Thermoanalytical characterization, stable isotope and paleoenvironmental considerations of kaolinite from two genetic sources

This study aimed at employing differential thermal analyses/ thermogravimetric analyses (DTA/TGA) and stable isotopes delta O-18 and delta D analytical techniques in understanding the mineral genesis of kaolinite from two genetically different sources in Botswana. The mineral contents of the samples were determined by X-ray powder diffraction (XRPD) technique and the loss on ignition by heating. Thermal characterization studies were conducted using differential thermal analyses/thermogravimetric analyses (DTA/TGA) techniques. Kaolinite was the dominant mineral in both deposits. Mean temperatures for endothermic peaks for Makoro kaolinite was 589 degrees C and for Kgwakgwe kaolinite 604 degrees C; and the mean temperatures for their exothermic peaks were 1025 degrees C for Makoro kaolinite and 1010 degrees C for Kgwakgwe kaolinite. Stable isotopes mean values for kaolinite from both Makoro and Kgwakgwe were as follows: delta O-18 for Makoro = +14.0 +/- 0.5 parts per thousand and for Kgwakgwe = +14.8 +/- 0.5 parts per thousand; and the delta D for Makoro = -71 parts per thousand and for Kgwakgwe = -77 parts per thousand. Low temperatures are inferred from the stable isotope values to have been involved in the kaolintisation, thereby eliminating hydrothermal fluids playing any major role. Whereas Makoro, kaolin is secondary, Kgwakgwe kaolin is primary but residual.