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Source-linked reports with geographic coverage including Nevada.

At least 1,045 records · Page 58Linked to original sources
USGS1976

Direct dating of mineralization at Goldfield, Nevada, by potassium-argon and fission-track methods

Potassium-argon dating of hypogene alunite and K-mica from hydrothermally altered rocks at Goldfield, Nevada, yields mineralization ages of 20 to 21 m.y., in good agreement with a mineralization age established by potassium-argon dating of unaltered premineralization and postmineralization volcanic units. Premineralization volcanic units that are pervasively propylitized cannot be dated by the potassium-argon method but yield zircon fission-track ages, and in several cases yield concordant apatite fission-track ages. Two samples from premineralization units yield apatite ages concordant with the age of mineralization established by potassium-argon geochronometry, reflecting annealing of the apatite during the hydrothermal episode.Potassium-argon dating of supergene alunite samples yields imprecise ages in the range 9 to 12 m.y. that probably record the first exposure of their hydrothermally altered host rocks to oxidizing conditions. Potassium-argon dating of postmineralization basalts and silicic tuffs interbedded with conglomerates bearing altered rock clasts shows that the altered area was eroded nearly to present topographic levels by 11 m.y. ago, at which time it was covered by basalt flows now represented only by scattered remnants. Apatites from premineralization volcanic units give fission-track ages of 20 m.y. or more, indicating that no significant thermal event has affected altered rocks at Goldfield since mineralization took place.

Nevada↗
USGS1976

Schlumberger soundings near Fallon, Nevada

In 1976, the U.S. Geological Survey, in cooperation with the Nevada Division of Water Resources, made thirty one Schlumberger resistivity soundings near the city of Fallon, Nevada. The survey was made to estimate and delineate the volume of fill containing fresh ground water and to map the lateral extent and thickness of basalt layers which act as the principle aquifer in the area.

Nevada↗
USGS1976

Chemical analyses of 183 rocks from the Modoc mine area, Lander County, Nevada

This report presents analytical data for 183 rock samples from the Modoc mine area and a statistical treatment of the data. The Modoc mine area is located in the southwestern part of the Antler Peak quadrangle, between Willow Creek and Rocky Canyon, Lander County, Nev. (fig. 1). The area we studied is centered on a small middle Tertiary pluton, cropping out across an area of less than 0.1 km 2 , which intrudes sandstone, quartzite, shale, limestone, and chert of the Pennsylvanian and Lower Permian Havallah Formation (fig. 2). Detailed descriptions of the geology and geochemistry of the porphyry-copper environment of the general area are given by Roberts (1964), Roberts and Arnold (1965), Nash and Theodore (1971), Theodore, Silberman, and Blake (1973), and Theodore and Blake (1975). Theodore, Silverman, and Blake (1973) determined ages of 41 and 39 m.y. by the K-Ar method on mineral separates of magmatic hornblende and biotite, respectively, from the pluton of the Modoc mine area. Gold mineralization in the immediate area was apparently first discovered in 1925, and the property has been worked intermittently since that time; mineral rights are presently held by Charles L. Caldwell of Battle Mountain, Nev. The major underground workings explore two steeply dipping and parallel shear zones that strike approx-imately N. 25° W. These zones are up to 1 m wide and contain steeply plunging shoots of high concentrations of precious metals. Little is known about the production from the area, but it appears that only a few thousand dollars in gold and small amounts of silver may have been produced. Gold was found in narrow quartz veinlets near the surface of the pluton, and sulfides were encountered at a depth of about 10 m. Assays indicate that the sulfide-rich rock contains gold and silver. Trace amounts of secondary copper minerals occur in both the underground workings and on the surface. Samples collected away from the two major veins also yielded anomalous gold concentrations.

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USGS1976

A preliminary evaluation of the chemical character of water near the northwest shore of Topaz Lake, Douglas County, Nevada

The potential for intensive development of land in the study area has raised concern regarding the possible effect of septic-tank effluents on the quality of local ground waters and the lake. Analyses of samples from 13 wells, one spring, the lake, and an inflowing creek were examined for trends in chemical composition. Sampled ground waters from sites upgradient in the hydrologic system have higher concentrations of sulfate and dissolved solids than ground waters near the creek and the lake. Preliminary data suggest that the ground-water reservoir in downgradient areas is locally recharged by the creek and perhaps by the lake. Additional data on both ground-water levels and quality would be required to further define the hydrologic system.

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USGS1976

Miscellaneous hydrologic data collected during a reconnaissance of streamflow and fluvial sediment transport, Incline Village area, Lake Tahoe Basin, Nevada, 1970-73

This report presents hydrologic data collected during water years 1970-73. The data include instantaneous measurements of water discharge, temperature, and specific conductance, as well as measurements of sediment concentration, load, and particle-size distribution. The data are supplemental to material included in three previously published progress reports, and include all unpublished information collected during the study period. The report also includes similar types of data collected from Secret and North Canyon Creeks, which are tributary to Lake Tahoe but S to 10 miles southeast of the study area.

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