ROLE OF CRUDE-OIL IN THE GENESIS OF MISSISSIPPI VALLEY-TYPE DEPOSITS - EVIDENCE FROM THE CINCINNATI ARCH

Mississippi Valley-type (MVT sulfide minerals and oil from deposits al ong the Cincinnati arch have almost identical deltaS-34 values (-9 par ts per thousand to +9 parts per thousand for MVT sulfides; -12 parts p er thousand to + 9 parts per thousand for oils). These values are very similar to those for MVT sulfides and oil in the Illinois-Kentucky di strict and support their proposed inclusion in a regional hydrothermal system. Many MVT deposits with low deltaS-34 values are closely assoc iated with oil, whereas MVT deposits with high deltaS-34 values often contain bitumen. Reduced sulfur in MVT deposits with high deltaS-34 va lues probably came from thermochemical sulfate reduction, whereas that in MVT deposits with low deltaS-34 values probably came from oil and related organic matter. Oil-related sulfur could have been derived fro m oil fields or disseminated oil and other organic matter in regional wallrocks.