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Re–Os isotope and PGE constraints on the timing and origin of gold mineralisation in the Witwatersrand Basin

Schaefer, B. F.; Pearson, D. G.; Rogers, N. W. and Barnicoat, A. C. (2010). Re–Os isotope and PGE constraints on the timing and origin of gold mineralisation in the Witwatersrand Basin. Chemical Geology, 276(1-2) pp. 88–94.

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Analyses of the Re–Os isotope system and PGE abundances have been used to investigate the timing and origin of mineralisation in the Vaal Reefs section of the Witwatersrand Basin, the world's largest gold deposit. Consistent interelement PGE fractionation in both organic and sulphide phases intimately associated with gold mineralisation suggests that the Re–Os isotope system was fractionated during gold mobilisation. The Re–Os isotope data on organic separates intimately associated with the gold in this part of the basin indicate open system behaviour until ˜2.26 ± 0.19 Ga (2σ), of the order of 450 Myr younger than the minimum age of sedimentation. The overlying Ventersdorp Volcanics preserve a Re–Os isochron age of 2.43 ± 0.21 Ga, ˜250 Ma younger than their U–Pb zircon emplacement age. These data indicate substantial post-sedimentary noble metal mobility within portions of the Witwatersrand Basin. Re–Os model age calculations on Os-rich fractions suggest that noble metals were derived from a 3.0–3.1 Ga terrain of granite–greenstone affinities, significantly younger than the Barberton Greenstone Belt. These data support a hybrid model involving post-depositional mobilisation of ancient, probably detrital, noble metals for the origin of mineralisation in this part of the Witwatersrand Basin. Such a model is applicable to other areas of gold mineralisation in the basin that display similar textural characteristics and geochemistry.

Item Type: Journal Article
Copyright Holders: 2010 Elsevier
ISSN: 0009-2541
Keywords: Re–Os geochronology; platinum group elements; Witwatersrand Basin; gold
Academic Unit/Department: Science > Environment, Earth and Ecosystems
Interdisciplinary Research Centre: Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR)
Item ID: 24319
Depositing User: Nick Rogers
Date Deposited: 10 Nov 2010 15:43
Last Modified: 15 Jan 2016 15:10
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