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.
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Since the first recorded discovery of lead in Southeast Missouri near Fredericktown about 1720, knowledge of the deposits has advanced in spurts as a result of outlying discoveries:
The original discoveries at Bonne Terre consisted of residual galena in clay, similar to that in the previous finds at Fredericktown. Occurrences in solid dolomite were not noted until mining of the clay pits exposed the walls of the weathered depressions. The St. Joseph Lead Co. had been established to conduct the operations and it was J. Wyman Jones. first President of St. Joe, who at that time brought about the first of the technological advances that were to occur in the district. He proposed use of the newly-invented diamond drill to explore the bed-rock showings, after observing the machines in the Vermont Marble Belt.
The first holes were drilled immediately behind the pit walls and were sufficiently successful that a shaft was sunk in 1859. Thus began the underground history of lead mining in southeast Missouri. The Bonne Terre area was the only producer from underground, hard-rock mining for the next 30 years; minor production came from shallow, surface “diggings” and veins near what is now Flat River but was insignificant and spotty. This shallow mineralization was not contiguous with the deep deposits found later.
Major discoveries of deep ore near Flat River were delayed by a negative theory of ore genesis. Although there were some advocates at that time of ore deposition from rising solutions, the most widely held theory called on downward-descending ground water. This resulted in a negative appraisal of areas where the Bonneterre Formation (the ore host) was overlain by the impervious Davis shale. It was felt that descending ground water would not be able to penetrate the 150 feet of shale. This ruled out most of the area to the south and southwest of Bonne Terre. Thus it was not until an unknown, venturesome individual drilled holes there anyway that what proved to be the largest orebodies in the “Old Lead Belt” were discovered. Great finds were made in an area nearly twelve miles long in a northwest-southeast direction. They totalled nearly 400,000,000 tons. The sub-districts of Deslodge, Leadwood, Rivermines, and Flat River eventually were interconnected underground.
The Southeast Missouri District has been the largest lead producer in the United States since 1890. Nearly a dozen companies had operations there at one time or another but, by 1933, the St. Joseph Lead Company had consolidated all the properties except those 30 miles to the southeast near Fredericktown.