Gold deposits of the northern margin of the North China Craton: multiple late Paleozoic–Mesozoic mineralizing events
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The northern margin of the North China craton is well-endowed with lode gold deposits hosting a resource of approximately 900 tonnes (t) of gold. The ~1,500-km-long region is characterized by east-trending blocks of metamorphosed Archean and Proterozoic strata that were episodically uplifted during Variscan, Indosinian, and Yanshanian deformational and magmatic events. At least 12 gold deposits from the Daqinshan, Yan-Liao (includes the Zhangjiakou, Yanshan, and Chifeng gold districts), and Changbaishan gold provinces contain resources of 20–100 t Au each. Most deposits are hosted in uplifted blocks of Precambrian metamorphic rocks, although felsic Paleozoic and Mesozoic plutons are typically proximal and host ~30% of the deposits. The lodes are characterized by sulfide-poor quartz veins in brittle structures with low base metal values and high Au:Ag ratios. Although phyllic alteration is most common, intensive alkali feldspar metasomatism characterizes the Wulashan, Dongping, and Zhongshangou deposits, but is apparently coeval with Variscan alkalic magmatism only at Wulashan. Stepwise 40Ar–39Ar geochronology on 16 samples from gangue and alteration phases, combined with unpublished SHRIMP U–Pb dates on associated granitoids, suggest that gold mineralizing events occurred during Variscan, Indosinian, and Yanshanian orogenies at circa 350, 250, 200, 180, 150, and 129 Ma. However, widespread Permo-Triassic (~250 Ma) and Early Jurassic (~180 Ma) thermal events caused variable resetting of most of the white mica and K-feldspar argon spectra, as well as previously reported K–Ar determinations. Compiled and new stable isotope and fluid inclusion data show that most δ18O values for ore-stage veins range from 8 to 14‰, indicating a fluid in equilibrium with the Precambrian metamorphic basement rocks; δD values from fluid inclusions range widely from –64 to –154‰, which is indicative of a local meteoric component in some veins; and highly variable δ34S data (+7 to –17‰), even within individual deposits, indicate various local country-rock sources for sulfur. Fluid inclusions from all districts show variable homogenization temperatures between 240 and 400 °C, and are consistently characterized by low salinity, H2O–CO2 ± CH4, N2 solutions. Although the data are largely consistent with that from orogenic gold veins, intrusion-related veins and epithermal veins are also recognized. The multiple episodes of mineralization are coincident with episodic tectonic reactivations and associated magmatism along the northern margin of the North China craton. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00126-001-0239-2.
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