Structural Controls on Gold Mineralization at the Ashanti Deposit, Obuasi, Ghana

Allibone, Andrew; McCuaig, T. Campbell; Harris, David B.; Etheridge, M. A.; Munroe, Stuart; Byrne, David P.; Amanor, J. A.; Gyapong, W.

doi:10.5382/sp.09.04

Cited by 45 publications

(72 citation statements)

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“…Arnould, 1961;Egal et al, 2002;Lompo, 2009). Following magmatic accretion of the juvenile crust between 2.25 and 2.15 Ga, the Paleoproterozoic crust was deformed during the 2.15-2.07 Ga Eburnean orogenic cycle (Bonhomme, 1962;Mil esi et al, 1989Mil esi et al, , 1992Feybesse, 1990;Ledru et al, 1991;Hirdes et al, 1996;Allibone et al, 2002;Feybesse et al, 2006;Pouclet et al, 2006;Vidal et al, 2009). Tarkwaian sedimentary rocks (conglomerates, phyllites and quartzites) form discordant basins on Birimian formations, and are interpreted to represent syn-orogenic to late-stage basins (Davis et al, 1994;Perrouty et al, 2012).…”

Section: Geological Bac Kgroundmentioning

confidence: 99%

“…The Paleoproterozoic West African Craton is considered as one of the youngest 'Archean-type' continental fragments. It is a vast (3.10 6 km 2 ) juvenile continental domain extracted from the mantle between 2.50 and 2.20 Ga (Abouchami et al, 1990;Boher et al, 1992;Gasquet et al, 2003;Peucat et al, 2005), and subsequently accreted against an older Archean nucleus during the 2.15-2.07 Ga Eburnean orogeny (Bonhomme, 1962;Mil esi et al, 1989Mil esi et al, , 1992Feybesse, 1990;Ledru et al, 1991;Hirdes et al, 1996;Allibone et al, 2002;Feybesse et al, 2006;Pouclet et al, 2006;Vidal et al, 2009). Consequently, the Eburnean rock record is key to exploring the geodynamic changes across the Archean-Proterozoic transition.…”

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confidence: 99%

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Petrological and geochronological constraints on lower crust exhumation during Paleoproterozoic (Eburnean) orogeny, NW Ghana, West African Craton

Block

Ganne

Baratoux

et al. 2015

Journal Metamorphic Geology

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New petrological and geochronological data are presented on high-grade ortho-and paragneisses from northwestern Ghana, forming part of the Paleoproterozoic (2.25-2.00 Ga) West African Craton. The study area is located in the interference zone between N-S and NE-SW-trending craton-scale shear zones, formed during the Eburnean orogeny (2.15-2.00 Ga). High-grade metamorphic domains are separated from low-grade greenstone belts by high-strain zones, including early thrusts, extensional detachments and late-stage strike-slip shear zones. Paragneisses sporadically preserve high-pressure, low-temperature (HP-LT) relicts, formed at the transition between the blueschist facies and the epidote-amphibolite sub-facies (10.0-14.0 kbar, 520-600°C), and represent a low (~15°C km À1 ) apparent geothermal gradient. Migmatites record metamorphic conditions at the amphibolite-granulite facies transition. They reveal a clockwise pressure-temperature-time (P-T-t) path characterized by melting at pressures over 10.0 kbar, followed by decompression and heating to peak temperatures of 750°C at 5.0-8.0 kbar, which fit a 30°C km À1 apparent geotherm. A regional amphibolite facies metamorphic overprint is recorded by rocks that followed a clockwise P-T-t path, characterized by peak metamorphic conditions of 7.0-10.0 kbar at 550-680°C, which match a 20-25°C km À1 apparent geotherm. These P-T conditions were reached after prograde burial and heating for some rock units, and after decompression and heating for others. The timing of anatexis and of the amphibolite facies metamorphic overprint is constrained by in-situ U-Pb dating of monazite crystallization at 2138 AE 7 and 2130 AE 7 Ma respectively. The new data set challenges the interpretation that metamorphic breaks in the West African Craton are due to diachronous Birimian 'basins' overlying a gneissic basement. It suggests that the lower crust was exhumed along reverse, normal and transcurrent shear zones and juxtaposed against shallow crustal slices during the Eburnean orogeny. The craton in NW Ghana is made of distinct fragments with contrasting tectono-metamorphic histories. The range of metamorphic conditions and the sharp lateral metamorphic gradients are inconsistent with 'hot orogeny' models proposed for many Precambrian provinces. These findings shed new light on the geodynamic setting of craton assembly and stabilization in the Paleoproterozoic. It is suggested that the metamorphic record of the West African Craton is characteristic of Paleoproterozoic plate tectonics and illustrates a transition between Archean and Phanerozoic orogens.

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Section: Geological Bac Kgroundmentioning

confidence: 99%

mentioning

confidence: 99%

Petrological and geochronological constraints on lower crust exhumation during Paleoproterozoic (Eburnean) orogeny, NW Ghana, West African Craton

Block

Ganne

Baratoux

et al. 2015

Journal Metamorphic Geology

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“…The intrusion was placed at the center of a fault zone with homogeneous permeability at a depth of 5 km and a temperature of 600°C. It was assumed to be 1 km wide and 3 km high, about the same or slightly larger in size than the mineralized plutons described by Allibone et al (2002b). The model intrusion was assumed to be less permeable than the surrounding fault zone (e.g.…”

Section: Fault Zone With a Magmatic Intrusion (Model 3)mentioning

confidence: 99%

“…Mineralizing processes involve heat and mass transfer during fluid flow through the permeable zones of the crust. Fluid circulation within the Earth's crust can be Eisenlohr et al (1989), Allibone et al (2002b) and Dubé & Gosselin (2005), respectively. driven by surface topography, pressure gradients or buoyancy effects.…”

Section: Introductionmentioning

confidence: 99%

Hydrothermal convection in and around mineralized fault zones: insights from two‐ and three‐dimensional numerical modeling applied to the Ashanti belt, Ghana

Harcouët-Menou¹,

Guillou-Frottier²,

Bonneville³

et al. 2009

Geofluids

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“…Coupling of these factors in numerical models can lead to new insights into different mineralizing systems, with implications for ore genesis and potential identification of exploration targets (Gow et al 2002;Zhang et al 2003;McLellan et al 2004;Oliver et al 2006;Rawling et al 2006;Schaubs et al 2006). Faults (and especially fault bends, jogs, and intersections) and contacts between different lithostratigraphic units can create an environment conducive to increased fluid flow in the system (Craw 2000;Allibone et al 2002a;Cox 2005;Hodkiewicz et al 2005;Ford & Blenkinsop 2008).…”

Section: Introductionmentioning

confidence: 99%

Factors affecting fluid flow in strike–slip fault systems: coupled deformation and fluid flow modelling with application to the western Mount Isa Inlier, Australia

Ford¹,

Blenkinsop²,

McLellan³

2009

Geofluids

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Deformation and focused fluid flow within a mineralized system are critical in the genesis of hydrothermal ore deposits. Dilation and integrated fluid flux due to coupled deformation and fluid flow in simple strike-slip fault geometries were examined using finite difference analysis in three dimensions. A series of generic fault bend and fault jog geometries consistent with those seen in the western Mount Isa Inlier were modelled in order to understand how fault geometry parameters influence the dilation and integrated fluid flux. Fault dip, fault width, bend ⁄ jog angle, and length were varied, and a cross-cutting fault and contrasting rock types were included. The results demonstrate that low fault dips, the presence of contrasts in rock type, and wide faults produce highest dilation and integrated fluid flux values. Increasing fault bend lengths and angles increases dilation and integrated fluid flux, but increasing fault jog length or angle has the opposite effect. There is minimal difference between the outputs from the releasing and restraining fault bend and jog geometries. Model characteristics producing greater fluid flows and ⁄ or gradients can be used in a predictive capacity in order to focus exploration on regions with more favorable fault geometries, provided that the mineralized rocks had Mohr-Coulomb rheologies similar to the ones used in the models.

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Structural Controls on Gold Mineralization at the Ashanti Deposit, Obuasi, Ghana

Cited by 45 publications

References 0 publications

Petrological and geochronological constraints on lower crust exhumation during Paleoproterozoic (Eburnean) orogeny, NW Ghana, West African Craton

Petrological and geochronological constraints on lower crust exhumation during Paleoproterozoic (Eburnean) orogeny, NW Ghana, West African Craton

Hydrothermal convection in and around mineralized fault zones: insights from two‐ and three‐dimensional numerical modeling applied to the Ashanti belt, Ghana

Factors affecting fluid flow in strike–slip fault systems: coupled deformation and fluid flow modelling with application to the western Mount Isa Inlier, Australia

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