Metalliferous hypersaline formation waters are widely regarded as modern analogs to the solutions that formed the Mississippi Valley- type (MVT) sediment-hosted pb-zn deposits that occur along margins of major sedimentary basins. Additionally, basin brines are interpreted to have played major roles in forming pb-zn +/- ag mineralization and sr concentrations in Gulf Coast Salt Dome Caprockes Within Basins. Na-ca-cl oilfield brines from upper Jurassic and lower Cretaceous formations in central Mississippi are some of the most metal-enriched formation waters yet documented, containing up to several hundred ppm pb + zn. The intrusion of the Jackson Dome alkalic igneous complex through these formations during the late Cretaceous set up a possible mineralizing system. This study presents evidence from existing hydrocarbon exploration wells, which penetrate only the top of the complex, that indicates igneous rocks have undergone extensive hydrothermal alteration and local metal enrichments. Geologic relationships, alteration and base- metal sulfide mineralogy, trace-element geochemistry, and light- stable isotopic analyses implicate basin brines as the altering fluid and the probable primary metal source. All lines of evidence indicate that the Jackson Dome is a previously unrecognized geologic environment in which metallic mineral deposits may occur. Results of this study suggest shallow Cretaceous intrusions elsewhere in the northern gulf coast region may also host similar mineralization.