Radiogenic Pb Enrichment of Mississippi Valley-Type Metallic Ore Deposits, Southern Ozarks: Constraints Based on Geochemical Studies of Source Rocks and Their Diagenetic History

Jonathan Chick,John R Samuelsen,Adriana Potra,Walter L Manger,Sydney E Mckim

doi:10.3390/geosciences11040172

Jonathan Chick, John R Samuelsen + Show 3 more

Open Access

https://doi.org/10.3390/geosciences11040172

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Abstract

Southern Ozark Mississippi Valley-type ores are enriched in radiogenic Pb, with isotopic signatures suggesting that metals were supplied by two end-member components. While the less radiogenic component appears to be derived from various shale and sandstone units, the source of the more radiogenic component has not yet been identified. Analyses of cherts from the Early Ordovician Cotter Dolomite and tripolitic chert from the Early Mississippian Boone Formation contain highly radiogenic Pb, with isotopic ratios comparable to those of ores. However, most samples have lower 208Pb/204Pb and 207Pb/204Pb for a given 206Pb/204Pb compared to ores. These relationships demonstrate that the enriched Pb isotopic values of the ore array cannot be related to the host and regional lithologies sampled, suggesting that the source of high ratios may lay further afield. The slope of the linear trend defined by the Pb isotope ratios of ores corresponds to an age of about 1.19 Ga. Therefore, an alternative for the linear array is the involvement of Precambrian basement in supplying ore Pb. Rare earth element patterns show that diagenetic processes involving the action of groundwater and hydrothermal fluids affected the sampled lithologies to various degrees, with Cotter Dolomite having experienced the highest degree of alteration.

Highlights

It has been hypothesized that Ordovician, Mississippian, and younger carbonate and clastic formations found within the Ouachita Uplift of west-central Arkansas, and northward onto the Ozark Dome, experienced interaction with hydrothermal fluids due to tectonic forces that caused the Ouachita Orogeny [1,2,3]
The Rare Earth Element (REE) concentration patterns produced by the analyzed samples are illustrated by REE diagrams (Figure 5A), which display REE depletion or REE enrichment relative to those of the North American Shale Composite (NASC) [72]
The REESN (NASC-normalized REE) values for all samples are less than 1, with the lowest normalized REE values found in the Cotter Dolomite

Summary

Introduction

It has been hypothesized that Ordovician, Mississippian, and younger carbonate and clastic formations found within the Ouachita Uplift of west-central Arkansas, and northward onto the Ozark Dome, experienced interaction with hydrothermal fluids due to tectonic forces that caused the Ouachita Orogeny [1,2,3]. In the Ozark region, the linear trend defined by the Pb isotope compositions of the MVT ores suggest their formation involved a mixing of metals from two end-member components [7,8,9,10]. Extensive geochemical studies of rocks from the southern Ozark region and the Ouachita Mountains (Figure 1) have been carried out in order to constrain the two end-member components in the ores from the Northern Arkansas and the Tri-State boniferous shales and sandstones of the Ouachita Mountains [10], the various cherts from the Devonian-Lower Mississippian Arkansas Novaculite [11,12], and from the Lower Mississippian Boone Formation

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