Hydrothermal Fluids and Diagenesis of Mississippian Carbonates, Implications for Regional Mineralization in Western Kansas U.S.A

Hydrothermal fluids altered Mississippian (Osagian) carbonates in the Rebecca K. Bounds (RKB) core in Western Kansas, U.S.A. Carbonate mineralization is similar to that asso-ciated with Mississippian Valley Type (MVT) mineralization. The RKB core displays fractures, vugs, channels, and breccias filled by saddle dolomite and blocky calcite ce-ments. Fluid inclusion microthermometry indicates that saddle dolomite (65 to 126 °C, 18.4 to 23 wt. % NaCl) and calcite (67 to 101 °C, 13.2 to 22.4 wt. % NaCl) cements were precipitated by hot, saline fluids. These data are consistent with previous studies on the southern midcontinent. Petroleum inclusions were identified in saddle dolomite and possibly in blocky calcite cement. Carbon and oxygen isotope analyses of carbonate cements indicate multiple pulses of fluids, likely sourced from basins to the south and west. Strontium isotopes indicate that mineralizing brines interacted with granitic basement or basement-derived siliciclastics. Fluid inclusion and isotope geochemistry is consistent with mixing of upwelling Ordovician-sourced fluids and Permian evaporitic brines, transported by advective and/or vertical migration. Although sulfide minerals were not observed in this study, earlier reports note sphalerite linked to ore-forming brines in underlying strata. The potential presence of MVT mineralization in the Mis-sissippian of Western Kansas cannot be excluded.