Paul R. Dingess, 1989. "Geology of the Asarco West Fork Deposit Viburnum Trend - Southeast Missouri", Mississippi Valley-Type Mineralization of the Viburnum Trend, Missouri, Richard D. Hagni, Raymond M. Coveney, Jr.
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The West Fork ore body was discovered in January 1960, during the early exploration and discovery phase of the Viburnum trend, but development of the deposit was delayed until 19RO. After partial development, the downturn in Pb prices resulted in shutdown until late 1984. Limited production of 1,000 tpd began in September 1985, increased to 1,500 tpd in May 1987, and finally to full production of 3,800 tpd in July 1988. The general location is shown in Figure 1.
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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.