Structural and alteration characteristics of the Indarama lode gold deposit, Zimbabwe : implications for craton-wide tectonism and mineralization
Structural and alteration characteristics of the Indarama lode gold deposit, Zimbabwe : implications for craton-wide tectonism and mineralization
The Indarama lode gold deposit is part of the Kwekwe gold camp in the Midlands greenstone belt, central Zimbabwe. Gold mineralization is hosted by vertically dipping, Bulawayan (c.2.9-2.7 Ga) metabasalts of low (greenschist facies) metamorphic grade.
Early deformation involved folding of the greenstone belt sequence and formation of an array of N-S-striking, sub-vertical ductile shear zones during E-W compression, possibly related to collision of the Zimbabwe Craton with the Motloutse Complex. Formation of the shear zone network preceded the main mineralizing event and established the structural framework of the area. After a time gap of c.100 Ma, brittle reactivation of the N-S striking shear zones occurred within a prolate stress field in which compression was directed ENE-WSW and NNW-SSE. Gold mineralization was synchronous with shear zone reactivation and was directly related to NNW-SSE-directed convergence of the Zimbabwe Craton with the Northern Marginal Zone of the Limpopo Belt at c. 2.58 Ga, and subsequent extrusion of the Rhodescale granitoid complex towards the WSW along strike-slip shear zones.
Geochemical modelling indicates that gold was deposited from a reduced H2O-CO2 fluid, with a pH between 5 and 5.6 under P-T conditions of 200-325°C and 0.25-1 kbar. Gold transport was dominantly as AuHS0, but Au(HS)2 was also important. Gold deposition occurred in response to destabilisation of the transporting complexes, mainly by fluid-rock interaction, but also by decreasing fluid pressure. Fluid-rock interaction controlled gold precipitation by decreasing the activities of reduced sulphur species (by sulphide mineral precipitation), increasing pH (by feldspar hydrolysis), and by host rock sulphidation. Phase separation, caused by abrupt fluid pressure drops during vein reactivation, contributed to gold precipitation by the escape of volatile components from the fluid.
The extent of fluid-rock interaction was tightly controlled by geological structure and provided the dominant control on gold precipitation. The key to mineralization was fluid access to the host rocks, which was greatly enhanced by development of the microvein networks (damage zones), and by wallrock alteration which led to subsequent local development of a spaced cleavage.
University of Southampton
McKeagney, Catherine Judith
1998
McKeagney, Catherine Judith
McKeagney, Catherine Judith
(1998)
Structural and alteration characteristics of the Indarama lode gold deposit, Zimbabwe : implications for craton-wide tectonism and mineralization.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
The Indarama lode gold deposit is part of the Kwekwe gold camp in the Midlands greenstone belt, central Zimbabwe. Gold mineralization is hosted by vertically dipping, Bulawayan (c.2.9-2.7 Ga) metabasalts of low (greenschist facies) metamorphic grade.
Early deformation involved folding of the greenstone belt sequence and formation of an array of N-S-striking, sub-vertical ductile shear zones during E-W compression, possibly related to collision of the Zimbabwe Craton with the Motloutse Complex. Formation of the shear zone network preceded the main mineralizing event and established the structural framework of the area. After a time gap of c.100 Ma, brittle reactivation of the N-S striking shear zones occurred within a prolate stress field in which compression was directed ENE-WSW and NNW-SSE. Gold mineralization was synchronous with shear zone reactivation and was directly related to NNW-SSE-directed convergence of the Zimbabwe Craton with the Northern Marginal Zone of the Limpopo Belt at c. 2.58 Ga, and subsequent extrusion of the Rhodescale granitoid complex towards the WSW along strike-slip shear zones.
Geochemical modelling indicates that gold was deposited from a reduced H2O-CO2 fluid, with a pH between 5 and 5.6 under P-T conditions of 200-325°C and 0.25-1 kbar. Gold transport was dominantly as AuHS0, but Au(HS)2 was also important. Gold deposition occurred in response to destabilisation of the transporting complexes, mainly by fluid-rock interaction, but also by decreasing fluid pressure. Fluid-rock interaction controlled gold precipitation by decreasing the activities of reduced sulphur species (by sulphide mineral precipitation), increasing pH (by feldspar hydrolysis), and by host rock sulphidation. Phase separation, caused by abrupt fluid pressure drops during vein reactivation, contributed to gold precipitation by the escape of volatile components from the fluid.
The extent of fluid-rock interaction was tightly controlled by geological structure and provided the dominant control on gold precipitation. The key to mineralization was fluid access to the host rocks, which was greatly enhanced by development of the microvein networks (damage zones), and by wallrock alteration which led to subsequent local development of a spaced cleavage.
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Published date: 1998
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Local EPrints ID: 463425
URI: http://eprints.soton.ac.uk/id/eprint/463425
PURE UUID: ddeb3f6c-ce6f-4f18-ae9b-505c0e59e084
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Date deposited: 04 Jul 2022 20:51
Last modified: 04 Jul 2022 20:51
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Author:
Catherine Judith McKeagney
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