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Butte, MT, United States

Bakun W.H.,U.S. Geological Survey | Stickney M.C.,Montana Bureau of Mines and Geology | Rogers G.C.,Geological Survey of Canada
Bulletin of the Seismological Society of America

The largest historical earthquake in the northern Great Plains occurred on 16 May 1909. Our analysis of intensity assignments places the earthquake location (48.81° N, 105.38° W) close to the Montana-Saskatchewan border with an intensity magnitude M I of 5.3-5.4. Observations from two seismic observatories in Europe give an average M s value of 5.3. The 1909 earthquake is near an alignment of epicenters of small earthquakes in Montana and Saskatchewan and on strike with the mapped Hinsdale fault in Montana. Thus, the 1909 earthquake may have occurred on a 300-km-long seismically active fault, which could have seismic-hazard implications for the region, particularly for the hydraulically emplaced earth-filled Fort Peck Dam, constructed in the 1930s on the Missouri River in northeast Montana. Source

Castendyk D.N.,New York University | Balistrieri L.S.,U.S. Geological Survey | Gammons C.,Montana Tech of the University of Montana | Tucci N.,Montana Bureau of Mines and Geology
Applied Geochemistry

Pit lakes, a common product of open pit mining techniques, may become long-term, post-mining environmental risks or long-term, post-mining water resources depending upon management decisions. This study reviews two published pit lake modeling studies and one pit lake monitoring program in order to increase the transparency of approaches used in pit lake prediction and management. The first model is a two-year limnological simulation of the existing Dexter pit lake, Nevada, USA that accurately modeled temperature profiles, salinity profiles, and turnover events observed between 1999 and 2000. The second model is a 55-year prediction of a future pit lake in the Martha Mine, New Zealand that identified the need for additional mitigation and evaluated potential effects of cost-effective mitigation options. The final study reviews eight years of monitoring data collected from the Berkeley pit lake, Montana, USA, from 2004 to 2012. This study identifies changes in the physical limnology and water quality of the pit lake that resulted from metal recovery operations, and highlights the value of monitoring programs in general. Whereas these pit lakes are different in many ways, the management tools discussed herein maximized the value and understanding of the post-mining resources. © 2014 Elsevier Ltd. Source

Gammons C.H.,Montana Tech of the University of Montana | Duaime T.E.,Montana Bureau of Mines and Geology | Parker S.R.,Montana Tech of the University of Montana | Poulson S.R.,University of Nevada, Reno | Kennelly P.,Long Island University
Chemical Geology

The Great Falls-Lewistown Coal Field (GFLCF) in central Montana contains over 400 abandoned underground coal mines, many of which are discharging acidic water with serious environmental consequences. Areas of the mines that are completely submerged by groundwater have circum-neutral pH and relatively low concentrations of metals, whereas areas that are only partially flooded or freely draining have acidic pH (<3) and high concentrations of metals. The pH of the mine drains either decreases or increases after discharging to the surface, depending on the initial ratio of acidity (mainly Al and Fe 2+) to alkalinity (mainly HCO 3 -). In acidic, Fe-rich waters, oxidation of Fe 2+ after exposure to air is microbially catalyzed and follows zero-order kinetics, with computed rate constants falling in the range of 0.97 to 1.25mmol L -1 h -1. In contrast, Fe 2+ oxidation in near-neutral pH waters appears to be first-order with respect to Fe 2+ concentration, although insufficient data were collected to constrain the rate law expression. Rates of Fe 2+ oxidation in the field are dependent on temperature such that lower Fe 2+ concentrations were measured in down-gradient waters during the day, and higher concentrations at night. Diel cycles in dissolved concentrations of Zn and other trace metals (Mn, Ni) were also noted for down-gradient waters that were net alkaline, but not in the acidic drains.The coal seams of the GFLCF and overlying Cretaceous sandstones form a perched aquifer that lies ~50m above the regional water table situated in the underlying Madison Limestone. The δD and δ 18O values of flooded mine waters suggest local derivation from meteoric water that has been partially evaporated in agricultural soils overlying the coal mines. The S and O isotopic composition of dissolved sulfate in the low pH mine drains is consistent with oxidation of biogenic pyrite in coal under aerated conditions. A clear distinction exists between the isotopic composition of sulfate in the acid mine waters and sulfate in the adjacent sedimentary aquifers, making it theoretically possible to determine if acid drainage from the coal mines has leaked into the underlying Madison aquifer. © 2009 Elsevier B.V. Source

Tucci N.J.,Montana Bureau of Mines and Geology | Gammons C.H.,Montana Tech of the University of Montana
Environmental Science and Technology

The Berkeley Pit lake in Butte, Montana, formed by flooding of an open-pit copper mine, is one of the worlds largest accumulations of acidic, metal-rich water. Between 2003 and 2012, approximately 2 × 1011 L of pit water, representing 1.3 lake volumes, were pumped from the bottom of the lake to a copper recovery plant, where dissolved Cu2+ was precipitated on scrap iron, releasing Fe2+ back to solution and thence back to the pit. Artificial mixing caused by this continuous pumping changed the lake from a meromictic to holomictic state, induced oxidation of dissolved Fe2+, and caused subsequent precipitation of more than 2 × 108 kg of secondary ferric compounds, mainly schwertmannite and jarosite, which settled to the bottom of the lake. A large mass of As, P, and sulfate was also lost from solution. These unforeseen changes in chemistry resulted in a roughly 25-30% reduction in the lakes calculated and measured total acidity, which represents a significant potential savings in the cost of lime treatment, which is not expected to commence until 2023. Future monitoring is needed to verify that schwertmannite and jarosite in the pit sediment do not convert to goethite, a process which would release stored acidity back to the water column. © 2015 American Chemical Society. Source

Porter M.C.,Montana Tech of the University of Montana | Rutherford B.S.,Montana Tech of the University of Montana | Speece M.A.,Montana Tech of the University of Montana | Mosolf J.G.,Montana Bureau of Mines and Geology
Journal of Structural Geology

Industry seismic reflection data spanning the Rocky Mountain Cordillera front ranges of northwest Montana were reprocessed and interpreted in this study. Five seismic profiles represent 160 km of deep reflection data collected in 1983 that span the eastern Purcell anticlinorium, Rocky Mountain Trench (RMT), Rocky Mountain Basal Décollement (RMBD), and Lewis thrust. The data were reprocessed using modern techniques including refraction statics, pre-stack time migration (PSTM), and pre- and post-stack depth migration. Results indicate the RMBD is 8-13 km below the Earth's surface and dip 3-10° west. Evidence for the autochthonous Mesoproterozoic Belt and basal Cambrian rocks beneath the RMBD is present in all of the profiles and appears to extend east of the RMT. The Lewis thrust was identified in the seismic profiles and appears to sole into the RMBD east of the RMT. The RMT fault system has a dip displacement of 3-4 km and forms a half graben filled with 1 km of unconsolidated Tertiary sedimentary deposits. The RMT and adjacent Flathead fault systems are interpreted to be structurally linked and may represent a synthetic, en echelon fault system. © 2016 Elsevier Ltd. Source

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