By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Nye County, founded in 1864, comprises more than 17,000 square miles in south-central Nevada and is studded with north-trending mountain ranges. The intermontane valleys are not drained, and streams terminate in sinks or salt-encrusted flats.
Sedimentary rocks of Paleozoic and Mesozoic ages are exposed in the mountains in the north; in the western ranges only Mesozoic formations are exposed. In the eastern and central parts of the county, the mountains are composed chiefly of Paleozoic rocks. Masses of granitic rocks of Jurassic and Cretaceous ages have intruded the older rocks and are exposed over large areas. Tertiary lava flows and intrusive rocks are abundant in the southern part of the county.
The most important mineral commodities of the county have been the precious metals. Some of the more successful gold districts are Bullfrog, Tonopah, Round Mountain, and Tybo, where gold and silver-bearing veins occur in Tertiary rocks. Another highly productive district is the Manhattan, where the highest yields were from veins in Paleozoic rocks.
Gold production for the county from 1903 through 1959 was 2,975,034 ounces - 298,593 ounces was from placers and 2,676,441 ounces was from lode mines.
The Bruner (Phomolite) district is in northwestern Nye County at lat 39"05' N. and long 117"46' E.
The district was founded in 1906 when small production was reported from the Paymaster mine. In 1936 the Penelas mine, the main producer of the district, was discovered (Krai, 1951, p. 26).
Production of gold from the district from 1936 through 1959 was 17,213 ounces. Earlier production could not be ascertained.
Tertiary rhyolite and andesites cover the area (Krai, 1951, p. 26). Metavolcanic rocks probably underlie the extrusives. The ore deposits are in quartz veins in the younger volcanic rocks with free gold associated with silver.
The Bullfrog district is in southern Nye County, 60 miles south-southeast of Goldfield. The principal town is Beatty.
The original claims were located in 1904; the customary rush ensued during which the settlements of Bullfrog, Bonanza, Beatty, and Rhyolite mushroomed and competed with one another for new settlers. Competition became so intense that three railroads served the area. The peak period was 1907-10 when $1,687,792 in gold and silver was produced (Krai, 1951, p. 29), mostly from the Montgomery-Shoshone mine.
In more recent years activity declined to sporadic small-scale mining. Gold production from 1905 to 1959 was 120,401 ounces, and considerable silver has also been produced.
Ransome, Emmons, and Garrey (1910) described the geology and ore deposits in considerable detail. The oldest rocks in the district are contorted quartzites and mica schists of Ordovician age or older, and they are overlain locally by limestone, shale, and quartzite of Silurian age. Overlying the Paleozoic rocks is a sequence of Tertiary flows and tuffs, 6,000 feet thick, composed of 16 rhyolite units, five flows of basalt, one flow of quartz latite, and one flow of quartz-bearing basalt that caps the sequence.
The entire area has been broken by normal faults that trend north to northwest, and the resulting fault blocks are tilted eastward. A late set of faults trends northeast. Ore deposits are mineralized faults or fault zones in the rhyolites.
Many of the veins are simple but there are many zones of stringers or veinlets with ill-defined boundaries. The vein material consists of quartz and calcite and finely divided auriferous pyrite. The quartz is crustified and has a porcelaneous texture. Oxidized ore contains gold in limonite; the calcite is partly dissolved, and manganese oxide has been introduced. Varying amounts of silver may be alloyed with the gold.
The Ellendale district is a few miles east of Tono-pah, in T. 2 N., R. 43 E. High-grade gold ore was discovered in 1909, and for the next few years the district flourished but by 1916 was deserted (Ferguson, 1917, p. 122). According to Krai (1951, p. 56), the only later activity was in 1938-39, when dump material valued at $7,215 was shipped from the Ellendale mine, the only mine of any importance in the district.
Total recorded production of gold to 1948 was $166,015 (about 8,060 ounces), but estimates put the total production at between $1/2 and $1 million (Krai, 1951, p. 55). Because much production by lessees was not reported, the true production of the district must be in excess of 8,000 ounces.
Ferguson (1917, p. 123) noted that most of the deposits are in rhyolite near its contact with andesite porphyry. The ore bodies are in irregular veins filled with iron-stained quartz.
GOLD HILL DISTRICT
The Gold Hill district is 6 miles north of Round Mountain, in the southern Toquima Range, in T. 11 N., R. 44 E. It is mentioned only briefly in the published literature. Ferguson and Cathcart (1954) noted that the major production of the district was in 1931-32, when 24,725 ounces of gold was mined. The district was dormant from 1933 through 1959. According to Couch and Carpenter (1943, p. 120), the total value of production of the district was $902,152, but how much of this was in gold is not known.
The major production came from a single quartz vein in rhyolite (Ferguson and Cathcart, 1954). The veinfilling is fine-grained banded quartz that contains some calcite, small particles of free gold, auriferous pyrite, and argentite.
The Jackson (Gold Park) district is on the west slope of the Shoshone Mountains in northwestern Nye County (lat 39"7' W., long 117"33' E.). Originally called the North Union district, the name was changed in 1878 to Jackson. Early production data are fragmentary, but Krai (1951, p. 76) estimated an output of $V2 to $1 million, principally in gold. There has been little activity in the area since 1911.
The oldest rock in the area is meta-andesite of Carboniferous (?) age which is overlain by Tertiary rhyolite tuff (Krai, 1951, p. 76). Ore occurs in quartz veins that cut the meta-andesite. Variable amounts of galena and pyrite and small amounts of chalcopyrite are present.
JEFFERSON CANYON DISTRICT
The Jefferson Canyon district is 6 miles northeast of Round Mountain (lat 38"43' N., long 117" E.) on the west slope of the Toquima Range.
Gold and silver were discovered here in 1866, but no activity was reported until 1871. The principal mines were the Jefferson and the Prussian. Lincoln (1923, p. 171) reported the early production of combined silver and gold at $1 million; the amount of gold represented by this figure is not given. In the past several decades there has been only sporadic activity in this district. Only 3 ounces of gold was produced from 1932 through 1959.
The country rock consists of Ordovician limestone, Cretaceous granite, and Tertiary rhyolite porphyry (Krai, 1951, p. 80-81). The Prussian vein, the principal vein in the district, is along the contact of the limestone and porphyry. Silver minerals - sulfides, sulfantimonides, and chlorides - are the most valuable constituents of the Prussian vein; however, gold is the important component in many other veins.
The Johnnie district is in the extreme southeast part of Nye County (lat 36"26' N., long 116"04' E.).
Organized in 1890, the district had a recorded production of $382,681 by 1913, although Krai (1951, p. 86) estimated that more than $1 million in ore was produced from 1910 through 1913. Nolan (1936b, p. 69) estimated $500,000 worth of gold was produced before 1904, and 24,653 ounces of gold was produced during 1908-32. Total gold production through 1959 was about 40,000 ounces, mostly from the Johnnie mine.
The bedrock is the Prospect Mountain Quartzite of Cambrian age (Krai, 1951, p. 86-87). The beds are predominantly quartzite, but some conglomerate, shale, and limestone units are also present. Well-defined gold-bearing quartz veins cut these sedimentary rocks. Gold and galena are the chief economic minerals.
The Lodi (Granite, Marble, Quartz Mountains) district is in northwest Nye County (T. 13 W., R. 36 E.). In 1863 the area was part of the original Mammoth district, but in 1874, the Lodi district was formed from the part of the Mammoth that included the Lodi Hills.
Gold is a byproduct of silver and lead ores which have been the mainstay of the district. Tungsten and some talc also have been produced. The most important mines in the district are the Illinois and the San Rafael (Krai, 1951, p. 94-96).
Available production data are not complete and give combined output only; therefore, the amount of gold represented can only be inferred. Couch and Carpenter (1943, p. 113) reported a total of $809,905 in silver, gold, lead, and copper from 1866 through 1940. The total for 1932 through 1959 was 1,079 ounces of gold (U.S. Bureau of Mines, 1933-66).
Krai (1951, p. 93-94) briefly summarized the geology of the district. The rocks of the district are deformed limestone and dolomite of Triassic age intruded by granodiorite of Jurassic or Cretaceous age. The major ore deposits of lead and silver were deposited in the deformed and ruptured limestone and dolomite during the closing stages of the intrusion.
In Tertiary time, lava flows covered the area. These were succeeded by andesite intrusions after which considerable faulting took place. A second period of mineralization filled the fault fissures.
Manhattan, at the south end of the Toquima Range about 35 miles north of Tonopah, is a gold district, silver being produced as a byproduct. Although mining had been done in the Toquima Range since 1865, it was not until 1905 that gold was found in the Manhattan area in sufficient quantity and grade to precipitate a rush. By 1906 there were 3,000 people in the general area (Ferguson, 1924, p. 8).
The next few years were marked by numerous fraudulent promotion schemes that gave the district widespread notoriety and seriously delayed its development. But placer mining flourished and reached its peak by 1912, after which there was a steady annual decline (Ferguson, 1924, p. 8-9). Lode mining became important after 1908.
From 1906 through 1921 the district produced 136,514 ounces of lode gold and 58,686 ounces of placer gold (Ferguson, 1924, p. 9) ; through 1959, the total was 280,022 ounces of lode gold and 206,340 ounces of placer gold.
The bedrock of the district is composed of quartzite, limestone, and schist of the Gold Hill Formation of Cambrian age and chert, slate, quartzite, and limestone of the Palmetto Formation of Ordovician age (Ferguson and Cathcart, 1954). Small patches of granite, of Jurassic age, are exposed locally. Tertiary lavas, tuffs, and intrusive bodies comprise the bedrock in the northern part of the district.
The Gold Hill Formation is thrust over the Palmetto Formation, and the productive deposits are in the hanging wall of this thrust fault, in limestones and quartzose schist of the Gold Hill Formation.
The ore bodies in the limestone show a complex assemblage of metals, including pyrite, stibnite, realgar, orpiment, cinnabar, and free gold in a gangue of calcite, quartz, fluorite, sericite, leverrier-ite, and sparse adularia. Ore bodies in the quartzose schist have been more productive and consist of networks of small quartz-adularia veins, carrying pyrite and free gold.
The placer gold has come from deep gravels in Manhattan Gulch.
The Northumberland district on on the east side of Toquima Range, 25 miles north of Belmont and 76 miles northeast of Tonopah. It is primarily a silver-producing district and was founded in 1866. By 1891 activity had ceased, and the district was dormant until 1936 when large deposits of low-grade gold ore, amenable to open pit mining, were discovered (Krai, 1951, p. 135-136).
During 1939-42, gold totaling 32,756 ounces was mined. The War Production Board Order L-208 of 1942 caused operations to be recessed until after World War II. Total gold production from 1936 through 1959 was 35,353 ounces.
The rocks consist of dolomitic limestone and carbonaceous and calcareous shale (Krai, 1951, p. 136). A mass of monzonite and a younger porphyritic rhyolite or quartz latite intruded the sediments. The gold deposits occur in a carbonaceous shale bed, 60 to 70 feet thick, in the vicinity of the roof of the monzonite intrusion.
ROUND MOUNTAIN DISTRICT
The Round Mountain district is on the west flank of the Toquima Range, 45 miles north of Tonopah and about 8 miles north of Manhattan.
Rich gold ore was discovered in 1906, but no production was recorded until 1907. Both placer and lode mines were worked from the beginning. The lodes were worked until 1935, but the placers were still being worked, on a fairly large scale, in the early 1950's by the Round Mountain Gold Dredging Corp. Their operations were suspended during 1953-57, but were resumed in 1958; in 1958-59 this company was the largest gold producer in Nevada.
Ferguson and Cathcart (1954) estimated the total gold production of the district to be worth $8 million, of which about 15 or 20 percent was from placers and the remainder was from lodes. This would amount to about 329,000 ounces of lode gold and 58,200 ounces of placer gold.
Most of the district's production during 1950-59 was combined with reports from other districts, but it was probably about 150,000 ounces. Total gold production for the district through 1959 was about 537,000 ounces.
The oldest rocks in the area are lower Paleozoic limestone, jasper, and dark slaty schist (Ferguson, 1922, p. 386-398). These rocks are intensely folded and were intruded during Cretaceous time by bodies of granitic magma. Tertiary rocks, chiefly porphyritic rhyolite (Oddie Rhyolite) and lake beds of the Siebert Formation, overlie the folded Paleozoic rocks.
There were two periods of mineralization. The first occurred just after the granitic intrusions and is characterized by huebnerite-bearing veins in the granite. The second period of mineralization is of Tertiary age and resulted in the formation of epithermal gold-bearing quartz veins in the rhyolite. The mineralogy of these veins is relatively simple and consists of gold, auriferous pyrite, and sparse realgar in a gangue of drusy and comb quartz, adularia, and alunite.
After the primary gold mineralization, additional fissures were formed in which iron and manganese oxides and gold were deposited by supergene solutions. The gold in these later fractures was probably derived from the primary auriferous pyrite.
This district is in the southern San Antonio Mountains near Tonopah, the county seat of Nye County and the largest town in the county.
Tonopah was predominantly a silver district, but it also yielded large amounts of gold. The first claims were staked in 1900, and by 1901 there was vigorous activity which lasted until the late 1940's; thereafter, production declined. The principal companies were the Tonopah Mining, the Tonopah Belmont Development, and the Tonopah Extension (Krai, 1951, p. 171).
Lincoln (1923, p. 186) listed the gold production of Tonopah from 1901 through 1921 as $30,360,903 (about 1,473,830 ounces). From 1901 through 1959, a total of 1,880,000 ounces of gold was produced.
The rocks exposed in the Tonopah district are all of Tertiary age and consist of a series of lava flows, volcanic breccias, tuffs, and intrusives that have been somewhat displaced from their original attitudes by extensive faulting.
Seven formations recognized in the district (Nolan, 1935b, p. 13) are, from oldest to youngest: the Tonopah Formation (volcanic tuffs, breccias, flows), Sandgrass Andesite (dark lavas interlayered with the Tonopah Formation), Mizpah Trachyte (2,000-foot-thick flows and breccias overlying the Tonopah), Extension Breccia (tabular intrusive mass in west half of district), West End Rhyolite (sills as much as 600 feet thick that intrude the older formations), Fraction Breccia Member of Esmeralda Formation (volcanic breccia unconformably overlying ore bodies), and postore rhyolite (dikes and lenticular bodies that intrude the older rocks).
Numerous faults cut the Tertiary rocks, and Nolan (1935b, p. 28-39) divided them into three general groups: the Halifax fault zone which strikes generally northward; the Tonopah, a compound fault that in cross section has a trace that is convex upward; and the youngest group which includes a fault which strikes northwest, another which strikes northeast, and a third which strikes north and dips west.
The ore bodies are replacement veins in faults or fractures (Nolan, 1935b, p. 409). The Tonopah fault is believed to have exerted a major control on the movement of mineralizing solutions. Ore bodies are found in all three groups of faults, but the Tonopah and Halifax seem to be more heavily mineralized. Hypogene ore contains electrum, argen-tite, polybasite, and pyrargyrite in a gangue of quartz, pink carbonate, barite, and altered wall-rocks. There has been some supergene enrichment locally, but the hypogene ore has been most important.
The Tybo (Hot Creek, Keystone, Empire) district is in northeastern Nye County, in the Hot Creek Range, 65 miles northeast of Tonopah and about 100 miles southwest of Ely (lat 38"23' N., long 116"23' E.). In the district, gold is a byproduct of ores mined primarily for their lead and silver content.
The first mineral discoveries were made in 1865, and the town of Hot Creek was the population center during the early days (Krai, 1951, p. 189). The district prospered from the rich near-surface silver ores until 1888. The principal mine during this period was the Tybo mine.
Despite several attempts at renewing operations, the district remained dormant from 1888 until 1929, when a concentrator was built that successfully separated the galena from sphalerite (Ferguson, 1933, p. 43-44). Gold production from 1872 to 1888 was 20,360 ounces (Ferguson, 1933, p. 43) ; from 1929 to 1958 it was 6,923 ounces.
The geology of the area was described by Ferguson (1933, p. 13-42). The rocks consist of Paleozoic sedimentary rocks and Tertiary fresh-water sediments, dikes, and flows. The Paleozoic rocks include Cambrian, Ordovician, and Silurian formations. These rocks were tightly folded and faulted; then Tertiary sediments and lavas were deposited. Dikes and masses of Tertiary quartz latite porphyry cut all the older rocks.
The Esmeralda Formation, consisting of water-deposited tuffs of late Miocene age, overlies the latite masses, and it in turn is overlain by a series of dacite and andesite flows. There were several periods of faulting that began before Tertiary time and ended after extrusion of the post-Esmeralda lavas.
The ore bodies were deposited after the intrusion of the quartz latite porphyry. They are tabular replacement bodies along the 2-G fault, the oldest major fault in the area. The primary minerals consist of pyrite, sphalerite, argentiferous galena, chalcopyrite, pyrrhotite, and arsenopyrite. Quartz and calcite accompany the sulfides. The ores first mined were oxidized deposits within 300 feet of the surface.
The Union district, in northwestern Nye County in the Shoshone Range (lat 38"55' N., long 117"35' E.), was organized in 1863, and the town of lone was soon built. After a few brief flurries of activity which yielded about $1 million in gold and silver by 1880 (Lincoln, 1923, p. 196), the district became almost dormant. The discovery of cinnabar in 1907 revived activity somewhat, and since then production of mercury has been fairly consistent; however, gold production from 1903 through 1959 was only 748 ounces.
Total gold production cannot be ascertained, but it is assumed that at least 10,000 ounces was produced before 1903.
The oldest rocks in the district are meta-andesites of Carboniferous age (Krai, 1951, p. 196). These are overlain by Triassic slates, limestones, and conglomerates. A small granodiorite stock cuts the sedimentary rocks. The youngest rocks in the area are Tertiary rhyolite and andesite.
The mercury and gold deposits are associated with the Tertiary rocks; however, the ore at the Berlin mine, the largest mine in the district, consists of lead-copper-zinc-antimony sulfides in quartz veins in the Carboniferous meta-andesites (Krai, 1951, p. 199-200).