DEVELOPMENT OF REGIONAL- TO NATIONAL-SCALE MINERAL ENVIRONMENTAL ASSESSMENT METHODOLOGIES

The U.S. Geological Survey’s Mineral Environmental Assessment Methodology Project (MEA) is developing, as one of a number of products, geospatial and non-spatial methodologies to identify and evaluate potential environmental impacts associated with unmined mineral deposits, mineral exploration, and future development of a diverse suite of mineral deposit types in various geological and environmental settings, and at national, regional, and watershed scales. The methodologies integrate process-based knowledge, developed at the watershed and finer scales, with regional data on geology, lithology, mineral deposits and deposit models, topography, climate, water quality, remote sensing, geophysics, vegetation, ecology, as well as the number and nature of other potential environmental stressors (i.e., un-remediated historical mine sites, logging, roads, or other land uses).

The GIS component of the methodology will provide information and detail appropriate for the scale at which the user is most interested. Analyses made at scales finer than the decision-space can easily be aggregated to match a coarser decision-space, whereas analyses made at scales coarser than the decision-space cannot be easily disaggregated, and usually must be redone to be useful. For example, the methodology will focus primarily on information appropriate for 12-digit hydrologic unit subwatersheds, as this is a common scale at which decisions are made by land management agencies (LMA). But to maximize the utility to the LMAs, the approach will also provide coverage and information aggregated for broader scales, such as for 10- and 8-digit hydrologic units across larger regions.

At the regional scale, a prototype MEA methodology is being developed based on information compiled for six southwestern states (CA, AZ, NM, CO, UT, NV). One aspect of the GIS approach will be the development of watershed carrying capacity maps, which will provide a qualitative to semi-quantitative indication of watershed sensitivity to potential environmental impacts from unmined mineralized areas and from future mining. Pre-mining environmental baseline maps will show naturally-impacted watersheds, based on known deposit types and watershed carrying capacity.

The MEA prototype methodology will be linked to the 1996 National Mineral Resource assessment permissive tracts for selected mineral deposit types. The prototype will be used to test a variety of methodologies, identify data gaps, determine appropriate scales of assessment and delivery, and investigate the extent to which a rigorous, quantitative approach can be applied practically to broader scales. The methodology will then serve as the basis for a National Mineral Environmental Assessment that will accompany the upcoming new National Mineral Resource Assessment, scheduled to begin in 2012.