"Hot" granites and mineralisation


There is a tremendous spatial correlation between high heat producing granites and mineralisation in the Australian Proterozoic. This is true at Mount Isa where the Mt Isa and Hilton deposits lie within a few kilometres of the Sybella Batholith (average heat production of 6.5 µ m-3). Other notable examples include the Roxby Downs granite and Cu-Au-U-REE mineralisation at Olympic Dam and the Pine Creek and the Tanami Au-provinces.

Pine Creek

The Pine Creek Au-province hosts a number of exceptional heat producing granites. The most notable is the Burnside Granite, which at 1700 Ma produced about 10.5 &micro W m-3 (average concentrations of U = 17 ppm, Th = 48 ppm, and K2O = 5.50 wt%, NTGS Metallogenic map series explanatory notes : Pine Creek SD-52-8). Heat production in other granites (at 17700 Ma) is : Allamber Springs Granite = 8.2 µ W m-3, McCarthys Granite = 5.8 µ W m-3, Driffeld Granite = 6.3 µ W m-3, Fingerpost Granite = 6.5 µ W m-3, Shoobridge Granite = 6.9 µ W m-3, Minglo Granite = 7.5 µ W m-3, respectively
 

Section of NTGS Metallogenic map series explanatory notes : Pine Creek SD- 52-8 showing distribution of Au-deposit (yellow circles) around the Burnside Granite.

Au-mineralisation form haloes around these granites, often about 5 km out from the edge of the granite. This spacing is difficult to understand in as much as the thermal effects due to magmatic heating are minimal a such distances. On the other hand, the long-term heating due to radiogenic heating may be significant.