Fluid convection stability in faulted rifts: a key to active epithermal mineralisation?

McLellan, John G., Oliver, Nick H.S., Hobbs, Bruce E., and Rowland, Julie V. (2009) Fluid convection stability in faulted rifts: a key to active epithermal mineralisation? In: Proceedings of the 10th Biennial Meeting of the the SGA 2009 (2) pp. 867-869. From: Smart Science for Exploration and Mining: 10th Biennial Meeting of the SGA 2009, 17-20 August 2009, Townsville, QLD, Australia.

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Convective upwelling of meteoric water in the Taupo Volcanic Zone (TVZ), New Zealand, is characterized by extreme heat flows of up to 750 mWm⁻². Despite the extreme heat fluxes and episodic seismic activity and faulting, the intensity and position of upwelling convective zones remains relatively fixed over many thousands of years. Epithermal deposits in the North island of New Zealand occur in Northland, Coromandel and Taupo regions, and all have a close association with Cenozoic volcanic rocks. Gold and silver are present in active geothermal fields and in extinct western geothermal systems of the TVZ. Here we attempt to simulate the effects of permeability contrasts, deformation and heat flow variations to constrain the importance of these different processes in controlling the localization of upflow zones. Given a high heat flow and a permeable homogeneous un-deforming crust our models predict highly vigorous and unstable convection patterns. If the permeability of the crust below 4 km is reduced by at least two orders of magnitude (to simulate greywacke) then a greater stability of convective cells is observed. If a convective heat loss is permitted from the model surface (rather than a fixed surface condition) then even greater stability is obtained. When deformation is introduced this results in an instant disruption of the convective cells, however on cessation of the deformation the convective cells quickly return to a similar position. In the TVZ seismic activity may be too transient to affect the overall location of upwelling convective cells.

Item ID: 27694
Item Type: Conference Item (Research - E1)
ISBN: 978-0-9805586-8-5
Keywords: taupo volcanic zone, convection, fluid flow, heat flow, deformation, seismic activity, epithermal, Au, Ag
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Date Deposited: 17 Jun 2013 22:53
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040307 Ore Deposit Petrology @ 100%
SEO Codes: 84 MINERAL RESOURCES (excl. Energy Resources) > 8401 Mineral Exploration > 840107 Titanium Minerals, Zircon, and Rare Earth Metal Ore (e.g. Monazite) Exploration @ 100%
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