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GEOREF RECORD

Assessing the geological sources of manganese in the Roanoke River watershed, Virginia

Abstract

The release of geogenic elements to water supplies is an issue of worldwide concern. Because these elements occur naturally and are often present in a variety of geologic materials, delineating sources and fates of these elements can be challenging. In this study, we examine connections between manganese (Mn) in modern groundwater, bedrock geology, and ores in the Roanoke River watershed of the Piedmont Province, Virginia. In the watershed, Mn concentrations in groundwater are often elevated above secondary drinking water standards. Evaluation of chemical characteristics of groundwater and geologic materials within the region suggests that carbonate-bearing lithologies are likely sources of Mn to groundwater. The inverse correlation of Mn with dissolved oxygen concentrations in groundwater suggests that once released from chemical weathering, Mn persists in groundwater under reducing conditions that develop along flowpaths. Analysis of Mn ores of the James River-Roanoke River Manganese District provides support that the ore deposits are supergene in origin, consistent with previous models. However, in contrast to previous models suggesting ore formation from downward flow of groundwater, our analysis of ore formation in the context of groundwater geochemistry supports an upwelling model of ore formation in which Mn-oxides were precipitated near discharge zones. Overall, our results suggest that Mn cycling is the region has been active over geologic time, as Mn-rich groundwater discharges to riverine systems, both past and present. Thus, the processes that formed the Mn ores in the past are still occurring in the modern day.


ISSN: 1078-7275
EISSN: 1558-9161
Coden: ENGEA9
Serial Title: Environmental & Engineering Geoscience
Serial Volume: 23
Serial Issue: 1
Title: Assessing the geological sources of manganese in the Roanoke River watershed, Virginia
Affiliation: Virginia Polytechnic Institute and State University, Department of Geosciences, Blacksburg, VA, United States
Pages: 43-64
Published: 20160822
Text Language: English
Publisher: Geological Society of America, Association of Engineering Geologists, College Station, TX, United States
Number of pages: 23
References: 50
Accession Number: 2016-088130
Categories: Economic geology, geology of ore depositsEnvironmental geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 5 tables, geol. sketch maps
N36°32'60" - N37°37'60", W79°49'60" - W78°49'60"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Abstract, Copyright, Association of Engineering Geologists and the Geological Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201643
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