objective is the description of metal complexing and mineral solubilities under a variety of geologically realistic conditions. Development of thermodynamic models for appropriate trace elements and volatile components will permit numerical modeling of magma differentiation and possible identification of critical variables affecting ore-bearing fluids.

Evolution of Mineral Deposits Through Time

The evolution of deposits presumably signals changes in the types and/or intensities of processes as well as in the atmosphere, oceans, thermal regimes, climate, and tectonics. Study of the evolution of resource types through time and their relations to other features should therefore guide our understanding of earth processes. In turn, this understanding should sharpen our knowledge of ore genesis and our ability to predict known and unknown deposit types that are associated with particular periods of earth history and particular geological features.

Concealed Ore Bodies

Even the largest of ore bodies occupies a tiny area of the land surface, so production of mineral wealth has been concentrated in those places where surface indications of ore bodies are strongest. A challenging research frontier is to find ways of locating buried ore bodies in the many areas where surface signs are lacking. This is rather like looking for a needle in a haystack, and part of the challenge is to develop coherent exploration strategies that are not prohibitively costly.

Intermediate-Scale Search for Ore Bodies

Mineral explorationists identify this level of search as a research frontier. The characterization of environments likely to be hosts to particular classes of ore body on the basis of recognition of ancient and modern plate tectonic environments has proved to be powerful in distinguishing blocks of land that are promising for exploration on the scale of thousands of square kilometers. On a very local scale new deposits can often be found in close proximity to existing mines. The challenge is to establish criteria permitting recognition of potential ore-bearing areas at scales intermediate between these extremes.

Energy Resources

Exploration for New Petroleum Reserves

In much of the world where the petroleum industry is less mature than in the United States, the challenge lies in exploration for new reserves in new oil fields, calling for an integrated approach to basin analysis that ranges from establishment of the tectonic environments in which basins have developed; through interpretation of depositional, structural, and thermal evolution; to an understanding of oil and gas generation within the basin, of fluid migration, and of related diagenetic change; and finally to definition of the types of traps in which oil and gas are held.

Advanced Production and Enhanced Recovery Methods

Because of the maturity of the petroleum industry in the United States, the challenge is to produce more oil from existing fields in well-known basins. Drilling, well testing, sampling, logging, advanced seismic methods, sedimentology and organic geochemistry, as well as modeling, need to be developed toward an integrated understanding of reservoir structure and dynamics. Advanced production methods such as those involving in situ bacterial modification will call for close interaction between solid-earth scientists and reservoir engineers. If bacterial techniques are to prove useful, they will depend greatly on current frontier research into the organic chemistry of petroleum.

Coal Availability and Accessibility

Total coal resources in the United States are large, but knowing only their size is not sufficient information. Some coals are not minable because their combustion produces unacceptable amounts of toxic material; others are less accessible to mining than appears from simply mapping the distribution of coal beds. The amount of coal that is available for mining and the accessibility of those "available coal resources" are much less than the overall deposit size. This is because of land-use restrictions, mining methods, and the thickness of individual beds. Such studies are being conducted in the Appalachian and Illinois coal basins. For a more realistic assessment of potentially available coal resources, they should be expanded to include all major coal-producing regions of this country.

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