Bauxite deposits of the Northern Territory

Bauxite occurrences in the Northern Territory are lateritic in origin. These deposits developed during the Tertiary on stable plateaux along the northern coastline. The giant Gove deposit with past production of 155 Mt of bauxite grading 50.5% Al₂O₃ and Total reserves of 176 Mt @ 51% Al₂O₃, averages 3.7 m 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.

Low-silica bauxite is present on the Dhupuma Plateau (21 km south of Nhulunbuy) which has potential for >35 Mt of untested lateritic bauxite. Several pockets of low-silica (4% reactive SiO₂) bauxite totalling 9.9 Mt @ 46% available Al₂O₃ exist on Marchinbar Island. These deposits average about 2 m 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 4 m 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 9.7 Mt @ 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.