Bonanza #1 Prospect, Chicagof District, Sitka Borough, Alaska, USA
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Geology: This deposit is one of many of similar deposits (PA002 to PA018) scattered over an area of about 6 square miles at the head of Silver Bay (Bittenbender and others, 1999). The deposits are gold-quartz veins with sparse sulfides, usually only pyrite and arsenopyrite. Samples that have been analyzed with modern methods usually show anomalous arsenic even if arsenopyrite is not identified in the rocks, and several parts per million mercury. The veins are often parallel to the bedding of the host rock which is graywacke and argillite of the Sitka Graywacke of Cretaceous age (Loney and others, 1975). Many of the so-called veins in the early literature are actually fault zones with lenses of quartz or concentrations of quartz stringers along the fault zone. Prospecting began in the area in 1871. The Stewart Mine (PA012) was located in 1872 and it was the first lode-gold mine in Alaska. The Silver Bay area has been prospected intermittently to the present but the veins are relatively small and most are low grade. The area has produced relatively little gold, many of the properties have not been active since before 1900, and there has been no production since the early 1940's. Little is known of the history of the Bonanza No. 1 prospect other than that it was shown on a 1940's map of the Edgecumbe Exploration Company. Bittenbender and others (1999, fig. 17) located a 105-foot adit that was driven along a fault zone in black slate and graywacke. They sampled scattered quartz stringers in the adit, but none had significant metal values except for one sample that contained more than 11 parts per million mercury.
Workings: A 105-foot adit of uncertain age.
Age: Cretaceous or younger based on the age of the host rocks.
Commodities (Minor) - Hg
Development Status: None
Deposit Model: Quartz vein with anomalous mercury.
1 entry listed. 1 valid mineral.
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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. B., and Pomeroy, J.S., 1975, Reconnaissance geology of Chichagof, Baranof, and Kruzof Islands, southeastern Alaska: U.S. Geological Survey Professional Paper 792, 105 p.