Under provisions of the Wilderness Act (Public Law 88-577, September 3, 1964), the U.S. Geological Survey and the U.S. Bureau of Mines have been conducting mineral surveys of areas selected for possible inclusion in the National Wilderness Preservation System. This report presents results of geochemical studies carried out in June and July, 1982, as part of the investigation of the Buffalo Peaks Wilderness Study Area, Colo. Stream-sediment and panned-concentrate samples were collected from about 80 sites on streams draining the study area. Analytical results and a sample locality map were published by Domenico and others (1984).

The geologic and mineral resource potential maps of the study area were prepared by Hedlund and others (1983). The Buffalo Peaks Wilderness Study Area encompasses a major portion of the Mosquito Range, which is structurally part of the east flank of the north-northwest-trending Sawatch anticline. Bedrock in the west two-thirds of the study area is made up of Precambrian igneous and metamorphic rocks of the core of the anticline, whereas bedrock in the east one-third is mostly east dipping Paleozoic sedimentary rocks. In the vicinity of East and West Buffalo Peaks, the sequence of Paleozoic sedimentary rocks is covered by Tertiary extrusive rocks.

Major faults generally run parallel to the north-northwest trend of the Arkansas River Valley, which is an expression of the Arkansas River segment of the Rio Grande depression, and the Sawatch anticline in the study area. Some faults are probably of late Precambrian age; major recurrent displacement is known to have occurred on most faults during Laramide time and in the Pliocene and Miocene.

The study area is bounded by several areas of known mineralization (Hedl und and others, 1983). Vein and bedding replacement deposits of silver, zinc, and lead were mined from 1890 until about 1918 in the vicinity of Weston Pass (map A), on the northeastern border of the study area. Gold and silver were mined from about 1860 until about 1880 from veins in the Granite area (map A), on the northwestern border of the study area; minor prospecting activity continues today. From 1935 to 1937, veins of gold, silver, and base metals were mined in the vicinity of Fourmile Creek, on the southwestern border of the study area (map A). Recently, active uranium prospecting has been taking place in the vicinity of the Middle Fork of Salt Creek, on the southeastern border of the study area (map A).