Stratabound Copper Deposits in East South-Central Alaska: Their Characteristics and Origin
Six stratabound Kennecott-type copper deposits are being studied to evaluate the characteristics of the ore-host rock system. Three (Mountain Grill, Radovan, and Clear-Porcupine) are in the Middle to Upper Triassic Nikolai Greenstone — a thick sequence of subaerial amygdaloidal tholeiite flows — and the other three (Binocular, Nelson, and Peavine) are in the Upper Triassic Chitistone Limestone, a platformal limestone and dolomite unit.
X-ray diffraction, petrographic and chemical studies have led to the identification of ten ore minerals in the deposits, the most abundant being digenite, chalcocite, djurleite, covellite, bornite, and chalcopyrite. Minor arsenic and antimony sulfide phases are also present. Mineral deposits in greenstones have both Cu and Cu - Fe sulfides in contrast to the essentially Cu-sulfides in limestones.
The mineralization is proposed to have formed in two stages. Hydration-dehydration reactions associated with alteration-metamorphism of the Nikolai Greenstone liberated copper from the metal oxides and the mafic minerals. Copper was carried by the circulating fluids along the existing fracture-fluid pathway system, reacting and precipitating ore minerals in them. The weak and widely distributed mineralization in the belt is probably of this type. Greenstone alteration was probably coincidental with Cretaceous accretionary orogeny as shown by K- Ar systematics (Silberman et al. 1981).
Cenozoic deformation induced a steep fracture system that enhanced the porosity and permeability of the rocks, thus focusing the meteoric water circulatory system for effective and efficient solution and transport of metals. Activity in such a system at this stage was probably driven by a thermal charge from the Tertiary intrusives. Lack of extensive alteration of the Chitistone Limestone and of recrystallization at the ore vein-limestone contacts suggests that the ore solutions were at relatively low temperatures. The mineral associations and textures suggest that the upper temperature that prevailed in the Triassic ore-host rock system was about 200 °C.
KeywordsCopper Deposit Contrib Mineral Petrol Native Copper Econ Geol Geol Surv
Unable to display preview. Download preview PDF.
- Armstrong AK, MacKevett EM Jr (1982) Stratigraphy and diagenetic history of the lower part of the Triassic chitistone limestone, Alaska. US Geol Surv Prof Pap 1212A: A1–A26Google Scholar
- Armstrong AK, MacKevett EM Jr, Silberling NJ (1969) The Chitistone and Nizinal limestones of part of the southern Wrangell Mountains, Alaska — a preliminary report stressing carbonate petrography and depositional environments. US Geol Surv Prof Pap 650-D:-49-D62Google Scholar
- Coombs DS (1960) Lower grade mineral facies in New Zealand. Rep Int Geol Congr, 21st Session Norden 13: 339–351Google Scholar
- Cornwall HR (1956) A summary of ideas on the origin of native copper deposits. Econ Geol 54: 351–373Google Scholar
- Csejtey B Jr, Nelson WH, Jones DL, Silberling NJ, Dean RM, Morris MS, Lanphere MA, Smith JG, Silberman ML (1978) Reconnaissance geologic map and geochronology, Talkeetna Mountains Quadrangle, northern part of Anchorage Quadrangle and southwest part of Healy Quadrangle, Alaska, Scale 1:250,000. US Geol Surv Open File Rep 78-558-A, 62 ppGoogle Scholar
- Csejtey B Jr, Foster HL, Nokleberg WJ (1980) Cretaceous accretion of the Talkeetna Superterrane and subsequent development of the Denali fault in Southcentral Alaska. Geol Soc Am (Abstracts with Programs) 12: 409Google Scholar
- Dunham RJ (1962) Classification of Carbonate Rocks according to depositional textures. In: Ham WE (ed) Classification of carbonate rocks. AAPG Mem, pp 108–122Google Scholar
- Folk RL (1962) Spectral division of limestone types Symp. Classification of carbonate rocks. In: Ham WE (ed) Classification of carbonate rocks. AAPG Mem, pp 62–84Google Scholar
- Jensen ML, Bateman Am (1979) Economic mineral deposits. John Wiley & Sons, New York, 593 ppGoogle Scholar
- Jones DL, Silberling NJ (1979) Mesozoic stratigraphy, the key to tectonic analysis of Southern and Central Alaska. US Geol Surv Open File Rep 79–1200, 41 ppGoogle Scholar
- Liou JG (1979) Zeolite facies metamorphism of basaltic rocks from the Taiwan ophiolite. Am Mineral 64: 1–14Google Scholar
- MacKevett EM Jr (1976) Mineral deposits and occurrence in McCarthy Quadrangle, Alaska. US Geol Surv Mise Field Stud Map M F 773-B Scale 1:250000, 2 sheetsGoogle Scholar
- MacKevett EM Jr (1978) Geologic map of McCarthy Quadrangle Alaska. US Geol Surv Mise Invest Ser Map 1-1032 Scale 1: 250000Google Scholar
- MacKevett EM Jr, Radtke AS (1966) Hydrothermal alteration near the Kennecott copper mines, Wrangell Mountains area, Alaska — A preliminary report. US Geol Surv Prof Pap 550-B: B165–B168Google Scholar
- MacKevett EM Jr, Richter DH (1974) The Nikolai Greenstone in the Wrangell Mountains, Alaska, and nearby areas. Geol Assoc Can, Cordilleran Section, Program and Abstracts 13: 14Google Scholar
- MacKevett EM Jr, Albert NRD, Barnes DF, Case JE, Robinson K, Singer DA (1977) The Alaskan mineral resource assessment program: background information. US Geol Surv Cir 739, 23 ppGoogle Scholar
- MacKevett EM Jr, Armstrong AK, Potter RW, Silberman ML (1981) Kennecott-type copper deposits, Wrangell mountains, Alaska, an update and summary. In: Silberman ML et al. (eds). Symp on Mineral Deposits of the Pacific Northwest. US Geol Surv Open File Rep 81–355: 51Google Scholar
- Muller JE, Northcote KE, Carlisle D (1974) Geology and mineral deposits of Alert-Cape Scott map area, Vancouver Island, British Columbia. Geol Surv Can Pap 74–8:77 ppGoogle Scholar
- Silberman ML, MacKevett EM Jr, Connor CL, Mathews A (1981) Metallogenic and tectonic significance of whole rock potassium — Argon ages of the Nikolai Greenstone, McCarthy Quadrangle, Alaska. In: Silberman ML et al. (eds). Symp on Mineral deposits of the Pacific northwest. US Geol Surv Open File Rep 81-355: 53 - 73Google Scholar
- Sinclair A J (1977) The White River Copper deposit, Southwestern Yukon. Geol Assoc Can (Program with Abstract) 2: 49Google Scholar
- Sood MK, Wagner RJ (1981) Copper mineralization at Glacier Creek, McCarthy Quadrangle, Alaska. Geol Soc Am Abstr (Northcentral Section) 13: 317Google Scholar
- Turner FJ (1981) Metamorphic petrology: mineralogical, field and tectonic aspects, 2nd edn. Mc¬Graw-Hill, New York, 451 ppGoogle Scholar
- Wilson JL (1975) Carbonate facies in geologic history. Springer, Berlin Heidelberg New York, 471 ppGoogle Scholar