By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Pershing County, created in 1919, is the youngest of the 17 counties of Nevada.
The topography of the county, although less rugged than in most of the State, is typical of that of the Great Basin and consists of north-trending mountain ranges separated by dry valleys.
Pershing County has a wide variety of mineral resources, but silver, gold, tungsten, and mercury have been the mainstays. Mining activity in the area now embraced by Pershing County began in 1860 in the Humboldt district. Soon afterward the Star and Buena Vista districts were discovered, and the town of Unionville became the center of mining activity in the county. The first successful smelter in the State was built at Oreana to treat the base-metal ores.
Gold placer deposits were discovered in 1881 in American Canyon, Spring Valley, and Dry Gulch, and these were worked successfully for about 10 years. Discoveries at Seven Troughs and Rochester highlight the mining in the county after 1900 (Vanderburg, 1936b, p. 6).
Production from Pershing County is recorded from 1919, when the county was created. Production of individual districts, in the descriptions that follow, includes the years before Pershing County existed, thus there is a considerable discrepancy between district and county totals.
From 1919 through 1958 Pershing County produced 16,233 ounces of placer gold and 162,109 ounces of lode gold, a total of 178,342 ounces.
The Humboldt (Imlay, Eldorado) district, on the north end and west flank of the Humboldt Range, was organized in 1860 as the first district in the area now included in Pershing County. By 1863, Humboldt City had been founded and had a population of 500. The principal mine was the Imlay, from which a considerable but unknown amount of silver ore was shipped.
The Star Peak mine yielded $130,000 in silver and gold up to 1935 (Vanderburg, 1936b, p. 17). Early production data for the entire district are lacking, but from 1932 through 1959 the district produced 35,483 ounces of gold.
The deposit at the Imlay mine consists of a gold-and silver-bearing quartz vein that contains a little lead and copper (Vanderburg, 1936b, p. 16). The country rock is shale, quartzite, and limestone, probably Triassic in age. Ransome (1909a, p. 46) stated that the ores of the northern Humboldt Range, called the Star Peak Range, have several common characteristics - they occur in Triassic rocks; they seem to have a common age, probably Early Cretaceous; and they contain antimony, more silver than gold, and very little lead or zinc.
In the Rochester district, in the central Humboldt Range 9 miles east of Oreana, activity began in the 1860's during the intensive search for silver in the Star Peak Range. The placers in nearby Limerick and American Canyons yielded $11 million in gold (Ransome, 1909a, p. 12). There was no great lode production until 1912, when the rich silver-gold ores on Nenzel Hill were discovered.
For the ensuing 16 years, production remained at a high level. In 1929, the Rochester Silver Corp., the principal operator, closed down, and activity remained at a low level through 1959.
The following summary of the geology and ore deposits of the Rochester district is from a more detailed account by Knopf (1924, p. 9-58).
The oldest rocks in the district are felsitic trachytes and keratophyres 5,000 feet thick, composing the Rochester Trachyte, of Triassic age. Overlying this is a sequence of rhyolite flows also of Triassic age. Downfaulted limestone beds of Triassic age are found in the western part of the district. Intrusive into the Triassic rocks are large masses of aplite of probable Late Jurassic age.
Coarse, angular detritus of possible Pliocene age, capped by basalt of late Pliocene age, occurs locally on the flanks of the Humboldt Range.
At the end of Jurassic time, the Triassic rocks were folded into a broad north-trending anticline. This was accompanied by reverse faulting. A later period of faulting occurred at the end of the Pliocene.
Mineralization occurred in Late Jurassic time and was associated with the intrusion of the igneous masses. All ore deposits are in the Triassic rocks; they consist of silver-bearing quartz veins, silver-bearing stockworks, and gold veins (of minor importance). The silver veins, enriched by supergene argentite, have been the most productive deposits.f
RYE PATCH DISTRICT
The Rye Patch (Echo) district is on the west flank of the Humboldt Range in central Pershing County, 4 miles east of Rye Patch.
Mining in the district began in 1864 in the principal mine, the Rye Patch. To 1874, this mine produced about $1 million chiefly in silver (Vanderburg, 1936b, p. 33). Presumably no gold was produced in the early days, but in 1935 intensive development was in progress at the Gold Standard property to test the possibility of mining large tonnages of low-grade gold ore.
The development apparently was moderately successful because during 1935-59, a total of 9,453 ounces of gold was produced.
The deposit at the Rye Patch mine is in black limestone, the basal unit of the Star Peak Formation, of Middle Triassic age (Lincoln, 1923, p. 204). Several irregular fissures filled with brecciated wall-rock, quartz, and calcite cut the limestone. The ore minerals, which are associated with the quartz in these fissures, consist of argentiferous tetrahedrite, galena, sphalerite, and small amounts of gold.
SEVEN TROUGHS DISTRICT
Located on the west slope of the Seven Troughs Range 30 miles west of Lovelock, the Seven Troughs district is primarily a gold-producing district, but the ores also contain considerable silver. Its first acclaim came in 1907 when the Mazuma Hills mine was opened.
Although the district never achieved a bonanza output, it maintained a small, but fairly steady gold production which from 1908 through 1959 totaled 160,182 ounces.
The following summary of the geology is based on Ransome (1909a, p. 16-25). The oldest rocks in the area are Jurassic (?) slates which were intruded by a mass of granodiorite. Overlying the slates are mica andesite, basalt, and rhyolite of Tertiary age. The ore deposits are in breccia zones or fissures in the extrusive rocks.
Veins are narrow and contain friable quartz and shattered country rock. Gold, in small particles or clusters of grains, is the valuable constituent. Some silver is alloyed with the gold.
The Sierra (Dun Glen, Chafey) district, at the north end of the East Range in the northeast part of T. 33 N., R. 36 E., was founded in 1863 when lode gold and placer gold were discovered in the area. Some of the important lode mines were the Tallulah, Auld Lang Syne, Munroe, Mayflower, and Auburn (Vanderburg, 1936b, p. 39).
The placers were very productive during the early days. Vanderburg (1936a, p. 156) estimated that $4 million worth of placer gold was mined during the 1880's and 1890's from Auburn, Barber, Wright, and Rock Hill Canyons. Most of this output was by Chinese operators, who habitually neglected to report any production; therefore, the estimate prob\ably is not very accurate. Placer mining in recent years has been on a small scale.
Vanderburg (1936b, p. 39) estimated $1 million, mostly in gold, as total lode production for the district. Most of this was mined between 1862 and 1880. From 1908 to 1921 gold production was valued at $314,441. In recent years, however, activity slackened considerably. Total gold production through 1959, including the early placer output, was about 241,000 ounces.
The rocks in the Sierra district dip steeply and consist of the Star Peak Formation of Triassic age, dark slates of Jurassic age, and a thick series of andesitic flows and flow breccias (Ransome, 1909a, p. 50-51). Diabase dikes cut the sedimentary and the extrusive rocks. Ore deposits are in veins, many of which follow the diabase dikes in the volcanics. Vein minerals are quartz, galena, pyrite, sphalerite, and native gold.
SPRING VALLEY DISTRICT
The Spring Valley district is on the east slope of the Humboldt Range, 14 miles east of Oreana.
The gold production has come chiefly from placer deposits. The only productive lode mine was the Bonanza King located in 1868 (Vanderburg, 1936b, p. 42). It produced at most only a few thousand ounces of gold. The placer deposits in American and Limerick Canyons and in Spring Valley were the most productive in the State.
Before 1900, a total of $11 million in gold was extracted from these gravels, mostly by the Chinese who operated the placers after the Americans skimmed off the more accessible deposits (Ransome, 1909a, p. 12). Periodically through the later years there was small-scale activity, but only 255 ounces was produced from 1932 through 1959.