The study of the undiscovered mineral resources of the Tongass National Forest and adjacent lands, Southeastern Alaska

Abstract

The quantitative probabilistic assessment of the undiscovered mineral resources of the 17.1-million-acre Tongass National Forest (the largest in the United States) and its adjacent lands is a nonaggregated, mineral-resource-tract-oriented assessment designed for land-planning purposes. As such, it includes the renewed use of gross-in-place values (GIPV's) in dollars of the estimated amounts of metal contained in the undiscovered resources as a measure for land-use planning.Southeastern Alaska is geologically complex and contains a wide variety of known mineral deposits, some of which have produced important amounts of metals during the past 100 years. Regional geological, economic geological, geochemical, geophysical, and mineral exploration history information for the region was integrated to define 124 tracts likely to contain undiscovered mineral resources. Some tracts were judged to contain more than one type of mineral deposit.Each type of deposit may contain one or more metallic elements of economic interest. For tracts where information was sufficient, the minimum number of as-yet-undiscovered deposits of each type was estimated at probability levels of 0.95, 0.90, 0.50, 0.10, and 0.05.The undiscovered mineral resources of the individual tracts were estimated using the U.S. Geological Survey's MARK3 mineral-resource endowment simulator; those estimates were used to calculate GIPV's for the individual tracts. Those GIPV's were aggregated to estimate the value of the undiscovered mineral resources of southeastern Alaska. The aggregated GIPV of the estimates is $40.9 billion.Analysis of this study indicates that (1) there is only a crude positive correlation between the size of individual tracts and their mean GIPV's: and (2) the number of mineral-deposit types in a tract does not dominate the GIPV's of the tracts, but the inferred presence of synorogenic-synvolcanic nickel-copper, porphyry copper skarn-related, iron skarn, and porphyry copper-molybdenum deposits does. The influence of this study on the U.S, Forest Service planning process is yet to be determined.

Finland’s Mineral Resources

“…The three-part quantitative assessment method was developed at the USGS starting in the mid-1970s (Singer and Menzie, 2010, and references therein), and has been increasingly used by the USGS and others since 1975 (e.g., Richter et al, 1975;Singer, 1975;Singer and Overshine, 1979;Drew et al, 1984;Bliss, 1989;Brew et al, 1992;Box et al, 1996;U.S. Geological Survey National Mineral Resource Assessment Team, 2000;Kilby, 2004;Lisitsin et al, 2007;Cunningham et al, 2008;Hammarstrom et al, 2010;FIGURE 11.9 Remaining known and assumed in situ resources of metals in Finnish mineral deposits compared with metals contained in mined resources.…”

Recommendations for assessments of undiscovered mineral resources

“…Most of these questions should be dealt with during the pre-assessment, as described below. Many of these issues and others are explored in "Decision points and strategies in quantitative probabilistic assessment of undiscovered mineral resources" (Brew, 1992), which serves as an example and a point of departure for guidelines to the assessment process.…”

“…Guidelines for and descriptions of different estimation methodologies, both quantified and unquantified, are available, see: Shawe (1981), Taylor and Steven (1983), Goudarzi (1984), Harris, (1984), Cargill and Green (1986), Brew (1992), Cox (1993), Harris and Pan (1993), McCammon and Finch (1993), and Singer (1993). Guidelines are discussed further in section A.3.2.2 of this report AS ISSUES, COMMENTS, AND RECOMMENDATIONS-COOT.…”

“…All too often quantified assessments are made as an add-on after the field studies are completed, a scenario that may separate those knowledgeable about the geology from those making the assessment. Field data of some sort are, of course, an absolute requirement for any estimate of undiscovered mineral resources, and lack of adequate information should mean that no assessment will be made (Brew, 1992 AS ISSUES, COMMENTS, AND RECOMMENDATIONS--CONT.…”

“…; and (2) presuming that they are, how should the different factors be weighted in deciding about the deposit type(s)? Brew (1992) presented a weighted-factor scheme that is an example of how these types of decisions can be pursued; Chen and Fang (1993) used possibility, rather than probability, theory to appraise oil and gas prospects using information analogous to that used in mineral-resource estimation; and Gettings and Bultman (1993) used the same approach to an actual mineral-resource assessment situation.…”