| Several studies have suggested a link between the generation of petroleum and the formation of base metal deposits, primarily Pb, Cu, and Zn deposits, in sedimentary basins. The metals incorporated into basinal brines could be derived from a number of sources, including host rock units. In this study we evaluated hydrocarbon source rocks, specifically organic-rich shales, as a source of trace metals for basinal brines using batch leaching experiments and analyzing the USGS' produced waters geochemical database. Batch leaching experiments were performed with powdered source rocks from the Eagle Ford, Marcellus, and Wolfcamp Shales. A subset of the samples was subjected to the destruction of organic matter through the loss-on-ignition method prior to leaching. All samples were subjected to batch leaching by combining approximately 1 g of rock with 10 mL of NaCl, acetate, or NaCl and acetate-electrolyte solution with molarities of 0.01, 0.1, 0.5, or 1. The experimental results showed that more trace (Pb, Zn, and Mo) metals were extracted from the Eagle Ford (EF 28) and Marcellus (Ma) source rocks post destruction of the organic matter prior to leaching using a NaCl and acetate-electrolyte solution. The leaching results also suggested that chloride complexes increased metal solubility in solution more than organic complexes (acetate) for trace metals (Zn and V) and some major elements (Mg). In the produced waters database, trace metal concentrations (Cu, Pb, and Zn) in samples from the Appalachian, Arkla, Gulf Coast, and Williston Basins exhibited a positive correlation with increasing chloride concentration. The produced waters database results hint that there are additional complexities associated with metal sources and loading such as pH and the presence of H2S. |
