By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Iron County is in southwestern Utah, south of Beaver County along the Nevada border. In the central part of the county, the Iron Springs district produced major amounts of iron; in the extreme western part, the Stateline district produced silver, lead, and gold. Most of the 12,760 ounces of gold credited to the county through 1959 came from the Stateline district.
The Stateline (Gold Springs) district is along the Utah-Nevada boundary at about lat 38Â° N. Though the area was well traveled for many years, the mineralized outcrops that mark the ore deposits were neglected, primarily because gold had not been found in the stream gravels and partly because the limestone containing rich silver and lead deposits elsewhere in the State was not exposed in the Stateline district. Prospecting began in earnest in 1896, and success was almost immediate (Heikes, in Butler and others, 1920, p. 564, 565). The district entered a period of sustained development about 1917, after which decreasing ore reserves and increasing pumping costs forced most mines to close. Some mines were reopened during 1932-42, but all were virtually inactive from 1943 through 1959.
The bedrock of the district consists of extrusive latite, rhyolite, and rhyolite tuff (Butler, in Butler and others, 1920, p. 563-567). In the vicinity of Gold Springs, latite is exposed in the lower areas and is overlain by rhyolite; to the north around Stateline, rhyolite is the prevailing rock. All the formations appear to be horizontal but are extensively fissured.
The ore deposits occur in north-trending veins; in the Gold Springs camp the most productive veins were found in the latite and in the Stateline area some of the best deposits were found in the rhyolite (Butler and others, 1920, p. 565). The veins are crustified and consist chiefly of chalcedonic to fine-grained quartz, adularia (locally known as "yellow quartz"), carbonates, and generally a small amount of fluorite. The ore minerals are pyrite and native gold. Some gold is light colored and probably contains considerable silver. Some rich ore carries abundant tellurium; thus, a telluride of gold and silver may be one of the primary minerals. Oxidized ores contain cerargyrite, molybdite, and native mercury. In general the deposits are relatively shallow, but some in the Ophir mine were explored to a depth of 500 feet. Some veins end at depths of less than 100 feet where they separate into numerous quartz stringers in highly altered rock.
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