Are High-Heat-Producing Granites Essential to the Origin of Giant Lead-Zinc Deposits at Mount Isa and McArthur River, Australia?

Exploration & Mining Geology, Vol. 1, No. 1, 1992

M. SOLOMON and C.A. HEINRICH, Bureau of Mineral Resources, Geology and Geophysics, G.P.O. Box 378, Canberra, ACT 2601, Australia

Giant, sediment-hosted lead-zinc deposits in northern Australia formed during development of Mid-Proterozoic extensional basins that overlie Lower Proterozoic basement. The basement in the Mount Isa area, exposed by folding and faulting, contains fractionated, high-heat-producing granites. These granites generate heat at a rate of about 6/iWm-3, probably sufficient to form giant lead-zinc deposits either by (a) driving episodic convection of saline basement and basin fluids for periods of 10s to 106 years at temperatures of about 230°C, or (b) heating basin fluids moving under the influence of topographic relief or fault movement. The presence or absence of such granites may form a vital component of the genetic model. Ore-forming fluid flow was probably initiated by continent-scale, extensional basin fracturing.