Jefferson County Montana Gold Production |
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CLANCY DISTRICT
The Clancy district is in the northern part of the county, about 10 miles south of Helena. Though primarily a placer district, most of the gold produced in the district before 1900 was a byproduct of flourishing silver mines.
Placer mining began about 1865 along Prickly Pear Creek and the following year rich silver lodes were found. By 1910, however, most of the mines were idle, and the once-thriving town of Lump Gulch City was deserted (Pardee and Schrader, 1933, p. 227). In 1933 a dredge was installed on Prickly Pear Creek. In 1937 and 1938 additional large-scale operations, which resulted in considerable placer production through 1948, were undertaken on Prickly Pear and Clancy Creeks. From 1949 through 1957 the placer operations were suspended. In 1958 and 1959 placers were again mined on Prickly Pear Creek, but production data were not recorded.
Total gold production of the district through 1959 was about 101,000 ounces from placers and at least 2,000 ounces from lodes.
The predominant bedrock in the district is quartz monzonite and is part of the Boulder batholith of Late Cretaceous or Tertiary age. Remnants of a once-extensive cover of Tertiary rhyolite occur in the eastern and northeastern parts of the district. The lode deposits are in veins in quartz monzonite. The richest deposits contained silver-bearing galena, sphalerite, and tetrahedrite in a chalcedonic quartz gangue. Other veins produced small amounts of gold. These consisted mainly of quartz and pyrite, and small amounts of galena, sphalerite, and arseno-pyrite (Knopf, 1913, p. 102-104).
ELKHORN DISTRICT
Located in the Elkhorn Mountains east of Boulder, the Elkhorn district was prospected before 1870, but the highly productive Holter lode in the Elkhorn mine was not discovered until 1875. The early economic importance of this district depended almost wholly on the Elkhorn mine (Knopf, 1913, p. 128) which produced mostly silver and lead ore and small amounts of byproduct gold. After 1911 as many as 16 mines operated in a single year, but the bulk of the more recent production came from the Golden Curry and Swissmont mines and the reworked tailings of the Elkhorn mine (Pardee and Schrader, 1933, p. 299-300). The total gold production of the district through 1953 was 70,015 ounces (Klepper and others, 1957, p. 64). From 1954 through 1959 only 97 ounces was recorded.
The Elkhorn district lies on the eastern margin of the Boulder batholith. The oldest rock in the district is metamorphosed shale of the Belt Series which is overlain by metamorphosed Paleozoic limestone, shale, and quartzite, ranging in age from Cambrian to Pennsylvanian, and by Mesozoic sandstone, shale, and impure limestone. These are overlain by a bedded series of andesitic breccias, tuffs, and lavas of Late Cretaceous age. The sedimentary and volcanic rocks are folded, faulted, and cut by small igneous masses of diverse composition that are slightly older than the Boulder batholith, by quartz monzonite of the batholith, and by aplite (M. R. Klepper, written commun., 1962).
A wide variety of ore deposits is found within the Elkorn district: magmatic sulfide deposits at the Golden Curry property, auriferous contact metamorphic deposits in the Dolcoath mine, auriferous lead-silver replacement deposits at the Elkhorn mine, and mineralized breccia pipes at the Elkhorn Queen and Skyline mines (Klepper and others, 1957, p. 64). Magmatic sulfide ore consists of a mixture of pyrrhotite and chalcopyrite intergrown with augite. The contact ore body in the Dolcoath mine consists of chalcopyrite and an auriferous sulfide and telluride of bismuth intergrown with silicates and calcite. The ore at the Elkhorn mine consists mainly of argentiferous galena, sphalerite, pyrite, and tetrahedrite as replacement bodies in dolomite beneath hornstone. At the Elkhorn Queen and Skyline mines pipelike bodies of brecciated rock are cemented by quartz, black tourmaline, pyrite, galena, sphalerite, and sparse chalcopyrite and arsenopyrite (Klepper and others, 1957, p. 64).
