Surficial Deposits
Surficial uranium deposits are broadly defined as young (Tertiary to Recent) near-surface uranium concentrations within sediments or soils. These deposits usually have secondary cementing minerals including calcite, gypsum, dolomite, ferric oxide and halite. Uranium deposits in calcrete (calcium and magnesium carbonates) are the most significant of the surficial deposits known in Australia. The calcrete bodies are typically interbedded with Tertiary sand and clay and are usually cemented by calcium and magnesium carbonates. Calcrete deposits form in regions where uranium-rich granites were deeply weathered in a semi-arid to arid climate. Surficial uranium deposits may also occur in peat bogs, karst caverns and soils.
In Western Australia, the calcrete uranium deposits occur in valley-fill sediments along Tertiary drainage channels (e.g. the Yeelirrie deposit) and in playa lake sediments (e.g. the Lake Maitland deposit). These deposits overlie or are proximal to Archaean granite and greenstone basement of the northern portion of the Yilgarn Craton with the granite providing the uranium source and the greenstone rocks providing the vanadium source. The primary uranium mineralisation is carnotite (hydrated potassium uranium vanadium oxide) which is readily extractable by acid or alkali leaching methods.
Calcrete deposits represent approximately 5% of Australia’s and 4% of the world’s total known ‘Identified Resources’ of uranium. Calcrete uranium deposits are also known to occur in the Central Namib Desert of Namibia, the largest being the Langer Heinrich deposit.
Regalpoint’s Gum Creek project belongs to this class of deposit.