A solid-solution model for the composition of chlorite has been used to calculate the physicochemical conditions of gold deposition for the slate-belt-hosted Hill End goldfield in the Paleozoic Lachlan Fold Belt of New South Wales, Australia, A P-T range of 295-340 degrees C and 1.4-3 kbar, and the redox conditions for three major stages of gold mineralization, are estimated by combining data for T, f(O 2 ) and f(S 2 ), calculated from chlorite compositions, with the results obtained from fluid-inclusion analyses and a knowledge of the mineral paragenesis. Gold deposition occurred in a redox environment where f(O 2 ) ranged from 10 (super -32) to 10 (super -36.4) , tracked by fluid and mineral species from below the CO 2 -CH 4 stability boundary to above the pyrite-pyrrhotite stability boundary, respectively. The temperature corrections to fluid-inclusion T h data provided by the chlorite model could be as high as 190 degrees C. With careful paragenetic control, the chlorite geothermometer seems to be a powerful tool in deciphering multistage fluid systems, and offers a solution to some of the ambiguities attending fluid-inclusion studies in metamorphic environments.

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