Goldfield Mining District, Esmeralda County, Nevada, USAi

Regional Level Types
Goldfield Mining District	Mining District
Esmeralda County	County
Nevada	State
USA	Country

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Structure: The N-S-trending Columbia Mountain Fault, with left lateral offsets at intersections with E-W-trending faults (800–900 feet of offset). Tertiary deposits, domed and faulted post Miocene: steeply dipping N-S and E-W faults

Alteration: silicification, hydrothermal; oxidation

Tectonics: Volcanic center, Basin and Range

Commodity: Commodity Info: Some early ore averaged $6000 to $7000 per ton in gold values. Ore Materials: pyrite, bismuthinite, goldfieldite, native gold, native silver (rare) Gangue Materials: quartz, alunite, barite, gypsum, limonite, kaolinite, and sulfide minerals

Deposit: The majority of Goldfield's historic production was derived from a small number of numerous silicified, sublinear fissures, or ledges, within a 100+ km² area of altered Miocene volcanic and pre-Tertiary rocks.

Ledges that contain the most ore consist of microcrystalline quartz that replaced andesites and rhyolites, and internal breccias with multiple generations of clasts encrusted and replaced by gold, pyrite, and a large number of Cu-As-Sb-Au-Ag-Bi-Sn-Te-Se minerals (e.g., enargite-luzonite, famatinite, goldfieldite, bismuthinite, and calaverite), minor sphalerite, galena, and chalcopyrite, alunite, kaolinite, dickite, and pyrophyllite.

Ledges are flanked by broad selvages of altered andesite consisting of proximal to distal quartz+alunite+kaolinite+pyrite, quartz+kaolinite+K-mica+pyrite, montmorillonite+pyrite, and calcite+chlorite, respectively.

More than 95% of the district's production came from a small area, the "main district", near the town of Goldfield.

Prominent lithologies in the district are Miocene rhyolites, latites and andesites, which overlie Mesozoic and Paleozoic granitic and sedimentary rocks. Most production came from silicified, sublinear fissures, or ledges, in Milltown Andesite and porphyritic andesite (dacite of Ransome, 1909; porphyritic rhyodacite of Ashley, 1974).

Ledges commonly consist of en echelon segments that form a broadly elliptical pattern in the district. Contiguous ledge segments are generally meters to tens of meters in length by meters in width.

The abundance of ledges coupled with coalescing alteration selvages resulted in a very large volume (tens of km3) of altered rocks in the district. Extremely rich Ore shoots show concentric banding.

Deposit type: Epithermal quartz-alunite Au

Development: Gold was discovered at Goldfield in 1902, its year of incorporation.

The first claims at Goldfield were staked by Billy Marsh and Harry Stimler late in 1902 on Columbia Mountain, 30 miles (ca. 48 km) due south of Tonopah.

By early in 1903 a tent camp had formed on the claim, and in October 1903 the Goldfield Townsite Company plotted the new town about halfway between the mines at Columbia Mountain and Malpais Mesa to the west.

By 1904 the Goldfield district produced about 800 tons of ore, valued at $2,300,000, 30% of the state's production that year.

Goldfield experienced very rapid growth; by 1906 more than 150 buildings were going up monthly, and the town had a population of over 15,000.

Goldfield reached a peak population of about 30,000 people in 1906 and in 1907 became the county seat.

Despite a miners' strike and a nation-wide financial panic in 1907, Goldfield continued to produce gold ore, and by 1908 Goldfield was Nevada's largest city with a population of more than 20,000 people.

The mines continued to do well, with a peak production of $11 million attained in 1910.

In 1913 heavy rains resulted in flash floods sweeping through Goldfield, and in 1923 a fire wiped out 53 square blocks of the city. These events combined with low metal prices resulted in mine closures and the gradual decline of the once great city.

Geology: Principal structure: Columbia Mt Fault, N-S, with left lateral offsets at intersections with E-W faults (800-900 ft offset) ore found at W turns of main fault (N 20 deg W). Lake deposits (Siebert Formation) 1000' thick. El Dorado siliceous shale, limestone. Malpais basalt. Rhyolite, dacite, andesite (post lacustrine). Pre-lacustrine volcanic rocks host the veins.

Abstract for Vikre et al. poster (2005): the purpose of this investigation was to determine if 40Ar/39Ar ages, chemical compositions and stable isotope compositions of magmatic hydrothermal alunites throughout the Goldfield district are useful in distinguishing mineralized ledges. Although alunites differ in age and composition, no single characteristic uniquely separates alunites in mineralized ledges in the main district from those associated with no known mineralization. However, mineralized ledge alunites are ~20.3 to 19.8 Ma, and have relatively homogeneous K/Na/Ca compositions, whereas alunites from smaller deposits and unmineralized ledges may be older or younger, and have more variable K/Na/Ca compositions. In addition, disequilibrium sulfur isotope (alunite-pyrite) temperatures at Preble Mountain contrast with sulfur isotope temperatures in main district mineralized ledges that are broadly similar to fluid inclusion homogenization temperatures.

Ore(s): Most ore was found in topographically prominent silicified zones. Mineralization was genetically related to the collapsed caldera rim of a volcanic center. Some ore was concentrated at offsets along the Columbia Mt fault.

Fossils

There are 1 fossil localities from the PaleoBioDB database within this region.

BETA TEST - These data are provided on an experimental basis and are taken from external databases. Mindat.org has no control currently over the accuracy of these data.

Occurrences	8
Youngest Fossil Listed	516 Ma (Cambrian)
Oldest Fossil Listed	530 Ma (Cambrian)
Stratigraphic Units	Unit No. Occurrences Age Poleta 8 516 - 513 Ma (Cambrian)
Fossils from Region	Click here to show the list.
Accepted Name Hierarchy Age Porifera phylum Animalia : Porifera 530 - 516 Ma Cambrian Archaeocyathida order Animalia : Porifera : Irregulares : Archaeocyathida 530 - 516 Ma Cambrian Archaeotrypa genus Animalia : Cnidaria : Anthozoa : Archaeotrypa 530 - 516 Ma Cambrian Epiphyton genus Plantae : Rhodophyta : Epiphytaceae : Epiphyton 530 - 516 Ma Cambrian Renalcis genus Bacteria : Cyanobacteria : Renalcis 530 - 516 Ma Cambrian Algae informal Algae 530 - 516 Ma Cambrian
Fossil Localities	Click to show 1 fossil locality

Other Databases

Link to USGS MRDS:	10310328

Mindat Articles

Goldfield-- Short but Sweet! by Nathalie Brandes

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References