Unnamed Occurrence (ARDF - SI129; east of Waterfall Lake), Chichagof District, Sitka Borough, Alaska, USA
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Location: This occurrence is at an elevation of about 1,000 feet, about 1.8 miles east of the outlet of Waterfall Lake. The occurrence is 0.2 mile southeast of the center of sec. 17, T. 50 S., R. 60 E. It is location 43 of Cobb (1972, 1978). The location probably is accurate within 0.2 mile.
Geology: Johnson and Karl (1985) map the rocks in the area of this occurrence as Triassic(?) greenstone that is intruded by a northwest-striking, linear sill(s) of Cretaceous(?) diorite. The rocks are cut by steeply-dipping, mainly northwest-striking faults; these include the regional-scale Border Ranges Fault whose trace is just southwest of the occurrence. The fault apparently is intruded by the sill(s). Cobb (1972, 1978), citing Loney and others (1963), describes the occurrence as secondary copper minerals in quartz and epidote amygdules in greenstone. Triassic(?) greenstone elsewhere on northwest Chichagof Island generally contains primary copper minerals that are about the same age as the greenstone host rock (see, for example, SI035 and SI036).
Age: Triassic(?) greenstone elsewhere on northwest Chichagof Island generally contains primary copper minerals that are about the same age as the greenstone host rock.
Commodities (Major) - Cu
Development Status: None
Deposit Model: Basaltic copper (Cox and Singer, 1986; model 23).
3 entries listed. 3 valid minerals.
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Cobb, E.H., 1972, Metallic mineral resources map of the Sitka quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-467, scale 1:250,000. Cobb, E.H., 1978, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Sitka quadrangle: U.S. Geological Survey Open-File Report 78-450, 124 p. Johnson, B.R, and Karl, S.M., 1985, Geologic map of western Chichagof and Yakobi Islands, southeastern Alaska: U.S. Geological Survey Miscellaneous Investigations Series Map 1-1506, 1 sheet, scale 1:125,000. Loney, R.A., Berg, H.C., Pomeroy, J.S., and Brew, D.A., 1963, Reconnaissance geologic map of Chichagof Island and northwestern Baranof Island, Alaska: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-388, 1 sheet, scale 1:250,000.