San Miguel County Colorado Gold Production

The Ophir district is 5 to 7 miles west of the Silverton caldera, and its ore deposits are in structures related to the caldera. Paleozoic and Mesozoic sedimentary rocks are exposed in the bottoms of the deeper valleys and are overlain, in ascending order, by the Telluride Conglomerate, the San Juan Tuff, and the Silverton Volcanic Series. These are all intruded by small igneous bodies ranging in composition from quartz monzonite to diorite. The rocks are cut by a network of fissures and veins. The most productive veins trend westerly and contain pyrite, galena, sphalerite, chalcopyrite, and freiburgite as the more common sulfide minerals. Hematite and magnetite also are present, and the gangue minerals are chiefly quartz, with some calcite, manganiferous iron carbonate, and barite. Some veins in the Ophir Valley trend north and northeast, and the minerals of these consist of quartz and pyrite carrying free gold and some silver. Gold also occurs in the altered and pyrite-impregnated country rock adjacent to the veins. The veins in the San Juan Tuff and overlying andesite commonly are more sharply denned than those in overlying volcanic rocks. Veins also occur within the sedimentary rocks. Replacement deposits are rare and of small extent (Cross and Purington, 1899; D. J. Varnes, in Vanderwilt and others, 1947, p. 425-427).

TELLURIDE DISTRICT
The Telluride (upper San Miguel) district is along the east border of San Miguel County immediately southwest of the Sneffels-Red Mountain district in Ouray County. The geology is described on pages 107-108; only the history and production will be discussed in this section.

The first discoveries in the Telluride district were made on the Smuggler vein in 1875 (Purington, 1898, p. 752-754). There was only a small production through 1882, but in 1883 a shipment of 4 tons of high-grade ore from the Smuggler vein yielded 800 ounces of silver and 18 ounces of gold per ton and thereafter production increased rapidly. Since 1898, the large output of the Telluride district has come chiefly from the mines of three large companies—the Liberty Bell, Smuggler-Union, and the Tomboy (Henderson, 1926, p. 53, 224-225). The Liberty Bell mine, which produced only silver and gold, was operated from 1898 to 1921 and during that period had an output of 633,021 ounces of gold (Henderson, 1926, p. 225). The Tomboy group of mines closed in 1927 and the Smuggler-Union closed in 1928 after operating 52 years (W. S. Burbank, in Vanderwilt and others, 1947, p. 421). In 1940 the Smuggler-Union group of mines and the Tomboy holdings were organized as the Telluride Mines, Inc., which was still active in 1959. Total production of gold through 1959 was at least 3 million ounces; thus Telluride is one of the 25 leading gold-producing districts in the United States. Large quantities of silver, lead, zinc, and copper have also been produced.

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