KFC Occurrence, Chistochina District, Matanuska-Susitna Borough, Alaska, USA
The KFC occurrence is within a belt of weakly metamorphosed sedimentary and volcanic rocks at least 50 miles long, informally called the Lichen Greenstone Belt (Castle and Degenhart, 1978, p. 12-16). It contains several other occurrences of copper (GU002 to GU008, excluding GU005) and the belt is favorable for the occurrence of other copper/silver deposits. Additional information can be obtained from Ahtna Minerals in Anchorage, Alaska.
Location: The KFC occurrence is about one-half mile, north-northwest of VABM Laren and about six and one-half miles south of the Maclaren River. The occurrence is at an elevation of about 4600 feet approximately on the center of the sideline which separates sections 27 and 28, T. 12 N., R. 9 W., Copper River Meridian. The prospect is located within 500 feet.
Geology: The KFC occurrence is in a belt of Pennsylvanian and Permian sedimentary and volcanic rocks informally called the 'Lichen Greenstone Belt' (Castle and Degenhart, 1978, p. 12-16). The Lichen Belt takes its name from the Lichen prospect about 20 miles northwest of the KFC occurrence in the Healy quadrangle (Smith, Bundtzen and Trible, 1975). At both the KFC location and the Lichen prospect, mineralized rocks in outcrop and talus invariably are partly covered by red-orange lichen (Trentepohia aurea). Copper minerals at the KFC occurrence are associated with three host rocks: 1) quartz-chlorite schist, 2) epidote-rich calcareous greenstone, and 3) orange-weathering impure marble. The rocks have been weakly metamorphosed and are tentatively correlated with the Tetelna Formation of Pennsylvanian to Permian age based on fossils collected near the Lichen prospect in the Healy quadrangle (Turner and Smith, 1974). At this occurrence, the primary copper minerals are bornite, chalcocite, and chalcopyrite that occur as stringers and dissemination's within a crudely stratabound sequence of schist, greenstone, and impure marble. The copper minerals have been partly oxidized to chrysocolla and malachite; outcrops are variably copper stained and partly covered by red-orange lichen. The maximum width of the exposed mineralization is about 10 feet. The zone can be traced along strike through a talus field for about 500 feet and soil samples suggests that the occurrence continues for at least another 200 feet (Castle and Dagenhart, 1978). A series of chip and channel samples cut across the occurrence contain from 0.8 to 3.15 percent copper, from 0.14 to 0.71 ounces of silver per ton, and as much as 0.01 ounces of gold per ton. A selected sample from a talus boulder about 3 feet in diameter contained 24.5 percent copper, 4.1 ounces of silver per ton,and 0.03 ounce of gold per ton.
Workings: The KFC occurrence was discovered in 1977 during a regional geochemical survey conducted by WGM Inc., a consulting company, for Ahtna Inc. a regional Native corporation. A soil-sample survey extended the deposit about 200 feet along strike beyond the 500 foot-long zone where mineralized samples are found on the talus slope. The occurrence has not been drilled.
Age: Tentatively the mineralization is assumed to be Pennsylvanian to Permian, the age of the Tetelna Formation that hosts the deposit. The occurrence is crudely stratabound. The copper minerals appear to be diagenetic as they occur in stringers and as dissemination's in three distinct lithologic units. Remobilization of copper may have occurred during green-schist metamorphism in the Jurassic(?).
Commodities (Major) - Ag, Cu; (Minor) - Au
Development Status: None
Deposit Model: Cyprus massive sulfide (Cox and Singer, 1986, model 24a)
ReferencesCastle, B., and Degenhart, C., 1978, Lichen Greenstone Belt, v. 9 of 1977 Annual Progress Report, Ahtna Project: WGM, Inc., 22 p., maps and appendices. (Report held by Ahtna Minerals Co., Anchorage, Alaska). Smith, T.E., Bundtzen, T.K., and Trible, T.C., 1975, Stratabound copper-gold occurrence, northern Talkeetna Mountains, Alaska: Alaska Division of Geological and Geophysical Surveys Miscellaneous Paper 3, 7 p. Turner, D.L, and Smith, T.E., 1974, Geochronology and generalized geology of the central Alaska Range, Clearwater Mountains and northern Talkeetna Mountains: Alaska Division of Geological and Geophysical Surveys Open-File Report AOF-72, 11 p., and map.
9 entries listed. 8 valid minerals.
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