Environmental Geochemistry to Evaluate Risks Associated with Past and Future Mining in the Lake Superior Region

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Activities and tasks of this project:

Task 1, Lake Superior Environmental Databases and Mineral-Environmental Assessment:

This task will take the concepts developed by the sunsetting mineral-environmental assessment methodology project and apply them in a regional, deposit type specific context to provide a scientifically based framework for decision-making regarding future mining to benefit all stakeholders including land managers, the mining industry, regulatory agencies, non-government organizations, and citizens. Data layers will include a variety of geologic, geochemical, hydrologic, climatic, ecological, demographic information to identify potential risks to the surrounding environment associated with future mining. The Geographic Information Systems activities will be coordinated with the other Midcontinent Rift projects to share data layers and to avoid duplication. The geologic data layers used will be derived from existing data sets or data sets being developed by concurrent Midcontinent Rift projects. This project will focus on the construction of environmental data layers such as those related to climate, hydrology, soil and sediment geochemistry, and ecosystems. These environmental data layers will also be supplemented by research being conducted in Tasks 2 and 3. The culminating assessment will be designed to better inform the discussion surrounding future mining in the region.

Task 2, Baseline Characterization:

Task 2 will design and execute a field sampling program to fill crucial data gaps identified in Task 1 (i.e., water chemistry, sediment chemistry, soil chemistry, etc.). An emphasis will be placed on developing a modern perspective on the Lake Superior region in terms of recent conceptual changes to regulatory guidelines by analyzing adequate sets of parameters to enable complete characterization. For example, in 2007 the Environmental Protection Agency adopted a new method for assessing the surface-water toxicity of copper called the "Biotic Ligand Model" that takes a more sophisticated approach that relies on a larger set of water quality parameters than previous regulatory guidelines, such as dissolved organic carbon concentrations in addition to standard inorganic water quality parameters. Likewise, the model for assessing metal toxicity in sediments now uses an approach known as the equilibrium-partitioning sediment benchmark, which relies on a more extensive set of analytes including the concentrations of acid-volatile sulfide, simultaneously extractable metals, and organic carbon.
Specific sampling areas will be coordinated with the Midwest Area Mining Initiative, for access to water resources data sets that otherwise would have been difficult to easily use, and worldclass stream gaging data for the watersheds being investigated. Watersheds being targeted include those associated with Duluth-type PGM deposits, banded iron formations, and sediment-hosted copper deposits. The sulfate budget of these watersheds will be of particular interest because of the ongoing interest in the Minnesota wild rice water-quality standard for sulfate. The stable isotope signatures of dissolved sulfate will be compared with known values for mineralized rocks to fingerprint contributions from various sources. Geographic emphasis for the Duluth-style platinum group metal deposits will likely be the entire strike length of the complex, for the iron ores it will likely be the Mesabi and Gogebic ranges, and for the sediment-hosted copper deposits it will be the Porcupine Mountains area between the inactive White Pine Mine to the east and the Copperwood advanced exploration project to the west. Results from this task will contribute to the environmental GIS data base in Task 1.

Task 3, Geoenvironmental Models:

Task 3 will focus on defining and refining our understanding of the environmental characteristics of Duluth-style PGM deposits, sediment-hosted copper deposits, and banded iron formation deposits through literature review and new data collection. Characteristics will include both pre-mining baseline conditions and the signatures associated with mine waste and drainage.
The goal is to identify specific risks associated with each deposit type to enable these risks to be ranked and addressed. An underlying theme will be to understand how the unique combination of geologic characteristics of the mineral deposits and the local hydrologic, geochemical, and climatic conditions conspire to determine the source, transport, and fate of elements of environmental interest from mining. Deposit specific details will include investigating mineralogic hosts of trace elements, acid-base accounting characteristics, and leaching properties of unmined rock, waste rock, and mine wastes. A major emphasis will be to understand controls of sulfate fluxes from unmined areas and mined areas to provide a scientific context for understanding sulfate loads in surrounding watersheds. These insights will be used to develop geoenvironmental models for these deposit types customized to the Lake Superior region.

Mineral Resources	Eastern / Central / Western / Alaska / National Minerals Information
	Crustal Geophysics and Geochemistry / Spatial Data

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U.S. Department of the Interior | U.S. Geological Survey
URL: http://minerals.usgs.gov/east/lakesuperior/activities.html
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Page Last Modified: 22-Feb-2013@17:37