USGS Science⌕ Search

Geology topics

D. R. Shawe

Publications and source records attributed to D. R. Shawe.

At least 19 recordsLinked to original sources
USGS2004

Geologic insights and suggestions on mineral potential based on analyses of geophysical data for the southern Toquima Range, Nye County, Nevada

Aeromagnetic and gravity data provide confirmation of major structural and lithologic units in the southern Toquima Range, Nevada. These units include Cretaceous granite plutons and Tertiary calderas. In addition, the geophysical maps pinpoint numerous faults and lesser intrusions, and they suggest locations of several inferred subsurface intrusions. They also corroborate a system of northwesterly and northeasterly conjugate structures that probably are fundamental to the structural framework of the Toquima Range. A combination of geophysical, geochemical, and geologic data available for the widely mineralized and productive area suggests additional mineral resource potential, especially in and (or) adjacent to the Round Mountain, Jefferson, Manhattan, and Belmont mining districts. Also, evidence for mineral potential exists for areas near the Flower mercury mine south of Mount Jefferson caldera, and in the Bald Mountain Canyon belt of gold-quartz veins in the Manhattan caldera. A few other areas also show potential for mineral resources. The various geologic environments indicated within the map area suggest base- and precious-metal potential in porphyry deposits as well as in quartz-vein and skarn deposits associated with intrusive stocks.

Nevada↗
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

Ages of igneous and hydrothermal events in the Round Mountain and Manhattan gold districts, Nye County, Nevada

About 60 new isotopic age determinations help clarify the geologic history of the Round Mountain and Manhattan gold districts, Nevada. Cretaceous granite of Shoshone Mountain, southeast of Round Mountain, was emplaced about 95 m.y. ago and was domed, metamorphosed, and mineralized with tungsten-bearing quartz veins 80 m.y. ago. The granite of Pipe Spring, south of Manhattan, was emplaced probably at about 80 m.y. ago. Mineralization associated with the Pipe Spring body occurred about 75 m.y. ago. A granodiorite stock and associated rhyolite and andesitc dikes intruded the granite southeast of Round Mountain 36 m.y. ago; apparently base and precious metals mineralization accompanied their intrusion, but mineralization has not been dated isotopically. Ash-flow tuff at Round Mountain was emplaced about 26 m.y. ago, the Manhattan caldera formed about 25 m.y. ago, and gold mineralization at Round Mountain occurred at about 25 m.y. ago. Gold mineralization at Manhattan took place 16 m.y. ago.The isotopic data allow interpretation of the cooling histories of some of the igneous rocks and suggest possible thermal events that reset mineral ages.

Economic Geology↗
USGS1978

Stable isotope studies of bedded barite at East Northumberland Canyon in Toquima Range, central Nevada

Several beds of barite occur in the Slaven Chert at East Northumberland Canyon in the Toquima Range of central Nevada. Most of the barite is internally laminated but shows massive weathering. However, rosette, disseminated, conglomeratic, and concretionary varieties also occur. New fossil evidence from conodonts and brachiopods indicates a Late Devonian age for the Slaven Chert at East Northumberland Canyon. Preliminary δ 34 S values of most disseminated and massive-laminated barite within the Slaven Chert average about 25 permil; these are within the range of values that is typical of sulfate from Late Devonian seawater and are distinctly different from δ 34 S values of most crosscutting hydrothermal barite veins in the area. Primary δ 34 S values of the bedded barite appear to be retained during recrystallization and hydrothermal alteration, suggesting that δ 34 S data of bedded barites could be developed into a useful stratigraphic tool. The δ 34 S values of rosette and concrectionary barites range from 29.1 to 56.3 permil and indicate that these varieties of barite formed in restricted microenvironments where extensive bacterial reduction of seawater sulfate occurred. The δ 18 O data on cherts associated with the barite beds and δ 14 C and δ 18 O data on carbonate beds within the Slaven Chert indicate that the depositional environment at tames had restricted communication with normal seawater of the open ocean.

Nevada↗