Gruyere project - Geology
The Gruyere deposit is located on a flexure point of the regional-scale Dorothy Hills Shear Zone within the Dorothy Hills Greenstone Belt, where the shear zone changes from a northerly direction to a north-northwest direction. Orogenic gold mineralisation is hosted within the steep easterly dipping Gruyere Porphyry, a medium-grained quartz monzonite porphyry that has intruded the country rocks, elongated in the direction of the shear zone. The host Gruyere Porphyry averages 90m in horizontal width through the deposit with a maximum width of 190m in the centre of the deposit and tapering to around 5m to 10m width at the northern and southern extremities. The entire Gruyere Porphyry is variably altered and gold grade is related to variations in style and intensity of alteration, structure, veining and sulphide species. Zones containing higher-grade gold mineralisation above 1.2 (g/t) gold generally have strong albite ± sericite ± chlorite ± biotite alteration and are associated with a sulphide assemblage of pyrrhotite + pyrite ± arsenopyrite, weak to moderate foliation, common micro-fracturing and steeply dipping quartz veining. Gold mineralisation at Attila and Alaric comprises steeply dipping shear hosted gold in volcaniclastic sequences, with gold associated with zones of albite ± sericite ± chlorite ± pyrite mineralisation.