Authigenic clay and sulfide minerals of the Upper Cambrian Lamotte Sandstone and Bonneterre Formation: : Fletcher and Brushy Creek mines, Viburnum Trend, southeastern Missouri
Huggins, Shirley A.
MetadataShow full item record
Authigenic clay and sulfide minerals were precipitated from formation waters in the pore spaces of the Upper Cambrian Lamotte Sandstone and in vugs and fracture planes in the Bonneterre Formation. The distribution of sulfide mineral precipitation was structurally influenced by knobs along the Precambrian Viburnum Trend ridge and was strati- graphically influenced by porosity and brecciation within the Bonneterre Formation. X-ray fluorescence analysis has revealed that sulfide minerals are more concentrated around the flanks of the Viburnum Trend in the Lamotte Sandstone even though trace amounts are present as far as 50 miles away from the ridge. Scanning electron micrographs show that authigenic illite was precipitated before sulfide minerals in the Lamotte Sandstone while kaolinite and dickite were precipitated afterwards in the Bonneterre Formation. The K-Ar dating method was applied to authigenic illite to attain a lower age limit for these precipitation events. Results indicate that illite was probably precipitated at or prior to 250-300 million years ago. Kaolinite and dickite from the Fletcher and Brushy Creek mines of the Viburnum Trend were extracted from vugs and fracture plane surfaces in the dolomite of the Bonneterre Formation. A mottled texture was often observed on the pinacoid planes of dickite crystals while these faces of kaolinite crystals are smooth. This feature may be the result of defects in the lattice structure, adsorption of foreign cations or fluctuations in the pH of formation waters from which dickite precipitated. It was also observed that kaolinite is usually associated with marcasite (FeS₂), whereas dickite is usually associated with chalcopyrite (CuFeS₂) and sphalerite (ZnS), especially when sulfides are in euhedral form. This observation suggests that metal cations in the associated sulfide minerals may have played a more important role in the genesis of kaolinite and dickite than the temperature of formation.