A COMPARISON OF KENTUCKY MISSISSIPPI VALLEY TYPE DEPOSITS

The compositions of Mississippi Valley Type (MVT) deposits in the Kentucky-Illinois Fluorspar District have been well-established through numerous regional studies. However; the nature of MVT deposits such as those found in Cumberland County, KY are less understood. Previous studies of the Andrew Jackson mine in Crittenden County in western Kentucky have shown trace amounts of Cu, Cd, Ga, and most notably, Ag. The purpose of this research is to augment what is known about MVT-type deposits in Kentucky by analyzing fluid-inclusions within samples of breccias from the Andrew Jackson mine in Columbia, KY as well as samples derived from three separate cores from a now inactive mine in Burkesville, KY. After suitable samples had been obtained doubly polished thick sections were made to preserve any fluid inclusions contained within the rock as well as facilitate their identification using a combination of reflected and transmitted light microscopy. Samples were prepared for use on a Linkam heating and cooling stage to examine inclusions as well as determine the temperature of formation. Analysis of these samples revealed the majority of fluid inclusions to be secondary and pseudo-secondary, with a lesser percentage of primary inclusions forming at temperatures less than 150°C. Additional analyses of matrix material conducted using LA-ICP-MS revealed dominant elements including: Pd, Ag, Cd, Ga, and Ge. The data indicate a high degree of heterogeneity amongst the Columbia samples with a factor of three difference between various trace elemental concentrations. This heterogeneity was shown to persist at various scales from sub-millimeter distances within the same sample to concentration differences between samples. Both the Columbia and Burkesville samples exhibited localized zones of high Cu concentrations often two to three times that of the rest of the sample. Trace amounts of In were observed in the Burkesville MVT but not in the Jackson mine samples. Additionally, well-delineated bands of particularly Ga-enriched matrix were observed in the Burkesville samples, suggesting the possibility of genetically distinct mineralizing fluids mixing in the area.