Uranium leaching tests were conducted on two naturally occurring, highly metamict brannerite ores from the Crockers Well and Roxby Downs deposits, South Australia. The ores were leached over a range of temperatures and Fe-(III) and H2SO4 concentrations. As well, samples of the ores were calcined at 1200 degrees C in air to investigate the effect of thermally induced recrystallisation on uranium dissolution. For the unheated samples, a maximum of similar to 80% U dissolution was obtained using an Fe-(III) concentration of 12 g/L, an acid concentration of 150 g/L H2SO4 and a temperature of 95 degrees C. The heat treated samples performed poorly under identical conditions, with maximum uranium dissolution of <10% recorded. High uranium dissolution from natural brannerite can be achieved providing; (i) acid strength, oxidant strength and temperatures are maintained at elevated levels (compared to those traditionally used for uraninite leaching), and, (ii) the brannerite has not undergone any significant recrystallisation (e.g. through metamorphism). (C) 2014 Published by Elsevier Ltd.