Title page for ETD etd-12212007-082547


Document Type Doctoral Thesis
Author Verryn, Sabine Marie Charlotte
URN etd-12212007-082547
Document Title Natural and synthetic phase relations of cooperite, braggite and vysotskite
Degree PhD (Geology)
Department Earth Sciences
Supervisor
Advisor Name Title
Prof R K W Merkle Committee Chair
Keywords
  • geochemistry
Date 2000-09-01
Availability unrestricted
Abstract
In this thesis, results of experimental investigations in the dry system PtS-PdS-NiS at 1200C, 11 OOC, 1 OOOC, 900C, 800C, and 700C are presented. Experimental results are compared with analyses of naturally occurring cooperite (ideally PtS), braggite ((Pt,Pd)S), and vysotskite (ideally PdS) of this study and with analyses reported in the literature.

Synthetic cooperite is stable at temperatures above 1200C, whereas synthetic braggite at temperatures below 1100C, and synthetic vysotskite below 1000C. Below 900C in the system PtS-PdS-NiS, Ni-saturated synthetic cooperite, -braggite, and -vysotskite coexist with Ni1_xS, At 900C only Ni-saturated, Pd-free synthetic cooperite coexists with Ni1_xS, and synthetic braggite and Pd-containing synthetic cooperite coexist with a Pd-Ni-Pt - sulphide melt. At temperatures > 1000C all Ni-saturated synthetic cooperite and -braggite coexists with a Pd-Ni-Pt - sulphide melt. There is a clearly defined miscibility gap between cooperite and braggite, but no gap was observed between braggite and vysotskite.

There are well defined, positive, relationships between the Pd-contents of synthetic cooperite, -braggite, and -vysotskite and the Pd-content of the coexisting melt or that of the coexisting Ni1_xS.

The Ni-content of synthetic braggite and -vysotskite with varying PtlPd ratios in a Ni-saturated environment is a function of temperature; a higher Ni-content resulting from a lower equilibration temperature. In synthetic cooperite, a similar relationship between the Ni-content and the temperature of formation or equilibration is applicable between 1200 and 900C. At 800C, the Ni-content is higher than that at 700C. The variation in the Ni-content in synthetic cooperite is more restricted than that for synthetic braggite and -vysotskite.

Sulphur fugacity has an effect on the system Pt-Pd-Ni-S. If formed under higher S-pressure, synthetic braggite synthesized at 1000C contains higher amounts of Ni than formed at lower S-pressure at given PtlPd ratios in the initial charge. At constant bulk PtlPd ratio, the PtlPd ratio of the synthetic braggite decreases with increasing sulphur fugacity. The inter-element relationships for synthetic braggite are not as pronounced for cooperite synthesized at 1000C.

Compositions of cooperite, braggite, and vysotskite have the potential to indicate at which stage of the development of an ore deposit these phases were exsolved or equilibrated. Comparison of the experimental results with analyses of natural cooperite, braggite, and vysotskite of this study and from the literature, indicate that:

(i) Cooperite and braggite from the Merensky Reef have equilibrated below 900C.

(ii) Analyses of cooperite, braggite, and vysotskite from the UG-2, coexisting with pentlandite follow the trend similar to that experimentally established for temperatures < 700C and where coexisting with millerite, the trend established for temperatures between 800C and 700C.

(iii) Temperatures of formation or equilibration of cooperite, braggite, and vysotskite from the Sompujvi Reef of the Penikat Intrusion and of Placer Deposits, as well as cooperite from the Stillwater Complex cannot be estimated with certainty.

(iv) Braggite and vysotskite from the Stillwater Complex may have formed at temperatures below 700C.

(v) Cooperite-, braggite-, and vysotskite analyses from Noril'sk indicate formation temperatures of < 700C.

2000 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria.

Please cite as follows:

Verryn SMC 2000, Natural and synthetic phase relations of cooperite, braggiteand vysotskite, PhD thesis, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-12212007-082547/ >

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