Assessment of New Kaolinitic Deposit in Western Blue Mountains
Ron Goldbery*1, Pramod Koshy2, and Charles Christopher Sorrell2
1Industrial Mineral Resources Australia, 3 Karingal Court, Marsfield,
NSW 2122, Australia;
2School of Materials Science and Engineering, The University of New South Wales, Sydney, NSW 2052, Australia;
*Email:
A newly developed kaolinitic deposit of diagenetic origin, occurring in a friable sandstone host rock, was evaluated as part of a major mining project at Newnes Junction in the Western Blue Mountains of NSW. Investigative work done on the deposit as a function of depth (to 40 m) has determined that the clay, which is relatively homogeneous and of the dickite polytype, comprises 10 wt% of the sandstone deposit; the Australasia Joint Ore Reserves Committee (JORC) has certified the presence of ~2 million tonnes of proven clay reserves. X-ray diffraction (XRD) and scanning electron microscopy (SEM) data show that the clay is well crystallised, with some grains exceeding 20 μm. Quartz is the only major secondary mineral and muscovite mica is present irregularly at trace levels. The deposit is of fairly consistent Al2O3/SiO2 wt% ratio (~0.5), with the alkali and Fe2O3 contents being ~1.2-1.7 wt% and ~0.3-0.4 wt%, respectively. Rational analysis indicates that the clay/quartz wt% ratio is ~70/30. Laser diffraction particle size analysis revealed a bimodal distribution, with mean sizes / fractions being, respectively, ~1 μm / 15 vol% cumulative and ~7 μm / 60 vol% cumulative. Since the true densities of clay and quartz are almost identical, this shows that, conversely to expectation, the coarse high-volume fraction is the clay and so it is likely that the majority of the coarser remainder (>7 μm / 40 vol% balance) also consists of clay. Dehydroxylation to form metakaolin occurred at <500°C, yielding an off-white product with strong reflectivity in the warm colour wavelengths. Potential applications include whitewares, structural clay products, and geopolymers.