Paleoenvironmental conditions underpinning kaolinitisation of Lwamondo and Zebediala Kaolin Deposits

Abstract

In the present study, the physico-chemical, applications, mineralogy, geochemistry and stable isotope of Lwamondo and Zebediela kaolin is documented, in order to understand the genesis, paleoenvironmental conditions and possible utilization. Mineral identification studies were conducted using X-ray diffractometer (XRD), Fourier transform infrared spectrophotometer (FTIR) and scanning electron microscope with energy dispersive X-ray micro analysis (SEM-EDX). Major oxides were identified by X-ray Florescence (XRF) whereas trace elements were identified by Laser Ablation Inductively Coupled Plasma-Mass Spectrometer (ICP-MS). Hydrogen and oxygen isotopic composition were determined by δ18O and δD isotopic measurements. Kaolinite was dominant mineral in all the kaolin samples whereas muscovite, quartz, goethite, hematite, smectite, anatase occurred in minor to trace quantities. The chemical data show that the kaolins are composed mainly of SiO2 and Al2O3 due to the presence of quartz and kaolinite, with minor to trace amounts of other elements such as Ca, Na, Cr, K, Fe, Mn, Mg, P and Ti which affected the kaolin application negatively. Lower concentration of Ca, Na, K, Fe, Mn, Mg, and Ti show the extent of the kaolinitisation. The samples were enriched in Ni and depleted in some other trace elements. The chondrite-normalised rare earth elements patterns show enrichmnent in Heavy Rare Earth Elements (HREE) than Light Rare Earth Elements (LREE) with slight positive Eu anomaly. The Rare Earth Elements (REE) pattern and the content of other trace elements show evidence of weathering processes related to kaolinitisatioon. Kaolin genesis is explained using kaolin mineralogy, particle morphology, structural order (functional group), major and trace elements geochemical data. The data suggest that kaolin is derived from the intensive chemical weathering of intermediate to mafic rocks deposited in non-marine environment. The stable isotopes were used to determine the paleoenvironmental conditions which influenced kaolinitisation of Lwamondo and Zebediela kaolins. Stable isotopes mean values for kaolinite from both Lwamondo and Zebediela were as follows: δ18O for Lwamondo= +18.57‰ and for Zebediela = +16.67 ‰ vii and δD for Lwamondo = -65‰ and for Zebediela = -64‰. The calculated mean temperatures were 26.94 ⁰C for Lwamondo kaolin and 36 ⁰C for Zebediela kaolin. Low temperatures were inferred from stable isotope values to have been involved in the kaolinitisation wherein hydrothermal processes were eliminated. The data suggests that kaolin was formed in a weathering environment. The kaolin is found to be suitable for brick making and based on the physico-chemical, mineralogical and chemical data it was suggested that the kaolin could also be used in producing low temperature ceramics, refractory materials, pottery and stoneware