The Skaergaard PGE and Gold Deposit: the Result of<i>in situ</i>Fractionation, Sulphide Saturation, and Magma Chamber-scale Precious Metal Redistribution by Immiscible Fe-rich Melt

Nielsen, Thorkild; Andersen, Jens C.Ø.; Holness, Marian B.; Keiding, Jakob K.; Rudashevsky, N. S.; Rudashevsky, V. N.; Salmonsen, L.; Tegner, Christian; Veksler, Ilya V.

doi:10.1093/petrology/egv049

Cited by 76 publications

(115 citation statements)

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“…Syn-magmatic S loss and an increase of metal tenor can occur through partial dissolution of the sulfide as proposed by Kerr and Leitch (2005). Dissolution of sulfide has been proposed to have occured in the Platinova Reef by Nielsen (2013), Godel et al (2014), Holwell andKeays (2014) and Nielsen et al (2015). Maier (2005) notes that sulfides associated with magnetite may have undergone late-magmatic S loss by Fe exchange with oxides through a similar process to that originally proposed by Naldrett and Lehmann (1987) for chomitites in the Bushveld Complex.…”

Section: Characteristicsmentioning

confidence: 95%

“…Sulfide mineralization is present as tiny (<100 µm) grains of bornite-digenite/chalcocite intergrowths with associated precious metal-bearing minerals, which are dominantly Pd-Pt-Au-Cu-Fe alloys (Bird et al 1991;Andersen et al 1998;Rudashevsky et al 2004;Cabri et al 2005;Nielsen et al 2005;McDonald et al 2009;Godel et al 2014;Rudashevsky et al 2014Rudashevsky et al , 2015Nielsen et al 2015). Figure 1d shows the typical geochemical variations and offsets of base and precious metals through a generalized section of the Triple Group.…”

Section: Geological Setting Of the Platinova Reef Skaergaard Intrusionmentioning

confidence: 99%

“…In particular, the main PGE peaks in all of these deposits are generally below the main Cu peak; the latter of which marks an increase in bulk sulfide content. The metal offsets have been attributed by some to be due to the effects of D sul/sil values, with elements with higher D values concentrated into the earliest (lowest) layers (Prendergast and Keays 1989;Prendergast 2000;Holwell and Keays 2014); the effects of kinetic fractionation of metals (Mungall 2002); fractionation of the sulfide liquid during filter pressing (e.g., Andersen et al 1998); and separation of and transport by a volatile-and Au-bearing residual of Fe-rich immiscible silicate melts Nielsen et al 2015).…”

Section: Characteristicsmentioning

confidence: 99%

“…The Skaergaard Intrusion in east Greenland is host to the Platinova Reef, which is an example of a rare subclass of magmatic sulfide deposit, manifested as stratiform PGE reef deposits in the upper parts of the host intrusions (Brooks 1989;Bird et al 1991;Andersen et al 1998;Nielsen et al 2005, Miller andAndersen 2002;Godel et al 2014;Holwell and Keays 2014;Nielsen et al 2015). These deposits differ from the more common disseminated and massive pyrrhotite-pentlandite-chalcopyrite ores found in the lower parts of layered mafic and ultramafic host intrusions, including along the margins and within conduits that feed larger intrusions (e.g., Maier 2005; Naldrett 2011 and references therein).…”

Section: Introductionmentioning

confidence: 99%

“…As such the Platinova Reef may represent an end member of this style of mineralization. While there are a number of common characteristics to all of these deposits, in detail, there are a great number of geochemical, mineralogical and stratigraphic variations and there is no current consensus on the magmatic and hydrothermal processes operating to explain all of these (e.g., Prendergast 2000;Andersen 2006;Nielsen and Bernstein 2009;Nielsen 2013;Holwell and Keays 2014;Godel et al 2014;Nielsen et al 2015;Keays and Tegner 2015).…”

Section: Introductionmentioning

confidence: 99%

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Extreme enrichment of Se, Te, PGE and Au in Cu sulfide microdroplets: evidence from LA-ICP-MS analysis of sulfides in the Skaergaard Intrusion, east Greenland

Holwell

Keays

McDonald

et al. 2015

Contrib Mineral Petrol

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evidence implies that there is no significant post-magmatic hydrothermal S loss and that the metal profiles are essentially a function of magmatic processes. We propose that to generate these extreme precious and semimetal contents, the sulfides must have formed from an anomalously metal-rich package of magma, possibly formed via the dissolution of a previously PGE-enriched sulfide. Other processes such as kinetic diffusion may have also occurred alongside this to produce the ultra-high tenors. The characteristic metal offset pattern observed is largely controlled by partitioning effects, producing offset peaks in the order Pt+Pd>Au>Te>Se>Cu that are entirely consistent with published D values. This study confirms that extreme enrichment in sulfide droplets can occur in closed-system layered intrusions in situ, but this will characteristically form ore deposits that are so low in sulfide that they do not conform to conventional deposit models for Cu-Ni-PGE sulfides which require very high R factors, and settling of sulfide liquids.

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Section: Characteristicsmentioning

confidence: 95%

Section: Geological Setting Of the Platinova Reef Skaergaard Intrusionmentioning

confidence: 99%

Section: Characteristicsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Extreme enrichment of Se, Te, PGE and Au in Cu sulfide microdroplets: evidence from LA-ICP-MS analysis of sulfides in the Skaergaard Intrusion, east Greenland

Holwell

Keays

McDonald

et al. 2015

Contrib Mineral Petrol

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A study of the trace sulfide mineral assemblages in the Stillwater Complex, Montana, USA

et al. 2016

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The sulfide assemblages of the Stillwater Complex away from the well-studied ore zones are composed mainly of variable proportions of pyrrhotite, chalcopyrite, pentlandite, and ±pyrite. Excluding vein assemblages and those affected by greenschist and lower temperature alteration, the majority can be classified into two broad assemblages, defined here as pristine (multiphase, often globular in shape) or volatilebearing (multiphase, high-temperature, volatile-rich minerals such as biotite, hornblende, or an unmixed calcite-dolomite assemblage). The volatile-bearing assemblages are mainly found within and below the J-M reef, where native copper and sphalerite are also locally present. Pristine sulfides are found throughout the stratigraphy. Both groups can be affected by apparent S loss in the form of pyrite being converted to magnetite and chalcopyrite to a Cu-Fe-oxide (delafossite), with little to no silicate alteration. An upward trend from pentlandite-rich to pyrrhotite-rich to pyrite-rich assemblages is observed in the footwall rocks in upper GN-I, and the same trend repeats from just below the reef and continues into the overlying N-II and GN-II. Modeling suggests that the sulfide Ni in the Peridotite Zone is largely controlled by silicate Ni. When taken together, observations are most readily explained by the remobilization of selected elements by a hightemperature fluid with the apparent loss of S > Cu > Ni. This could concentrate ore metals by vapor refining, eventually producing a platinum group element-enriched sulfide ore zone, such as the J-M reef.

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Weathering of PGE sulfides and Pt–Fe alloys in the Freetown Layered Complex, Sierra Leone

et al. 2017

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Fresh and weathered rocks and saprolite from Horizon B of the Freetown Layered Complex contain platinum-group minerals (PGM). The PGM in the fresh rocks are 1-7 μm across, including cooperite (PtS), isoferroplatinum (Pt 3 Fe), minor tetraferroplatinum (PtFe), tulameenite (Pt 2 FeCu), Os-bearing laurite (RuS 2 ), and other base metalsulfide (BMS)-bearing PGM. The weathered rocks contain fewer of those PGM but a high proportion of disordered Cu-(±Pd)-bearing Pt-Fe alloys. The saprolite hosts scarce, smaller (1-3 μm) ordered PtFe and disordered PtFe 3 . The PtFe alloys became increasingly Fe rich as weathering proceeded. Pt-Fe oxides appeared during weathering. Copper sulfides associated with the primary PGM and cooperite (with <3% Pd) were destroyed to provide the minor Cu and Pd found in some of the disordered Pt-Fe alloys. Platinum-and Pd-bearing saprolites have retained the original rock fabric and, to a depth of about 2 m, surround residual rocks that show progressive weathering (corestones). Ground water passing through the saprolite has transported Pt and Pd (and probably Au) in solution down slope into saprolite over unmineralized rocks. Transport is marked by changes in the Pt/Pd ratio indicating that the metals have moved independently. Palladium is present in marginally higher concentrations in the deeper saprolite than in the corestones suggesting some retention of Pd in the deeper saprolite. Platinum and Pd are less concentrated in the upper saprolite than the deeper saprolite indicating surface leaching. Alteration occurred over a long period in an organic and microbial rich environment that may have contributed to the leaching and transport of PGE.

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The Skaergaard PGE and Gold Deposit: the Result ofin situFractionation, Sulphide Saturation, and Magma Chamber-scale Precious Metal Redistribution by Immiscible Fe-rich Melt

Cited by 76 publications

References 57 publications

Extreme enrichment of Se, Te, PGE and Au in Cu sulfide microdroplets: evidence from LA-ICP-MS analysis of sulfides in the Skaergaard Intrusion, east Greenland

Extreme enrichment of Se, Te, PGE and Au in Cu sulfide microdroplets: evidence from LA-ICP-MS analysis of sulfides in the Skaergaard Intrusion, east Greenland

A study of the trace sulfide mineral assemblages in the Stillwater Complex, Montana, USA

Weathering of PGE sulfides and Pt–Fe alloys in the Freetown Layered Complex, Sierra Leone

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