Two distinct platinum-group mineral (PGM) assemblages have been identified in the Fazenda Mirabela intrusion that hosts the Ni–Cu–platinum-group element (PGE) Santa Rita ore zone in Bahia State, north-eastern Brazil: (i) Pt–Pd–Ni tellurides accompanied by Ag–Te, with minor electrum and native Au, and (ii) Pd alloys accompanied by minor PGE arsenides and sulphides. Assemblage (i) is present in the Santa Rita ore zone and underlying S-poor footwall dunite whereas assemblage (ii) is observed in the dunite only. The assemblage (i) PGE tellurides crystallised from a late stage semimetal-rich PGE-bearing melt produced by sulphide fractionation and/or via exsolution from sulphides during subsolidus cooling. In assemblage (i) in the Santa Rita ore zone, PGM are also commonly found within base metal sulphide (BMS) veinlets which have either formed as a result of post-magmatic hydrothermal remobilisation or by the simultaneous crystallisation of PGM and BMS from a late stage volatile-rich melt. In the S-poor footwall dunite that hosts assemblage (ii), Pd alloys have formed through the interaction of sulphides with a late stage melt or high temperature hydrothermal fluid. This liquid had a high oxygen fugacity (
) that caused S loss evidenced by the formation of micro-scale textures that resemble symplectites or intergrowths of sulphides with olivine and occasionally orthopyroxene, and the formation of magnetite. During sulphur loss, semimetals (particularly Te) were also stripped from the dunite while PGE were expelled from the symplectite-like sulphides forming Pd alloys. PGE tellurides are present in the dunite where S and semimetals have not been completely stripped from the rock suggesting that this late stage melt or high temperature hydrothermal fluid was not pervasive throughout the dunite.
AndersonJCØ. 2006. Postmagmatic sulphur loss in the Skaergaard Intrusion: implications for the formation of the Platinova Reef, Lithos, 92, 198–221.
2.
BallhausC, TredouxM, SpäthA. 2001. Phase relations in the Fe-Ni-Cu-PGE-S system at magmatic temperature and application to massive sulphide ores of the Sudbury Igneous Complex, J. Petrol., 42, 1911–1926.
3.
BarbosaJSF, SabatéP. 2004. Archean and Paleoproterozoic crust of the São Francisco Craton, Bahia, Brazil: geodynamic features, Precamb. Res., 133, 1–27.
4.
BarnesSJ, HoatsonDM, KeaysRR. 1992. Distribution of sulfides and PGE within the mineralized porphyritic Websterite zone of the Munni Munni Complex, Western Australia, Aust. J. Earth Sci., 39, 289–302.
5.
BarnesSJ, OsborneGA, CookD, BarnesL, MaierWD, GodelB. 2011. The Santa Rita nickel sulfide Deposit in the Fazenda Mirabela Intrusion, Bahia, Brazil: geology, sulfide geochemistry, and genesis, Econ. Geol., 106, 1083–1110.
6.
BarnesS.-J, PrichardHM, CoxRA, FisherPC, GodelB. 2008. The location of the chalcophile and siderophile elements in platinum-group element ore deposits (a textural, microbeam and whole rock geochemical study): implications for the formation of the deposits, Chem. Geol., 248, 295–317.
7.
CabriLJ. 2002. The platinum-group minerals, in The geology, geochemistry, mineralogy and mineral beneficiation of the platinum-group elements, (ed. , CabriL J, ed), Sp. Vol. 54, 13–131, Montreal, Canadian Institute of Mining, Metallurgy and Petroleum.
8.
CabriLJ, LaflammeJHG. 1976. The Mineralogy of the platinum-group elements from some copper-nickel deposits of the Sudbury Area, Ontario, Econ. Geol., 71, 1159–1195.
9.
CawthornRG, MerkleRKW, ViljoenMJ. 2002. Platinum-group element deposits in the Bushveld Complex, South Africa, in The geology, geochemistry, mineralogy and mineral beneficiation of the platinum-group elements, (ed. , CabriL J, ed), Sp. Vol. 54, 389–429, Montreal, Canadian Institute of Mining, Metallurgy and Petroleum.
10.
El GoresyA, ZinnerE, PellasP, CailletC. 2005. A menagerie of graphite morphologies in the Acapulco meteorite with diverse carbon and nitrogen isotopic signatures: implications for the evolution history of acapulcoite meteorites, Geochim. Cosmochim. Acta, 69, 4535–4556.
11.
FarrowCEG, LightfootPC. 2002. Sudbury PGE revisited: towards an integrated model, in The geology, geochemistry, mineralogy and mineral beneficiation of the platinum-group elements, (ed. , CabriL J, ed), Sp. Vol. 54, 273–297, Montreal, Canadian Institute of Mining, Metallurgy and Petroleum.
12.
Ferreira FilhoCF, CançadoF, CorreaC, MacambiraEMB, SiepierskiL, BrodTCJ. 2007. Mineralizações estratiformes de EGP-Ni associadas a complexos acamadados em Carajás: os exemplos de Luanga e Serra da Onça, in Contribuições à Geologia da Amazônia, Sociedade Brasileira de Geologia - Núcleo Norte, 5, 01–14.
13.
FleetME, ChryssoulisSL, StoneWE, WeisenerCG. 1993. Partitioning of platinum-group elements and Au in the Fe–Ni–Cu–S system: experiments on the fractional crystallization of sulphide melt, Contrib. Mineral. Petrol., 115, 36–44.
14.
HelmyHA, BallhausC, BerndtJ, BockrathC, Wohlgemuth-UeberwassarC. 2007. Formation of Pt, Pd and Ni tellurides: experiments in sulphide-telluride systems, Contrib. Mineral. Petrol., 153, 577–591.
15.
HelmyHA, BallhausC, Wohlgemuth-UeberwassarC, FonsecaROC, LaurenzV. 2010. Partitioning of Se, As, Sb, Te and Bi between monosulfide solid solution and sulfide melt – application to magmatic sulfide deposits, Geochim. Cosmochim. Acta, 74, 6174–6179.
16.
HolwellDA, McDonaldI. 2007. Distribution of platinum-group elements in the Platreef at Overysel, northern Bushveld Complex: a combined PGM and LA-ICP-MS study, Contrib. Mineral. Petrol., 154, 171–190.
17.
HolwellDA, McDonaldI. 2010. A review of the behaviour of platinum-group elements within natural magmatic sulphide ore systems, Platin. Met. Rev., 54, 26–36.
18.
HolwellDA, McDonaldI, ArmitagePEB. 2006. Platinum-group mineral assemblages in the Platreef at the South Central Pit, Sandsloot Mine, northern Bushveld Complex, South Africa, Mineral. Mag., 70, 83–101.
19.
HutchinsonD, McDonaldI. 2008. Laser ablation ICP-MS study of platinum-group elements in sulfides from the Platreef at Turfspruit, northern limb of the Bushveld Complex, South Africa, Mineral. Depos., 43, 695–711.
KinlochED. 1982. Regional trends in the platinum-group mineralogy of the critical zone of the Bushveld Complex, South Africa, Econ. Geol., 77, 1328–1347.
22.
LiC, BarnesS.-J, MakovickyE, Rose-HansenJ, MakovickyM. 1996. Partitioning of nickel, copper, iridium, rhenium, platinum, and palladium between monosulfide solid solution and sulphide liquid: effects of composition and temperature.Geochim. Cosmochim. Acta, 60, 1231–1238.
23.
MaierWD. 2005. Platinum-group element (PGE) deposits and occurrences: mineralization styles, genetic concepts, and exploration criteria. Invited presidential review, J. Afr. Earth Sci., 41, 165–191.
24.
MarmaJC. 2002. Magmatic and hydrothermal PGE mineralization of the Birch Lake Cu–Ni–PGE deposit in the South Kawishiwi Intrusion, Duluth Complec, Northeast Minnesota, Unpublished MSc thesis, University of Wisconsin, USA, 101.
25.
McDonaldI, OhnenstetterD, OhnenstetterM, VaughanDJ. 1999. Palladium oxides in ultramafic complexes near Lavatrafo, Western Andriamena, Madagascar, Mineral. Mag., 63, 345–352.
26.
MungallJE, AndrewsDRA, CabriLJ, SylvesterPJ, TubrettM. 2005. Partitioning of Cu, Ni, Au, and platinum-group elements between monosulfide solid solution and sulphide melt under controlled oxygen and sulphur fugacities, Geochim. Cosmochim. Acta, 69, 4349–4360.
27.
NaldrettAJ, WilsonA, KinnairdJA, ChunnettG. 2009. PGE tenor and metal ratios within and below the Merensky Reef, Bushveld Complex: implications for its genesis, J. Petrol., 50, 625–659.
28.
PeregoedovaAV. 1998. The experimental study of the Pt–Pd partitioning behaviour between monosulfide solid solution and Cu–Ni–sulfide melt at 900–840°C, Proc. 8th Int. Platinum Symp. Abs., Series S18, 325–327, Johannesburg, Geological Society of South Africa and South African Institute of Mining and Metallurgy Symposium.
29.
PrichardHM, BarnesS.-J, MaierWD, FisherPC. 2004b. Variations in the nature of the platinum-group minerals in a cross-section through the Merensky Reef at Impala Platinum: implications for the mode of formation of the reef, Can. Mineral., 42, 423–437.
30.
PrichardHM, HutchinsonD, FisherPC. 2004a. Petrology and crystallisation history of multiphase sulphide droplets in a mafic dike from Uruguay: implications for the origin of Cu–Ni–PGE–sulphide deposits, Econ. Geol., 99, 365–376.
31.
PrichardHM, SáJHS, FisherPC. 2001. Platinum-group mineral assemblages and chromite composition in the altered and deformed Bacuri Complex, Amapa, Northeastern Brazil, Can. Mineral., 39, 377–396.
32.
SalpéteurI, Martel-JantinB, RakotomananaD. 1995. Pt and Pd mobility in ferralitic soils of the West Andriamena area (Madagascar); evidence of a supergene origin of some Pt and Pd minerals, Chronique de la Recherche Minière, 520, 27–45.
33.
SilvaMGda, MartinH, AbramMB. 1996. Datação do corpo máfico-ultramáfico da Fazenda Mirabela (Ipiaú-BA.) pelo método Sm-Nd: Implicações petrogenéticas e geotectônicas, Congresso Brasileiro De Geológia, 39, 217–220.
34.
TomkinsAG. 2010. Wetting facilitates late-stage segregation of precious metal-enriched sulfosalt melt in magmatic sulfide systems, Geology, 38, 951–954.
35.
WangCY, PrichardHM, ZhouM.-F, FisherPC. 2008. Platinum-group minerals from the Jinbaoshan Pd–Pt deposit, SW China: evidence for magmatic origin and hydrothermal alteration, Mineral. Depos., 43, 791–803.
36.
WilsonAH, NaldrettAJ, TredouxM. 1989. Distribution and controls of platinum-group element and base element mineralization in the Darwendale subchamber of the Great Dyke, Zimbabwe, Geology, 17, 649–652.
37.
ZientekMJ, CooperRW, CorsonSR, GeraghtyEP. 2002. PGE mineralisation in the Stillwater Complex, Montana, in The geology, geochemistry, mineralogy and mineral beneficiation of the platinum-group elements, (ed. , CabriL J, ed), Sp. Vol. 54, 459–481, Montreal, Canadian Institute of Mining, Metallurgy and Petroleum.
) that caused S loss evidenced by the formation of micro-scale textures that resemble symplectites or intergrowths of sulphides with olivine and occasionally orthopyroxene, and the formation of magnetite. During sulphur loss, semimetals (particularly Te) were also stripped from the dunite while PGE were expelled from the symplectite-like sulphides forming Pd alloys. PGE tellurides are present in the dunite where S and semimetals have not been completely stripped from the rock suggesting that this late stage melt or high temperature hydrothermal fluid was not pervasive throughout the dunite.