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Compositional variation of cooperite, braggite, and vysotskite from the Bushveld Complex

Published online by Cambridge University Press:  05 July 2018

Sabine M. C. Verryn  and
Roland K. W. Merkle
Sabine M. C. Verryn
Affiliation:
Department of Geology, University of Pretoria, Pretoria, 0002 South Africa
Roland K. W. Merkle
Affiliation:
Department of Geology, University of Pretoria, Pretoria, 0002 South Africa
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Abstract

The compositions of coexisting and individual cooperite (ideally PtS) and braggite (ideally (Pt,Pd)S) grains from the Merensky Reef of the Bushveld Complex, as well as cooperite, braggite and vysotskite (ideally PdS) grains from the UG-2 of the Bushveld Complex were investigated. There is a clearly defined miscibility gap between cooperite and braggite, but no evident gap between braggite and vysotskite. Partition coefficients between cooperite and braggite are determined on coexisting phases. The KDbraggite/cooperite in atomic ratios are estimated to be 0.54 for Pt, 15.81 for Pd and 5.93 for Ni. For Rh and Co the KDbraggite/cooperite are estimated to be > 1.40 and > 1.46 respectively. No systematic behaviour is detected for Fe and Cu. Coupled substitutions of Pd + Ni for Pt in cooperite and braggite/vysotskite are indicated. Within the cooperite of the Merensky Reef, the Pd:Ni ratio is approximately 9:11. The substitution trend in braggite, which extends to vysotskite in the UG-2, is dependent on the base-metal sulphide (BMS) association. If pentlandite is the dominant Ni-bearing BMS, the Pd:Ni ratio is about 7:3 in the Merensky Reef and in the UG-2. Millerite as the dominant Ni-bearing BMS in the UG-2 changes this ratio to 3:1. It is concluded that the Ni-content in braggite/vysotskite from BMS assemblages does not depend on the NiS activity, but rather on temperature of formation.

Keywords

cooperitebraggitevysotskiteMerensky ReefBushveld ComplexUG-2
Type
Mineralogy
Information
Mineralogical Magazine , Volume 58 , Issue 391 , June 1994 , pp. 223 - 234
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1994

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