Preliminary Report on the Origin and Chemical Evolution of Lead-and Zinc-Rich Oil Field Brines in Central Mississippi

Oil field brines containing high concentrations of lead and zinc occur at depths ranging from 8,000 to 13,000 feet over a 2,000-square-mile portion of central Mississippi in the Gulf Coast of the United States. The chloride-bromide and potassium-bromide relationships in the brines indicate that these brines originated from the evaporation of sea water past the point of halite deposition. We suggest that the brines probably originated as interstitial fluids in the Louann Salt and that these fluids have been expelled upwards as a result of loading by younger sediments. The relationship between the lead and zinc concentrations in the brines and their stratigraphic position suggests that the source of metals in the brines may be the shale (Dorcheat) member of the Cotton Valley group. We believe that the cross-formational movement of potassium-rich brines across metal-rich marine shales may be an important mechanism for the origin of metal-rich brines in sedimentary basins.