Privacy | Legal

Table of Contents Back | Next | Cover Page

Technology & Development Center

Adit Discharge Summary for the Elkhorn and Charter Oak Mines, MT

The Elkhorn Mine

The Elkhorn Mine is on patented mining claims and land administered by the Beaverhead-Deerlodge National Forest in T4S-R12W, Section 14 (AADD) and Section 11 (DDDB) near the “ghost town” of Coolidge, MT. The site was identified in 1998 by the Montana Bureau of Mines and Geology and the Forest Service as having several potential environmental impacts to water and soil (Marvin and others 1998). At the lower site, the adit was discharging over 100 gallons per minute of poor quality water (figure 6).

Figure 6—The Elkhorn Mine lower adit is gated to prevent persons
from being exposed to toxic gases at the mine’s entrance.

The mine was first worked in 1872. It eventually expanded to 24,000 feet of workings on two levels, each exploiting a large vein. The Park vein strikes N50E; the Idahna vein strikes east-west (Geach 1972). In its initial development, the mine produced 15 tons of high-grade ore that contained 500 to 800 ounces of silver per ton. Ore from the first 50 feet of shaft had 15- percent copper. After a period of inactivity from 1893 to 1906, the Boston-Montana Development Company operated the mine. The mine was serviced by rail along the Wise River. In 1927 the reservoir at Pattengil breached and destroyed a large section of the line; this, along with low silver prices closed the mine and mill in 1930. The railroad, completed in 1919, cost $1,500,000 to build. The mill, completed in 1922, cost $900,000 (Sassman 1941). The mine was reorganized in 1944 as the Boston Mines Co.

Ruppel and others (1983) reported that the ore is hosted in a Late Cretaceous quartz monzonite or granite associated with the Pioneer Batholith. One set of veins strikes north 50 degrees east and dips 65 to 85 degrees southeast. The other minor set strikes generally east-west and dips steeply to the north (Evans 1946). Vein minerals included quartz, pyrite, tetrahedrite, galena, sphalerite, chalcopyrite, and molybdenite.

The discharge from the adit at the Elkhorn Mine was monitored with a 3-inch parshall flume and a chart recorder (figures 7a, 7b, and 7c). The flume and recorder were installed just inside the portal, which had recently been repaired.

Figure 7a—The flume used to measure flow at the
Elkhorn Mine is shown left of center.

Figure 7b— The field water-quality parameters were
recorded by a sonde suspended from a rope in
the pool upstream of the flume.

Figure 7c— Note the dark staining on the timbers in the
lower right of the photograph. These stains are the high-water mark.

Top Back | Next Table of Contents Cover Page

E-mail: wo_mtdc_webmaster@fs.fed.us	Technology & Development Center

Visitor since March 17, 2005