Wallace Prospect, Aniak District, Bethel Borough, Alaska, USA
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Geology: In 1945, R. E. Wallace of the U.S. Geological Survey discovered free gold in quartz veins cutting a granitic dike at this site. He described the deposit in unpublished notes and memoranda and the U.S. Geological Survey announced the discovery in a press release on August 4, 1945. The steeply dipping or vertical, granitic dike is about 40 feet wide and trends N 20 E, subparallel to the ridge. Wallace traced it along strike for about 300 feet. He noted that quartz veinlets were localized in the southeastern half of the dike and that the gold occupied open spaces in the interior of the veinlets. He collected two samples. One contained 0.59 ounce of gold per ton and the other 1.3 ounces of gold per ton. The gold was associated with a slightly more abundant, soft (hardness of 2 to 3), silvery-white mineral with laminar cleavage. This mineral was tentatively identified as a telluride. Limonite and traces of sphalerite, chlorite, and amphibole were also present in the veins. The dike, which may be an apophysis of a nearby mid-Cretaceous pluton, intrudes Jurassic volcanic rocks (Box and others, 1993). Frost (1990) described gold- and pyrite-bearing quartz veins at this site as cutting sericitized andesite and volcaniclastic hornfels. The veins are vuggy and contain euhedral quartz prisms extending into open spaces. Other gangue minerals in the iron oxide-stained veins are commonly calcite and sprays of chlorite. A sample from a quartz vein contained 4.5 parts per million (ppm) gold (Frost, 1990, sample locality 3). Bedrock in the area includes thermally metamorphosed Jurassic volcanic or volcaniclastic rocks and a small granitic stock or dike (Box and others, 1993). Wenz (2004, 2005) reported tellurobismuthite, gold, tetradymite, and very minor amounts of chalcopyrite in quartz veins at the Wallace prospect. Alteration was not present next to the veins. In 2005, Tonogold Resources, Inc. negotiated a mining lease agreement with Calista Corporation covering the general Nyac area. They completed detailed soil geochemical surveys in several areas including the Wallace prospect in the summer of 2005. A rock chip sample from the Wallace prospect contained 7.2 ppm gold. Strachan (2005) shows a map of soil sample sites in the general area of the Wallace prospect; several samples contained a few hundred parts per billion gold. Tonogold (2007) drilled two holes on the Wallace prospect in the summer of 2006 and did considerable trenching Both holes cut quartz-calcite-pyrrhotite-chalcopyrite veins at depth that are unlike other mineralization in the area. The veins are in Jurassic andesitic volcanic rocks and have narrow chalcedonic envelopes surrounded by wide propylitic zones.
Workings: As of 2005, Tonogold Resources, Inc. has a mining lease agreement with Calista Corporation covering the general Nyac area. They completed detailed soil geochemical surveys in several areas including the Wallace prospect in the summer of 2005. Strachan (2005) shows a map of soil sample sites in the general area of the Wallace prospect; two or three samples contained a few hundred parts per billion gold. Tonogold drilled two holes on the Wallace prospect in 2006 and did considerable trenching.
Age: Cretaceous or Tertiary. The gold-bearing quartz veins crosscut a granitic dike that may be mid-Cretaceous in age. The dike intrudes Jurassic volcanic rocks.
Alteration: Chalcedonic and propylitic.
Commodities (Major) - Au; (Minor) - Bi, Cu, Te, Zn
Development Status: None
Deposit Model: Au-Bi-Te veins; pyrrhotite-chalcopyrite-pyrite veins.
9 entries listed. 8 valid minerals.
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Box, S. E, Moll-Stalcup, E. J., Frost, T. P., and Murphy, J. M., 1993, Preliminary geologic map of the Bethel and southern Russian Mission quadrangles, southwestern Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-2226-A, 20 p., scale 1:250,000. Frost, T.P., 1990, Geology and geochemistry of mineralization in the Bethel quadrangle, southwestern Alaska, in Goldfarb, R.J., Nash, J.T., and Stoeser, J.W., eds., Geochemical studies in Alaska by the U.S. Geological Survey, 1989: U.S. Geological Survey Bulletin 1950, p. C1-C9. Strachan, D. G., 2005, A summary and interim status report on Tonogold's 2005 geochemical exploration of the Nyac gold district, southwest Alaska: Private report for Tonogold Resources, 20 p. (Available online at: http://www.tonogold.com/i/pdf/2005_Final_Report_5m.pdf.) Tonogold Resources, Inc., 2006: www.tonogold.com/s/Nyac.asp (as of April, 2007) Wenz, Z.. J., 2004, Geology and gold mineralization of the Nyac district, southwest Alaska: MS thesis, University of Alaska, Fairbanks, 133 p. Wenz, Z.J., 2005, An investigation of the geology and gold mineralization in the Nyac district, southwest Alaska: Bureau of Mines Open File Report 103, 156 p.