Date of Graduation

1-2017

Document Type

Thesis

Degree Name

Master of Science in Geology (MS)

Degree Level

Graduate

Department

Geosciences

Advisor/Mentor

Adriana Potra

Committee Member

Phil Hays

Second Committee Member

Chris Liner

Third Committee Member

Thomas McGilvery

Keywords

Chattanooga Shale, Mississippi Valley-Type, Ores, Pb Isotopes, Shales

Abstract

Mississippi Valley-type (MVT) deposits are base metal sulfide deposits that are important economic sources of both Pb and Zn, accounting for 24% of the global Pb and Zn reserves. They are found all over the world, often hosted in platform carbonates on the flanks of sedimentary basins, and often in proximity to hydrocarbons. They are epigenetic, not related to igneous activity, and thought to be sourced from low temperature, highly saline basinal brines that are expelled from sedimentary basins during compaction and/or in conjunction with an orogenic event. The basinal lithologies responsible for providing the metals for the ores are still a matter of debate. The ores are highly enriched in radiogenic Pb and thus potential sources must also share this same isotopic signature. Shales have been hypothesized to represent the original source of the metals due to their radioactive nature, the large volumes of connate fluid associated with their sediments before compaction, and their association with hydrocarbons.

The Pb isotopic compositions of 20 sphalerite samples from the Northern Arkansas and the Tri-State MVT mining districts, 23 shales from the Chattanooga and Fayetteville formations, and 2 granitic basement rocks from the southern Ozarks have been analyzed and compared in order to evaluate the potential source(s) of the metals. The granites and most of the shales do not match the isotopic signature of the ores and thus may not represent a viable metal source. However, one sample taken from the base of the Chattanooga shale has similar Pb isotopic ratios to the ores, suggesting that the shale may have provided the metals. The depositional environment of the aforementioned shale sample explains the isotopic signature and sheds some light on the origin of the ore deposits.

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