Honours Abstract (2005) Lyndall FREER

Deep weathering profiles are abundant in the south-western Yilgarn Shield. Their dominance in this area is related to the mobility of major and trace elements and the factors that influence chemical processes of weathering. Granite is the dominant bedrock in this area from which minerals leaches and form secondary minerals such as kaolinite. Kaolinite is one of the dominant minerals found in weathering profiles and this thesis focuses on the development of high quality kaolin in granitic weathering profiles with respect to the industrial specifications for kaolin processing in the paper industry. This thesis suggests reasons for the development of high quality kaolin in the south-western Yilgarn Shield. Detailed regolith mapping was carried out to determine the relationship between the outcrops and the weathering profiles under the surface. X-ray diffraction was conducted on 42 samples that were situated within the various zones in the weathering profile, i.e. pallid zone, mottled zone and ferricrete. Of the 42 samples, 18 samples were selected for x-ray fluorescence to test element mobility within the weathering zones and to interpret the mobility of these elements with the leaching of minerals from the parent rock.

This thesis discusses the factors influencing the weathering of granite, such as drainage and groundwater, the topography and slope of the area, climate, time and age, and tectonic stability. Significant findings suggest that groundwater and drainage are major factors in the development of high quality kaolin in this area and hence is associated with the slope of the areas in which kaolin develops. Calculations of the slope of the drilled areas suggest less than 1º slope is ideal for the development of high quality kaolin. Seismic activity may also play a role in the development of high quality kaolin. Fractures from uplift in the area may allow groundwater to seep into layers within the pallid zone and further develop the quality of the kaolin. This is discussed in response to Mulcahy’s development of the Meckering Line and its association with seismic activity in the area. Overall, this thesis aims to give reasons for the development of high quality kaolin in deep weathering profiles on granite in the south-western Yilgarn Shield.