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

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.     

Main concepts of the "European approach" to karst-groundwater-vulnerability assessment and mapping

In order to achieve some consistency in the establishment of groundwater intrinsic vulnerability maps in Europe, a new approach is proposed by Working Group 1 of the European COST Action 620 on "Vulnerability mapping for the protection of carbonate (karst) aquifers". A general procedure is offered which provides consistency while allowing the required flexibility for application to a continent and under conditions of varying geology, scale, information availability, time, and resources. The proposed methodology is designed to be clearly more physically based than the existing vulnerability-mapping techniques. It takes the specificity of the karstic environments into account without necessarily excluding the applicability to other geological conditions. Combined "core factors" for overlying layers and for concentration of flow account for the relative protection of groundwater from contamination while taking into account any bypass of the overlying layers. A precipitation factor is distinguished for describing characteristics of the input of water to the system. Differentiation is made between groundwater resource intrinsic vulnerability mapping and source intrinsic vulnerability mapping. For the latter, a factor describing the karst network development is relevant. This short technical note describes a first step in the work program of Working Group 1 of the COST Action 620. Future steps are now in progress to quantify the approach and to apply it in various European pilot areas. Electronic Publication