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At least 1,099 records · Page 61Linked to original sources
USGS1974

Stratigraphic evidence on the age of the Roberts Mountains thrust, Eureka and White Pine Counties, Nevada

Several stratigraphic discontinuities in Devonian and Mississippian sedimentary sequences in folded thrust plates east of the Roberts Mountains thrust of central Nevada indicate that the thrust was sporadically active during this interval. From estimates for displacement and time involved for the thrust, the average rate of movement was 1 cm/5 yr, which is comparable to current concepts of the rate of orogenic movements. A further extrapolation of this rate to the longer period during which orogenies have been recognized in the Great Basin suggests total horizontal shortening of 400 to 500 mi (640-800 km).

Nevada↗
USGS1974

Folds and overthrusts of late Jurassic or early Cretaceous age in northern Nevada

The partly isoclinal, partly overturned Adobe syncline extends for at least 75 mi northeastward across the northern Cortez Mountains, the northern Pinon Range, and along the entire length of the Adobe Range. The folded rocks range in age from Ordovician through Jurassic and may include some rocks of Cretaceous age. This syncline is flanked by anticlines in the central and southern parts of the Pinon Range and in the southern Independence Mountains. In places the Adobe syncline is discordantly overlain by nearly flat-lying thrust plates composed of Ordovician, Devonian, Mississippian, and Permian rocks. The geometric relations indicate that these thrust plates moved at least 6 mi, but postfold thrust movement was not great, because the Mississippian and Permian rocks of the thrust plates closely resemble correlative autochthonous rocks nearby. The Ordovician and Devonian rocks have been thrust to their present position in at least two stages; the earlier movement or movements took place long before folding of the Adobe syncline and the later movement immediately afterward. The folding and last stage of thrusting were in Late Jurassic or Early Cretaceous time.

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USGS1974

Stratigraphy, structure, and geologic history of the Lunar Lake Caldera of northern Nye County, Nevada

The Lunar Lake caldera is in northern Nye County, Nev., about 70 mi (110 km) east-northeast of Tonopah. It is the youngest caldera in the central Nevada multiple-caldron complex and the source of the tuff of Lunar Cuesta, a multiple-flow simple cooling unit of quarts latitic welded tuff that is about 25 m.y. old. The tuff was distributed over an area of nearly 3,000 mi 2 (7,770 km 2 ) and has a volume of approximately 90 mi 3 (375 km 3 ). The Lunar Lake caldera is the site of the Lunar Crater basalt field which contains basalts of Pleistocene and probably Holocene age. These basalts were fed from northeast-trending fissures that had much earlier served as vents for ash-flow tuffs and lavas, possibly including the tuff of Lunar Cuesta.

Nevada↗
USGS1973

Gold-bearing arsenian pyrite determined by microprobe analysis, Cortez and Carlin Gold Mines, Nevada

Studies of polished sections and chemical analyses made by electron microprobe show that gold and arsenic in the unoxidized ores from the Cortez and Carlin mines are most abundant in pyrite. Gold, as particles too small to be seen under the microscope, along with arsenic is concentrated in tiny pyrite grains (<0.005 mm) and in thin rims of larger pyrite grains. It is concentrated also in arsenopyrite which is sparsely distributed in the Cortez ore. Traces of gold are contained in sphalerite and chalcopyrite sparsely disseminated in Carlin ore. Mercury and antimony occur also in the pyrite, and antimony is in illite as well. Little if any gold or arsenic is contained in quartz, carbonate, clay, and carbonaceous material. In oxidized ore, the sulfur and carbonaceous material have been removed and gold and arsenic occur in iron oxide pseudomorphs after pyrite. Gold can be seen in the oxidized ore, indicating that it has been mobilized and concentrated. No association was found between gold and the carbonaceous material. During mineralization, calcite was removed from the fractured silty carbonate of the Roberts Mountains Formation, creating micropore space in which pyrite, quartz, and illite were deposited. The average tenor of the pyrite, if all the gold were in the pyrite, would be 0.10 percent at Cortez and 0.14 percent at Carlin. These calculated values are similar to the analytical values. The calculated tenor of the carbonaceous material, however-if such material were considered to be the mineral host of the gold-would be 0.28 percent at Cortez and 1 percent at Carlin. These figures are unreasonable when compared with the analytical data, which show that the carbonaceous material contains no detectable amounts of gold. © 1973 Society of Economic Geologists, Inc.

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