Structural controls on gold-bearing quartz mineralization in a duplex thrust system, Hyde-Macraes shear zone, Otago Schist, New Zealand

Abstract

The Hyde-Macraes shear zone in east Otago, New Zealand, is a low-angle north- to northeast-dipping thrust system in which gold-bearing quartz veins have been deposited. Mineralization accompanied deformation in the shear zone which is preferentially developed in graphitic pelitic schist. The shear zone is a duplex system dominated by steep hinterland-dipping thrust faults between well-defined shallow-dipping upper and lower bounding thrusts. Imbrication and stacking have occurred in the shear zone, especially where intrashear schist is psammitic and relatively brittle. This stacking contributes to lateral thickness changes from 2 up to 125 m. Mineralized veins formed mainly in dilational jogs or localized extensional zones on the relatively shallow-dipping parts of the intrashear thrust faults. Late-stage shallow south-dipping extensional veins crosscut the duplex structures but are related to the same overall deformation. From analysis of the shear zone structure, it is possible to make predictions about the geometry of mineralized schist within unexposed parts of the shear zone. This is a potentially useful tool for further prospecting and mining in hydrothermally mineralized duplex systems.