The Mud Tank Carbonatite, Strangways Range, central Australia

The Mud Tank Carbonatite at the eastern end of the Strangways Range, about 100 km northeast of Alice Springs, was the first to be recognised in Australia. Crystalline carbonate rocks containing apatite, magnetite and zircon occur in a northeast-trending zone about 2 km long and up to 700 m wide, and in a second, much smaller, lens about 2 km to the southwest. The rocks show banding, owing to differences in texture and composition, and can be broadly divided into crystalline carbonate rocks with subordinate apatite, magnetite, phlogopite, chlorite, and soda-amphibole; foliated micaceous carbonate rocks rich in pale brown phlogopite; and feldspathic carbonate rocks with various amounts of biotite. This last group is considered to be largely of hybrid origin.
Calcite and dolomite occur in various proportions in all the rock types. Country rocks are schists and gneisses of the Early Proterozoic Arunta Block. Trace element concentrations, particularly of niobium and rare earths, are within established ranges for carbonatites, but well below economic values. On the other hand, zircon crystals of gem quality are present in the soil and colluvium overlying the carbonatite, and vermiculitic mica has developed in the weathered zone within about 40 m of the surface.