By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Eureka County was formed in 1873 from the eastern part of Lander County and from small parts of White Pine and Elko Counties. North-trending mountain ranges separated by wide valleys, typical of Great Basin terrain, are the predominant land forms in the county.
The first mineral discoveries were made in 1863 in the Cortez district, and the following year additional discoveries were made in the Eureka and Diamond districts. The Eureka district quickly emerged as the county's leading producer; the mining history of the county is largely a history of the Eureka district.
Gold production before 1902 is difficult to determine because of the practice in the early days of combining production of all metals and reporting it in dollar values. It can be stated, however, that a minimum of 1 million ounces of gold was mined from the Eureka district alone up to 1883 (Vanderburg, 1938a, p. 13). From 1902 through 1959 a total of 203,597 ounces of gold was mined in the county 9,618 ounces was from placers, and the remainder was a byproduct from silver ores.
The Buckhorn district is in the south end of the Cortez Mountains, 5 miles northeast of Cortez.
The production of the district, which is virtually that of the Buckhorn mine discovered in 1908, was 39,632 ounces in gold from 1910 through 1959. The Buckhorn was mined for gold, and silver was a byproduct.
The highest grade ore occurs along a nearly vertical fault that disrupts country rock composed of basalt and interbedded scoria. Both sulfide and oxide ore are present. The oxide ore consists of kaolinized breccia with high gold and silver values; the sulfide ore is primarily fine grained pyrite in talc-rich rock (Vanderburg, 1938a, p. 19-21).
The Cortez district is about 36 miles south of Beowawe at about the middle of the boundary line between Eureka and Lander Counties.
The district was founded in 1863 and was an active producer for many years. The principal mine is the Garrison mine. Silver has been the chief commodity, and lead, copper, and gold have been byproducts. From 1863 to 1903, a minimum of $500,000 (about 24,270 ounces) in gold was produced, and from 1902 to 1936, a total of 8,267 ounces of gold was produced (Vanderburg, 1938a, p. 23-24). Total recorded production of gold from 1863 to 1958 was about 48,720 ounces.
The country rock consists of Paleozoic limestone of probable Cambrian age, overlain by quartzite of probable Ordovician age (Emmons, 1910, p. 101-103). These were intruded by a mass of granite and by porphyry dikes. Ore occurs as replacement bodies in the limestone and in the quartzite. Most of it is in fissures parallel to the dikes. The ore minerals are galena, stibnite, pyrite, sphalerite, stromeyerite. Gangue minerals are quartz and calcite. The galena is rich in silver. Ore such as this is reported (Emmons, 1910, p. 104) to carry from $3 to $15 per ton in gold. Some of the ore is oxidized and consists of silver chloride, copper carbonates, and iron and manganese oxides.
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