The rare-earth elements (REE) are a group of seventeen speciality metals that have unique
and diverse chemical, magnetic,
and luminescent properties that make them strategically important in a number of high-technology industries. Consequently, the REE are increasingly becoming more attractive commodity targets for the
mineral industry. This paper presents a comprehensive review of the distribution, geological characteristics
and resources of Australia's major REE deposits. REE in Australia are associated with igneous, sedimentary,
and metamorphic rocks in a wide range of geological environments. Elevated concentrations of these elements have been documented in various heavy-
mineral s
and deposits (beach, dune, marine tidal,
and channel), carbonatite intrusions, (per)alkaline igneous rocks, iron-oxide breccia complexes, calc-silicate rocks (skarns), fluorapatite veins, pegmatites, phosphorites, fluviatile s
andstones, unconformity-related uranium deposits,
and lignites. The distribution
and concentration of REE in these deposits are influenced by various rock-forming processes including enrichment in magmatic or hydrothermal fluids, separation into
mineral species
and precipitation,
and subsequent redistribution
and concentration through weathering
and other surface processes. The lanthanide series of REE (lanthanum to lutetium)
and yttrium show a close genetic
and spatial association with alkaline felsic igneous rocks, however, sc
andium in laterite profiles has a closer affinity with ultramafic/mafic igneous rocks.
A mineral-system approach has been used in this review to classify the major Australian REE deposits according to various mineralising criteria and/or associated geological events. This hierarchical classification framework has the advantage over more traditional descriptive classifications in that it has the benefits of attempting to understand those geological processes considered critical to the formation of a particular deposit type, and also it has a more predictive capacity for identifying potential new areas and types of REE mineralisation. The highest level of the classification comprises four general ‘mineral-system association’ categories, regolith, basinal, metamorphic, and magmatic, which in turn contain sixteen ‘deposit type’ members, namely: regolith — carbonatite-associated; ultramafic/mafic rock-associated; basinal — heavy mineral sand deposits in beach, high dune, offshore shallow marine tidal, and tidal environments; phosphorite; lignite; unconformity-related; metamorphic — calc-silicate; and magmatic — (per)alkaline rocks; carbonatite; pegmatite; skarn; apatite and/or fluorite veins; and iron-oxide breccia complex.
The review summarises the geological factors considered important for the formation of REE deposits. These factors can be used to identify mappable features in databases, which in turn can be applied to produce mineral potential/prospectivity maps.