The Thompson River mining district in Sanders County encompasses most of the Thompson River drainage (the northwestern portion is not included in the district). The Thompson River flows south into the Clark Fork River, entering it near Thompson Falls. The primary mines are located in the southwest corner of the district about nine miles northeast of Thompson Falls (Sahinen 1935; Crowley 1963).
The most prominent mines in the district are grouped in a small area on both sides of the river about 3 1/2 miles north of the highway along the Clark Fork. In the early 1880s a number of mines in the area were being developed. Many of these produced small lots of rich ore, such as the Silver King, Buckeye, Ohio, Climax, Pay-Master, and Treasury. There are no production records for the period prior to 1906, but production of placer gold from Sanders County between 1906 and 1961 totaled 571 ounces of gold and 86 ounces of silver, for a total value of $17,184. In 1915 the Montana Power Company completed a hydroelectric plant at Thompson Falls which provided electricity for mining operations. The town of Thompson was renamed Thompson Falls at that time (Crowley 1963; Wyss & Axline 1991).
The real development of the region began in 1883 with the arrival of the Northern Pacific Railroad. The total production from the district from 1906 to 1958 was 943 tons of ore yielding 3 ounces gold, 27,118 ounces silver, 143,535 pounds copper, 115,602 pounds lead, and 5,700 pounds zinc. The average grade for all the ore was 28.76 ounces silver per ton, 7.6 percent copper, 6.1 percent lead, and 0.97 percent zinc (Crowley 1963).
The bedrock along the Clark Fork and Flathead River valleys between Ravalli and the Idaho boundary formed during the Precambrian era and is mostly sedimentary (Belt) formations. Much of the rock is of the Prichard formation. Glacial Lake Missoula was created about 15,000 years ago by an ice dam and covered much of the Clark Fork River valley as well as land to the east. The entire flow of the Clark Fork River backed up behind the dam, and the glacial lake reached an elevation of about 4350 feet When the ice dam failed, Glacial Lake Missoula emptied through the Clark Fork Valley in just a few days, releasing the greatest flood of known geologic record. This process occurred repeatedly, each time resulting in colossal floods. The passage of the torrents of water during the flooding scoured the narrow stretches of the valley, especially between Perma and Plains and several miles east of Thompson Falls. Exposed bedrock and sedimentary deposits provide evidence of the long - ago rushing floodwaters through the valley, as do ripple marks in Camas Prairie (Alt & Hyndman 1986).
The ore deposits in the district are associated with sedimentary rocks of the Belt series of Proterozoic age (Sahinen 1935). According to Crowley (1963):
...the Thompson River transects a series of folded Beltian sediments composed predominantly of Ravalli group and Wallace Formations. For the northern two-thirds of its length the river flows through a broad area of Quarternary alluvium composed of reworked glacial moraines, normal stream gravels, and glacial clays. It can be inferred, however, that the axis of a broad syncline is buried beneath this unconsolidated material. The southern end of the river near its junction with the Clark Fork River cuts diagonally across a major anticline which exposes a core of Ravalli Formation rock and flanks of overlying Wallace Formation farther upstream.
BOUNDARIES OF THE DISTRICT
Crowley (1963) defined the Thompson River district as encompassing the entire drainage system of the river. Figure 1 shows the AMRB (1994) district which essentially follows Crowley's (1963) definition. However, most of the mines are located in small area which is also delineated on the map.
HISTORIES OF SELECTED MINES
The Copper King mine (also known as the Mascot) is located in the SE1/4 of Section 33, T22N, R28W, on the west slope of the Thompson River about 3 1/2 miles north of the Clark Fork River. The vein was discovered in the 1880s, when 30 men were working at copper mines and shipping copper ore to Butte from this area. In 1909 the mine was reopened after an apparent shutdown, then was closed again until 1911. In 1913 a small shipment of copper-silver ore was made, and then production ceased until 1919. The mine produced on a small scale for about eight years. A small lot of copper ore was shipped from the mine in 1919, and a lot of sulphide copper ore was shipped in 1920. In 1922 copper ore containing some silver was shipped, and it also produced in 1923 and 1925. In 1926 a car of sulphide copper ore was shipped from the dump of the Copper King. In 1948, F. R. Walkely shipped the largest tonnage from the Mascot claim. Total production between 1913 and 1948, from 368 tons of ore, was 2 ounces gold, 5,647 ounces silver, and 97,904 pounds copper (Crowley 1963; Sahinen 1935; WPA 1941;
1919, 1920, 1922, 1923, 1925).
The minerals are predominantly copper. Argentiferous tetrahedrite is most abundant, followed by chalcopyrite, then bornite, with pyrite and enargite in small amounts (Crowley 1963).
The Copper Mask mine (also known as the Raven) is located in the SW1/4 of Section 33, T22N, R28W, and the NW1/4 of Section 4, T21N, R28W, on the northwest slope of the Thompson River canyon about 3 1/4 miles north of the Clark Fork River. A mill and lower adit are located several hundred yards northwest of the Thompson River road, and the main working adit is 400 feet higher on the slope (Crowley 1963).
The mine was probably worked in the 1880s, but its name at that time is not known. It was called the Copper Mask beginning in 1919, and in 1959 new owners changed the name to the Raven. In 1931 the Copper Mask Mining Company operated the mine and shipped ore to the Washoe reduction works at Anaconda. The ore yielded copper, silver, and gold. A small lot of copper ore was shipped from the Copper Mask in 1919. The mine also produced in 1923 and 1925. Development continued in 1929 and 1930, and in 1931 a car of sulphide copper ore was shipped from the mine. In 1935 the mine had three employees. Production from 85 tons of ore at the Copper Mask in the years 1919 to 1934 was one ounce gold, 5,695 ounces silver, and 33,173 pounds copper. The last recorded production prior to 1958 was in 1934 (Crowley 1963; Sahinen 1935; Mineral Resources 1919, 1923, 1925, 1929, 1930, 1931).
In the early 1960s, there were four adits at the mine and surface facilities including mine roads, a small concentrating mill, and a storage shed (Crowley 1963).
Some sulphide copper ore was shipped from the Iron Mask property in 1920. The ore at the mine carried some gold and silver (
1920; Sahinen 1935).
The Sales prospect is located in the northern part of the district on the ridge between the headwaters of the east fork of Whitney Creek and the headwaters of Indian Creek in parts of Section 1, T25N, R28W, Section 6, T25N, R27W, and Section 36, T26N, R28W. It was owned by Ruth and Gordon Sales of Kalispell in the early 1960s (Crowley 1963).
The Sales Mining Corporation was organized in 1920 and drove about 600 feet of tunnel that year. Assays ran $25.38 to $96 per ton in silver and copper. There were apparently two adits on the property, one near creek level and the other 150 feet above that, and a copper-precipitating plant. Bedrock in the area belongs to the Striped Peak Formation, and several faults cut through the area. Chalcopyrite was the only sulfide mineral found at the prospect. More common were the secondary copper minerals (Crowley 1963).
The Silver Cable mine on the Thompson River, nine miles northeast of Thompson Falls, was a silver-lead mine. It was discovered in 1884 or 1895 and was moderately active beginning in 1919, with shipments averaging $1,000 a year (Wolle 1963).
The Silver King mine is located on the southeast side of the Thompson River about 3 1/2 miles north of the highway along the Clark Fork River. It is in the NW1/4 of Section 3, T21N, R28W (Crowley 1963).
In 1890 the mine (then known as the Belle Stowe) was the most productive in the district. Shipments were rich in silver, copper, and lead (with some nickel and cobalt), and yielded $900 to $1,000 per carload. In 1890 the mine had been developed by two perpendicular tunnels. The mine was shipping about 20 tons of silver-bearing lead sulphide ore per week and employed 30 men. It reportedly produced $100,000 up to 1919 (Crowley 1963).
In 1920 the Silver King Mining Company was developing the property. One vein assayed 54 percent lead and 4 ounces of silver per ton. At that time one tunnel was 1800 feet long. Ore was shipped from the mine in 1917. In 1921 one shipment of lead ore was made from the Silver King mine, and the next year a shipment of copper ore containing some silver was shipped. The mine also shipped silver-lead ore in 1923, 1924, 1925, and 1926. In 1928 a lessee operated the mine and shipped one car of sulphide silver-lead ore (and opened a body of first-class silver-lead ore). By 1928 the Silver King Leasing Company was developing the mine, leasing it from A. L. Anderson. Test shipments brought returns of $70.60 per ton. That same year the Lloyd Mining Company was organized to operate the mine and build a lower tunnel. In 1929 Judge George Turner leased the property and was working on the lower tunnel, and ore was shipped in 1931 and 1934. R. D. Trebolet leased the group of claims at the Silver King in 1950 and hired two men. He made ore shipments high in lead (Crowley 1963; Mineral Resources 1921-1926, 1928; WPA 1941).
Total production at the mine was 477 tons of ore yielding no gold, 15,272 ounces of silver, 13,089 pounds of copper 110,332 pounds of lead, and 5,300 pounds of zinc. The Silver King was the only mine that produced lead and zinc in the immediate area (the Copper King and the Copper Mask did not) (Crowley 1963).
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
Alt, David, and Donald W. Hyndman
Roadside Geology of Montana
. Missoula: Mountain Press Publishing Company.
Crowley, F. A.
1963 "Mines and Mineral Deposits (Except Fuels), Sanders County, Montana." Butte: Bureau of Mines and Geology, Bull. 34.
1919 p. 526. 1920 p. 214. 1921 p. 1922. 1922 p. 481. 1923 pp. 473-474. 1924 p. 360. 1925 p. 654. 1926 p. 408. 1928 p. 600. 1929 p. 869. 1930 p. 424. 1931 p. 507.
Sahinen, Uuno Mathias
Mining Districts of Montana
. M. S. thesis, Montana School of Mines.
Wolle, Muriel Sibell
Montana Pay Dirt: A Guide to the Mining Camps of the Treasure State
. Denver: Sage Books.
Works 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.
Wyss, Marilyn, and Jon Axline
1991 "Cultural Resource Inventory and Assessment of F6-1(48)52, Thompson Falls - East." Prepared for Montana Department of Highways.