Jefferson County Montana Gold Production

  
Posted July 16, 2009 in Gold Mining

By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968

Click here for the Principle Gold Producing Districts of the United States Index

From 1864, when gold was discovered in the county, through 1959, Jefferson County produced at least 700,000 ounces of gold - about 575,000 ounces from lodes and about 125,000 ounces from placers.

Mining began in Jefferson County in about 1864 with the discovery of silver, lead, and gold ore near Wickes (Pardee and Schrader, 1933, p. 232-234) and has continued at a fluctuating rate to the present time. Gold mining declined during the late 1920's, increased after the price of gold was raised in 1934, and again declined sharply in 1950.

Most of the deposits, both lode and placer, are in the northern part of the county. The most productive placer deposits have been the gravels along Prickly Pear Creek and its tributaries in the Clancy district, about 14 miles southeast of Helena, but small production has also come from placers in the Basin and Boulder district. The output of lode gold has come chiefly from the Clancy, Basin and Boulder, Elkhorn, and Whitehall districts.

Some of the ore deposits are in granitic rocks of the Boulder batholith, and some are in sedimentary and volcanic wallrocks and roofrocks near the contact with the batholith.

BASIN AND BOULDER DISTRICT
In the Basin and Boulder district, in central Jefferson County near the headwaters of Boulder River, gold has been recovered from gold lodes, from silver and base metal ores, and from placers. The district includes Basin Creek, Cataract Creek, Lowland Creek, and the upper Boulder River.

Lodes were discovered in this area before 1870, but mining has been sporadic (Pardee and Schrader, 1933, p. 286). The periods of peak activity were 1905-8, 1916-20, 1924-26, and 1935-41. From the end of World War II through 1954 activity was on a small scale, and from 1954 through 1959, no production was recorded. Relatively small amounts of gold were mined from gravels along Lowland Creek, Basin Creek, Cataract Creek, and Boulder River (Lyden, 1948, p. 48-50). Total gold production of the district through 1959 was about 188,200 ounces, about two-thirds of which was produced before 1928 (Pardee and Schrader, 1933, p. 186). About 12,000 ounces of gold from placers is included in the total figure.

Bedrock in the Basin and Boulder district is predominantly quartz monzonite of the Boulder batholith and remnants of older andesitic flows of Late Cretaceous age that were intruded by the quartz monzonite. Patches of dacite flows of Tertiary age unconformably overlie the quartz monzonite. Dikes of dacite and rhyolite cut all these rocks (Pardee and Schrader, 1933, p. 286-287).

The ore deposits are of at least two ages. The principal group of lodes is older than the Tertiary volcanics and is valuable for silver, lead, gold, zinc, and copper. Younger lodes in Tertiary volcanics are found in a small area along Lowland Creek. These are epithermal veins and are mined for gold and silver (M. R. Klepper, written commun., 1962).

Billingsley and Grimes (1918, p. 313) noted a tendency toward mineral zoning in veins near Basin. Veins in the upper part of the batholith and in the roofrocks contain quartz, tourmaline, and arsenopyrite. Underneath this zone, from 200 to 500 feet below the roof of the batholith, galena predominates but gives way downward to sphalerite. The deepest ore is the lowest in grade and contains pyrite and copper minerals.


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