By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Gold deposits in Owyhee County are grouped in the Silver City district, in the northwestern part of the county. Placers along the Snake River also yielded gold, but the quantity yielded and the locations of the placers are not known.
Total gold production of Owyhee County from 1863 through 1942 was 1,058,694 ounces (Staley, 1946, p. 25) from 1943 through 1959 it was 44,851 ounces a total of 1,103,545 ounces from 1863 through 1959.
SILVER CITY DISTRICT
The Silver City district, which includes the De Lamar, Flint, and Florida Mountain-War Eagle Mountain camps, is in parts of Tps. 3, 4, and 5 S., Rs. 1, 2, 3, and 4 W., in northwestern Owyhee County.
The first mineral discoveries were gold placers found along Jordan Creek in 1863. That same year, prospectors followed the Jordan Creek placers to their source - the lodes on War Eagle Mountain. By 1865 the richest placers were exhausted, but the Chinese continued lower grade placer mining for a number of years.
After the discovery of rich oxidized gold-silver ores at the Poorman and Orofino mines in 1865, the district erupted into a period of frantic activity accompanied by so much violence and disorder that federal troops were called in to quell the disturbances. The area prospered, developed, and grew despite extremely high costs engendered by poor transportation facilities.
Silver City, with a population of 4,000, was the largest settlement, but the towns of Ruby City, Fairview, Booneville, and Wagontown were also thriving communities (Piper and Laney, 1926, p. 51-52).
By the early 1870's much of the rich oxidized ore was mined out, and in 1876, when the Bank of California failed, financial support was withdrawn and mining in the Silver City area collapsed. Thus the first phase of mining in the Silver City district ended with a production of $12.5 million in gold and silver (Piper and Laney, 1926, p. 53).
In 1889, discoveries at the Black Jack mine at Florida Mountain and the De Lamar mine at Wagontown started a second boom of greater magnitude but with less hysteria than the first. This was a period of consolidation and systematic development. By 1914, after $23 million in precious metals had been mined, the ores were depleted, and the activity again ended (Piper and Laney, 1926, p. 55-56).
Since then, there has been no major revival; operations have been sporadic and on a small scale. Piper (in Piper and Laney, 1926, p. 58) estimated the gold production of Owyhee County (which would in effect be the production of Silver City) as 900,000 ounces. Ross (1941, p. 81) estimated the total gold production of the district at "over 1,000,000 ounces." Recorded gold production from 1941 through 1959 was only about 8,500 ounces and would not greatly change Ross' estimate.
Metasedimentary rocks consisting of graphite and biotite schists are the oldest rocks in the district, though they are present in only a few outcrops. The most abundant rock unit is a granodiorite stock probably related to the Idaho batholith. The granodiorite is cut by aplite, dacite, and diorite porphyry dikes, which may or may not be genetically related to the stock (Ross, 1941, p. 81).
During Miocene time, basaltic lavas were poured onto an erosion surface cut on the granodiorite, and rhyolite flows covered the basalt (Piper and Laney, 1926, p.20-36).
The rocks of the Silver City district are cut by faults of several ages. The oldest are a set of high-angle fractures and joints in the stock. After extrusion of the rhyolite flows, the rocks were dislocated by a second system of fractures that strike northwest and are nearly vertical (Piper and Laney, 1926, p. 39-40). The youngest faulting occurred after the ore deposits were formed.
The veins of the district are fracture fillings and may be classified into four types (Piper and Laney, 1926, p. 63) : (1) veins characterized by white or milky quartz as in the Flint district, (2) veins composed of lamellar quartz typical of the De Lamar district, (3) silicified shear zones such as the Poorman, and (4) quartz-cemented breccias of which the Orofino-Golden Chariot vein is an example. All types are remarkably persistent and are traceable for thousands of feet along strike and as much as 2,500 feet below the surface (Ross, 1941, p. 81).
The ore minerals are argentite, electrum, jamesonite, ruby, silver, naumannite, owyheeite, stibnite, and tetrahedrite. Arsenopyrite, galena, pyrite, and marcasite occur in minor amounts (Ross, 1941, p. 81). Included in the gangue are quartz, barite, calcite, chalcedony, and valencianite, a rare variety of orthoclase occurring as gangue in some ore deposits (Lindgren, 1900, p. 166-167).