The Merensky Reef at the Atok platinum mine and its environs

Schwellnus, J. S. I.; Hiemstra, S. A.; Gasparrini, E.

doi:10.2113/gsecongeo.71.1.249

Cited by 21 publications

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“…Solid lines represent the limits of the stability fields of cooperite and braggite at 700°C Merkle 2000, 2002). Data from: Bannister and Hey (1932), Genkin and Zvyagintsev (1962), Laputina and Genkin (1975), Brynard et al (1976), Schwellnus et al (1976), Cabri et al (1978Cabri et al ( , 1996, Toma and Murphy (1978), Watkinson and Dunning (1979), Kingston and El-Dosuky (1982), Mostert et al (1982), Todd et al (1982), Vuorelainen et al (1982), Talkington and Watkinson (1984), Criddle and Stanley (1985), Genkin and Evstigneeva (1986), Volborth et al (1986), Tarkian (1987), Halkoaho (1989), Johan et al (1989), Corrivaux and Laflamme (1990), Cowden et al (1990), Shcheka et al (1991), Auge´and Legendre (1992), Legendre and Auge´(1992), Barkov and Lednev (1993), Coghill and Wilson (1993), Weiser and Schmidt-Thome( 1993), Auge´and Maurizot (1995), Barkov et al (1995), Rudashevsky et al (1995), Cabri and Laflamme (1997), Tolstykh and Krivenko (1997), Auge´et al (1998), Mitrofanov et al (1998), Distler et al (1999, Gornostayev et al (1999), …”

Section: Observationsmentioning

confidence: 99%

“…A substantial part of the remaining braggite compositions is consistent with lower temperature of formation or equilibration. Analyses plotting in the gap area are reported from the Merensky Reef and Platreef of the Bushveld Complex (Schwellnus et al 1976;Cabri et al 1978;Kingston and El-Dosuky 1982;Mostert et al 1982), but also from the J-M Reef of the Stillwater Complex (Criddle and Stanley 1985;Volborth et al 1986), the Fedorova-Pansky intrusion (Mitrofanov et al 1998), Noril'sk andTalnakh (Sluzhenikin, personal communication, 1999), and the Kovdorsky carbonatite (Rudashevsky et al 1995). Zoned braggite grains from the Lukkulaisvaara layered intrusion (Barkov et al 1995) also plot in the gap area.…”

Section: Observationsmentioning

confidence: 99%

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Cooperite and braggite from the Bushveld Complex: implications for the miscibility gap and identification

Merkle

Verryn

2003

Miner Deposita

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Analyses of the Pt-Pd±Ni sulphides cooperite, braggite, and vysotskite reported from worldwide occurrences seem to imply a continuum of compositions between vysotskite and cooperite, with no obvious miscibility gap. This is contrary to the experimentally confirmed miscibility gap between cooperite and braggite, and the established compositional gap between co-existing cooperite and braggite from the Merensky Reef. Although the only unambiguous way of distinguishing between cooperite and braggite is to obtain structural information through X-ray diffraction or equivalent techniques, most identification of Pt-Pd±Ni sulphides is based on microanalytical techniques due to the small grain size of most platinum-group minerals. Ni contents also have to be considered because a classification based on the Pt/Pd ratio alone can be very misleading. Naming of Pt-Pd±Ni sulphide compositions with high Pt contents based on qualitative or semiquantitative analyses should be avoided. Natural PtPd±Ni sulphides which project into the compositional gap (established by experimental work) cannot be named without supporting structural information. Compositions of grains, which plot inside the gap, are considered to be metastable and to result from the loss of Pd through interaction with hydrothermal fluids.Keywords Braggite AE Cooperite AE Pt-Pd-Ni-S AE Miscibility gap AE Bushveld AE South Africa Recent experimental investigations of the system PtS- PdS-NiS (Verryn and Merkle 2000, 2002) confirmed the presence of a miscibility gap between cooperite and braggite and a continuous solid solution series between braggite and vysotskite. Contrary to the experimentally confirmed miscibility gap between cooperite and braggite, a compilation of analyses reported in the literature from worldwide occurrences seems to imply a continuum of compositions between vysotskite and cooperite with no obvious gap (Fig. 1). This contribution focuses on the reasons for the discrepancy between experiments and natural occurrences. The question also arises of which criteria to use for identification of minerals inside the experimentally established miscibility gap. The data baseA compilation of published analyses from the literature (for sources see caption of Fig. 1) was used to evaluate the miscibility gap between cooperite and braggite and the problem of identifying some natural Pt-Pd-Ni sulphides. The database of 592 microprobe analyses from Miner Deposita (2003) 38: 381-388

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Section: Observationsmentioning

confidence: 99%

Section: Observationsmentioning

confidence: 99%

Cooperite and braggite from the Bushveld Complex: implications for the miscibility gap and identification

Merkle

Verryn

2003

Miner Deposita

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“…The rock-forming silicate minerals, base-metal sulfides and the PGM (Table 1) display general compositional and textural similarities with those reported from various parts of the Merensky Reef (cf. Brynard et al 1976, Schwellnus et al 1976, Vermaak & Hendriks 1976, Kingston & El-Dosuky 1982, Kinloch & Peyerl 1990.…”

Section: The Platinum-group Mineralsmentioning

confidence: 99%

THE OCCURRENCE OF Pb Cl (OH) AND Pt Sn S COMPOUNDS IN THE MERENSKY REEF, BUSHVELD LAYERED COMPLEX, SOUTH AFRICA

Barkov¹,

Martin²,

Kaukonen³

et al. 2001

The Canadian Mineralogist

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An unusual phase rich in Cl (78.4 wt.% Pb, 19.2% Cl) and close in composition to penfieldite [Pb 2 Cl 3 (OH)] was found as ã 5 m inclusion in chalcopyrite, in a spatial association with platinum-group minerals, in a sulfide-poor (≤5 vol.% of base-metal sulfides) enstatite orthocumulate of the Merensky Reef, Bushveld layered complex, South Africa. This seems to be the first reported occurrence of a Pb-Cl-(OH) compound in mafic-ultramafic rocks. The associated platinum-group minerals are members of the braggite series, cooperite (which forms large intergrowths with braggite: up to 0.5 mm in the longest dimension), members of the rustenburgite-atokite and merenskyite-moncheite series, zoned laurite, and an unknown stannosulfide of Pt, the likely chemical formula of which is PtSnS. The stannosulfide probably formed at a hydrothermal stage from microvolumes of a latestage fluid or liquid. The Cl-rich phase precipitated from a late-stage solution rich in Cl, or formed as a result of replacement of a precursor mineral (probably galena) by an aqueous hydrochloric solution at a very low temperature, at the final stage of hydrothermal alteration.Keywords: Cl-rich phase, platinum-group minerals, stannosulfide of Pt, Merensky Reef, Bushveld complex, mafic-ultramafic rocks, layered intrusion, South Africa. SOMMAIRENous documentons la présence d'une phase inhabituelle riche in Cl (78.4% Pb, 19.2% Cl, en poids) se rapprochant de la composition de la penfieldite [Pb 2 Cl 3 (OH)] en inclusion d'environ 5 m dans la chalcopyrite, étroitement associée à des minéraux du groupe du platine dans un orthocumulat à enstatite à faible teneur en sulfures de métaux de base (≤5% du volume) provenant du banc minéralisé de Merensky, complexe stratiforme de Bushveld, en Afrique du Sud. Cet indice semble offrir le premier exemple d'un composé à Pb-Cl-(OH) dans des roches mafiques-ultramafiques. Lui sont associés des minéraux du groupe du platine: membres de la série de la braggite, cooperite (en intercroissance avec la braggite, atteignant jusqu'à 0.5 mm en dimension maximale), membres des séries rustenburgite-atokite et merenskyite-monchéite, laurite zonée, et un stannosulfure de Pt méconnu, dont la composition serait PtSnS. Le stannosulfure se serait probablement formé à un stade hydrothermal à partir de microvolumes d'un fluide ou liquide tardif. Le minéral riche en Cl a précipité d'une solution tardive chlorée, ou bien s'est formée par remplacement d'un précurseur, probablement la galène, en présence d'une solution aqueuse hydrochlorique à température très faible, au stade ultime de l'altération hydrothermale.

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“…In contrast, cooperite and braggite are frequently encountered in the silicate dominated Merensky Reef samples (Kinloch, 1982); occasionally, these two phases coexist. The PGM in the Merensky Reef are associated with chalcopyrite, penflandite, pyrrhotite and minor pyrite (Brynard et al, 1976;Schwellnus et aL, 1976;Vermaak and Hendriks, 1976;Mostert et al, 1982).…”

Section: Samplesmentioning

confidence: 99%

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

Verryn

Merkle

1994

Mineral. mag.

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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 gbD raggite/c~176 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/~D ~ 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.

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The Merensky Reef at the Atok platinum mine and its environs

Cited by 21 publications

References 0 publications

Cooperite and braggite from the Bushveld Complex: implications for the miscibility gap and identification

Cooperite and braggite from the Bushveld Complex: implications for the miscibility gap and identification

THE OCCURRENCE OF Pb Cl (OH) AND Pt Sn S COMPOUNDS IN THE MERENSKY REEF, BUSHVELD LAYERED COMPLEX, SOUTH AFRICA

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

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