Odom, J. Edgar||Keighin, C. William
M.S. (Master of Science)
Department of Geology
The clay mineral composition of 12 lithic units within and immediately above the mineralized zone in the Nonesuch Shale at White Pine, Ontonagon County, Michigan was investigated at 24 locations in an area of approximately 80 square miles. Chlorite, illite (mica), and a slightly expansible mixed-layer clay type were found to be the clay components of the mineralized zone. Evaluation of the relative abundance of the three clay types in 336 samples, made by comparing the intensities of the basal reflections, showed that chlorite was usually the most abundant and mixed-layer material usually the least abundant of the clay mineral types present. In a few samples, chlorite was the only clay mineral present. In general, illite averaged less than 30 percent while mixed-layer material averaged less than 10 percent of the total clay mineral diffraction effects from each sample. No regional or stratigraphic patterns in the abundance of the clay types were observed except in the Widely unit, which usually occurs above the mineralized zone. In the Widely unit, chlorite increased and illite and mixed-layer material decreased in a northeasterly direction. This pattern is thought to be related to differential sorting of the clay types during sedimentation with the direction of sediment transport being from southwest to northeast. The iron content of chlorite, evaluated from the ratio of the relative intensities of the 7A to the 14A basal reflections, varies over a wide range within individual stratigraphic units, but the mean iron content of the chlorite increased upward through the ore column. No direct relationship between copper grade and clay mineral composition or iron content of the chlorite was observed. An investigation of chlorite polytypes was made on six samples. The IIb chlorite polytype was the most abundant chlorite in all six samples. Two samples, one from the Lower Sandstone member and one from the Widely unit, also contained the lb chlorite polytype. It is concluded that most of the chlorite in the rocks studied is the lib structural form and that this chlorite is detrital. The lb chlorite is thought to be the product of diagenesis. The relationship, if any, of the Ib or IIb chlorite polytypes to copper sulfide and native copper mineralization was not studied. Scanning electron microphotographs show that the chlorite crystals in the Lower Nonesuch Shale have quite rounded edges compared to the euhedral morphology of the IIb chlorite crystals found as amygdaloidal fillings in a nearby basalt. The morphological character of the chlorite crystals in the Nonesuch Shale is interpreted to be due to abrasion during transport.
Harrison, William James, "Clay mineral assemblages and chlorite polytypes in the basal Nonesuch Shale White Pine, Michigan" (1971). Graduate Research Theses & Dissertations. 1815.
ix, 84 pages
Northern Illinois University
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