Date of Graduation

8-2019

Document Type

Thesis

Degree Name

Master of Science in Geology (MS)

Degree Level

Graduate

Department

Geosciences

Advisor/Mentor

Adriana Potra

Committee Member

Thomas McGilvery

Second Committee Member

Phillip D. Hays

Keywords

Economic Geology, Geochemistry, Geofluids, Hydrogeochemistry, Hydrogeology, Mineral resources

Abstract

Cluster of Pb and/or Zn deposits of the well-known Tri-State and Northern Arkansas Mississippi Valley Type (MVT) districts located north of the Arkoma basin and the Ouachita fold-thrust belt in north America are genetically connected to the Pennsylvanian-Permian Ouachita orogeny which triggered a South-North topographic gradient flow of basinal brines, leaching metal rich sediments en route. The objective of the research is twofold. First, to ascertain whether the organic-rich shales and sandstones from the study area provided metals during the mineralization event, which was coeval with the Ouachita orogeny. Second, to assess the depositional environment of the potential source rocks, which will shed light on their ability to sequester metals. The Pb isotope compositions of the ores (sphalerite) have been compared to their associated sedimentary rocks (Collier, Mazarn, and Polk Creek, Womble, Fayetteville, Stanley and Chattanooga shales and Jackfork Sandstone) and metal sources have been evaluated. In addition, the role of depositional redox of sedimentary rocks to sequester adequate amounts of metals has been appraised using redox sensitive trace elements (U, V, Mo, Cr, etc.). The Pb isotope compositions of the ores (sphalerite) have been compared to those of the sedimentary rocks of the Ouachita Mountains (Cambrian Collier Shale, Early Ordovician Mazarn Shale, Middle Ordovician Womble Shale, Late Ordovician Polk Creek Shale, Mississippian Stanley Shale, and Pennsylvanian Jackfork Sandstone) and the Ozark Plateau (Devonian/Mississippian Chattanooga Shale and Mississippian Fayetteville Shale).Metal sources evaluation indicate a mixing model of fluids sourced from high and less radiogenic rocks shown by a broad and linear trend of Pb isotope composition, with the Chattanooga rock and the Jackfork sandstone samples being the most prominent source rocks. Paleoredox proxies indicate deposition under anoxic and Euxinic conditions, which are favorable for metal enrichment. How-ever, oxic-suboxic conditions are also indicated by other geochemical proxies, suggesting the possible first order control of primary production that has resulted in increased flux of organic matter. Additional factors such as the basin geometry, the rates of sediment accumulation, the post depositional alteration processes associated with diagenesis and low-grade metamorphism during the Ouachita orogeny might have overprinted the depositional signatures.

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