Organic matter and thermochemical sulfate reduction in the Viburnum Trend, southeast Missouri

The role of organic matter in Mississippi Valley-type Pb-Zn deposits has been studied by systematically sampling and characterizing various types of organic matter in the Upper Cambrian Bonneterre Formation in lead-zinc mines from the Viburnum Trend and from rocks as far as 20 km away from the Trend. Organic matter that is several kilometers from ore consists of insoluble disseminated kerogen in carbonates. Within meters to centimeters of ore in the Milliken mine, at the south end of the Viburnum Trend, organic matter occurs as solid, partly soluble tacky bitumen and insoluble hard blebs of millimeter to centimeter size. The solid insoluble organic matter in intimate contact (intergrown) with ore (galena and chalcopyrite) is friable and brittle. The sulfur content of solid organic matter from the Milliken mine varies and is lowest for tacky material away from ore, intermediate for blebs near ore, and highest for friable material in intimate contact with ore. Pyrolysis-gas chromatography of this sample suite documents the progression of kerogen (far from ore) through solid petroleumlike material (near ore) to degraded organic matter (in contact with ore). -from Author