Sources of lithium and barium in Gulf of Mexico Basin formation waters, USA

Barium concentrations in formation waters produced along with hydrocarbons from the Gulf of Mexico sedimentary basin range from less than one to nearly 2000 mg/L. Unaltered detrital potassium feldspars contain about 0.3 weight per cent barium. Barite probably controls the barium concentration of formation waters, but barium content of whole-rock sandstones (Oligocene) may decrease with depth, suggesting that barium is not conserved in the sandstones during diagenesis. The amount of barium in whole-rock sandstones is greater than that calculated using the barium content of potassium-feldspar, suggesting that either altered detrital feldspars contained more barium than the amount in remaining feldspars or that feldspar content of sandstones was much greater than that of the least-altered sandstone in the Oligocene-Frio Formation today. Lithium concentrations in formation waters range from less than one to more than 300 mg/L. Variation in lithium content with depth in sandstones and mudstones suggests that the lithium content is not clearly related to local mineral diagenesis. The highest concentrations of lithium in formation waters occur in deeply buried Cenozoic and Mesozoic reservoirs. These concentrations cannot be the result of mineral diagenesis, nor do they indicate the presence of a brine residual from evaporite deposition. The Gulf basin is apparently open with respect to lithium. Because lithium is a volatile element which is lost from rocks during metamorphism, lithium in formation waters may result from metamorphic processes occurring much deeper in the Gulf Basin.