SOURCING DIAGENETIC AND MINERALIZING FLUIDS OF MISSISSIPPI VALLEY-TYPE ORES ALONG THE CINCINNATI ARCH

MVT ores in south-central KY and north-central TN are predominantly hosted within the Ordovician Knox Dolostone. The sphalerite ores occur as vein-fill in fractures and as breccias in solution-collapse pipes, and are mineralized along both the calcite and dolomite facies of a regional dolomitization front within the Upper Knox. Deposits lie near the highly fractured crest of the Cincinnati Arch, which divides the Appalachian Basin to the east from the Illinois Basin to the northwest. Both basins host geochemically distinct MVT deposits. Sphalerites from the Kentucky-Illinois fluorspar district in the Illinois Basin are predominantly red and brown, while the East Tennessee district sphalerite crystals are typically translucent yellow. Regional diagenesis and ore metal sourcing along the arch has been debated for several decades. Current workers believe the metals were mobilized from the Appalachian Basin during multiple collisional orogenic events, with concurrent sulfide mineralization, dolomitization, and petroleum brine migration. Former industry workers from the area agree with this ore genesis mechanism, but believe the metals traveled with petroleum brines of the Illinois Basin during the Ouachita orogeny and the uplift of the Ozark Plateau. Both hypotheses agree that petroleum brine migration influenced sulfide mineralization, dolomitization, and diagenesis throughout the region. Lead isotope data was collected with a Nu-Plasma MC-ICP-MS at the University of Arkansas from samples gathered from the Burkesville mine in south-central KY and from the Gordonsville and Elmwood mines in north-central TN. Collected sphalerite samples are predominantly black and red with yellow intergrowth bands, bearing similarities to ores from both suspected brine sources. The isotopic data from north-central TN and south-central KY also reveal similarities with both basins over a broad range of lead isotope distributions, suggesting varying degrees of fluid mixing and multiple diagenetic regimes occurred throughout the region. This result is in agreement with current hydrogeologic models of the region, which call for four to seven distinct diagenetic events along the Cincinnati Arch, which resulted in secondary deposits of calcite, dolomite, sphalerite, chert, barite, fluorite, and galena.