The Gold Conveyor Belt: Large-scale gold mobility in an active orogen
The Gold Conveyor Belt: Large-scale gold mobility in an active orogen
The Southern Alps of New Zealand are part of an active collisional orogen where metamorphism, hydrothermal fluid flow and the formation of orogenic gold deposits are ongoing. The Southern Alps are forming due to transpressional collision between continental crust fragments on the Pacific and Australian tectonic plates. The plate tectonic rates and geometries, the sources of fluid and broad-scale fluid pathways in the hydrogeological system, and the geochemical compositions of the Torlesse Terrane rock that is being advected through the orogen are well defined so that a mass balance of metal mobility during active orogenic processing in the Southern Alps of New Zealand can be calculated. Advection of a 10 km wide x 5 km deep section of Torlesse rock through the orogen at tectonic rates (0.01 m/yr) that is then metamorphosed up to amphibolite facies, causes mobilisation of over 1127 t Au, 10.1Mt As, 47000 t Hg, 560000 t Sb and 14000 Mt H2O in 1 Myrs. The masses of elements mobilised at the same rate along the length of the Southern Alps (> 200 km) for 5 Myrs would be more than 100 times greater. The metals were mobilised by the metamorphic fluid produced during the orogenic processing of the Torlesse Terrane rocks and the concentrations of Au, As, Hg and Sb in this fluid are calculated to be 0.08, 711, 3, and 40 mg/kg respectively. The mobilised metals form the orogenic gold deposits that occur in the Southern Alps. Different styles of gold deposits form contemporaneously during the active orogenesis of the Southern Alps, including those with a fluid temperature > rock temperature that may appear have formed after the peak of metamorphism but are instead just the product hydrothermal fluid mineralising rocks on their retrograde metamorphic path. The mass balance shows that there has been orders of magnitude more metal mobilised in the orogen than resides in the currently known deposits. There is clear potential for large gold deposits occurring in the yet to be uplifted parts of the Southern Alps if there have been efficient enough fluid focussing and metal precipitation mechanisms occurring under the Southern Alps.
129-142
Pitcairn, Iain K.
e6c79a72-1150-49fe-8b03-95db13e69c2e
Craw, Dave
c5701ce3-cff8-41c0-916a-5479e18b9bfc
Teagle, Damon A.H.
396539c5-acbe-4dfa-bb9b-94af878fe286
October 2014
Pitcairn, Iain K.
e6c79a72-1150-49fe-8b03-95db13e69c2e
Craw, Dave
c5701ce3-cff8-41c0-916a-5479e18b9bfc
Teagle, Damon A.H.
396539c5-acbe-4dfa-bb9b-94af878fe286
Pitcairn, Iain K., Craw, Dave and Teagle, Damon A.H.
(2014)
The Gold Conveyor Belt: Large-scale gold mobility in an active orogen.
Ore Geology Reviews, 62, .
(doi:10.1016/j.oregeorev.2014.03.006).
Abstract
The Southern Alps of New Zealand are part of an active collisional orogen where metamorphism, hydrothermal fluid flow and the formation of orogenic gold deposits are ongoing. The Southern Alps are forming due to transpressional collision between continental crust fragments on the Pacific and Australian tectonic plates. The plate tectonic rates and geometries, the sources of fluid and broad-scale fluid pathways in the hydrogeological system, and the geochemical compositions of the Torlesse Terrane rock that is being advected through the orogen are well defined so that a mass balance of metal mobility during active orogenic processing in the Southern Alps of New Zealand can be calculated. Advection of a 10 km wide x 5 km deep section of Torlesse rock through the orogen at tectonic rates (0.01 m/yr) that is then metamorphosed up to amphibolite facies, causes mobilisation of over 1127 t Au, 10.1Mt As, 47000 t Hg, 560000 t Sb and 14000 Mt H2O in 1 Myrs. The masses of elements mobilised at the same rate along the length of the Southern Alps (> 200 km) for 5 Myrs would be more than 100 times greater. The metals were mobilised by the metamorphic fluid produced during the orogenic processing of the Torlesse Terrane rocks and the concentrations of Au, As, Hg and Sb in this fluid are calculated to be 0.08, 711, 3, and 40 mg/kg respectively. The mobilised metals form the orogenic gold deposits that occur in the Southern Alps. Different styles of gold deposits form contemporaneously during the active orogenesis of the Southern Alps, including those with a fluid temperature > rock temperature that may appear have formed after the peak of metamorphism but are instead just the product hydrothermal fluid mineralising rocks on their retrograde metamorphic path. The mass balance shows that there has been orders of magnitude more metal mobilised in the orogen than resides in the currently known deposits. There is clear potential for large gold deposits occurring in the yet to be uplifted parts of the Southern Alps if there have been efficient enough fluid focussing and metal precipitation mechanisms occurring under the Southern Alps.
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Accepted/In Press date: March 2014
e-pub ahead of print date: 22 March 2014
Published date: October 2014
Organisations:
Geochemistry
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Local EPrints ID: 363438
URI: http://eprints.soton.ac.uk/id/eprint/363438
ISSN: 0169-1368
PURE UUID: 05a4bc3b-e183-4c2c-9fa3-371258d8ca00
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Date deposited: 24 Mar 2014 16:27
Last modified: 15 Mar 2024 03:05
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Author:
Iain K. Pitcairn
Author:
Dave Craw
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