The Mineralogical and Geochemical Controls that Source Rocks Impose on Sedimentary Kaolins
Robert J. Pruett, Haydn H. Murray, 1993. "The Mineralogical and Geochemical Controls that Source Rocks Impose on Sedimentary Kaolins", Kaolin Genesis and Utilization, Haydn H. Murray, Wayne M. Bundy, Colin C. Harvey
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The degree that sedimentary kaolin properties are influenced by primary source materials has rarely been fully determined. Samples of sedimentary kaolin, primary kaolin, and crystalline rock were collected from Latah County, Idaho to examine the mineralogical and geochemical relationship between sedimentary kaolins and their primary kaolin provenances. The geological setting of the Latah County kaolins establishes a connection between sediment and provenance. The parent materials for the sedimentary kaolins are saprolites developed on Idaho Batholith granodiorite and Belt Group metamorphic rocks. Kaolinitic sediments were eroded from these saprolites during the Miocene and were deposited in lakes formed in valleys dammed by flows of Columbia River flood basalt. Volcanic ash deposited within these lakes devitrified to tonsteins containing spherical halloysite. Mineralogy, crystallinity, and particle morphology were evaluated by combined X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). Elemental abundances were determined by ICP. Stable isotopic ratios of oxygen and hydrogen extracted from kaolins were obtained by mass spectrometry.
The sedimentary kaolins contain tubular halloysite distinctive of the igneous saprolites and kaolinite stacks distinctive of the metamorphic saprolites. Some sedimentary kaolin strata contain halloysite spheroids emplaced from the volcanic source. Sedimentary kaolin crystallinity may correlate with content of kaolinite stacks derived from the metamorphic saprolite. The ratio of Ba, La, Sr, Th, Zn, Fe2O3, A12O3, and alkalies concentrations are explained by mixing sediment from all three sources. Oxygen isotope values are explained by mixing sediment from the saprolites and the volcanic source. Hydrogen isotope values indicate exchange between the kaolin and pore fluids.
Results show the saprolite and volcanic provenances may influence Latah Formation sedimentary kaolin mineralogy, particle morphology, chemistry, oxygen isotope ratios, and crystallinity. Therefore, provenance could significantly influence the physical properties of a sedimentary kaolin.