RELATIONSHIPS BETWEEN GOLD CONCENTRATION AND STRUCTURE IN QUARTZ VEINS FROM THE HODGKINSON PROVINCE, NORTHEASTERN AUSTRALIA

The Hodgkinson Province is a tract of multiply deformed Silurian-Devon ian rocks in north Queensland, Australia. Gold-bearing quartz veins fr om the West Normanby Goldfield in the northern Hodgkinson Province wer e emplaced during the Permian D-4 event, broadly coeval with regional granite emplacement. Taylors Fault, a major structure that formed duri ng D-2, hosts the veins which infill dilatational jogs opened during s inistral-normal reactivation of the fault in D-4 Veins contain graphit ic laminations that formed when fault planes segmented wallrocks adjac ent to the veins, producing tabular clasts that were tectonically slic ed into the reefs. Laminations are the result of progressive shear str ain, associated with continued movement on the faults, which caused st rain-enhanced dissolution of silicate minerals and residual graphite e nrichment in the clasts. This process produced graphite-coated shear p lanes that delimit zones of grain size reduction in the veins. Laminat ions commonly contain stylolites, which nucleated on pronounced sinuos ities of the shear planes due to progressive shortening during D-4 Gol d particles have preferentially nucleated in zones of relatively coars er-grained quartz adjacent to the shear planes, where shortening strai n caused microfracturing and allowed fluid access. Gold may have been introduced with the quartz, but was redistributed within the reefs and localized along the laminations by the effects of synchronous, progre ssive deformation. Regionally, gold deposits show close spatial relati onships with granite plutons of the Permian Whypalla Supersuite. Relat ionships in the West Normanby Gold Field support a regional model of r eef emplacement and gold mineralization during the Permian D-4 event.