Secondary Enrichment of Copper at the Madison Gold Skarn Deposit, Silver Star District, Montana

Secondary Enrichment of Copper at the Madison Gold Skarn Deposit, Silver Star District, Montana. This paper focuses on the chemical reactions responsible for secondary enrichment of copper...we argue that most of the secondary Cu enrichment occurred during a late hydrothermal event that replaced the high temperature skarn mineral assemblage with hematitic jasperoid. Evidence favoring this hypogene Cu enrichment hypothesis is presented

Creating Lakes from Open Pit Mines: Processes and Considerations, Emphasis on Northern Environments

Creating Lakes from Open Pit Mines: Processes and Considerations, Emphasis on Northern Environments. This document summarizes the literature of mining pit lakes (through 2007), with a particular focus on issues that are likely to be of special relevance to the creation and management of pit lakes in northern climates. Pit lakes are simply waterbodies formed by filling the open pit left upon the completion of mining operations with water. Like natural lakes, mining pit lakes display a huge diversity in each of these subject areas. However, pit lakes are young and therefore are typically in a non-equilibrium state with respect to their rate of filling, water quality, and biology. Separate sections deal with different aspects of pit lakes, including their morphometry, geology, hydrogeology, geochemistry, and biology. Depending on the type and location of the mine, there may be opportunities to enhance the recreational or ecological benefits of a given pit lake, for example, by re-landscaping and re-vegetating the shoreline, by adding engineered habitat for aquatic life, and maintaining water quality. The creation of a pit lake may be a regulatory requirement to mitigate environmental impacts from mining operations, and/or be included as part of a closure and reclamation plan. Based on published case studies of pit lakes, large-scale bio-engineering projects have had mixed success. A common consensus is that manipulation of pit lake chemistry is difficult, expensive, and takes many years to achieve remediation goals. For this reason, it is prudent to take steps throughout mine operation to reduce the likelihood of future water quality problems upon closure. Also, it makes sense to engineer the lake in such a way that it will achieve its maximal end-use potential, whether it be permanent and safe storage of mine waste, habitat for aquatic life, recreation, or water supply

Valorisation of sawdust through the combined microwave-assisted hydrothermal pre-treatment and fermentation using an oleaginous yeast

Oleaginous yeast, cultured on second-generation lignocellulosic resources, has the potential to be a key part of the future energy sector. However, the multiple unit operations necessary to produce concentrated hydrolysates, with a minimum of fermentation inhibitors, limit the applicability to date. In this study, a simple microwave-assisted hydrothermal pre-treatment step of oak or beech sawdust was deployed to produce an oligosaccharide-rich hydrolysate. This was then catabolised by the oleaginous yeast, Metschnikowia pulcherrima, avoiding the need for costly enzymatic or further chemical steps in the processing. Up to 85% of the sawdust’s hemicelluloses could be solubilised under these conditions, and 8 g/L DCW yeast with a 42% lipid content produced. While a number of studies have demonstrated that oleaginous yeasts possess high inhibitor tolerance, using this real lignocellulosic hydrolysate, we demonstrate that lipid production is actually very sensitive to inhibitor and carbon availability, and the optimal system is not the one that gives the highest hydrolysate or cell biomass. Indeed, the yeast was shown to detoxify the inhibitors in the process, but at high inhibitor loading, this leads to very poor lipid production, especially at high furfural levels. These findings clearly highlight the importance of considering multiple variables when real, complex lignocellulosic media are involved, tuning process conditions based on the desired fermentation outcomes.</p

Biogeochemical and microbial seasonal dynamics between water column and sediment processes in a productive mountain lake: Georgetown Lake, MT, USA

This manuscript details investigations of a productive, mountain freshwater lake and examines the dynamic relationship between the chemical and stable isotopes and microbial composition of lake bed sediments with the geochemistry of the lake water column. A multidisciplinary approach was used in order to better understand the lake water- sediment interactions including quantification and sequencing of microbial 16S rRNA genes in a sediment core as well as stable isotope analysis of C, S, and N. One visit included the use of a pore water sampler to gain insight into the composition of dissolved solutes within the sediment matrix. Sediment cores showed a general decrease in total C with depth which included a decrease in the fraction of organic C combined with an increase in the fraction of inorganic C. One sediment core showed a maximum concentration of dissolved organic C, dissolved inorganic C, and dissolved methane in pore water at 4 cm depth which corresponded with a sharp increase in the abundance of 16S rRNA templates as a proxy for the microbial population size as well as the peak abundance of a sequence affiliated with a putative methanotroph. The isotopic separation between dissolved inorganic and dissolved organic carbon is consistent with largely aerobic microbial processes dominating the upper water column, while anaerobic microbial activity dominates the sediment bed. Using sediment core carbon concentrations, predictions were made regarding the breakdown and return of stored carbon per year from this temperate climate lake with as much as 1.3 Gg C yr(-1) being released in the form of CO2 and CH4

Geochemistry of smelter slag and stream sediment-pore water in Lower Area One

This talk will summarize the results of two NRDP-funded student projects to help understand metal cycling in Lower Area One. Despite great progress, the lower Blacktail Creek-upper Silver Bow Creek corridor in Butte still experiences loading of heavy metals, including zinc and copper. Part one of the talk will address the slagwalls that border Silver Bow Creek below Montana Street. The mineralogy and leaching behavior of the slag is reviewed. Although freshly broken slag is relatively inert, secondary salts formed by chemical weathering that are stored in cracks in the walls have the potential to release metals during rain events. Part two of the talk will summarize the results of sediment pore-water (“peeper”) sampling in the creeks to better understand cycling of metals between surface water and fine-grained stream sediment. Metals such as Cu, Pb, and Zn are stable in the mucky sediment, but may be remobilized and redissolved during storm events

Inorganic Precipitation of Calcite in Mine Tailings Using Trona

Mine tailings pose environmental risks such as dust emission and acid mine drainage (AMD) and also present geotechnical risks, i.e. tailings dam failures. In-situ cementation of tailings has the potential to reduce the risks associated with such failures as well as the related environmental problems. In this paper, a new inorganic method of inducing tailings cementation is introduced using a naturally occurring mineral called trona (Na2CO3⋅NaHCO3⋅2H2O). Three methods of introducing dissolved trona, i.e. injection, slurry mixing, and infiltration, were tested and the results were compared. All methods proved successful on a laboratory scale but with different amounts of precipitated calcite at different sample depths. The precipitation profile distinctions could have applications in solving common problems associated with tailings including dust emission and liquefaction. Additionally, even distribution of precipitated calcite in the slurry mixing method shows potential for AMD prevention

Influence of Copper Recovery on the Water Quality of the Acidic Berkeley Pit Lake, Montana, U.S.A.

The Berkeley Pit lake in Butte, Montana, formed by flooding of an open-pit copper mine, is one of the world’s 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 lake’s 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

Fate and transport of metals in H₂S-rich waters at a treatment wetland

<p/> <p>The aqueous geochemistry of Zn, Cu, Cd, Fe, Mn and As is discussed within the context of an anaerobic treatment wetland in Butte, Montana. The water being treated had a circum-neutral pH with high concentrations of trace metals and sulfate. Reducing conditions in the wetland substrate promoted bacterial sulfate reduction (BSR) and precipitation of dissolved metal as sulfide minerals. ZnS was the most common sulfide phase found, and consisted of framboidal clusters of individual spheres with diameters in the submicron range. Some of the ZnS particles passed through the subsurface flow, anaerobic cells in suspended form. The concentration of "dissolved" trace metals (passing through a 0.45 μm filter) was monitored as a function of H₂S concentration, and compared to predicted solubilities based on experimental studies of aqueous metal complexation with dissolved sulfide. Whereas the theoretical predictions produce "U-shaped" solubility curves as a function of H₂S, the field data show a flat dependence of metal concentration on H₂S. Observed metal concentrations for Zn, Cu and Cd were greater than the predicted values, particularly at low H₂S concentration, whereas Mn and As were undersaturated with their respective metal sulfides. Results from this study show that water treatment facilities employing BSR have the potential to mobilize arsenic out of mineral substrates at levels that may exceed regulatory criteria. Dissolved iron was close to equilibrium saturation with amorphous FeS at the higher range of sulfide concentrations observed (>0.1 mmol H₂S), but was more likely constrained by goethite at lower H₂S levels. Inconsistencies between our field results and theoretical predictions may be due to several problems, including: (i) a lack of understanding of the form, valence, and thermodynamic stability of poorly crystalline metal sulfide precipitates; (ii) the possible influence of metal sulfide colloids imparting an erroneously high "dissolved" metal concentration; (iii) inaccurate or incomplete thermodynamic data for aqueous metal complexes at the conditions of the treatment facility; and (iv) difficulties in accurately measuring low concentrations of dissolved sulfide in the field.</p