GREEN, DALE J., and JEFFREY B. HULEN, University of Utah Research Institute, Salt Lake City, UT

ABSTRACT: Hydrothermal Speleogenesis in the Eastern Basin and Range Province-Implications for Petroleum and Precious-Metal Exploration

Previous investigations based on geometric and textural analysis have shown that most caverns in the eastern Basin and Range province were excavated not by cool, descending, meteoric waters at or above the water table, but by ascending, moderate-temperature hydrothermal fluids. This conclusion, borne out by fluid-inclusion studies, has important implications for both petroleum and precious-metal exploration in the region. Cavernous porosity has been reported in some of the area's carbonate-hosted oil reservoirs, such as the geothermally active Grant Canyon field in Railroad Valley, as well as in massive carbonates directly beneath some Carlin-type, sediment-hosted gold deposits. Moreover, at virtually all such deposits, hydrothermal carbonate-dissolution (decalcification) is known to e an important porosity-inducing process. Rather than being accidental components of these oil and gold occurrences, we contend that such caverns may have formed in the same hydrothermal systems ultimately responsible for petroleum entrapment and precious-metal mineralization. The fluids that excavated the caverns must have been at least mildly acidic. Carbonic acid is the traditionally cited cavern solvent, but organic and sulfur-based acids thermally generated from regionally prevalent hydrocarbon source rocks, such as the Mississippian Chainman Shale, are equally likely as agents of dissolution. We suggest that thermal waters charged with these acids locally may have created or enhanced not only caverns, but migration pathways and depositional sites for gold and oil alike.

AAPG Search and Discovery Article #90993©1993 AAPG Rocky Mountain Section Meeting, Salt Lake City, Utah, September 12-15, 1993.