Constraints on the nature of metamorphism in the Kalgoorlie gold camp (Yilgarn Craton, Western Australia) and implications for genetic models of gold mineralisation

Abstract

The timing and nature of metamorphism in the Kalgoorlie gold camp (Yilgarn Craton, Western Australia) are key aspects to genetic models for gold mineralisation. Despite this, existing constraints on metamorphism are equivocal as to whether the Fimiston and Oroya Au–Te lodes formed pre- or post-peak regional metamorphism. Evaluation of an actinolite (S1)–chlorite (S2) crenulation cleavage in the Hannan’s Lake Serpentinite on the western margin of the Golden Mile Super Pit supports a syn-D1 timing for peak metamorphism and a post-peak metamorphic timing for the Fimiston and Oroya Au–Te lodes. These results support a key aspect of metamorphic models for gold mineralisation. If intrusion-related models are correct, they should not be premised on the argument that the Fimiston and Oroya Au–Te lodes are equivalent to other examples of metamorphosed, epithermal-type mineralisation in orogenic belts. KEY POINTS The definition of an S1 cleavage in the Hannan’s Lake Serpentinite by actinolite supports a syn-D1 timing (ca 2685–2680 Ma) for peak regional metamorphism (sub- to lower-greenschist facies) in the Kalgoorlie gold camp. A syn-D1 timing for peak regional metamorphism suggests that the D2 (ca 2675–2665 Ma) Fimiston and Oroya Au–Te lodes and D3 (ca 2650–2640 Ma) Mt Charlotte stockwork Au orebodies developed in post-peak metamorphic settings. A post-peak metamorphic timing for the Fimiston and Oroya Au–Te lodes suggests that these mineralisation types do not represent metamorphosed equivalents of epithermal Au–Te mineralisation.