HYDROLOGY OF THE WESTERN ARKOMA BASIN DURING THE OUACHITA OROGENY: IMPLICATIONS FOR MISSISSIPPI VALLEY-TYPE ORE FORMATION IN THE TRI-STATE ZN-PB DISTRICT

The Zn-Pb ores of the Tri-State district of Oklahoma, Missouri, and Kansas represent one of the world’s foremost examples of Mississippi Valley-type (MVT) mineralization. The ores are part of a family of MVT deposits located within the Ozark Plateau that appear to have been precipitated from a regional groundwater flow regime set in motion by uplift of the Arkoma foreland basin during the Pennsylvanian-Permian Ouachita orogeny. The present study seeks to characterize the flow regime in the western part of the Arkoma basin that was responsible for depositing the Tri-State ores. Construction of a flexurally compensated stratigraphic profile for Late Pennsylvanian to Early Permian time indicates that the ores formed at a depth of 2.5-3 km. Numerical modeling of basinal fluid flow and heat transport indicates that ore-forming temperatures were reached largely by conduction under the existing geothermal gradient, with additional heat supplied by advection from the deeper parts of the basin. The modeling predicts a decrease in temperature of approximately 10° C laterally across the district, which may have contributed to deposition of the ores by cooling. The modeling also shows Tri-State to have been a region of the basin where fluid velocities were maximized, which may have further contributed to the localization of mineralization in the district. The association of the Tri-State ores with a local pinchout or “window” in the underlying Ozark Confining Unit and with deep-seated faults and fractures has led to speculation by previous workers that a component of the mineralizing fluid ascended from deeper aquifers in the basin. The results of the present modeling confirm that faults and fractures in particular would have been effective in conducting fluid from depth to the ore-hosting formations in the district.