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Conference Proceedings

2002 AusIMM New Zealand Branch Annual Conference - 150 Years of Mining

Conference Proceedings

2002 AusIMM New Zealand Branch Annual Conference - 150 Years of Mining

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Structural Controls on the Development of a Mineralised Fault - Fracture Network, NW Otago, New Zealand

Vein swarms in metamorphic terranes such as the Otago Schist Belt, New Zealand provide evidence of past hydrothermal flow systems leading to fault initiation and reactivation. A major episode of hydrofracturing and fluid redistribution occurred during early Cretaceous exhumation of the schist belt. As a result, presently exposed lower greenschist facies greyschists in NW Otago are pervaded by abundant quartz-filled hydraulic extension fractures with associated normal faults hosting quartzscheelitegold mineralisation. Once the effects of Cenozoic folding have been removed, a regional subhorizontal schist foliation contains an aligned array of subvertical hydrofractures striking NNW, striking parallel to a set of low-slip conjugate normal faults; the array extends over an area >1500 km2 and over a depth interval >5 km. The hydrofracture array comprises a mesh of interlinked extensional-shear and pure extension veins. These veins show mutually cross-cutting relations. Extensional hydrofracturing apparently preceded the development of major throughgoing normal faults. Low-displacement normal faults are infilled with laminated quartz ( scheelite) veins (< 2 m thick), which typically formed at local dilational sites around fault irregularities. Total displacement across individual faults is on the order of a few tens of metres. Fault-fracture hosted veins display incremental growth textures, suggesting intermittent episodes of brittle fracturing and mineralisation that correspond with cyclical slip, fluid discharge and hydrothermal sealing events...
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  • Structural Controls on the Development of a Mineralised Fault - Fracture Network, NW Otago, New Zealand
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  • Published: 2002
  • PDF Size: 1.264 Mb.
  • Unique ID: P200206031

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