Development of Mineral Environmental Assessment Techniques at the Watershed Scale

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Task Contact: Kathy Smith

Task Objectives

Task Statement of Work

Task Objectives

The potential impact of a mineralized area or a mine site on the environment depends not only on the characteristics of the mineral deposit present (i.e., geology, mineralogy, alteration, host rocks, grade, tonnage, trace metal content, etc.), but also the characteristics of the surrounding environment (watershed lithology, structure, geology, climate, hydrology, ground- and surface water compositions, precipitation, vegetation, topography, etc.). For example, for aquatic ecosystems, water chemistry factors such as the pH, alkalinity, hardness, and dissolved organic carbon (DOC) concentrations of the impacted water body greatly influence the toxicity of metals and related compounds. Likewise, the diluting role of precipitation also affects the concentration, and thus toxicity of toxic compounds. In assessing the potential environmental consequences of mineral deposits prior to mining and that may result from mining and/or mineral processing, it is essential to develop methodologies that account for these and many other disparate factors.

Commonly, a major concern of mineral development in watersheds is impact on biota, particularly aquatic biota or humans. The form, or species, of metals in the environment will affect both metal bioavailability and toxicity. Total aqueous metal concentrations are not good predictors of potential metal bioavailability and toxicity because water chemistry affects speciation and can greatly impact bioavailability and toxicity. Similarly, the form of ingested metals greatly affects their toxicity to humans. Without knowledge of speciation, the bioavailability and toxicity of metals tends to be considerably overestimated. Therefore, a methodology is needed that can account for metal speciation (and site-specific characteristics that influence metal speciation) in the assessment of potential consequences of mineral development in specific watersheds. Once metal speciation is accounted for, the link to potential metal toxicity can be made using toxicological models. One such model, the Biotic Ligand Model, has been incorporated into the U.S. Environmental Protection Agency's updated water-quality criteria for copper.

The objective of this task is to develop an integrated geological, hydrological, geochemical, and ecological methodology for modeling the potential toxicological consequences of particular mineral deposit types (both prior to and as a result of mining) in watersheds of various geologic, ecological, and climatic settings.

Subtasks to accomplish these objectives are:

Statement of Work

This year,

compilation of stream-water chemistry associated with particular lithologies will begin,
compilation of dissolved organic carbon data in stream water will begin,
identification and evaluation of various hydrologic models and reactive transport models will begin, and
evaluation of the Biotic Ligand Model for use in mineralized systems will continue.

Work will continue on ways to estimate volumes of mine wastes, mill tailings and/or other mineral processing byproducts as a function of deposit type, mining method, grade / tonnage, and stripping ratio. This has already been accomplished for porphyry copper deposits. This information is needed to model the potential physical footprint and resulting environmental footprint of a mine site developed on a particular deposit type.

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Mineral Resources	Eastern / Central / Western / Alaska / Minerals Information
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