Esmeralda County Nevada Gold Production
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.