A review of Australian carbonatites and associated REE-Nb mineralisation

Australia has 16 known carbonatites, and two other occurrences of REE mineralisation interpreted as carbonatite-related. These are all located within Precambrian crust, and host known resources of c. 7.2 Mt. of rare earth oxides (containing c. 1.73 Mt. of Nd₂O₃ and Pr₆O₁₁), and c. 2.7 Mt. of Nb₂O₅.

Australia's carbonatites range from Neoarchean to Jurassic, and display extreme diversity in geological characteristics, ranging from large, multiphase intrusive complexes dominated by either carbonatite (e.g. Gifford Creek and Mt. Weld, Western Australia) or silicate rocks (e.g. Cummins Range and Cundeelee, Western Australia), to single phase and small volume carbonatite dykes (e.g. Yungal dykes, Western Australia). Studied occurrences show similarly diverse radiogenic isotopic signatures (Rb/Sr and Sm/Nd), indicating derivation from a variety of mantle sources ranging from HIMU through to EM1.

Significant rare earth element (REE) and niobium (Nb) mineralisation occurs in both fresh and weathered carbonatites throughout Australia, with markedly different mineralogical and grade characteristics. While weathering history and preservation are crucial to the formation of supergene enrichments in REE and Nb, analysis of whole-rock geochemical data for different carbonatite types from the Mt. Weld and Gifford Creek complexes suggest primary magmatic composition plays the strongest determinant in the magnitude of grade increase, with siderite-dominated carbonatites having less potential for supergene upgrade than dolomite, ankerite and calcite-dominated examples.

The distinct geophysical signatures of Australia's known carbonatites have aided exploration efforts leading to early discoveries of deposits within highly magnetic complexes such as Mt. Weld and Cummins Range. Recent discoveries of geophysically subtle complexes (e.g. Gifford Creek complex, West Arunta) suggests both alternative geophysical techniques and a comprehensive structural understanding are crucial to discovery.

Explorers should focus on areas of known carbonatite magmatism, with a particular focus on developing an understanding of the regional structures that can facilitate carbonatite intrusion. On a local scale, the selection of relevant carbonatite geophysical and exploration signatures leveraging previous local discoveries should be prioritised. The small number of known carbonatites in Australia compared to the other continents abundances indicates further carbonatites and associated mineralisation may be discovered with increased exploration.