corundum, Australia.12, gems

The diamondiferous and the sapphire-zircon gemmiferous gravels of eastern Queensland and New South Wales are buried Tertiary fluvial clastics preserved from erosion by overlying basalt flows. The igneous sources of the gemmiferous fraction are unknown. The Great Artesian Basin (Cretaceous) across western New South Wales, Queensland, and northern South Australia hosts the continent's precious opal districts. Igneous and metamorphic host rocks for gemstone deposits are rare on the continent. Notable exceptions are the chrysoprase veins associated with serpentite belts of eastern Queensland and the emerald deposits in the Precambrian Shield of Western Australia.