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
Download citation file:
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.
Figures & Tables
Kaolin is an important industrial mineral in several world markets including uses in paper coating and filling, ceramics, paint, plastics, rubber, ink, fiberglass, cracking catalysts and many other uses (Murray, 1991). The kaolin minerals kaolinite, halloysite, dickite, and nacrite have essentially similar chemical composition but each has important structural and stacking differences. The most common kaolin mineral and the one that is the most important industrially is kaolinite [Al2Si205(OH)4]. Kaolinite can be formed as a residual weathering product, by hydrothermal alteration, and as an authigenic sedimentary mineral. The residual and hydrothermal occurrences are classed as primary and the sedimentary occurrences as secondary. Primary kaolins are those that have formed in situ usually by the alteration of crystalline rocks such as granites and rhyolites. The alteration results from surface weathering, groundwater movement below the surface or action of hydrothermal fluids. Secondary kaolins are sedimentary which were eroded, transported and deposited as beds or lenses associated with other sedimentary rocks. Most kaolin deposits of secondary origin were formed by the deposition of kaolinite which had been formed elsewhere. Some secondary deposits were formed from arkosic sediments that were altered after deposition, primarily by groundwater. There are far more deposits of primary kaolins in the world than secondary kaolin deposits because special geologic conditions are necessary for both the deposition and preservation of secondary kaolins.