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Geology topics

T. A. Steven

Publications and source records attributed to T. A. Steven.

At least 19 recordsLinked to original sources
USGS1995

Photogeologic map showing distribution of sinkholes south of Fairplay, Park County, Colorado — A possible geologic hazard

A large group of at least 50, and perhaps significantly more, sinkholes partially surrounds Black Mountain 6-10 mi south Fairplay in South Park, Park County, Colorado. The sinkholes occur in bedrock in the evaporite facies of the Middle Pennsylvania Minturn Formation, and in Quaternary soil, alluvium, and glacial outwash gravels that overlie the evaporite beds. Sinkholes range in size from small depressions a few feet across to large holes several hundred feet across. Measured sinkholes range in size from about 25 ft in diameter and 2 ft deep to about 235 ft in diameter and 25 ft deep. In places, several sinkholes have coalesced to form depressions as much as 750 ft long and 400 ft wide. One large cluster of small craters is about 1,8000 ft long and 600 ft wide. As reported to us by a resident rancher, one small sinkhole collapsed about 10 years ago. The area of sinkholes extends into land now under development for residences, and the sinkholes thus pose a potential hazard that needs to be considered in future development. Also, they might jeopardize existing farmland, structures, ans roads (including U.S. Highway 285), as well as projected roads and airstrips. This report is not a comprehensive evaluation of the distribution and origin of the sinkholes; its intent is to call attention to their presence and to encourage further study. Many by not all of the sinkholes were visited; the geologic map is based mainly on the interpretation of aerial photographs by D.R. Shawe.

Colorado↗
USGS1986

Geology and geochemistry of the Deer Trail Pb-Zn-Ag-Cu manto deposits, Marysvale District, west-central Utah

Strata-bound sulphide replacement bodies in the Deer Trail mine are sinuous pipes in carbonate beds, approximately localized by an anticlinal axis, and radiate from a fault across the lower part of the Permian Toroweap formation. Indistinct sericitic envelopes provide a K/Ar age of 14 m.y., correlative with barren, altered volcanic rocks above a hypothesized intrusion, 1 km to the west. Lead and sulphur isotope data imply an igneous source. Inclusion data and deuterium and oxygen isotopes imply a magmatic fluid progressively diluted with meteoric waters. The deposits are the outer zone of a volcanic hydrothermal system. -G.J.N.

Utah↗
USGS1984

Origins and exploration significance of replacement and vein-type alunite deposits in the Marysvale volcanic field, west central Utah

Alunite deposits formed 23 m.y. ago in near-surface, highly oxidizing conditions at the tops of hydrothermal plumes that were spaced at 3- to 4-km intervals around a monzonite stock. The delta 34 S values of 11.5 to 15.4 per mil for replacement alunite along with geologic constraints indicate that sulfate sulfur was derived from underlying Mesozoic evaporites. The delta 34 S values of -15.3 to +5.1 per mil of underlying pyrite, however, indicate that reduced sulfur, necessary to produce low pH during oxidation, either was produced by partial reduction of the evaporite sulfate or came from another source. Vein-type alunite deposits formed 14 m.y. ago as open-space fillings in extension fractures above a concealed stock. Crystals of alunite grew inward from the walls, forming veins of nearly pure alunite as much as 20 m thick. The delta 34 S values near zero per mil indicate that the vein-type alunite sulfur probably had a magmatic source, and it appears that the sulfur may have been present as SO 2 shortly after degassing from the magma. The probable magmatic origin for sulfur in the 14-m.y.-old vein-type alunite and its deposition from vapor-rich fluids, as well as the probable magmatic origin for sulfur in the surrounding base and precious metal deposits, suggest that the underlying stock may host porphyry-type deposits.

Economic Geology↗
USGS1981

Origin and structural implications of upper Miocene rhyolites in Kingston Canyon, Piute County, Utah

Kingston Canyon is one of the deepest antecedent canyons in the High Plateaus subprovince of the Colorado Plateaus. Here the East Fork of the Sevier River flows westward transversely across the gently east tilted Sevier Plateau, which is developed on a basin-range fault block uplifted more than 1,500 m along the Sevier fault zone on the west. Upper Tertiary rhyolites, uncommon in southwestern Utah, occur both on the northern rim and in the bottom of Kingston Canyon. Those on the northern rim consist of lava flows and volcanic domes of the rhyolite of Forshea Mountain, dated by K-Ar methods at 7.6 m.y. old. Those in the bottom of Kingston Canyon, the rhyolite of Phonolite Hill, are especially well exposed and provide spectacular examples of a pyroclastic cone whose base is about at river level and a steep-sided volcanic dome emplaced into and through these deposits. The pyroclastic deposits, formerly 500 or more metres thick, consist of airfall, mudflow, and ash-flow(?) material of rhyolite and foreign lithic fragments, especially olivine basalt. The dome consists of flow-banded, mostly devitrified rhyolite as much as 500 m thick; it has been dated by K-Ar methods at 5.4 m.y. In addition to the rhyolites, a dome and lava-flow complex, the rhyodacite of Dry Lake, occurs near the northern rim and is considered to postdate the rhyolite of Forshea Mountain and predate the rhyolite of Phonolite Hill. The rhyolite of Forshea Mountain was deposited near basin-range faults, before the uplift of the Sevier Plateau and before the cutting of Kingston Canyon. Before uplift, a river flowed across the site of the present Sevier Plateau toward the east-southeast and perhaps also across the Awapa and Aquarius Plateaus to the east. The rhyodacite of Dry Lake was deposited during uplift and perhaps before canyon cutting. During uplift, the river maintained itself and cut Kingston Canyon. The rhyolite of Phonolite Hill was deposited in this canyon, blocking the river flow, which probably formed new outlets to the east. The Awapa and Aquarius Plateaus later were uplifted along faults, disrupting the eastern part of the river segment. The topography then took on its present appearance, and drainage was re-established through Kingston Canyon. There has been little deepening since the reopening of Kingston Canyon.

Utah↗
USGS1981

Integrated uranium system in the Marysvale volcanic field, west-central Utah

Uranium in the Marysvale volcanic field is known to occur in several geologic environments and is thought to occur in others. These known and hypothetical occurrences are of various kinds, ranging in derivation from rhyolite magma, through porphyry-type deposits, hydrothermal vein deposits, dispersed hydrothermal deposits, and, after secondary transport in ground and surface water, roll–front or sedimentary–trap deposits in basin-fill sediments. To date, only the hydrothermal vein environment has been productive, but billions of pounds of uranium were available in all other environments, and if proper conditions existed, significant concentrations probably formed by other processes. The intracaldera fill of the Mount Belknap caldera and sediment-filled basins adjoining the Tushar Mountains are especially favorable exploration targets for the undiscovered uranium believed to exist.

Utah↗