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U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2007-5039

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Summary

The (Bristol) Bay Resource Management Plan area in southwestern Alaska contains significant potential for base and precious metals, in addition to metallic mineral deposits already known. A probabilistic assessment of undiscovered locatable mineral resource potential within the BMPA identified seventeen different mineral deposit models as prospective for exploration or development within the next fifteen years. Twenty-four tracts outlining permissive areas were delineated within the BMPA. Quantitative estimates of the number of undiscovered deposits at three probability levels were made for porphyry copper, epithermal vein, copper skarn, iron skarn, hot-spring mercury, placer gold, placer platinum, and shallow to intermediate intrusion-related gold deposits in eight of those permissive tracts. The number of tracts quantified was limited to those with sufficient geoscience information available to adequately characterize the potential resources. The estimate for intrusion-related gold deposits comprises only deposits emplaced at shallow to intermediate depths in the crust as described in published models and current literature. In the absence of a published grade and tonnage model, the most current grade and tonnage data available from 13 deposits of this type worldwide were used to provide the probabilistic estimate of undiscovered deposits.

Significant resources of Ag, Au, Cu, Fe, Hg, Mo, Pb, and Pt are estimated to occur in the Bay Management Plan area in the eight tracts described above. At the 10^th percentile probability level, the BMPA is estimated to contain 10,067 metric tons silver, 1,485 metric tons gold, 12.66 million metric tons copper, 560 million metric tons iron, 8,100 metric tons mercury, 500,000 metric tons molybdenum, 150 metric tons lead, and 17 metric tons of platinum in undiscovered deposits of the eight quantified deposit types. At the 90^th percentile probability level, the BMPA is estimated to contain 89 metric tons silver, 14 metric tons gold, 911,215 metric tons copper, 330,000 metric tons iron, 1 metric ton mercury, 8,600 metric tons molybdenum, and 1 metric ton platinum in the eight deposit types. Additional resources of copper, iron, and gold in skarn and placer deposits may occur in the three permissive tracts that were not subject to quantitative assessment.

Other commodities that may occur in the BMPA include Cr, Sn, W, Zn, and platinum-group elements such as Ir, Os, and Pd. Thirteen of the permissive tracts outlined have potential for nine additional deposit model types. These are Besshi and Cyprus, and Kuroko-volcanogenic massive sulfides, hot spring gold, low-sulfide gold veins, Mississippi Valley Pb-Zn, tin greisen, zinc skarn and Alaskan-type zoned ultramafic platinum-group element deposits. Resources in undiscovered deposits of these nine types have not been quantified and would be in addition to those in known deposits and to the estimated undiscovered resources listed above. Additional mineral resources also may occur in the Bay RMP area in deposit types that were not considered here. These may include commodities whose demand is increasing over time, deposit models unlikely to be explored for or developed within a 15-year period, or deposit types not yet fully understood or developed into coherent models.

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