TRACE-METAL CONTENT OF MISSISSIPPI OIL-FIELD BRINES

Lead-and zinc-rich oil field brines from lowermost Cretaceous formations in central Mississippi locally contain geochemically significant levels of trace metals that are found in several types of sediment-hosted metallic mineral deposits, providing additional support for the genetic link between sedimentary formation waters and these deposits. Copper content of brine samples from Lower Cretaceous formations ranges from < 0.02 mg 1-1 to 0.37 mg 1-1, and silver was detected in 2 samples with a maximum value of 0.021 mg 1-1. Cobalt values range from <0.04 mg 1-1 to 0.22 mg 1-1, and molybdenum is present in the range of <0.03 mg 1-1 to 0.05 mg 1-1. Gold, platinum, and palladium were not found at levels above their respective lower detection limits of 0.0001 mg 1-1, 0.003 mg 1-1, and 0.002 mg 1-1 for the graphite furnace AA procedure used. Comparison of the results from this study to recent published studies of trace-metal solubilities in chloride-rich hydrothermal solutions suggests that the brines are approximately saturated with respect to Pb, Zn and Fe, and apparently are undersaturated with respect to Au, Pt, Pd, Sb, Co and probably Ag. The composite effects of the reduced sulfur content and physicochemical characteristics of the brines (i.e., salinity, temperature, redox state and pH), along with formation metal sources and brine migration history, apparently control the observed present-day concentrations of trace metals in Mississippi oil field brines. © 1990.