Search USGS⌕ Search

Geology topics

Research about Lander County, Nevada

Source-linked reports with geographic coverage including Lander County, Nevada.

At least 19 recordsLinked to original sources
USGS1978

Implications of the petrochemistry of palladium at Iron Canyon, Lander County, Nevada

Approximately one-half of the 270 samples from the Iron Canyon area, Nevada, analyzed for platinum-group metals, contain measurable amounts of palladium in the 0.001- to 0.02-part per million range with an average of 0.0034 ppm. The rocks include lower Paleozoic sedimentary and volcanic rocks, Tertiary granitic porphyries, and breccia, all of which exhibit various degrees of hydrothermal alteration. Fault-related iron oxides and vein quartz are also present. The area lies astride the outermost fringes of the zone of dispersed alteration visible in outcrops around the middle Tertiary porphyry-copper system at Copper Canyon, Nevada. At Iron Canyon, the palladium concentrations greater than 0.003 ppm seem to be spatially related to the Butte fault zone, a north-striking fault system active during the time of porphyry-type mineralization. Palladium contents vary directly with those of mercury, arsenic, strontium, silver, lanthanum, and boron, as well as with lead, gold, and copper in obviously metallized rocks. This relation probably reflects the mobility of palladium during porphyry-type mineralization. However, our study failed to document conclusively the overall introduction of palladium during mineralization. Among the likely sources of palladium are the lower Paleozoic volcanic rocks or fluids equilibrated with magma (s) associated with the middle Tertiary porphyries.

Nevada↗
USGS1971

Ore fluids in the porphyry copper deposit at Copper Canyon, Nevada

The large, low-grade copper and gold deposit at Copper Canyon, Lander County, Nevada, formed in the contact metasomatic environment adjacent to a shallow Tertiary intrusion. Vein and disseminated chalcopyrite-pyrite-pyrrhotite-arsenopyrite mineralization, with lesser amounts of gold, galena, sphalerite, marcasite, and siderite occur in the Upper Cambrian Harmony and Middle Pennsylvanian Battle Formations. Studies of fluid inclusions in stages of vein quartz and in healed fractures through quartz phenocrysts and pebbles reveal the presence of very saline, sometimes CO 2 -rich fluids in the early and middle stages of mineralization. Ore fluid salinities during the base metal mineralization were approximately 40 wt percent, and temperatures were near 375 degrees C. Circulation of this hot brine was apparently restricted to an elongate highly fractured zone within 3,000 feet laterally of the intrusive. Later fluids in this central zone were somewhat cooler, near 300 degrees C, and had significantly lower salinities in the range 12 to 1.2 wt percent. Smaller lode deposits approximately 1 to 5 miles from the intrusion appear to have formed from low to moderate salinity fluids at temperatures generally in the range 250 to 335 degrees C. Geologic and fluid considerations suggest formation at approximately 6,000 feet in depth.

Nevada↗
USGS1970

Geochronology of Tertiary igneous rocks in central Nevada

Potassium-argon dating of Tertiary igneous rocks in Lander County, central Nevada, indicates that igneous activity was episodic and can be separated into three periods. Igneous activity started abruptly about 37 m.y. ago with local extrusion of andesitic to quartz-latitic lava flows and intrusion of hypabyssal rocks of similar composition. This activity ceased about 33 m.y. ago and was followed by extrusion of rhyolite ash-flow sheets that blanketed large parts of the region. These ash-flow sheets range from about 34 to 22 m.y. in age. The final phase, represented by basalt and basaltic-andesite flows and intrusive rhyolite flow-dome complexes, took place about 16 to 10 m.y. ago. Andesitic to dacitic lava and hypabyssal rocks about 35 m.y. old are widespread east of Lander County and rhyolitic ash-flow tuffs 34 to 20 m.y. old are found south and east of Lander County. The younger (16 to 10 m.y.) basalt and basaltic-andesite flows are related to volcanism of the Snake River plain province to the north. The precision of the ages was evaluated by means of: (1) repeat analyses of the same mineral separate, (2) age determination of mineral pairs from the same hand specimen, and (3) age determinations on widely spaced samples from the same geologic body or formation. The last method seems most meaningful from a geologic point of view.

Nevada↗
USGS1970

Fission-track and K-Ar ages of Tertiary ash-flow tuffs, north-central Nevada

Ages obtained from three Tertiary ash-flow tuffs in central Nevada by fission-track and K-Ar dating are concordant. Samples dated by these methods from the same localities give the same age within the limits of analytical uncertainty. Samples of three units from widely separated localities were dated further to confirm the concordance of the dating methods and to establish that ages can be used, in conjunction with normal geologic techniques, as a criteria for correlation. The minerals dated by K-Ar were biotite and sanidine; and sphene zircon and apatite were used to determine the fission track ages. The Bates Mountain Tuff was dated at 24.0 m.y. (F.T.) and 24.0 m.y. (K-Ar). The Fish Creek Mountains Tuff has a fission-track age of 24.4 m.y., and a K-Ar age of 23.9 m.y. The average fission-track age for the Caetano Tuff is 34.9 m.y., and it has an average K-Ar age of 32.3 m.y. The amount of analytical uncertainty is slightly greater in the fission track method. Sampling, preparation, and determination of the age by the fission-track method is competitive with the K-Ar method.

Nevada↗