Geothermal measurements at Mount Isa, Queensland

A detailed geothermal study has been made in the region of Mount Isa in the Precambrian shield of northeastern Australia, involving 14 vertical or steeply dipping diamond-drilled holes in the Mount Isa Mine, 11 surface holes in the surrounding area, and 3 holes 50km to the east of Mount Isa. The measured temperatures have been combined with 188 thermal conductivity determinations to give heat fluxes varying from 1.49 to 2.57 μcal/ cm2 sec, with a weighted mean for the Mount Isa region of 1.96±0.03. The errors introduced by conductivity determinations, the method of computation of the heat flux, structural features; surface water, ventilation, and leaching and oxidation are discussed. The need for geothermal studies involving more than one borehole and detailed geological information, if a reliable value for the geothermal heat flux is to be obtained, is emphasized, particularly in areas with large conductivity contrasts and steeply dipping structures.