Unnamed Prospect (ARDF - SI189; north shore of Warm Springs Bay), Chichagof District, Sitka Borough, Alaska, USA
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Location: This prospect is plotted near the site of Manleyville (which is shown on the 1:63,360-scale U.S. Geological Survey topographic map) on the north side of Warm Springs Bay. The prospect covers an area of about a square mile north of Manleyville. The occurrence is at the northeast corner of sec. 19, T. 55 S., R. 67 E. It is location P-113 of Bittenbender and others (1999) and MAS no. 0021140154 (U.S. Bureau of Land Management, 2002). The location is accurate.
Geology: This prospect is a porphyry copper deposit about a square mile in area that was first identified and staked by El Paso Natural Gas company in 1973. There apparently has been little or no further work by private industry but Bittenbender and others (1999) of the U.S. Bureau of Mines sampled extensively in the area. The rocks in the area are mostly part of a large Tertiary batholith that consists mainly of hornblende-biotite tonalite with subordinate hornblende-biotite granodiorite and garnet-muscovite-biotite trondhjemite (Loney and others, 1975). The northern part of the mineralized area borders on or extends into a mass of Triassic and Jurassic schist and gneiss about 3 miles long and 2 miles wide within the batholith. The deposit consists of: 1) disseminated sulfides in silicified tonalite; 2) pyrite and chalcopyrite at the edges of granodiorite inclusions; and 3) quartz veinlets with pyrite, chalcopyrite, and sphalerite in the tonalite. The mineralization is extensive but relatively low grade. Bittenbender and others (1999) collected 74 samples over the deposit; 20 representative samples of the deposit average 600 parts per million (ppm) copper and 85 ppm molybdenum. Samples of the quartz veinlets with sulfides gave higher values, the highest of which were 9,000 ppm copper, 1,650 ppm molybdenum, and 544 ppm bismuth. Gold and silver values were below detection or negligible in all samples.
Workings: Apparently only surface sampling.
Age: Tertiary or younger based on the age of the granodiorite host rocks.
Alteration: The granodiorite host rock is silicified and cut by quartz veinlets.
Commodities (Major) - Cu, Mo, Zn; (Minor) - Bi
Development Status: None
Deposit Model: Porphyry copper.
4 entries listed. 4 valid minerals.
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Bittenbender, P., Still, J.C., Maas, K., and McDonald, M., Jr., 1999, Mineral resources of the Chichagof and Baranof Islands area, southeast Alaska: Bureau of Land Management, BLM-Alaska Technical Report 19, 222 p. Loney, R.A., Brew, D.A., Muffler, L.J.P., and Pomeroy, J.S., 1975, Reconnaissance geology of Chichagof, Baranof, and Kruzof Islands, southeastern Alaska: U.S. Geological Survey Professional Paper 792, 105 p. U.S. Bureau of Land Management, 2002, Alaska mineral locations database report (Sitka quadrangle), July 2, 2002, 205 p. [http://imcg.wr.usgs.gov/dem.html]