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Location: 85 km N from Rocky Point, Queensland, Australia
Level 4, 135 Wickham TceGPO Box 10955BrisbaneQueensland, Australia4000
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The deposit type is lateritic bauxite derived from the weathering of aluminous sediments in a tropical to sub-tropical environment. The Bauxite Hills area forms part of the Weipa Plateau and is underlain by rocks of the Carpentaria Basin. The oldest rocks intersected by drilling in the area are grey-black marine shales, which have been assigned to the Cretaceous Rolling Downs Group. This is up to 250 m thick and is underlain by sandstones of the Helby Beds. These rocks are a source of artesian water. The bauxite deposits generally consist of a single bauxite layer, 0.5 m – 3 m thick, that is underlain by a kaolin horizon.The bauxite deposits are overlain by lateritic overburden and topsoil. Under the bauxite there is often a cemented ironstone and a kaolin clay layer. Kaolin, sandy clays and minor quartz sand deposits occur beneath the bauxite layer and extend beyond the bauxite areas, beneath the Namaleta Creek flood plain. Bauxite occurs over the majority of the plateau areas. It is pisolitic in form and is generally covered only by a thin layer of soil, but in the western parts of the project area bauxite is sometimes found beneath sand dunes at depths of up to 6 m. The bauxite passes down into an iron rich horizon (ferricrete) and then into mottled, bleached Bulimba Formation sandy clays. Bauxite pisoliths generally form 55-80% of high-quality bauxite, with the remainder being sand, silt and clay. The pisoliths are well rounded, and generally 5 to 20 mm in size, although larger pisoliths of up to 30 mm do occur in the bauxite horizon. Larger, irregular shaped pisoliths and concretions are typical of the underlying ironstone horizon and form a visual marker of the base of the bauxite. Most of the bauxite is loose and free flowing although a proportion is cemented. The aircore drilling method used for exploration is efficient at drilling through thin layers of cemented bauxite, so from the exploration drilling alone it is difficult to make any accurate assessment of the proportion of cemented bauxite in this deposit. Mining experience in Weipa and Andoom has demonstrated that cemented bauxite is typically a small percentage of the total bauxite in this region. The geological interpretation is grade-based using a threshold of =45% total Al2O3 and =15% total SiO2 for BH1 and BH2 and of =45% total Al2O3 and =20% total SiO2 for BH6 (including the old Gulf Alumina areas), to define economic bauxite. The continuity of the geological interpretation is confirmed with a reasonable degree of confidence. The data points are spaced at 80 m in a nominal grid pattern for almost the entire BH1 deposit and at 160 m in a nominal grid pattern over the BH2 and BH6 deposits. The data points for the Gulf Alumina area are more variable but generally less than 400 m on a nominal grid. Information from other deposits in the Weipa area provides additional confidence in the geological model.The regional geological setting has been well known since discovery of the Weipa deposits, 80 km to the south. The considerable drilling already completed has given confidence in the local geological setting although it is noted that the definition of bauxite is essentially a chemical one, initially guided by lithological logging.The deposit type is lateritic bauxite derived from the weathering of aluminous sediments in a tropical to sub-tropical environment. The mineralisation within the Bauxite Hills Mine forms part of the Weipa Plateau, a widespread area of aluminous laterite on the west coast of Cape York Peninsula that includes Rio Tinto Alcan’s Weipa, Andoom and Amrun bauxite deposits. The bauxite deposits generally consist of a single flat-lying pisolitic bauxite layer, 0.5 m – 3 m thick, which is underlain by a kaolin horizon. Within the resource area the average bauxite thickness is 1.6 m. The bauxite deposits are overlain by lateritic overburden and topsoil. Under the bauxite deposits there is often a ferruginous cemented layer and a kaolin clay layer. Kaolin, sandy clays and minor quartz sand deposits occur beneath the bauxite layer and extend beyond the bauxite areas.DimensionsThe mineralisation within the bauxite plateaus is flat lying and tabular in form. The Mineral Resource has the following surface area, average bauxite thickness and average overburden thicknesses:- BH1: Area 8.4 km2. Bauxite thickness 1.6 m. Overburden 0.6 m- BH2: Area 4.2 km2. Bauxite thickness 1.4 m. Overburden 0.5 m- BH6/Gulf Alumina: Area 39.6 km2. Bauxite thickness 1.3 m. Overburden 0.8 m
