Stratigraphy and structure of the northern and western flanks of the Black Hills uplift, Wyoming, Montana, and South Dakota
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Montana, South Dakota, Wyoming↗
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Bentonite deposits of the northern Black Hills district, Wyoming, Montana, and South Dakota
The northern Black Hills bentonite mining district includes parts of Crook County, Wyo., Carter County, Mont., and Butte County, S. Dak. Within this district, many beds of bentonite occur interspersed with sedimentary strata of Cretaceous age that have an average total thickness of about 3,000 feet and consist chiefly of marine shale, marl, and argillaceous sandstone. The bentonite beds occur in formations ranging upward from the Newcastle sandstone to the lower part of the Mitten black shale member of the Pierre shale. Tertiary (?) and Quaternary deposits of gravel, sand, and silt are present on extensive terraces, and deposits of such materials also extend along stream courses in all parts of the district. The overall geologic structure of the district is that of a broad northwestward- plunging anticline, in which the strata dip gently toward the northeast, north, and northwest. The overall structure is interrupted, however, by several subordinate folds which bring the bentonite beds to the surface repeatedly, so that large resources of bentonite are present under light overburden. The northern Black Hills district is an important source of commercial gel-forming sodium-type bentonite. During the period 1941-56 more than 5 million tons of raw bentonite was mined, most of which came from the Clay Spur bed near the top of the Mowry shale; a few thousand tons was mined from bed A in the Newcastle sandstone. Calcium-type bentonite occurs in bed B in the Mowry shale and in bed I at the base of the Mitten black shale member. Seven other beds are sufficiently thick and continuous to warrant consideration as prospective sources of bentonite for industrial use. Most of the bentonite produced is sold for use (a) as an ingredient of drilling mud; (b) for preparing metallurgical molding sand of superior dry strength; and (c) for the bonding material used in pelletizing taconite iron ore of the Lake Superior region. The results of drilling-mud and foundry-sand bonding-clay tests of several hundred samples, as well as analyses of selected samples, chiefly by X-ray, differential thermal, base exchange and spectrographic methods, are included in this report.
Montana, South Dakota, Wyoming↗
Uranium migration and geochemistry of uranium deposits in sandstone above, at, and below the water table; Part 2, Relationship of uranium migration dates, geology, and chemistry of the uranium deposits
The time of U migration in deposits in sandstone can be determined by correlating apparent age calculations, based on radiochemical analyses, with the geology of a particular deposit. Data were obtained from U ore samples representing deposits above the water table, deposits just above and below perched water tables, and deposits at least 250 ft. below the water table in the Hulett Creek area, Wyoming. The first U deposition occurred more than 250,000 years ago for the deposits now at or above the water table. Approximately 60,000 to 80,000 years ago these deposits were oxidized, leached, and locally enriched. Accumulation of U in the deposits below the water table probably did not start before 180,000 years ago and has continued to the present.
Montana, South Dakota, Wyoming↗
Geologic and structure contour maps of the northern and western flanks of the Black Hills, Wyoming, Montana, and South Dakota
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Montana, South Dakota, Wyoming↗
Bentonite deposits of the northern Black Hills district, Montana, Wyoming, and South Dakota
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Montana, South Dakota, Wyoming↗