By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
The total recorded gold output of Lincoln County through 1959 was 556,800 ounces. The only major gold districts in the county are the Delamar, the largest gold producer, and the Pioche, which yielded considerable gold from silver-copper-lead-zinc ores from 1935 through 1959.
The Delamar district is in south-central Lincoln County on the west slope of the Meadow Valley Range, 29 miles southwest of Caliente.
Callaghan's (1937) report of the district is the chief reference for the summary of the history and geology that follows:
The first gold discovery was in 1891, and the district was organized the following year. The Delamar mine soon became the major mine in the district. Statewide, it outproduced all but a few mines at Goldfield and Tonopah. Despite primitive and costly means of transportation and lack of water in its early years, the district developed steadily until 1909, when the Delamar mine was closed. Only a few ounces of gold was produced in the ensuing two decades. In 1931, exploration at the Magnolia mine, the Jumbo claim, and several other leased properties was successful, and significant production began again in 1932.
Before 1902, district production of precious metals was reported in dollar values instead of ounces, but it may be assumed that most of this early production was in gold. According to Callaghan (1937, p. 38-40) the gross yield of the major mines from 1894 through 1901 was $9,407,555. From 1902 through 1957 the district produced 217,240 ounces of gold, all from lode mines.
A thick section of tilted and faulted Cambrian sedimentary rocks is exposed in the district. These rocks are overlain by Tertiary latites, andesites, tuff, and rhyolite that are also faulted but are less tilted than the Cambrian rocks. Small bodies of diorite and dikes and sills of basalt and rhyolite cut the sedimentary rocks. The rhyolite dikes are related to the flows. The mineral deposits were emplaced some time during the period of volcanic activity, as indicated by the fact that some dikes are older and some are younger than the ores.
The major deposits of the district were in the oldest rock, the Prospect Mountain Quartzite of Early Cambrian age. The deposits are of three types: (1) quartzite breccia, cemented and partly replaced by vuggy fine-grained quartz containing comb quartz and sulfides in the vugs, (2) small veins of fine-grained quartz containing free gold and sulfides, and (3) bedded quartzite with gold deposited in small fractures and along bedding planes. Other deposits are in volcanic breccia, intruded by rhyolite dikes, as at the Magnolia mine and in several of the limestone units where scattered prospect pits have revealed small amounts of silver.
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