Iron Ore, Bauxite and Manganese deposits of NT report
The Northern Territory (NT) contains a number of lateritic bauxite deposits along its northern coastline that have produced 236Mt of bauxite to the end of 2014. There is currently one mine in operation, Rio Tinto Alcan’s Gove mine at Nhulunbuy. This world-class deposit accounts for 100% of past bauxite production and 90% of identified bauxite resources in the NT.
Total remaining reserves and resources at Gove are 201Mt at 49.5% Al2O3 . The deposit averages 3.7m in thickness and has developed over arkosic Cretaceous rocks (Yirrkala Formation). The gibbsitic bauxite is low in silica (3% reactive SiO2) and is mainly pisolitic and tubular in nature. Profiles through the deposit indicate that some bauxite layers are residual (tubular) while others (loose and cemented pisoliths) have been transported. An alumina refinery operated in Gove from 1972 to 2014 but is now in care and maintenance, with all bauxite now exported. Production at Gove in 2014/15 was seven million tonnes of bauxite.
A number of other lateritic bauxite deposits are known along the northern coastline of the NT. These deposits (like Gove) have developed over Cretaceous rocks during the Cenozoic. Further potential exists in Arnhem Land across untested lateritic areas west of Woolen River, north of the Peter John River and in the King River area.
Low-silica bauxite is present on the Dhupuma Plateau (21km south of Nhulunbuy) which has potential for >35 Mt of untested lateritic bauxite. Several pockets of low-silica (4% reactive SiO2) bauxite totalling 9.9Mt @ 46% available Al2O3 exist on Marchinbar Island. These deposits average about 2m in thickness and rest unconformably on laterite-resistant Marchinbar Sandstone. The bauxite is very similar in composition and character to Gove ore and was probably derived from Cretaceous remnants. Further potential exists in untested bauxite occurrences on Elcho Island.
A north-sloping lateritic bauxite sheet up to 4m in thickness has developed along the northern coastline of the Cobourg Peninsula and Croker Island, over the Cretaceous Bathurst Island Formation. These bauxite deposits are small and relatively low-grade (<35% available Al2O3), and have high (>13%) reactive silica. The largest deposit is at Vashon Head with 9.7Mt @ 46.2% Al2O3 and 16.1% SiO2. Further potential exists in Arnhem Land across untested lateritic areas west of Woolen River, north of Peter John River and in the King River area, where Cretaceous sediments overlie Proterozoic granites.