Geochemical footprints and structural localisation of ore-grade Au mineralisation: insights from the Karangahake deposit, New Zealand.

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dc.contributor.advisor Rowland, J en
dc.contributor.advisor Durance, P en
dc.contributor.advisor Barker, S en Schofield, Marina en 2016-09-20T21:32:39Z en 2016 en
dc.identifier.uri en
dc.description Full text is available to authenticated members of The University of Auckland only. en
dc.description.abstract The Karangahake adularia-sericite epithermal Au-Ag deposit, located in the southern Coromandel Peninsula, New Zealand, represents an encouraging prospect for future development, with potential for untapped resources. Historically, the Karangahake deposit has contributed 9% of the total gold from the Hauraki Goldfield making it the third largest producer in the region. The vein style mineralisation exhibits undulating strike and, variations in dip, with the main Maria and, Welcome lodes, comprising steeply dipping NE segments and, more moderately dipping NNW segments. Slip and dilation tendency analysis in 3D Stress® indicates that the steeper NE striking portions of the veins are more favourable for slip and dilation under the inferred paleo-stress regime and, hydrostatic conditions. This study indicates that the greatest paleopermeability at Karangahake was sub-vertical, plunging steeply NW, indicating dextral oblique movement. Vein morphology and, slip and dilation tendency analysis suggest that transient, oblique, slip events resulted in NE striking linkage structures between adjacent NNW-oriented fault segments, creating sub-vertical conduits of localised high-flux fluid flow in accommodation zones between adjacent fault segments. Such a configuration is conducive to the formation of near vertical ore shoots. Regional ESE tilting could have resulted in the current exposure of the Welcome/Crown vein to be 90m shallower than the Maria vein along the same level, under the assumption that tilting was latestage or post-mineralisation, which is supported by lower base metal contents and higher kaolinite contents along the Crown/Welcome lodes. This would indicate potential for high-grade mineralisation at depth beneath the currently mined portions of the Crown/ Welcome lodes. Simulations in 3D Stress® indicate that portions of the Maria vein were still favourably oriented for slip and dilation after the inferred 20°ESE rotation of the area, indicating that these structures would have remained active during and after tilting. A comparison of ore grade distribution along the Maria lode, using legacy data to create grade shell interpolants in Leapfrog®, and slip and dilation tendencies indicated by 3D Stress® indicates potential for predictive targeting of high-grade ore using slip and dilation tendency mapping. This is supported by spatial correlations with adularia, a known permeability indicator with an inferred cogenetic relationship with Au. Clay mineral distribution and typical pathfinder element distribution along the number 8 level and 5a level are complicated by supergene alteration, making determining geochemical vectors to high-grade ore using geochemical gradients difficult and more data is needed over the vertical extent of the deposit. This inferred conceptual model for the Karangahake deposit is consistent with regional studies in the CVZ and it supports the notion that recognition of transfer zones and localised rift basins in the CVZ may aid targeting of blind deposits, reducing exploration risk. This study provides promising results for cost-efficient methods of predictive targeting of high-grade ore, which can be further refined with additional data. en
dc.publisher ResearchSpace@Auckland en
dc.relation.ispartof Masters Thesis - University of Auckland en
dc.relation.isreferencedby UoA99264883105002091 en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher. en
dc.rights Restricted Item. Available to authenticated members of The University of Auckland. en
dc.rights.uri en
dc.rights.uri en
dc.title Geochemical footprints and structural localisation of ore-grade Au mineralisation: insights from the Karangahake deposit, New Zealand. en
dc.type Thesis en Geology en The University of Auckland en Masters en
dc.rights.holder Copyright: The author en
pubs.elements-id 541526 en
pubs.record-created-at-source-date 2016-09-21 en

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