By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Custer County lies in south-central Colorado, west of Pueblo. Its western boundary is formed by the crest of the Sangre de Cristo Range, and its central and eastern parts include segments of the Wet Mountain Valley and the Wet Mountains.
Custer County through 1959 produced about 107,300 ounces of gold and ranks 17th in gold production in Colorado. It has also produced silver and lead and small amounts of copper and zinc. Nearly all the gold has been derived from silver-gold lodes and some is a byproduct of lead-silver ore.
The first significant ore discovery was in 1872, when rich silver-lead ore was found in the Rosita Hills district, though ore specimens had been found earlier in the county by herdsmen searching for stray cattle (Emmons, 1896, p. 412-416). Prospectors flocked to the Rosita Hills; in 1874 silver-copper ore was found in the Humboldt-Pocahontas vein, and in 1877 the rich gold ore of the Bassick mine was discovered. In 1878, important silver discoveries were made in the Silver Cliff area, a few miles northwest of Rosita Hills.
Great excitement was generated by the ore discoveries in Custer County, and for a few years the properties were developed with much vigor, but the boom was short lived. For a variety of reasons - transportation problems, over-optimism, unsuccessful mining methods, and reduction techniques - many of the ventures failed, and by 1892, production for the county was valued at only a few thousand dollars (Emmons, 1896, p. 412-420). Some of the mines were reactivated during World War I and at brief intervals thereafter. For the most part, the mineral wealth of Custer County was earned before 1900.
Gold production of the county through 1959 was about 84,700 ounces, all of which is credited to the Rosita Hills district.
ROSITA HILLS DISTRICT
The Rosita Hills district, in the low western foothills of the Wet Mountains about 7 miles southeast of Westcliffe, has produced gold, silver, lead, copper, and a small amount of zinc.
The district was most active during 1877-90. Thereafter the mines were operated only sporadically; from 1932 through 1959 they were virtually dormant. The minimum total gold production through 1959 was about 84,660 ounces, most of which came from the Bassick mine.
The rocks of the Rosita Hills district consist of tuffs, breccias, agglomerates, and flows of andesite, rhyolite, and trachyte, all of Tertiary age, which overlie Precambrian gneiss, schist, and granite. The Bassick mine is in an elliptical volcanic pipe about 1,200 feet wide and 2,000 feet long that is enclosed in gneiss. The pipe is composed of andesitic agglomerate in which are embedded fragments and boulders of granite and gneiss. A dike of limburgite cuts the agglomerate.
Most of the smaller ore bodies are in veins in the volcanic rocks; however, the Bassick ore body is a body of mineralized agglomerate about 30 feet wide, 100 feet long, and at least 1,500 feet deep. The ore consists of thin concentric shells of minerals deposited on boulders. The minerals noted were sphalerite, galena, jamesonite, tetrahedrite, smithsonite, calamine, native gold, quartz, chalcopyrite, and gold-silver tellurides (Cross, 1896, p. 338-344; Em-mons, 1896, p. 430-434).
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