  Privacy
| Legal |
Table of Contents Back | Next | Home | Cover Page |
 Technology & Development Center |
Investigative Methods for Controlling Groundwater Flow to Underground Mine Workings
 |
| Figure 3—The discharge from the lower Elkhorn Mine adit ranges from 80 to 135 gallons per minute. The discharge stream eventually reaches Elkhorn Creek, a tributary to the Wise River. |
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 on Elkhorn Creek, the adit was discharging over 100 gallons per minute of poor-quality water. Additional flow and chemistry data were collected from the lower adit in 1998 and 1999. The concentration of several dissolved constituents in the main adit discharge (figure 3) exceeded secondary and primary drinking water standards as well as acute and chronic aquatic life criteria (table 1).
The Park Mine is also associated with the Boston and Montana group of mining claims forming the Elkhorn mining district. The mine is included in this investigation because the workings of the Elkhorn Mine extend toward the Park Mine. Loen and Pearson (1989) listed the mine as being associated with the Cretaceous granodiorite or quartz monzonite of the Pioneer Batholith. Winchell (1914) stated that the Park Group’s fissure veins are 20 to 30 feet thick, striking northeast and dipping 75° NW. He said the veins are associated with aplite dikes in the quartz monzonite. One sample taken by the U.S. Bureau of Mines (1995) ran 3.8 ounces per ton gold, 0.67-percent copper, 2.7-percent lead, and 3.9-percent zinc. Another ran 0.07 ounces per ton silver, 4.7 ounces per ton gold, 0.17-percent copper, 0.59-percent lead, and 0.60-percent zinc. A third sample ran 1.05 ounces per ton gold, a fourth ran 5.8 ounces per ton gold, and a fifth ran 2.6 ounces per ton gold—all with minor copper, lead, and zinc. Work-ings at the site consist of two adits, three shafts, and several small prospects. They are presently flooded. At certain times of the year, the area has standing water in many of the depressions resulting from mining. Table 2 presents selected water quality data for the Park Mine.
|
Elkhorn Mine Water Quality Data
|
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
|
Sample date |
pH |
Iron (mg/L) |
Sulphate (mg/L) |
Aluminum (µg/L) |
Arsenic (µg/L) |
Cadmium (µg/L) |
Copper (µg/L) |
Nickel (µg/L) |
Lead (µg/L) |
Zinc (µg/L) |
9/09/96 |
4.83 |
1.6 |
130 |
851 |
4.0 |
21.5 |
1,115 |
4.2 |
66.9 |
3,812 |
11/25/98 |
6.11 |
0.04 |
111 |
<30 |
4.20 |
12.6 |
264 |
5.8 |
<2.0 |
2,380 |
6/02/99 |
5.88 |
0.316 |
105 |
110 |
4.01 |
10.2 |
381 |
<2.0 |
16.3 |
3,520 |
7/30/99 |
5.52 |
0.334 |
103 |
360 |
3.44 |
17.2 |
526 |
2.2 |
80.2 |
2,860 |
9/02/99 |
5.61 |
1.490 |
118 |
232 |
3.29 |
14.9 |
483 |
2.4 |
36.9 |
2,810 |
10/05/99 |
6.17 |
0.309 |
103 |
126 |
3.39 |
13.1 |
283 |
2.6 |
7.8 |
2,380 |
11/09/99 |
6.06 |
0.193 |
103 |
108 |
3.36 |
11.9 |
263 |
2.5 |
9.8 |
2,390 |
|
Park
Mine Water Quality Data |
|||||||||
|---|---|---|---|---|---|---|---|---|---|
|
pH |
Iron (mg/L) |
Sulphate (mg/L) |
Aluminum (µg/L) |
Arsenic (µg/L) |
Cadmium (µg/L) |
Copper (µg/L) |
Nickel (µg/L) |
Lead (µg/L) |
Zinc (µg/L) |
| 9/12/96,
at adit discharge |
|||||||||
| 6.4 | 0.55 | 19.5 | <30 | 2.1 | <2 | 47.3 | <2 | 21.9 | 348.6 |
| 9/12/96,
upstream of mine |
|||||||||
| 6.1 | 0.14 | 2.8 | <30 | <1.0 | <2 | <2 | <2 | <2 | 12.7 |
The Elkhorn Mine has been described as consisting of 15 miles (almost 80,000 feet) of tunnels (in a Montana Bureau of Mines and Geology mineral property file), 40,000 feet of tunnels (Sassman 1941), or 24,000 feet of workings on two levels—each exploiting a large vein (Evans 1946, Geach 1972). The discrepancy reflects the reliance on company records and promotional articles. Unpublished maps in the Montana Bureau of Mines and Geology files are probably incomplete, but they do give some indication of the extent of the workings. A compilation of these maps (figure 2) shows workings extending from the main adit of the lower Elkhorn Mine to the upper Elkhorn Mine west of the main adit, and toward the Park Mine southwest of the main adit. Only a small amount of information is available on the underground workings for the mine. There was no information indicating that the workings of the Elkhorn Mine had reached the workings of the Park Mine. The No. 1 raise, a 700-foot working, was driven from the 1,000-foot level through the Idanha vein system to the 300-foot level (Evans 1946). It was reported to be open and in good condition in 1946. A 400-foot level and an 800-foot level were driven off of this raise. These workings not only may serve as conduits for water, but also may serve as storage reservoirs.
Unpublished reports from the time the mines were operating described the conditions encountered in the mine. Information gleaned from the Montana Bureau of Mines and Geology mineral property files found reference to water in the workings from the early days of mining. The shaft at the upper Elkhorn was “unwatered” as early as 1909 to allow work in the mine to resume (Montana Bureau of Mines and Geology mineral property file, no author, no date). The 2,300-foot-deep shaft was full of water to within 250 feet of the mouth. Evans (1946) stated that workings were “sunk as deep as excessive flows of water would permit.” W.R. Butler (no date) mentioned an 8- by 7-foot tunnel driven to access the veins that had been worked from above (this would be the lower Elkhorn adit). The 300-foot level and the 1,000-foot-level tunnels were not only drilled to develop the ore bodies, but also to drain the workings. Of at least 24,000 feet of tunnel at the Elkhorn Mine, 10,000 feet were on the 300-foot level and 14,000 feet or more were on the lower, 1,000-foot level. The report says that development “served to drain all the vast area above the 1,000-foot level and to dry up the water in many of the vein fissures.” The same report describes the “excessive downpours of water over the stopes.”
A report on the Park Mine (Dickman 1913), stated that groundwater in the mine “has proven an obstacle to development by shaft work.” This report describes the mineralization filling “breaks” or fissures in the host rock. These fissures trended east-west and northwest-southeast. A third set of fissures were crosscutting. These fissures were a series of faulted and mineralized zones. The report does not state that these are water-bearing openings, but there is a strong possibility that they are.
These references to water in the workings as they were being mined leads to the conclusion that the flooding and subsequent discharges in the Elkhorn mining district are directly related to groundwater flow along the numerous faults and fractures in the area. Controlling the discharge through surface remediation may not be feasible.
 |
E-mail: