Date of Graduation

5-2016

Document Type

Thesis

Degree Name

Master of Science in Geology (MS)

Degree Level

Graduate

Department

Geosciences

Advisor

Adriana Potra

Committee Member

Greg Dumond

Second Committee Member

Phil Hays

Third Committee Member

Doy Zachry

Fourth Committee Member

Andrew Wulff

Keywords

Earth sciences; Hydrotectonics; Isotope geochemistry; Kentucky; Lead isotopes; Mississippi valley-type; Ore deposits; Sphalerite

Abstract

Mississippi Valley-Type (MVT) ores are economically-viable deposits of sulfide minerals, often dominated by sphalerite (zinc-sulfide) in carbonate facies, and galena (lead-sulfide) in siliciclastic facies. MVT ores precipitate from migrating fluids, which carry base metals often complexed with chlorine ions within a basinal brine. This study identifies metal-contributing source-regions of the Burkesville MVT deposit using Pb-isotope ratios within sphalerite samples collected from the Burkesville deposit. The deposit is found in south-central Kentucky within the Middle-Tennessee ore district along the crest of the Cincinnati Arch, which is the anticlinal divide between the Appalachian Basin and the Illinois Basin. Competing theories argue that MVT ores along the Cincinnati Arch were precipitated from either Appalachian or Illinois Basin brines that were mobilized during orogenic events within the Appalachian Mountains, Oachita Mountains, and/or Ozark Plateau. The orogenic events were considered concurrent with sulfide mineralization, dolomitization, and petroleum brine migration throughout the region. Ratios for 206Pb/204Pb ranged from 19.639 to 19.803, ratios for 207Pb/204Pb ranged from 15.709 to 15.806, and ratios for 208Pb/204Pb ranged from 39.294 to 39.583. Results from this study of Pb-isotopes imply that the Burkesville deposit correlates strongly with the southern Appalachian Basin, but also suggest that there were some contributions from the Illinois Basin due to brine mixing or multiple paragenetic events. Isotopic ratios were obtained via analysis with a Nu-Plasma MC-ICP-MS. These results provide an explanation to the contradictory works of previous researchers, who sought to constrain the contributing basin of the Middle Tennessee district via trace-element, crystallographic, and fluid-inclusion analyses. The current research has produced a new model for MVT ore formation near the Cincinnati Arch, in which the majority of the ore minerals precipitated from brines from the southern Appalachian Basin, but which either mixed with or were later altered by a higher-temperature brine originating from the Illinois Basin which contributed the higher concentrations of Cd, Cu, Ge, and Ga observed in the district today.

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