Unnamed Occurrence (ARDF - IL028; southeast of Upper Copper Lake), Bristol Bay District, Lake and Peninsula Borough, Alaska, USA
Location: This occurrence is at an elevation of about 1,000 feet on the north slope of the divide between Upper Copper Lake and Boot Lake. It is about in the center of the S1/2 NE1/4 sec. 7, T. 7 S., R. 28 W., Seward Meridian. The location is accurate within about 0.5 mile. The site is locality 13 of Detterman and Cobb (1972).
Geology: This occurrence is near the contact between granitic plutons of Tertiary and Cretaceous or Tertiary age (Read, 1967; Detterman and Reed, 1980). It consists of pyritized, argillized, and sericitized(?) granitic intrusive rock in a 400-foot-long exposure along a fault-controlled, unnamed northerly-flowing stream. The granitic rocks are cut by a mafic dike. The altered rocks contain disseminated flakes of molybdenite. Copper and molybdenum occur in anomalous concentrations in stream-sediment samples collected below the occurrence (Reed,1967), suggesting that the occurrence also contains chalcopyrite. Reed's rock samples, however, did not detect the gold reported by Detterman and Cobb (1972). The fault that controls the exposure may be a splay of a shear zone extending northeastward through the Meadow Lake valley (Reed, 1967).
Workings: Exploration consists of reconnaissance geologic mapping and rock and stream-sediment sampling. Reed's (1967) stream-sediment samples were anomalous for copper and molybdenum, but his rock samples did not detect the gold reported by Detterman and Cobb (1972).
Age: Probably Tertiary.
Alteration: Pyritization and argillic and sericitic(?) alteration.
Commodities (Major) - Au?, Mo; (Minor) - Cu?
Development Status: None
Deposit Model: Porphyry Cu-Mo (Cox and Singer, 1986; model 21a).
| Chalcopyrite ?|| Molybdenite|| Pyrite|
3 entries listed. 3 valid minerals.
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Detterman, R.L., and Cobb, E.H., 1972, Metallic mineral resources map of the Iliamna quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-364, 1 sheet, scale 1:250,000. Detterman, R.L., and Reed, B.L., 1980, Stratigraphy, structure, and economic geology of the Iliamna quadrangle, Alaska: U.S. Geological Survey Bulletin 1368-B, 86 p. Reed, B.L., 1967, Results of stream sediment sampling and bedrock analyses in the eastern part of the Iliamna quadrangle, and at Kasna Creek, Lake Clark quadrangle, Alaska: U.S. Geological Survey Open-File Report 272, 18 p.
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