The Lost Creek mining district, also called the Rock Creek or Brown's Lake District, is on the east slope of the northern Pioneer range. The mines are generally located along Rock Creek near Brown's Lake and on Twin Adams Mountain at the head of Lost Creek. The district was of minor importance with most of the total production coming from the Browns Lake (Ivanhoe) mine. With the end of the silver mining boom in 1893, the emphasis of mining switched to a search for non-precious metals. Increasing demand for metals such as lead, zinc, copper and tungsten resulted in the development of mines of non-precious metals. Work on mining properties of this type has been undertaken since the turn of the century, although usually on a small-scale, intermittent basis in the Pioneer range.
Improved technology, largely developed during World War II, and the post-war government stockpiling policy encouraged mining of non-precious metals. The tungsten deposits in the
Pioneers grew in significance. One such mine was the Ivanhoe located in Rock Creek Canyon, just west of Brown's Lake. The Ivanhoe claim was first opened in 1902, patented in 1903 and produced a small amount of ore in 1928 and 1929 which yielded 647 ounces of silver and 12,629 pounds of copper. Decades later, in 1942, R. C. McLaughlin studied some of the stockpiled ore with ultraviolet light and found fluorescent tungsten minerals. Following this discovery, McLaughlin and his associates organized Fluorescent Mines, Inc., and staked 17 mining claims, 15 on the north side of Rock Creek and two on the south side. A small tabling mill was set up in 1944 which produced tungsten concentrates from about 30 tons of tactite mined from the workings. The concentrate averaged 26 percent tungsten (Geach 1972).
Nothing more was done with the property until 1952 when the holdings were taken over by American Alloy Metals, Inc. who did some exploration work on the Ivanhoe claim. The next year American Alloy Metals leased the property to Minerals Engineering Company who worked the deposits. In 1954, Minerals Engineering Company bought the stock and assets from American Alloy and mined the deposits from an open-pit operation. The ore was treated at a 300-ton flotation mill located at Glen and the concentrates were processed by the Salt Lake Tungsten Company's mill where high purity synthetic scheelite was produced and then delivered to the General Services Administration.
From 1954 to 1956, the Brown's Lake deposit was Montana's leading producer of tungsten.
Production was stopped in 1958 after the government terminated its domestic stockpiling program. Up to that point, the mine produced 625,107 tons of ore, which in turn produced 2,188 tons of concentrate averaging 35 percent tungsten. It has been reported that the original mine tunnels of the Ivanhoe remain intact with some of the original machinery still inside, although the entrances have been covered by talus from recent workings on the property (Geach 1972).
The Minerals Engineering Company also developed the Lost Creek mine in 1951. The mine was located on the north slope of Twin Adams Mountain at an altitude of 6,800 to 7,900 feet and was the district's second largest producer of tungsten ore. From 1952 to August 1956, the property produced 21,150 tons of 18 percent tungsten ore (Geach 1972).
The Lost Creek district straddles the contact between quartz monzonite rocks of the Mount Torrey batholith and north-trending upturned sedimentary rocks. The batholithic rocks occupy the west half of the district and are bordered on the east by metamorphosed Paleozoic and Mesozoic sedimentary rocks The mineral wealth of the district has come from tungsten-bearing tactite zones developed in the Amsden Formation (Pennsylvanian). The Browns Lake (Ivanhoe) mine ore deposit is a tungsten-bearing tactite zone in the Amsden Formation at its contact with granitic rocks of the Mount Torrey batholith. The Lost Creek mine contains similar ores from the contact zone between the Amsden Formation and the quartz monzonite of the Mount Torrey batholith (Geach 1972).
BOUNDARIES OF THE DISTRICT
The boundaries of the Lost Creek district is described by Geach (1972) as the area on the east flank of the Pioneer Mountains which is drained by the two creeks for which the district is named -- Rock Creek and Lost Creek. Figure 1 is an arbitrary boundary which encompasses the mines of the district.
HISTORIES OF SELECTED MINES
There are few historic mining features left in the district. As noted above the Ivanhoe was the primary mine in the area with the Lost Creek mine developed in 1951. Other mining activity in the district was minimal. A "Reservoir Claim" was made by Brown in the 1890s. Brown, for whom the lake is named, constructed the first dam at the lake outlet. Log structures and other remains in the area of the lake also date to the 1890s and early 1900s and suggest minor prospecting activity.
Geach, R. D.
1972 Mines and Mineral Deposits (Except Fuels) Beaverhead County, Montana.
Montana Bureau of Mines and Geology Bulletin 85. Montana College of Mineral Science and Technology, Butte.
Krohn, Douglas H. and Margaret Mlynarczyk Weist
1977 Principal Information on Montana Mines. Montana Bureau of Mines and Geology Special Publication 75. Montana College of Mineral Science and Technology, Butte.
Mining Districts of Beaverhead County
n.d. Compiled under Federal Emergency Relief Act Projects No. 8 F4-82 (unpublished). Montana Bureau of Mines and Geology's files of Montana mining properties, Montana College of Mineral Science and Technology, Butte.
Montana Bureau of Mines and Geology
n.d. Files of Montana mining properties. Montana College of Mineral Science and Technology, Butte.
Pattee, Eldon C.
1960 Tungsten Resources of Montana: Deposits of the Mount Torrey Batholith, Beaverhead County. United States Bureau of Mines Report of Investigations 5552. U.S. Department of the Interior Bureau of Mines, Washington, D.C.
Trauerman, Carl J. and Millard L. Reyner
1950 Directory of Montana Mining Properties: 1949. Montana Bureau of Mines and Geology Memoir No. 31. Montana School of Mines, Butte.
United States Department of Interior
n.d. Bureau of Land Management, Mineral Survey Records, Butte, Montana.
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