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In the summer of 1991, we conducted a reconnaissance geochemical survey around the Fortyseven Creek Au-As-Sb-W prospect that is located in the southwestern part of the Sleetmute quadrangle. At that time, this project was a small part of a more comprehensive Alaska Mineral Resource Assessment Program (AMRAP) study of the Sleemute quadrangle. AMRAP studies were conducted by the U.S. Geological Survey (USGS) to fulfill requirements of the Alaska National Interests Lands Conservation Act (Public Law 96-487, 1980) to survey certain federal lands to determine their mineral potential. Although AMRAP is no longer in operation, this study represents a small topical study that was conducted during the Sleetmute quadrangle AMRAP study. The objective of the Fortyseven Creek work was to characterize the geochemistry of samples collected downstream from the Fortyseven Creek prospect, as well as mineralized and altered rock samples collected from the prospect. In this report, we describe the samples collected in 1991, the methods used for the analysis of the samples, and the geochemical data for these samples. The data in this report are also available in digital form on computer diskette in Gray and others (1999). An interpretation of these data appears in Gray and others (1998). SITE DESCRIPTION AND HISTORY The Fortyseven Creek Au-As-Sb-W prospect is located about 95 km southeast of Aniak, on the ridge crest at the headwaters of Fortyseven Creek, a tributary of the Holitna River (fig. 1). This lode and an associated gold placer mine on Fortyseven Creek about 3 km downstream from the prospect were discovered in 1947 by Russell Schaeffer. The lode was first described by Cady and others (1955) as a quartz-scheelite-gold-bearing shear zone cutting highly silicified graywacke and shale of the Kuskokwim Group. Additional exploration and geologic mapping of the Fortyseven Creek area was conducted by Hawley (1989), who described quartz veins cutting silicified sedimentary rock hornfels of the Kuskokwim Group; granite porphyry intrusions also cut the sedimentary rocks in this area. Hawley (1989) also found minor amounts of arsenopyrite, scheelite, stibnite, gold, pyrite, wolframite, jamesonite, and argentite in the veins, with locally abundant sericite (hydrothermal muscovite); these veins were traceable laterally for greater than 1,000 m. Some mineralized samples contain greater than 34 ppm Au (1 oz/t) (Hawley, 1989). The vein has not been mined. However, between 1948-1954, about 28 kg of gold (891 oz) and about 1,900 kg (5000 Ibs) of scheelite, containing 67-77 percent WO3, …

u.s. geological survey open file report/open-file report

Geochemical data for stream-sediment, heavy-mineral-concentrate and rock samples collected from the Fortyseven Creek gold-arsenic-antimony-tungsten prospect, southwestern Alaska