During 6,000 years of mining, many different kinds of mineral deposits have been found and much has been learned about their formative processes. In no example can we explain completely why a deposit formed where and when it did. Mining focuses on the deposit itself and leaves untested the much larger volumes of rock that were also involved in the formative processes. One major objective of a continental scientific drilling program will be to fill that gap.

The program will select several areas where extensively studied mineral deposits are known to be the result of old hydrothermal convection systems. Drilling will explore regions far below and beyond the known limits of mineralization to determine the extent and chemistry of the old system. Proposed sites are: Tonopah, Nevada; Tintic, Utah; Butte, Montana; and Santa Rita, New Mexico. Modern hydrothermal systems would also be drilled to study the hydrology and chemistry of presentday equivalents of the fossil ore-forming systems. Examples are the geothermal systems at the Geysers and the Salton Sea, California, and Yellowstone National Park, Montana. The metal-rich formation waters discovered in the Mississippi embayment and believed to be precursors of Mississippi Valley-type deposits ould also be studied in situ.

Finally, it is proposed that a deep-drilling program be used to fill in gaps in our knowledge regarding the chemical heterogeneity of the crust. We must determine whether the heterogeneities control the observed distribution of mineral deposits or whether the chemistry and the deposits are both manifestations of larger scale processes.

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