Central Mineral and Environmental Resources Science Center
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The objective of our work was to understand and ultimately quantify the behavior and distribution of environmentally significant elements as they are dispersed from their sources through the environment. Sources of elements in mineralized terranes include natural and anthropogenic entities such as ore deposits, mine tailings, and waste rock. Characterization of these source materials involved identifying the solid phases where the toxic elements reside, the speciation of the toxic elements (e.g., oxidation state and type of bonding to the mineral structure), and the rates and mechanisms of release from the mineral structure. Once released from their sources, physical, inorganic, and biogeochemical processes act to re-distribute and transform both dissolved and particulate forms of the elements.
Our specific objective was to determine rates and mechanisms of sulfide mineral oxidation and toxic element release due to chemical and microbiological processes. Laboratory experiments conducted in the last decade have determined the rates of inorganic oxidation of some common sulfide minerals under certain ranges of conditions, but much more needs to be done, especially with alteration of specific minerals and chemical reactions mediated by microorganisms. In addition, little has been done experimentally to determine the behavior of potentially toxic trace elements that exist as intergrown refractory minerals and non-sulfide mineral inclusions (usually silicates or oxides), in discrete inclusions of sulfides or sulfosalts, in defect sites, or in solid-solution within the host minerals. Trace minerals containing toxic elements may have very irregular distribution in the host sulfides. This project conducted experimental reactions of fully characterized natural sulfide minerals and will be fully integrated and interactive with pertinent Mineral Resource Program field investigations. These data were incorporated into geochemical reaction models in the form of reaction rates, solidsolution activity coefficients or specific interaction models, distribution coefficients, sorption models, and thermodynamic stability of minor or secondary phases. New fundamental information was made available to be utilized in geochemical and biogeochemical reaction progress calculations for specific field sites to provide a predictive capability of environmental behavior of ore deposits.
This Project advanced the development and application of geoenvironmental mineral deposit models by identifying the processes that control environmental signatures of mineral deposits and the fate of metals in the environment. The studies supported the development of predictive models necessary for future mineral-environmental assessments, and provided the private sector and government agencies involved in regulatory and stewardship activities with the tools to make informed and rational decisions about (1) land use before exploration and mining and (2) post-mining remediation.
Additional work continued in the Modeling Near-Surface Processes in Mineral Systems project.