The Plains mining district is located in Sanders County south of the Clark Fork River and the town of Plains and south of the Mineral County line. Both Eddy Creek and Swamp Creek in the northern half of the district were prospected beginning in the early 1900s. Production in the district was quite low. For example, in 1933 one lode mine produced one ton of ore valued at $44 (WPA 1941; Crowley 1963).
The ore consists of free gold, some gold tellurides and fine gold in iron pyrites. The gangue mineral is mainly quartz, but there is also some galena and apatite. The average value of all the ore assayed is $30-40 per ton (Rowe 1911).
Although the area became accessible in 1872 when a trail was built over the mountains following Swamp Creek connecting with the Mullan Road at St. Regis, the real development of the region began in 1883 with the arrival of the Northern Pacific Railroad. A find of rich tellurium float on Prospect and Eddy Creeks started a stampede of prospectors into the area in 1906 but nothing further was reported on the telluride finds. Between 1906 and 1919 many companies did development work in the Eddy Creek area, but apparently none succeeded in finding economically recoverable ore (Helterline 1984; Crowley 1963).
Eleven patented claims on Eddy Creek were named for W. B. Russell, who patented the claims. They were later owned by the State Mining Company and by John W. Miller, who also developed several galena-bearing quartz veins on Swamp Creek (the latter workings were known as the Johnny Miller). In 1962 both of these prospects were reopened (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. The surficial geology of the district was formed by Glacial Lake Missoula which 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 Parma 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 and Hyndman 1986).
Most of the district is underlain by argillites of the Prichard Formation, although the lower Ravalli Formation conformably overlies the Prichard along the western margin of T18N, T19N, and T20N, R26W. Massive sills of gabbro are conformable with the bedding in the Prichard west of Plains and west and south of Paradise. Mineralization is associated with, or is near, a sill especially in areas intruded by gabbro. Eddy Creek and Swamp Creek have cut steep canyons across a northwest-striking anticline, exposing the Prichard Formation at its center and the overlying Ravalli formation on its limbs. Many quartz veins containing galena and arsenopyrite have been uncovered on both creeks (Crowley 1963).
Five veins run through the area, varying in width from a few inches to several feet. Those found in the diabase or basic igneous rock are true fissure veins, and those found in the shales or slates conform to the bedding planes but were deposited after the country rock was pushed up by the igneous intrusion. According to Rowe (1911), the monocline is "probably one side of an anticline pushed up by the igneous rocks from below."
BOUNDARIES OF THE DISTRICT
Crowley (1963) described the Plains district as "an almost indefinable area surrounding the town of Plains." He considered the drainages of Eddy Creek and Swamp Creek as a separate district, which he called the Eddy Creek-Swamp Creek mining district (T20N and northern parts of T19N, R27W and R28W):
...the Plains district embraces T. 20 N., R. 25 and 26 W., T. 19 N., R. 25 and 26 W. and the N1/2 of T. 18N., R. 25 and 26 W. The northern two townships are included only because Rainbow (Dog) Lake is in this area. The southern portion is included because of the arsenic-cobalt occurrence and No. 10 Tunnel prospect, which are along the northwest side of the Clark Fork River.
A 1906 article referred to the Eddy Creek district as being located "on the south side of the river between Thompson [Falls] and Plains" (Anaconda Standard 1906).
The AMRB (1994) map (Figure 1) shows the Plains district as encompassing what is noted by Crowley (1963) and the Anaconda Standard (1906) as the Eddy Creek-Swamp Creek sub-district. Figure 1 shows the divisions of the Plains and Eddy-Swamp Creek sub-districts.
HISTORIES OF SELECTED MINES
There were reportedly one or two prospects between the West Fork of Swamp Creek and Dee Creek, with mineralization similar to that at the Johnny Miller and the R & M # 1 mines (Crowley 1963).
The Dog Lake mine was presumably located near Rainbow Lake, which used to be known as Dog Lake (this lake is located in the northeast corner of the district) (Crowley 1963).
The Eddy Mining and Milling Company was organized in November 1905 to develop claims on Eddy Creek. A 1906 newspaper article mentioned the Eddy, Coeur d'Alene Star, Big Missouri, and other properties owned by W. B. Russell, being developed and worked. The Eddy mine was being developed in 1906 by an adit, and the ore reportedly contained $8 to $36 per ton in gold, silver, and lead. Later that year the adit intercepted a vein containing high-grade, lead-silver ore. The "big ledge" at the mine ran from 26 percent to 42 percent lead and had good values in silver. A crosscut was driven to intercept the lead. Three miles of road led to the mine, a gravity waterworks system was installed at the camp, and a 6-drill compressor was planned (Crowley 1963; Helterline 1984; Anaconda Standard 1906).
The Johnny Miller prospect (also known as the Miller mine) is located in the SW1/4 of Section 31, T20N, R27W, on the West Fork of Swamp Creek about 14 miles southwest of Plains. It was developed with adits and shafts, with about 800-1000 feet of underground workings (Crowley 1963).
The Montana Premier mine was also known as the Plains Gold mine, and as the Letterman for the man who discovered the prospect and did the early development work. It is located two miles south of Plains in parts of Sections 3 and 10, T19N, R26W, and Section 34, T20N, R26W (Crowley 1963; Rowe 1911).
The mine was first mentioned in 1911. The controlling company was the Clark Fork Gold Mining Company. Average values per ton of ore were reportedly $30 to $40 in free gold and gold tellurides, plus small amounts of galena. In early 1929 the Montana Premier Gold Mining Company formed to operate the property. Pits and shallow shafts exposed a vein for 200 feet at that time. Samples taken along the vein carried $2.40 to $72 in gold and a trace to 14.46 ounces of silver, with an average value of $36.80 per ton. In 1932 C. L. Wickstrom leased the mine, but in 1939 the Montana Premier Gold Mining Company was again operating it. The mine was reportedly last operated in 1940, although in 1947 it was reporeted to have values in gold, silver and lead. The principal development at the mine is a 470-foot crosscut adit (Crowley 1963; Sandvig 1947).
No. 10 Tunnel
A small prospect adit is located just south of the No. 10 Tunnel on the Northern Pacific Railroad between St. Regis and Paradise, in Section 9,T18N, R25W. The 20-foot adit intersects a vein composed of quartz with scattered pods of galena, pyrite, native silver, and sphalerite. A sample contained 11.1% lead, 0.02 ounces gold, and 4 ounces of silver per ton (Crowley 1963).
The location of the Poorman mine is not known. It produced in the early 1900s, shipping gold-bearing ore to a smelter in 1906 (Crowley 1963; WPA 1941).
R & M #1
The R & M #1 prospect is located about 1 1/2 miles west (by trail) of the Johnny Miller on Swamp Creek. It was developed by a short adit driven along a vein in argillite (Crowley 1963).
The Russell Group of claims is located on the western edge of the district in Sections 16 and 21, T20N, R28W. The area is underlain by one or more sill-like bodies with a mineral composition ranging from diorite to gabbro. The outline of the mineral bodies parallels the prevailing strike of the bedded argillites, which are believed to be a part of the upper Prichard Formation (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
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Crowley, F. A.
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Horse Plains, Montana Territory
. Plains: The Printery.
1906 "In New County of Sanders." 16 December, p. 4.
Rowe, Jesse Perry
1911 "Gold Quartz Mining in Western Montana",
, Vol. 34, No. 20, pp. 1033-1034.
Sandvig, Robert L.
1947 "General Geology and Mines of Northwestern Montana." B.S. thesis, Montana School of Mines.
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
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