Figure 9-The Beatrice Mine is in the Helena National Forest about 13 miles southwest of Helena, MT. The mine's upper workings discharge water only during the spring and early summer. The water that contributes to the discharge probably comes from the flooded pits above the mine workings.

The ore body mined at the Beatrice Mine is a roughly east-west striking, steeply dipping, 4-foot-thick vein of quartz, pyrite, galena, sphalerite, and chalcopyrite. Ruppel (1963) described the workings as including a 450-foot-long adit, a 600-foot crosscut, a 300-foot drift and a 400-foot inclined shaft. The mine operated from 1901 to 1903. No production records are available.

Figure 10-Mine waste was deposited in the wetlands below the Vindicator Mine in southwestern Montana. Waste rock at the site is generating acid mine drainage. Precipitates are deposited in the stream below the mine site.

The mine was visited twice. In early summer, several active discharges visibly affected the water quality of the unnamed tributary. The upper adit had an estimated discharge 20 gal/min that increased the specific conductance of the tributary by a factor of five (conductance upstream of the tributary: 47 µmhos/cm; conductance downstream of the tributary: 243 µmhos/cm). Precipitation of iron-oxyhydroxides was extensive along the entire drainage near the mine. In the uppermost portion of the disturbed area were several open pits, both natural and excavated, with standing or flowing water. All of the mine openings and associated waste-rock dumps are within the same shallow, ephemeral drainage.

In late summer, most of the upper area was dry. There was some standing water in a few of the open pits, but no flowing water. Both adits were dry. In fact, the only flowing water in the area was a small unnamed stream to the south and a spring emerging from the wetlands (Figure 10) well below the workings. Samples collected at that time indicated increased loading of aluminum, copper, and iron to the drainage. The specific conductance and pH of the water collected within the wetlands below the site suggested a significant groundwater contribution from the mine workings.

The large seasonal change in the rate of flow from the underground workings (about 20 gal/min in early summer to zero in late summer) indicates that the groundwater recharge zone is close to the mine. The natural depressions and excavations in the area above the mine probably serve as retention and infiltration basins for the workings. If the elevation of the highest discharge point is taken as an approximation of the groundwater surface, the seasonal fluctuation of groundwater levels within the workings is on the order of tens of feet.

Figure 11-A disturbed stream channel at the Beatrice Mine site near Helena, MT. The stream is filled with iron hydroxide (precipitated by acid mine drainage).

Reducing or eliminating adit discharges on this site should probably focus on two aspects. Backfilling and regrading both the natural and excavated area above the mine would probably reduce a significant amount of the recharge to the mine workings. Soil treatment with low-permeability material may further reduce infiltration. Additional removal of waste material from the drainage (Figure 11), along with regrading and soil treatments, would reduce metals loading and infiltration in the vicinity of the lower shaft and adits.

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