Search

A number of regolith-hosted REE occurrences have recently been discovered in the Esperance region in southern Western Australia. This paper summarizes major characteristics of REE mineralization and discusses contributing factors and potential controls. The main aim is to explain why there is a lack of highly sought-after ion-adsorption-clay-type REE deposits across the region despite the presence of the regolith-hosted REE mineralization on a regional scale. Local mineralization mostly occurs as continuous flat-lying enrichment "blankets" within the residual regolith developed over Archaean–Proterozoic granite gneisses and granitoids with elevated REE content. The enriched horizon is commonly located in the lower saprolite and saprock and is accompanied by an overlying REE-depleted zone. This distribution pattern, together with the data on HREE fractionation and the presence of the supergene REE minerals, indicates chemogenic type enrichment formed by supergene REE mobilization into groundwater, downward transport, and accumulation in the lower part of the weathering profile. Residual REE accumulation processes due to bulk rock volume and mass reduction during weathering also contribute to mineralization. It is proposed that climate and groundwater chemistry are the critical regional controls on the distribution of REEs in the weathering profile and on their speciation in the enrichment zone. Cenozoic aridification of climate in southwest Australia heavily overprinted pre-existing REE distributions in the weathering profile. Acidic (pH < 4), highly saline groundwaters intensely leached away any relatively weakly bound, adsorbed or colloidal REE forms, moving them downward. Dissolved REEs precipitated as secondary phosphates in neutral to alkaline environment at lower Eh near the base of the weathering profile forming the supergene enrichment zone. Low denudation rates, characteristic of areas of low relief under the arid climate, are favourable for the preservation of the existing weathering profiles with REE mineralization. [ABSTRACT FROM AUTHOR]

The Forest Fire Danger Index (FFDI) is the main measure used in Australia for estimating fire risk. Recent work by the authors showed that the FFDI forms stable state regimes, nominated as fire climate regimes. These regimes shifted to greater intensity in southern and eastern Australia around the year 2000 and, a decade later, further north. Reductions in atmospheric moisture were the primary contributor. These changes have not been fully incorporated into future projections. This paper compares the recent regime shifts with the most recent national projections of FFDI, published in 2015. They show that for most states and regions, the 2030 upper limit is approached or exceeded by the recent shift, except for two states with large arid zones, South Australia and Western Australia. Methods for attributing past changes, constructing projections, and the inability of climate models to reproduce the recent decreases in atmospheric moisture, all contribute to these underestimates. To address these shortcomings, we make some suggestions to modify efforts aiming to develop seamless predictions and projections of future fire risk. [ABSTRACT FROM AUTHOR]