By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
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Until the discoveries at Goldfield in 1902, the gold deposits of Esmeralda County were in themselves relatively insignificant; most of the gold had been produced as a byproduct of rich silver ores. Yet, gold was the metal sought in the early days, and in at least one instance, at Gold Mountain in the Divide district, the search for gold led to the discovery of rich silver deposits.
The silver-gold deposits of the county are of two general types: veins associated with granitic bodies of Late Jurassic or Early Cretaceous age, and fissure filling in Tertiary volcanics. The deposits at Silver Peak, Windypah, Hornsilver, Lida, Montezuma, and Klondike belong to the first type; those at Divide and Goldfield to the second. Production in the county from 1903 through 1959 was 4,912,112 ounces of lode gold, mostly from Goldfield, and 2,071 ounces of placer gold.
The Divide (Gold Mountain) district, 5 miles south of Tonopah, has been primarily a silver camp; it was founded in 1901. Between 1901 and 1917 there was only sporadic exploitation of the gold-bearing veins on Gold Mountain and the silver lodes in the Crown Divide property. Then, in 1917, a rich silver lode was discovered on Gold Mountain which immediately created a boom that lasted until 1919. The principal mines in the district are the Tonopah Divide, the Divide Extension, and the Tonopah Hasbrouck (Knopf, 1921b, p. 148-170).
Gold production from 1910 through 1959 was 26,483 ounces, mostly as a byproduct of ores mined for silver.
The predominant rock in the district is the Fraction Rhyolite Breccia (of the Siebert Formation) of probable late Miocene age. Several stocks of Oddie Rhyolite and Divide Andesite (of late Miocene age) intrude the rhyolite breccia. Latite flows of Pliocene age cap the higher peaks. The ore bodies are mineralized fracture zones in the Fraction Rhyolite Breccia. Cerargyrite is the main silver-bearing mineral; some sooty argentite is present, and molybdite and powellite are abundant locally.
A few narrow gold-quartz veins have been found in the Oddie Rhyolite. Veinfilling in these consists of rhyolite fragments, quartz, and pyrite.
GOLDFIELD DISTRICT
Located near the east border of Esmeralda County, 28 miles south of Tonopah, the Goldfield district is on the south rim of a desert basin which is the southern extension of a much larger basin west of Tonopah. This rim is formed by a group of hills, known as the Goldfield Hills.
Gold was discovered in the district in 1902, but no important shipments were made until 1904 (Ransome, 1909a, p. 17) during a brief period of high production. In 1905 the district declined because of exhaustion of many of the high-grade ore shoots. In 1906 important new discoveries on the Mohawk property spurred exploration and development throughout the district.
High-grading and strife between labor unions and management curtailed production and eventually assumed such proportions during this period that Federal troops were called in to maintain order. In March 1908 labor troubles were settled and soon the district settled down to a more peaceful era of development and production.
From 1903 through 1959 the district produced about 4,194,800 ounces of gold. Small amounts of silver were produced as a byproduct.
The oldest rocks in the district are dark flinty shale and quartzite of Cambrian age (Ransome, 1909a, p. 32). Intruded into these metasedimentary rocks are masses of alaskite and granite, of probable Early Cretaceous age. Overlying these rocks is a thick series of volcanic rocks and lake deposits, all of Tertiary age. Ransome (1909a, p. 36-74) divided them into the prelacustrine volcanic rocks, lacustrine rocks composing the Siebert Formation, of Miocene age, and postlacustrine volcanic rocks. Both sets of volcanic rocks consist of rhyolite, dacite, tuff, and andesite.
The lake sediments consist of volcanic ash, gravel, and scattered beds of diatomaceous earth. A thick flow of mica basalt occurs in the sediments. The postlacustrine volcanics are capped by the Malpais Basalt. This entire Tertiary sequence has been warped into a dome and faulted.
Most of the ore deposits are found in topographically prominent silicified zones of small intersecting ramifying shears in the dacite, one of the prelacustrine rocks. Other deposits occur in andesite, and a few, in rhyolite (Ransome, 1909a, p. 150-155).
The ores are complex sulfides consisting of pyrite, bismuthinite, goldfieldite, and a mineral resembling famatinite in a dark-gray flinty quartz gangue. Alunite is a common gangue in some ore. Native gold, commonly very fine grained, is associated with these minerals. Typical of the ore is its concentric banded character, its extreme richness, and the erratic behavior of ore shoots (Ransome, 1909a, p. 165-167).
Later work by Searls (1948) modified some of Ransome's earlier conclusions regarding the age of mineralization, the relation of faulting to mineralization, and relation of the dacite to earlier flows. Searls concluded (1) that the dacite was not intrusive into any of the earlier rocks (whereas Ransome had indicated that it was), (2) that the age of mineralization was somewhat earlier than Ransome had thought, and (3) that the Columbia Mountain fault, the major fault in the district, was the distributing agent for the mineralizing solutions. Ransome (1909a, p. 196, 197) postulated that the hot mineralizing solutions rose along complicated fissures in the dacite.
HORNSILVER DISTRICT
In the Hornsilver district, which is 20 miles south-southwest of Goldfield, prospectors were active in 1868, but their discoveries were not very productive (Ransome, 1909b, p. 41-42). In 1907 larger ore bodies were found, and the district prospered for a few years. No activity was reported from 1956 through 1959.
Total gold production from the Hornsilver district from 1903 through 1959 was about 25,000 ounces.
The rocks of the district are limestone and calcareous shale that were intruded and metamorphosed by masses of granite (Ransome, 1909b, p. 41-42). The veins strike N. 55°-60° W. and cut across the bedding of the shale. Most production has come from the Great Western and Grand Central veins. The important ore constituents are native gold and silver chloride (Ransome, 1909a, p. 41-42).
LONE MOUNTAIN DISTRICT
Located in eastern Esmeralda County, in T. 1 S., R. 41 E., the Lone Mountain district is predominantly a silver camp with a recorded production from 1903 through 1949 of 31,961 ounces of gold. No activity was reported from 1949 through 1959.
The bedrock is Cambrian limestone and shale complexly folded and intruded by masses of diorite and by dikes and sheets of diorite porphyry (Ball, 1906, p. 57, 58). Deposits containing cerussite, malachite, azurite, chrysocolla, galena, and pyrite occur in altered limonite-stained limestone near its contact with diorite porphyry sheets.
SILVER PEAK DISTRICT
The Silver Peak (Mineral Ridge) district is in central Esmeralda County, in T. 5 S., R. 39 E.
The first discoveries in this district were made in 1864. These were silver deposits which were worked for several years with rather meager returns. Some time later gold lodes were discovered, and these soon became the more important. The Drinkwater and Crowning Glory have been the major mines.
The gold production to 1905 was about 59,100 ounces (Spurr, 1906, p. 35). The interval 1906-15 was one of high production, but during 1915-31 only about $50,000 in gold was produced per year. Total production during 1903-32 was 323,085 ounces (Nolan, 1936b, p. 60). The mid-1930's to early 1940's was another period of high production, followed by the abrupt decline in production caused by World War II. From 1943 through 1959 there was only small-scale activity in the district. Total gold production of the district through 1959 was about 568,000 ounces.
The rocks of the district consist of Cambrian and Ordovician limestones, slates, and quartzites that were intruded by a Late Jurassic or Early Cretaceous alaskitic rock (Spurr, 1906, p. 9-12). The gold deposits are in quartz lenses in the limestones and probably are genetically related to the late siliceous phase of the alaskite. Native gold is finely disseminated in the quartz. Gold is also associated with scattered sulfides in the lenses.
