The following brief history of the Leadville mining district and its production was abstracted from reports by Henderson (1926, p. 40-43, 130-176). The early history of Lake County is virtually the history of mining in the Leadville district.
The first ores found and mined in Lake County, as in most of the mining camps in Western United States, were gold placers. At the time of the "Pikes Peak excitement," some of the early prospectors, searching for gold in stream gravels, wandered across the Rampart, Tarryall, and Mosquito Ranges into South Park and the Arkansas River valley. Early in the spring of 1860, placers were discovered in Iowa and California Gulches, tributaries of the Arkansas River, in what was to become the Leadville district. News of the rich discoveries spread with amazing rapidity, and by July 1860 the placer camp called Oro City boasted a population of 10,000. The placers, though rich, were quickly depleted, and within 3 or 4 years only a few hundred of the more persistent souls remained. It was reported that $2 million in gold was taken out the first summer, and the placers continued to be productive, but at a diminishing rate, until 1886.
In June 1868 gold lodes were discovered which were mined with great success until 1877, after which gold production was overshadowed by silver and lead.
The mining of rich silver-bearing lead carbonate ore began in the summer of 1874 and brought great prosperity to the Leadville district, especially from 1876 until 1902, which was the most productive period in its history. The first railroad to reach Leadville was the Denver and Rio Grande in August 1880. The Colorado Midland Railway, running westward from Colorado Springs and across South Park, reached Leadville in September 1887. The period of general prosperity, however, was marred by declining silver content of the ores, by the financial depression of 1893, and by labor troubles. As a result, there was increased prospecting for gold which culminated in increased gold production from the Breece Hill area after 1893. Gold continued to be an important commodity through 1917, though its proportion of the total output of the district was overwhelmed by the development of the huge zinc ore bodies after 1903 (Emmons and others, 1927, p. 111-133). The Leadville mines closed in 1957, and from 1957 to 1959 only small amounts of gold were recovered from fluxing material. The total gold output of the district through 1959 was about 2,970,000 ounces.
According to Behre (1953, p. 18-60), the bedrock in the Leadville district consists of a Precambrian basement complex of gneiss, schist, and granite, overlain by about 500 feet of Cambrian, Ordovician, Devonian, and Mississippian sedimentary rocks and 2,500 feet of Pennsylvanian sedimentary rocks. The Precambrian and Paleozoic rocks are intruded by numerous sills and dikes and by a few stocks of porphyry and pipelike bodies of volcanic breccia, all of Tertiary age. The igneous rocks are chiefly quartz monzonitic, but some are granitic or rhyolitic. Several irregular, roughly funnel-shaped pipes of Tertiary agglomerate have been partly outlined by mine workings.
The rocks in the Leadville district have been tilted and extensively faulted. According to Tweto (1960), all the porphyries are older than the ores, and nearly all of the faults originated before the ore, although many faults were reactivated after mineralization.
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