Pre-field study and mineral resource assessment of the Sleetmule quadrangle, southwestern Alaska

Abstract

ill 3 -gold-tungsten-quartz vein, 4 -tin-silver-boron enriched, 5 -Mississippi Valley type lead-zinc, and 6 -zinc-lead-silver, copper, or iron skarn. CHAPTER 1. LOCATION. ACCESS. CLIMATE. AND LAND STATUSThe Sleetmute 1° x 3" quadrangle (scale 1:250,000) is located in southwest Alaska, 210 miles west of Anchorage (fig. 1). The area comprises nearly 18,000 km2 (7000 mi2) of variable terrain encompassing portions of two physiographic provinces: the Kuskokwim Mountains and the Holitna Lowland (Wahrhaftig, 1965). The Kuskokwim Mountains, a succession of rounded ridges and broad lowlands, lie along a northeast-trending axis; the southeastern range boundary diagonally bisects the quadrangle. The average elevation is 370 to 760 m (1,200 to 2,500 ft) but some of the more rugged terrain rises to between 900 and 1,250 m (3,000 and 4,100 ft) and has been glaciated. The intervening well-drained lowlands have an elevation of 90 to 180 m (300 to 600 ft). Timberline occurs at an elevation of about 370 m (1,200 ft). The broad, northwest-sloping plain of the Holitna Lowland lies east of the mountains, is 90 to 240 m (300 to 800 ft) in elevation, and drains part of the west side of the Alaska Range. The Kuskokwim River, the second largest in Alaska, roughly bisects the northern half of the quadrangle and several of its tributaries the Holitna, Stony, and Swift Rivers flow across the Holitna Lowland.Access to the quadrangle is essentially by aircraft since no roads or summer trails exist. Commercial air service from Aniak, 20 miles west of the quadrangle, is available to the villages of Sleetmute, Crooked Creek, Red Devil, and Stony River. Several other native villages along the Kuskokwim River have gravel airstrips suitable for small aircraft. During the summer months, the Kuskokwim River is navigable for small craft and suitable for float plane landings. Petroleum and heavy supplies are brought to the riverside villages by shallow-draft barge from Bethel. Although much of the quadrangle is heavily vegetated, ridgetops above timberline can be traversed on foot.The climate of the region is subarctic, characterized by short, typically wet summers, and by dry, cold, windy winters . Average summer temperatures are approximately 55" F, and the quadrangle has discontinuous permafrost.Land jurisdiction in the quadrangle is divisible into three categories (fig. 2). About 55% of the land is owned by the State of Alaska; 25% is Native land (5% of which is under multiple ownership); and about 20% of the land is Federally owned and administered by the Bureau of Land Management (BLM). The area contains no Federal or State designated park or wilderness lands.

Late Cretaceous through Cenozoic Strike‐Slip Tectonics of Southwestern Alaska

“…Calc-alkaline volcanic-plutonic complexes of Late Cretaceous and early Tertiary age intrude and locally overlie strata of the Kuskokwim Group (Bundtzen et al 1988;Miller and Bundtzen 1994). About 20 of these complexes, which range from as small as 8 km 2 to as large as 650 km , crop out in a broad, 450-km-long, northeast-trending belt (Miller et al 1989;Moll-Stalcup 1994;Bundtzen and Miller 1997). rocks range from about 76 to 63 Ma (Moll et al 1981;Miller and Bundtzen 1994;Decker et al 1995; Bundtzen et al 1999).…”

“…Between these major faults lie a number of lesser faults that roughly parallel the main structures. These are not discussed in detail, but are shown on regional quadrangle maps (e. , Patton et al 1980;Miller et al 1989;Miller and Bundtzen 1994).…”

Possible active fault traces on or near the Castle Mountain fault between Houston and the Hatcher Pass Road: A section in RGeologic studies in Alaska by the U.S. Geological Survey, 1993

“…Mercury analyses indicate that at least 90 percent of the total mercury is methylmercury, a form that accumulates in fish. Miller, M.L., Belkin, H.E., Blodgett, R.B., Bundtzen, T.K., Cady, J.W., Goldfarb, R.J., Gray, J.E., McGimsey, R.G., and Simpson, S.L., 1989, Pre-field study and mineral resource assessment of the Sleetmute quadrangle, southwestern Alaska: U.S. Geological Survey Open-File Report 89-363, 115 p., 3 plates, scale 1:250,000. Miller, M.L., and Bundtzen, T.K., 1987, Geology and Water, Air, and Soil Pollution, v. 29, p. 57-76.…”

“…Other unmapped granitic bodies may intrude andesitic volcanic rocks (Patton, 1966). Immediately north of the Kateel River quadrangle are several large granitic intrusions that are part of a 500km-long plutonic belt of varied age and composition (Patton and others, 1968;Miller, 1989). Tertiary to Quaternary olivine basalt crops out in the northwestern corner of the quadrangle and is part of the Buckland River field (Patton and Box, 1989).…”