The period 1860-80 was one of intermittent bonanza production that made the Comstock Lode the most important and productive camp in the world (Smith, 1943, p. 19). The initial rush in 1860 was followed by a larger one in 1863, when the Ophir and the Gould and Curry mines yielded a record $12,400,000 in gold and silver (Smith, 1943, p. 27). In 1862 the "Washoe process" was developed to treat the Comstock Lode ores. This was a rapid technique of crushing, grinding, and amalgamating the gold and silver from the pulp by steam heating (Smith, 1943, p. 41-45). The near-surface bonanzas were exhausted by 1869, but the discovery of the deeper Crown Point-Belcher ore body in 1871 revived the district (Lincoln, 1923, p. 223). The later discovery and development of the "Big Bonanza" by the Bonanza Kings- Mackay, Fair, O'Brien, and Flood -brought the district its greatest period of prosperity, 1875-80. By 1881 the large ore bodies of the Consolidated Virginia, Yellow Jacket, and other mines were nearly depleted and in the following decade the existing mines were explored to greater depths -more than 3,000 feet. Heat that was almost unbearable, soft ground, and enormous volumes of hot water were encountered. There were no significant discoveries of ore at these greater depths, and for some time most of the production came from low-grade ore that had been overlooked in the early days. In 1894 the first cyanide plant in Nevada was built on the Comstock Lode, and it enabled profitable extraction of gold from low-grade ores and tailings (Stoddard and Carpenter, 1950, p. 22).
After 1900, consolidation made it possible to de-water many of the old workings and to do more extensive development work. The most productive mines during this period were the old Ophir, the Mexican, and the Consolidated Virginia (Stoddard and Carpenter, 1950, p. 23-25). In the mid-1920's the Consolidated Gold Fields of South Africa entered the Comstock Lode, and, after merging and consolidating several properties in the central part of the district, became the chief operator for a few years (Stoddard and Carpenter, 1950, p. 30). A significant spurt in activity marked the increase in the price of gold in 1934, and the district enjoyed a mild prosperity until the imposition of Order L-208 of the War Production Board, which closed nearly all gold and silver mines. After World War II, the Comstock Lode district slowly reawakened, but annual output in the 1950's was meager compared to that of the early years.
From 1859 through 1921, $164,023,917 (about 7,935,360 ounces) in gold was mined (Lincoln, 1923, p. 225-226). Total gold production through 1959 was about 8,560,000 ounces.
The geology of the Comstock Lode was described first by Richthofen (1866), a German geologist employed by the Sutro Tunnel Co. His report was reproduced almost entirely by Becker (1882). Others who have reported on the geology of the district are King (1870), Lincoln (1923), Gianella (1936), and F. C. Calkins (unpub. data, 1944). Stoddard and Carpenter (1950, p. 55-73) briefly reviewed the reports of the earlier workers and summarized the geology of the district.
The oldest rocks of the district are folded and faulted limestone, shale, schist, quartzite, and meta-volcanic rocks of Triassic(?) age. These are intruded by quartz monzonite of Late Jurassic age and are covered by a series of Tertiary volcanic rocks consisting of the Hartford Hill Rhyolite of Eocene age, Alta Andesite of Miocene age, Kate Peak Andesite and Knickerbocker Andesite of Pliocene age, and American Flat Basalt of Quaternary age. The Hartford Hill Rhyolite and Alta Andesite are cut by the Davidson Diorite of late Miocene age. This intrusion was followed by normal faulting, and veins, including the Comstock Lode, were deposited along the faults. Later movement in late Pliocene or early Pleistocene time produced new faults and additional displacement along the older ones.
The lode is a complex shear zone-Y-shaped in cross section, about 13,000 feet long, and several hundred feet wide. Many large blocks of country rock were found in the dominantly quartz gangue in the upper part of the vein system. Calcite is a minor component of the gangue. The ore minerals are argentite, stephanite, and native gold. Coats (1936, p. 532) reported the silver sulfoselenide, aguilarite, associated with silver and argentite in the ores. Sphalerite, galena, pyrite, and chalcopyrite are usually present but not necessarily abundant. Within a few hundred feet of the surface, oxidized ores contained native silver, gold, polybasite, argentite, covellite, chalcocite, anglesite, and wulfenite. Widespread propylitized and sericitized wallrock is characteristic of the Comstock Lode.
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