orogenic-type Au metallogenic system developed in the intracontinental tectonic transition environment is strictly controlled by the large-scale shear tectonic belt. The Ailaoshan mineralization belt is a typical product of the metallogenic system. Dependable dating data and deposit distribution characteristics show that the Ailaoshan mineralization belt was controlled by the Ailaoshan shear zone, the gold fields and deposits were controlled by the intersection of the NW brittle shear zone and the nearly EW thrust fault zone, individual deposits or ore bodies are controlled by brittle-ductile shear zones of different lithologic characters (Hu 1995). The mineralization ages mainly range from 35 to 40 Ma (Sun et al. 2009). The main gold-bearing formation is the Paleozoic ophiolite melange, which suffered greenschist facies metamorphism. The main ore bodies include the Au-bearing quartz veins filling fracture zones and the Au-bearing tectonic altered rocks in metasomatic surrounding rocks (Hu 1995). The available hydrogen, oxygen and sulfur isotopic data show that the ore-forming fluids were mainly metamorphic fluids containing meteoric water, while S and Au came from ore-bearing metamorphic mafic formations (Hu 1995; Xiong et al. 2006). The He–Ne–Xe isotopic evidence shows that mantle gas contributed to the ore-forming fluids (Hu et al. 1999; Sun et al. 2009).

4.6.2.3 Regional Pb–Zn Polymetallic Brine Metallogenic System

In the Sanjiang area, the regional brine Pb–Zn polymetallic metallogenic system was mainly developed in a tectonic transition zone and controlled by the large-scale regional thrust nappe and strike-slip pull-apart basin. According to the ore-controlling patterns and mineralization characteristics of the thrust nappe structures, three deposit models can be identified: Jinding-type Pb–Zn deposit developed in the “structural dome + lithologic trap” assemblage in the front zone of the thrust nappe structure system (Wang et al. 2007; Xue et al. 2007), Hexi-Sanshan-type Pb–Zn–Ag deposit controlled by the decollement structure in the front zone and Fulong Factory-type Ag–Pb–Zn–Cu deposit developed in a secondary or translation fault of the main thrust fault zone (Hou et al. 2008a). The distribution of these deposits in the region was controlled by the thrust nappe structure, but their locations were controlled by the extension structure. Most of the deposits and ore bodies here are vein-like and a few are plate-like shape; some are located in the continental siliceous clastic rock formations and some in carbonate rock formations, showing strata-bound characteristics, but the mineralizations are characterized by open space filling (Hou et al. 2008a). The ore-forming fluids show basin brine characteristics, with relatively low temperatures (mostly between 80 and 190 °C). The metal assemblages of the deposits might be related to the properties of the rocks experienced during the migration-convergence process of the ore-forming fluids (He et al. 2009). Its overall characteristics are different from those of MVT, SEDEX, Ireland and Laisvall Pb–Zn deposits (Xue et al. 2007; Hou et al. 2008a).

It is obvious that the intracontinental tectonic transition mineralization featuring Different metallogenic systems (magma-hydrothermal metallogenic system, metamorphic-hydrothermal metallogenic system and regional brine metallogenic system), super-large-scale metal accumulations and large and super-large deposits of different metal assemblages cannot be covered by the existing mineralization models or explained by any existing metallogenic theory.

4.6.3 Metallogenic Systems and Development Mechanisms of Large Deposits

A collision and continuous subduction of a continent inevitably would inevitably lead to dramatic lithosphere shortening and strain, which would be inevitably adjusted through tectonic transitions, as through faulting. Such a tectonic transition adjustment zone was mainly developed on a flank of a forward collision zone, such as the eastern margin of Qinghai-Tibet Plateau (Dewey et al. 1989), and was characterized by large-scale strike-slip fault system (shear and escape), thrust nappe structure system (internal deformation) and block rotation. In the tectonic transition adjustment zone, the internal deformation in the block, as an important way to adjust the collision strain, often forms a thrust nappe structural system or a compressive fold zone. For example, Lanping Basin had characteristics of foreland basins in Paleogene and Neogene (Wang et al. 2001) and the regional compressional torsion since Eocene makes the Mesozoic stratigraphic system before collision overlap the foreland basin, forming a thrust nappe structural system (He et al. 2009). Driven by the gravity or compressional force of the orogenic belt, the regional fluids (or the basin brine) traveled a long distance along the detachment and decollement zone under the thrust nappe structure toward the foreland basin and leached the metallic materials in the surrounding rocks during their migration process, into low-temperature mineralizing fluids with high salinity and rich metal elements (Hou et al. 2008a). During the thrust-strike-slip transformation period, these ore-forming fluids were rapidly drained under compressive and tensile torsion stresses and converged into the secondary structures through the main thrust fault or a strike-slip fault (such as a structural dome, tensile structure, recoil structure, recoil structure, interlayer decollement structure), thus developing the Pb–Zn polymetallic fluid metallogenic system as well as various Pb–Zn–Cu–Ag deposits such as MVT-like Pb–Zn deposits in carbonatite formations, Zn–Pb deposits in clastic rock formations and Cu–Ag deposits in red beds (Fig. 4.33; Hou et al. 2008a).

Fig. 4.33
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Intracontinental Tectonic transition and development of different metallogenic systems in Sanjiang Area

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Continuous intracontinental subduction might induce the upwelling of the asthenospheric materials under SCLM (Zhong et al. 2001), thus providing necessary heat energy for partial melting of SCLM, while the strike-slip faults cutting the lithosphere deep accelerated the decompressional melting of SCLM (Fig. 4.33; Hou et al. 2005), thus forming igneous provinces (belts) dominated by mantle-derived magma and crust/mantle-derived magma in the tectonic transition zone. These potassic magma originated from SCLM enriched mantle or crust-mantle transition zone (Chung et al. 1998; Wang et al. 2001; Hou et al. 2003a, b; Guo et al. 2005; Jiang et al. 2006) may rise along the ductile shear zone deep in the strike-slip fault system in the deep crust, showing dike-like ascending emplacement; Large magma chambers were developed in the shallow crust, which were transported by strike-slip faults (Richard 2003). In the local tension and stress release environment, the ore-forming magma fluid was segregated from the felsic magma to develop the porphyry magmatic hydrothermal metallogenic system (Hou et al. 2003a, b). The Cu-rich fluid was segregated from the monzogranite porphyry magma from the crust-mantle transition zone to develop the porphyry copper deposits (Hou et al. 2007b); the Au-rich fluid was segregated from the syenite porphyry magma from the enriched mantle to develop the porphyry gold deposits (Xu et al. 2007). The SCLM’s enriched portion that suffered the deep crust materials cycle melted to produce the CO2-rich silicate melt (Hou et al. 2006b), from which the REE-rich ore-forming fluid was derived due to its unmixing property during its rising process (Niu and Lin 1994; Xie et al. 2009; Hou et al. 2009), thus developing the REE deposits related to the carbonate-alkaline rock complex (Fig. 4.33; Yuan et al. 1995; Yang et al. 2001; Hou et al. 2008b).

In the deep system of a large-scale strike-slip fault zone, there mainly occurred ductile and ductile-brittle shear zones, accompanied by mantle-derived magma emplacement and granulite-greenschist facies metamorphism. This strong shear and metamorphism process produced the CO2-rich metamorphic ore-forming fluid, which rose along the ductile shear zone and developed vein-type Au–As deposits in deep ductile-brittle transformation structures and Au–Sb deposits in shallow brittle fissures (Fig. 4.33; Goldfarb et al. 2001; Sun et al. 2009).

4.6.4 Definition of Intracontinental Tectonic Transition Metallogenic Theory

In the Sanjiang area, the large-scale Cenozoic mineralizations developed many large and super-large deposits (commonly known as “late bloomers”), which occurred in the dynamic background of intracontinental transformation. All of its MABT, collision orogenic belt and metallogenic belts show the abnormally strong regional magma-fluid mineralization process induced by the tectonic transition. In Lanping Basin, the large-scale thrust-napping process that started 65 Ma ago developed a large number of structural traps, and migrations and convergences of large amounts of fluid during the collision and compression period as well as fluid drainages and metal depositions during the stress release period resulted in the development of Jinding- or Baiyangping-type Pb–Zn and silver deposits. At the eastern margin of the plateau, the magmatic activities controlled by the large-scale strike-slip fault system developed a 1000 km-long large-scale alkali-rich porphyry belt; during the compressive-to-tensile torsion transformation period (40–30 Ma), pulsating epithermal emplacements of the ore-bearing porphyry at three stages resulted in three porphyry hydrothermal metallogenic systems (40 Ma, 36 Ma and 32 Ma), thus developing the porphyry mineralization belt represented by Yulong porphyry Cu deposits and Beiya porphyry Au deposits. In the Tengliang area, the syn-collision granite emplacement (50–65 Ma) controlled by the Gaoligong strike-slip fault system resulted in the Sn polymetallic superimposition mineralization that developed the large Sn deposit cluster superimposed on the Hercynian VMS, which is represented by Lailishan Sn deposit. In the Ailaoshan belt, the large-scale strike-slip-shear process (23–38 Ma) developed the huge Ailaoshan shear zone. The strongly sheared ophiolite melange zone controlled the development of the gold deposit belt, and the ductile-brittle-ductile shear belt transformation site controlled the development of the gold fields and deposits. Based on these systematic studies, we put forward the intracontinental tectonic transition metallogenic theory. The main points are as follows: 65 Ma ago, the Indian and Asian continents collided and uplifted to develop the Qinghai-Tibet Plateau, and with the intensification of the collision, the middle and south sections of the Sanjiang area on the eastern edge of the Qinghai-Tibet Plateau underwent great rotation, great strike-slip, great napping and great fluid migration (Fig. 4.34); large-scale strike-slip faults cut the lithosphere and induced copper-bearing crust/mantle magma activities, thus developing a large porphyry copper deposit system (such as Yulong copper deposit); a large-scale shear led to the formation of a ductile shear zone up to hundreds of kilometers in length, as well as the gold activation to form a large-scale shear zone gold deposit system (such as Zhenyuan copper deposit); the large-scale napping and strike-slip pull-apart developed a series of hydrothermal activity centers and the hydrothermal Ag polymetallic deposit systems (such as Lanping Jinding Pb-Zn deposit and Baiyangping Ag polymetallic deposit). This tectonic transition along with the stress-strain adjustment caused by a large-scale collision induced unusually strong regional tectonic-magmatic-fluid mineralizations. We call this process the intracontinental tectonic transition metallogenic theory.

Fig. 4.34
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Cenozoic strike-slip-shear action and metallogenic systems in Sanjiang Orogenic Belt

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