The Potosi district is, by road, about 14 miles southwest of Pony at the headwaters of the South Fork of Willow Creek on the eastern slope of the Tobacco Root Mountain range. The silver veins of Potosi were discovered around 1875. In 1890, the Potosi was described as a new mining camp connected to the outside world by a 12 mile trail. Better transportation was said to be needed before the district's silver and lead deposits could be exploited. The silver collapse of the early 1890s ended most of the district's tenuous production. However, by 1901 some companies, such as the Royal Potosi, were reported to be operating with good silver values. When the district was visited in 1911 none of the mines in the district were active or had been extensively developed (Swallow 1891; Western Mining World 1901; Winchell 1914; Sahinen 1935).
The country rock is quartz monzonite of the Tobacco Root batholith. Zones of aplite are extensive and contain most of the important silver and tungsten deposits. The veins trend easterly and dip steeply to the south. Although productive in past years, the silver veins have not been developed in recent years. Fluorite is also present (Sahinen 1935).
The district is remarkable for the large number of minerals located within it. These include quartz, pyrite, chalcopyrite, galena, sphalerite, pyrargyrite, molybdenite, florite, hübnerite, cerargyrite, native silver, pyrolusite, and limonite. The tungsten mineral hübernite, occurs in seams in wide massive white quartz veins or dikes of pegmatitic character. It is present in at least a dozen different claims including the Green Jacket, Mountain Rose, Keystone, Crown Point, Granite Mountain, Sunnyside and Rockefeller. A 20 inch wide streak of hübnerite was found on the Rockefeller claim (Winchell 1914).
The district experienced a one mine revival in 1907 when the Butte-Potosi Mining Company, associated with the W. A. Clark mining empire, began development of the Independent mining claim. Although the mine was active for four years, there is no record of production (Eyde 1958). In 1911 C. E. Morris took ore samples from the Green Jacket Lode to Virginia City to be assayed. The ore revealed rather surprising tungsten values. Little came of the discovery, but Hübernite, which was initially thought of as a zinc mineral, was finally identified as a tungsten mineral by Thomas Evans (Eyde 1958).
In 1930 the Potosi Tungsten Mining Company was organized and obtained the Rogers, Independent, Lucky Joe, Margie and Rockefeller claims. In 1933, the company made what may be the district's only tungsten ore shipment. Around 16 tons of the ore was worked at the Strawberry mill in Pony. The load yielded 935 pounds of tungsten concentrate which assayed 65% tungsten trioxide. The load had a net value of $356 (Eyde 1958).
BOUNDARIES OF THE DISTRICT
Sahinen (1935) places the district about six miles south of the town of Pony or about 12 miles west of Norris, near the terminus of the Norris branch of the Northern Pacific Railroad. Figure 1 shows the district as defined by the AMRB (1994) which basically includes the headwaters of the South Fork of Willow Creek.
HISTORIES OF SELECTED MINES
The Independent was first developed around 1907 by the Butte-Potosi Mining Company which was affiliated with W. A. Clark. The company drove a 940 foot crosscut adit to intersect a silver / tungsten vein at depth. Although the mine was active until 1911, there is no record of production. In 1930 the claim was part of the Potosi Tungsten Mining properties which produced 16 tons of tungsten ore that returned $356 (Eyde 1958).
The Lucky Strike (also known as the Erma and the Jean) mine is located 9 miles south of Harrison. It consisted of 1 patented placer claim and 2 unpatented lode claims. It produced both gold and silver, and development work consisted of drift and shaft. It was last reported to be operating in 1934 (Gilbert 1935).
Abandoned Mine Reclamation Bureau (AMRB)
1994 Mining districts of Montana. Maps 1:100,000 and Map #94-NRIS-129. Compiled and edited by Joel Chavez. Prepared by Montana State Library Natural Resource Information System (NRIS) for Montana Department of State Lands. Helena
Cope, George F.
1936 "Statistical and Descriptive Report Upon the Mines of Madison County Montana", (Compiled by George F. Cope, Sept. 1888),
Montana School of Mines
Eyde, Theodore H.
1958 "The Potosi Tungsten District, Madison County, Montana",
Montana Bureau of Mines Information Circular #21
Sahinen, Uuno M.
1935 "Mining Districts of Montana", M.S. Thesis, Montana School of Mines, Butte.
Swallow, G. C., J. B. Trevarthen and Jacob Oliver
Reports of Inspectors of Mines, State of Montana, year ending November 30th, 1890
. Journal Publishing Company, Helena.
Tansley, Wilfred and Schafer, Paul A. , and Hart, Lyman H.
1933 "A Geological Reconnaissance of the Tobacco Root Mountains, Madison County, Montana",
Montana Bureau of Mines and Geology
, Mem. 9.
Trauerian, Carl J.
1941 "Strategic Minerals of Montana; Tungsten",
Western Min. News
, Vol. 15, No. 6, p. 9.
Western Mining World
1901 "Potosi District", Vol. 15, No. 18, p. 23. November 2, 1901.
Winchell, Alexander Newton
1911 "A Theory for the Origin of Graphite as Exemplified in the Graphite Deposit near Dillon, Montana",
, Vol. 6, pp 218-230.
1914 "Mining Districts of the Dillon Quadrangle, Montana and Adjacent Areas", U. S. Geological Survey, Bulletin 574.
Work Projects Administration (WPA) Mineral Resources Survey
Montana Mine Index, An Alphabetical Index Arranged by Counties, Districts and Mines of Information on Montana Mines from 1867-1940
. Montana School of Mines, Butte.