Madison County Montana Gold Production |
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PONY DISTRICT
The Pony district, which includes Mineral Hill and South Boulder (Mammoth), is in the northeastern part of Madison County in the Willow Creek drainage basin. Almost its entire output has come from lodes which have produced chiefly gold and small amounts of silver, lead, zinc, and copper. Placer gold was noted in 1870 (Lyden, 1948, p. 89), but placer production of the district has been small. Lode deposits were discovered in the early 1870's and were actively exploited during the 1880's and 1890's (Winchell, 1914a, p. 119). Production apparently was continuous through 1918, but it declined thereafter. The district again was active from 1928 through 1944. There was no significant gold production from 1944 through 1959.
Winchell (1914a, p. 126) estimated that the mine production of the Pony district, exclusive of the South Boulder camp, through 1901 was valued at about $2,600,000. Based on production records from 1902 to 1912, it would seem reasonable that gold constituted about 90 to 95 percent of the early production or about $2,350,000 (113,690 ounces). The gold production of the South Boulder camp before 1900, all from lodes, was estimated at about $2 million (96,758 ounces) (Lyden, 1948, p. 87). From 1902 through 1930 the district produced about 76,500 ounces (Hart, in Tansley and others, 1933, p. 24), and from 1933 through 1944, about 58,950 ounces. The total gold production of the district through 1959 was about 346,000 ounces; probably less than 250 ounces was placer gold.
Most of the mines in the Pony district are in Precambrian gneiss near the contact with quartz monzonite of the Tobacco Root batholith, but some are in the marginal part of the batholith; others are associated with aplitic and pegmatitic dikes (Winchell, 1914a, p. 119-120).
The mineral deposits in the district are arranged in a rude zonal pattern (Hart, in Tansley and others, 1933, p. 25). At or near the gneiss-quartz monzonite contact, the veins consist of either (1) chalcopyrite, pyrite, and molybdenite in quartz, (2) auriferous pyrite, chalcopyrite, and quartz, or (3) tungsten-fluorite minerals. Galena and silver are the important vein constituents peripheral to these deposits, and auriferous pyrite is less abundant.
In the Clipper mine, the most productive in the district, and in the adjacent Boss Tweed mine, the ore deposits consist mostly of silicified and pyritized gneiss between two approximately parallel faults from 10 to 160 feet apart (Winchell, 1914a, p. 121-124). Some of the ore is oxidized. The economic deposits are found chiefly in shoots, but much of the gneiss between the faults contains gold.
