Relationships Among Metal-Rich Pennsylvanian Marine Black Shales, Minor Occurrences of Sphalerite in Country Rocks and Mississippi Valley-Type Ore Deposits of the Midwestern United States
Raymond M. Coveney, Jr., 1989. "Relationships Among Metal-Rich Pennsylvanian Marine Black Shales, Minor Occurrences of Sphalerite in Country Rocks and Mississippi Valley-Type Ore Deposits of the Midwestern United States", Mississippi Valley-Type Mineralization of the Viburnum Trend, Missouri, Richard D. Hagni, Raymond M. Coveney, Jr.
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This article does not specifically concern the Viburnum Trend, object of this November 1989 SEG/GSA-sponsored field trip, but rather focusses on features in country rocks of the Midwest which may have bearing on the origins of Mississippi Valley-type (MVT) deposits like those of the Missouri Lead Belt. Fluid inclusions with high salinities and moderately high homogenization temperatures (Th = ca. 80-120°C+) are widespread in minor and trace occurrences of sphalerite in the Midwest (Fig. 1). Metal-rich Pennsylvanian black shales, enriched in Zn, v, U, Mo and other elements, occur in the same region. If these widespread saline fluid inclusions were formed by the same processes that formed the main MVT ore deposits of the Midwest, they imply that ore deposition involved extremely broad scale flow of mineralizing fluids. Various authors believe the black shales to have been source beds for MVT ores. Although no certain answer exists, available evidence suggests that the exceptionally metal-rich black shales of the Pennsylvanian were sinks rather than sources during MVT ore deposition.