Madison County Montana Gold Production
Located in northwestern Madison County, west of the Jefferson River, the Silver Star-Rochester district produced ores that were valuable chiefly for gold, but silver, lead, zinc, and copper also were recovered. Though mining began in the 1860's, it did not reach its peak until 1935-42. Interest declined thereafter, and the district was virtually dormant from 1951 through 1959. The Watseca mine in the Rochester area and the Green Campbell, Iron Rod, and Broadway mines in the Silver Star area were the major mines of the district.
Incomplete records indicate that the gold output through 1903 was worth about $2 million (about 97,000 ounces) (Sahinen, 1939, p. 5-7; Winchell, 1914a, p. 144). Total production through 1959 was about 185,700 ounces, all from lodes.
The geology and ore deposits of the district were briefly described by Winchell (1914a, p. 126-132; 139-144) and Sahinen (1939), from which this summary is abstracted.
The Silver Star-Rochester district lies at the south end of the Boulder batholith. The bedrock consists dominantly of schist and gneiss of Precambrian age which in the western part of the district and in the area around Silver Star are locally overlain by sedimentary rocks that range in age from late Precambrian to Pennsylvanian. All the older rocks are intruded by quartz monzonite of the Boulder batholith, by a stock of diorite, by small aplite intrusive bodies, and by dikes and sills of acidic rocks, all of Cretaceous or Tertiary age. Remnants of andesite and basalt flows are found locally.
The most important ore deposits are northeast-trending veins in gneiss and schist (Sahinen, 1939, p. 26-34). These veins are rich in gold and silver and contain arsenopyrite, pyrite, and subordinate amounts of lead, zinc, and copper minerals in a quartz gangue. A few veins in this group are rich in lead-silver ore. Several narrow veins that trend east carry gold with small amounts of pyrite in greasy-appearing quartz. Much of the ore has been oxidized to a depth of 600 feet and consists of quartz, limonite, and oxidized copper and lead minerals.
Considerable gold has been mined from contact deposits in the Silver Star area. The ore deposits form irregular shoots in Paleozoic limestone along the quartz monzonite contact. Much of the ore was highly oxidized and consisted of jasper, gold, and oxidized minerals of iron and copper. The unoxidized ore consists of pyrite, chalcopyrite, bornite, and covellite in a gangue of quartz and contact silicate minerals.
TIDAL WAVE DISTRICT
Located in northwestern Madison County, along the western slope of the Tobacco Root Mountains, the Tidal Wave (Twin Bridges) district has produced chiefly gold, silver, and lead, and smaller amounts of copper. The initial discoveries in about 1864 were silver-lead ore but these aroused little excitement. Only gold was sought in those early days. By 1874, however, the value of the argentiferous lead ores was realized, and claims were rapidly located and developed (Winchell, 1914a, p. 145). Production records date back only to 1904, but the production during the latter part of the 19th century probably was greater than in the early 1900's (Winchell, 1914a, p. 146). The district remained active from 1904 through 1955, and the total recorded gold production through 1959 was about 33,400 ounces; nearly all production was from lodes.
The Tidal Wave district lies on the west side of the Tobacco Root batholith, a mass of quartz monzonite of Cretaceous or Tertiary age which here has intruded, faulted, and tilted Precambrian gneiss and schist and Paleozoic limestone, quartzite, and interbedded shale. These rocks also are cut locally by sills of porphyry and by aplite dikes.
The ore deposits in the district are contact deposits in limestone and lodes in gneiss and schist, and more rarely they occur in the quartz monzonite near its contact with the country rocks. Most of the veins contain gold and lesser amounts of lead, silver, copper, and zinc. A few veins in the Paleozoic limestone near the contact were mined for lead and silver, or copper and gold. The contact metamorphic deposits are valued mainly for copper and lead, with silver and gold as minor constituents (Winchell, 1914a, p. 145-158; Hart, in Tansley and others, 1933, p. 34-39).