Geology Reports⌕ Search

Geology topics

Willis H. Nelson

Publications and source records attributed to Willis H. Nelson.

12 recordsLinked to original sources
USGS1980

Geology and mineral resources of the North Absaroka Wilderness and vicinity, Park County, Wyoming, with sections on mineralization of the Sunlight mining region and geology and mineralization of the Cooke City mining district, and a section on aeromagnetic interpretation

SUMMARY The North Absaroka Wilderness is approximately 560 square miles (1,450 km 2 ) of rugged scenic mountainous terrain that adjoins the eastern boundary of Yellowstone National Park in northwestern Wyoming. The area was studied during 1970, 1971, and 1972 by personnel of the U. S. Geological Survey and the U. S. Bureau of Mines to evaluate its mineral-resource potential as required by the Wilderness Act of 1964. This evaluation is based on a search of the literature courthouse and production records, geologic field mapping, field inspection of claims and prospects, analyses of bedrock and stream-sediment samples, and an aeromagnetic survey. The North Absaroka Wilderness is underlain almost entirely by andesitic and basaltic volcanic rocks of Eocene age. These volcanics rest on deformed sedimentary rocks of Paleozoic and, locally, of Mesozoic age that are exposed at places along the northern and eastern edges of the wilderness. Dikes and other igneous intrusive bodies cut both the volcanic and sedimentary rocks. A nearly flat detachment fault, the Heart Mountain fault, and a related steep break-away fault have displaced middle and upper Paleozoic rocks and some of the older part of the volcanic sequence to the southeast. A much greater thickness of volcanic rocks was found to be involved in Heart Mountain faulting than had previously been recognized; however, most of the volcanic rocks and many of the intrusives were emplaced after Heart Mountain faulting. Local folding and high-angle faulting in mid-Eocene time have deformed all but the youngest part of the volcanic sequence in the southeastern part of the wilderness. This deformation is interpreted as the last pulse of Laramide orogeny. The results of this study indicate that the mineral-resource potential of the wilderness is minimal. Bentonite, petroleum, low-quality coal, and localized deposits of uranium and chromite have been produced in the surrounding region from rocks that underlie the volcanic rocks; but such deposits, if present in the wilderness, would be too deeply buried, too small, or too sporadically distributed to be profitably located and exploited. Copper and gold mines and prospects are present on the fringes of the wilderness, but otherwise the area seems to be devoid of economically valuable concentrations of metallic minerals. No surface evidence of geothermal-energy potential was found. Known mineral deposits in the vicinity of the North Absaroka Wilderness are associated with intrusive rocks. From the Cooke City mining district, just north of the wilderness, replacement deposits in Upper Cambrian carbonate rocks may extend a short distance into the north edge of the wilderness, In the Sunlight mining region, an enclave nearly surrounded by the wilderness, mineralization occurs in veins and is disseminated in volcanic and plutonic rocks. Richer concentrations of metallic minerals may occur in carbonate rocks adjacent to intrusive bodies at depth beneath the volcanic rocks in the Sunlight region. A few small intrusive bodies occur in the wilderness, but no significant associated mineralization was detected. Aeromagnetic data indicate that other intrusives not exposed by erosion may occur in the wilderness; however, no significant metamorphism or alteration is evident at the surface to indicate their presence. Although most of the rocks of the wilderness are of igneous origin, they are all so old (Eocene) that it is unlikely that they retain any original heat. The Pleistocene rhyolitic ash-flow tuffs in the southwestern part of the wilderness were erupted from sources in Yellowstone National Park just to the west; however, in the wilderness these tuffs are too thin to contain any residual heat.

Wyoming↗
USGS1969

Geology of the Mackay 30-minute quadrangle, Idaho

The Jefferson Dolomite, Grand View Dolomite, and Three Forks Limestone, all of Devonian age, are the oldest rocks exposed in the quadrangle. Rocks that range from Mississippian to Permian in age are widespread; they are represented by the White Knob Limestone in the eastern part of the quadrangle and the Copper Basin Formation in the western part. The Copper Basin Formation, which is composed of non-carbonate detrital rocks, is interlayered with the White Knob Limestone near the middle of the quadrangle. This interlayering is herein interpreted to be the result of depositional interbedding, but it could be in part due to juxtaposition by faulting. The Challis Volcanics, of Tertiary age, cover much of the quadrangle, and except for a conspicuous basal conglomerate, lack distinctive subdivisions similar to those in neighboring areas. Alluvial deposits which may be in part as old as Pliocene are scattered through the quadrangle. Glaciation affected all higher parts of the quadrangle, and locally glacial deposits of at least three ages can be distinguished The latest two of these are probably of late Wisconsin Bull Lake and Pinedale ages. Basalt flows of probable Recent age extend into the southernmost part of the quadrangle and originate in part from vents there. Intrusive rocks, including plutons and related dikes of Tertiary age, are scattered throughout the quadrangle. They range from granite to quartz diorite in composition. The intrusive rocks seem to be related to the Challis Volcanics. The rocks of the quadrangle were strongly deformed and eroded prior to the deposition of the Challis Volcanics. No thrust faults have been recognized although such faults are plentiful in the adjacent region. Deformation has continued until recent times. All or parts of five mining districts are included in the quadrangle, and the total production probably exceeded $10,000,000. Mining has been quiet since World War II but activity has been renewed at times in the past and possibilities for the discovery of substantial new deposits seem promising. The mineral deposits formed largely by replacement, partly in areas of contact metamorphism. The metals present are varied but copper has been the main product. All of the deposits are believed to be related to the intrusions of Tertiary age.

Open-File Report↗