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By David G. Frank, Thomas P. Frost, Warren C. Day and the USGS SaMiRA team. USGS Fact Sheet 2016–3074, October 2016.
Sagebrush lands in southwestern Wyoming. Photo: Anna Wilson, USGS.
At the request of the Bureau of Land Management (BLM), USGS scientists assessed the mineral-resource potential of nearly 10 million acres of Federal and nearby lands in Idaho, Montana, Nevada, Oregon, Utah and Wyoming. The Department of the Interior was weighing whether to withdraw these lands from mining claims to protect large blocks of sagebrush habitat for the greater sage-grouse.
A tight deadline
BLM asked in October 2015 and needed preliminary results by mid-July 2016, to inform its National Environmental Policy Act review and environmental impact statement. The full results fill five volumes of Scientific Investigations Report 2016–5089 (chapters A–E) and seven data releases.
What was studied
The Sagebrush Mineral-Resource Assessment (SaMiRA) looked at:
- the lands proposed for withdrawal within seven Sagebrush Focal Areas (SFAs);
- two "Nevada additions," proposed by the State as substitutes for other withdrawal areas.
The study areas are whole Public Land Survey System townships around the proposed areas, because those areas have complex shapes. Including private or other lands implies nothing about their value or management. Native American lands were excluded.
Three kinds of minerals
| Kind | Law | Examples |
|---|---|---|
| Leasable | Mineral Leasing Act of 1920 | coal, oil and gas, oil shale, potash, phosphate, sodium, geothermal steam |
| Salable | Materials Act of 1947 | construction materials such as sand and gravel |
| Locatable | General Mining Act of 1872 | everything else: antimony, copper, gemstones, gold, lithium, molybdenum, silver, tungsten, zeolites, zinc |
The withdrawal would affect locatable minerals, so SaMiRA rated their potential; it also inventoried leasable and salable ones.
How it was done
61 USGS experts in geology, geochemistry, geophysics, mineral deposits and assessment methods, with input from State geological surveys, followed BLM's manual (sections 3031 and 3060) and a matrix from USGS Open-File Report 84–787 that ranks potential (none, low, moderate, high) against certainty (from insufficient to abundant evidence).
- By deposit type: about 40 types, each with its own geology, commodities, size and grade, value, mining method and footprint. Gold alone ranges from stream placers to small high-grade veins to huge low-grade deposits in altered sedimentary rock.
- Data: geologic maps, geophysical, geochemical and satellite data; a new USGS Mineral Deposit Database (USMIN) drawn from company websites, technical reports and public comments; and BLM claim and permit records.
Results
The USGS found moderate or high potential for deposits of antimony, barite, bentonite, hectorite, copper, gemstones, gold, gypsum, lead, lithium, mercury, molybdenum, opal, silver, sunstone, tungsten, uranium, zeolites and zinc.
| Sagebrush Focal Area (report chapter) | Proposed withdrawal (acres) | Moderate potential | High potential |
|---|---|---|---|
| Sheldon–Hart Mountain National Wildlife Refuge Complex (B) | 955,068 | 2% | 1% |
| Southern Idaho and Northern Nevada (B) | 3,517,786 | 8% | 7% |
| Southeast Oregon and North-Central Nevada (B) | 1,608,269 | 3% | 14% |
| Nevada additions (B) | 394,288 | 2% | 0% |
| North-Central Idaho (C) | 1,558,573 | 6% | 1% |
| North-Central Montana (D) | 876,035 | 5% | 7% |
| Southwestern and South-Central Wyoming (E) | 138,470 | 65% | 1% |
| Bear River Watershed (E) | 276,702 | 17% | 0% |
| Total | 9,325,191 | 7% | 6% |
Percentages are of each proposed withdrawal area.
The assessment helps weigh the economic and environmental trade-offs of a withdrawal, and informs decisions on the lands' future, sage-grouse protection and Western economies. Full reports and data: SIR 2016–5089.
Sources
Based on USGS Mineral-Resource Assessment of Sagebrush Focal Areas in the Western United States, by David G. Frank, Thomas P. Frost, Warren C. Day and the USGS SaMiRA team, USGS Fact Sheet 2016–3074, U.S. Geological Survey; a work of the United States government in the public domain. The photograph, the mineral-terms box and the results table are taken from the fact sheet's PDF; its maps, drawn with Esri roads and political data, are not reproduced.
Licence : CC0 1.0 (domaine public) · Adapté de pubs.usgs.gov
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