Geochemistry and Stable Isotopes of Surface Water and Groundwater in the Continental Pit in Butte, Montana, USA

The Continental porphyry Cu‐Mo mine, located 2 km east of the famous Berkeley Pit lake of Butte, Montana, contains two small lakes that vary in size depending on mining activity. In contrast to the acidic Berkeley Pit lake, the Continental Pit waters have near-neutral pH and relatively low metal concentrations. The main reason is geological: whereas the Berkeley Pit mined highly‐altered granite rich in pyrite with no neutralizing potential, the Continental Pit is mining weakly‐altered granite with lower pyrite concentrations and up to 1‐2% hydrothermal calcite. The purpose of this study was to gather and interpret information that bears on the chemistry of surface water and groundwater in the active Continental Pit. Pre‐existing chemistry data from sampling of the Continental Pit were compiled from the Montana Bureau of Mines and Geology and Montana Department of Environmental Quality records. In addition, in March of 2013, new water samples were collected from the mine’s main dewatering well, the Sarsfield well, and a nearby acidic seep (Pavilion Seep) and analyzed for trace metals and several stable isotopes, including dD and d18O of water, d13C of dissolved inorganic carbon, and d34S of dissolved sulfate. In December 2013, several soil samples were collected from the shore of the frozen pit lake and surrounding area. The soil samples were analyzed using X‐ray diffraction to determine mineral content. Based on Visual Minteq modeling, water in the Continental Pit lake is near equilibrium with a number of carbonate, sulfate, and molybdate minerals, including calcite, dolomite, rhodochrosite (MnCO3), brochantite (CuSO4·3Cu(OH)2), malachite (Cu2CO3(OH)2), hydrozincite (Zn5(CO3)2(OH)6), gypsum, and powellite (CaMoO4). The fact that these minerals are close to equilibrium suggests that they are present on the weathered mine walls and/or in the sediment of the surface water ponds. X‐Ray Diffraction (XRD) analysis of the pond “beach” sample failed to show any discrete metal‐bearing phases. One of the soil samples collected higher in the mine, near an area of active weathering of chalcocite‐rich ore, contained over 50% chalcanthite (CuSO4·5H2O). This water‐soluble copper salt is easily dissolved in water, and is probably a major source of copper to the pond and underlying groundwater system. However, concentrations of copper in the latter are probably controlled by other, less‐soluble minerals, such as brochantite or malachite. Although the acidity of the Pavilion Seep is high (~ 11 meq/L), the flow is much less than the Sarsfield Well at the current time. Thus, the pH, major and minor element chemistry in the Continental Pit lakes are buffered by calcite and other carbonate minerals. For the Continental Pit waters to become acidic, the influx of acidic seepage (e.g., Pavilion Seep) would need to increase substantially over its present volume.

A Discussion of the Geology and an Isopach Map of the Pennsylvanian System in Wyoming and Adjacent Areas

Pennsylvanian strata in Wyoming and adjacent areas have been the subject of much work and discussion. Most of the work has been due to the economic importance of the system as an oil producer in this region. Oil production from strata of Pennsylvanian age is rather recent history; and therefore, much of the available information is local­ized and incomplete.

Remembering Lee Metcalf - Natural Resources, Environmental and Conservation Excerpts (done for 75th Anniversary of Montana State Parks System - 2014)

Montana's Lee Metcalf was an extraordinary Montana leader with an unbelievable record of accomplishment fighting for the little people against the forces of economic and political power. The public memory is so short that this film will serve to help reacquaint Lee & Donna Metcalf to most of those who were around during their time. But it will also provide an opportunity for new generations to receive a perspective of an important leader from an important time. (Language from YouTube version of the film, written and provided by Executive Producer Evan Barrett) Lee Warren Metcalf (January 28, 1911 – January 12, 1978) was an American lawyer, judge, and politician. A member of the Democratic Party, he served as a U.S. Representative (1953–1961) and a U.S. Senator (1961–1978) from Montana. He was permanent acting President pro tempore of the Senate, the only person to hold that position, from 1963 until his death in 1978. Excerpts from main film for 75th Anniversary of Montana State Parks System