The Formation of Stratiform PGE Deposits in Layered Intrusions

Naldrett, A. J.; Cameron, Geoffrey; Gruenewaldt, G. von; Sharpe, Martin R.

doi:10.1007/978-94-017-2509-5_10

Cited by 49 publications

(19 citation statements)

References 50 publications

(120 reference statements)

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Furthermore, the enrichment would not only be a function of the high D matte-sil Pt but, due to mass balance considerations, would also be constrained by the mass ratio of the silicate liquid to sulphide liquid, R. The R-factor model, which was initially proposed by Campbell and Naldrett (1979), has been used to explain the high PGE enrichments observed in horizons found in a number of mafic layered intrusions such as the Merensky Reef, Stillwater complex, etc. (e.g., Keays and Campbell, 1981;Campbell et al, 1983;Campbell and Barnes, 1984;Barnes and Naldrett, 1985;Naldrett et al, 1987;Barnes and Campbell, 1988;Godel et al, 2007). However, the R-factor model was almost immediately criticized, because until recently, D matte-sil Pt available in the literature (e.g., Helz and Rait, 1988;Peach et al, 1990Peach et al, , 1994Stone et al, 1990;Fleet et al, , 1996Fleet et al, , 1999Bezmen et al, 1994;Crocket et al, 1997) were lower than required by the model to explain the level of PGE enrichment in sulphides observed in many magmatic PGE deposits.…”

Section: Introductionmentioning

confidence: 90%

“…Moreover, base metals such as, Fe, Cu and Ni were shown to be over an order of magnitude more mobile than the PGE, which would cause an enrichment of base metals over the PGE. In PGE-rich horizons associated with mafic intrusions PGE tend to be greatly enriched relative to the base metals (see for example, Naldrett et al, 1987).…”

Section: Matte/silicate-melt Equilibrium As the Primary Cause For Pgementioning

confidence: 99%

See 1 more Smart Citation

Solubility of Pt in sulphide mattes: Implications for the genesis of PGE-rich horizons in layered intrusions

Fonseca

Campbell

O’Neill

et al. 2009

Geochimica et Cosmochimica Acta

108

View full text Add to dashboard Cite

The partitioning of Pt in sulphide melt (matte) has been studied as a function of fS 2 and fO 2 at 1200 and 1300°C. The results show that the solubility of Pt in mattes increases strongly with increasing fS 2 and decreases weakly with increasing fO 2 . The increase in Pt solubility with increasing fS 2 is attributed to Pt dissolving in the melt as a sulphide species and the weak inverse dependence of Pt solubility on fO 2 to the diluting effect of increasing O in the melt at high fO 2 . These results, coupled with measurements of Pt solubility in silicate melts taken from the literature, allow the calculation of Pt matte/silicate-melt partition coefficients (D matte-sil Pt ) for a range of conditions pertinent to the formation of Pt-rich horizons in layered intrusions. The calculated values range between 10 7 and 10 11 , depending on fO 2 and fS 2 , several orders of magnitude higher than previously published values. Our preferred value for D matte-sil Pt for conditions appropriate to the Merensky Reef is 10 7 and for the Stillwater Pt-rich horizon 10 8 . The new results are consistent with the magmatic hypothesis for Pt-rich horizons in layered intrusions.

show abstract

Section: Introductionmentioning

confidence: 90%

Section: Matte/silicate-melt Equilibrium As the Primary Cause For Pgementioning

confidence: 99%

Solubility of Pt in sulphide mattes: Implications for the genesis of PGE-rich horizons in layered intrusions

Fonseca

Campbell

O’Neill

et al. 2009

Geochimica et Cosmochimica Acta

108

View full text Add to dashboard Cite

show abstract

“…Layered gabbroic intrusions host the major Cr, Ni and PGE (platinum group elements) deposits (Naldrett et al, 1987;Cawthorn, 1996;Lee, 1996). It is now widely recognized (e.g.…”

Section: Introductionmentioning

confidence: 99%

Petrogenesis of the Kabanga–Musongati layered mafic–ultramafic intrusions in Burundi (Kibaran Belt): geochemical, Sr–Nd isotopic constraints and Cr–Ni behaviour

Duchesne

Liégeois

Deblond

et al. 2004

Journal of African Earth Sciences

View full text Add to dashboard Cite

A succession of mafic-ultramafic layered intrusions forms an alignment in the boundary zone between the Kibaran belt and the Tanzania craton. The intrusions represent a continuous series of cumulate rocks. For instance, in the Mukanda-Buhoro and Musongati (MBM) contiguous bodies, the series starts with dunite and passes to lherzolite, pyroxenite, norite, gabbronorite and anorthosite on top. Cumulate textures are conspicuous in all rock types and cryptic layering characterises cumulus mineral compositions, thus evidencing fractional crystallization as a major differentiation mechanism. The increase of Cr in the ultramafic members of the series indicates that chromite was not a liquidus mineral in dunite and lherzolite rocks, thus unable to form chromitite layers. The high Ni-content of dunite seems to preclude the existence of conjugate Ni-rich sulphide deposits. The 87 Sr/ 86 Sr initial ratio is relatively constant and averages 0.7087, with some values up to 0.712 due to local assimilation. Fine-grained rocks from the MBM area are isotopically (Nd and Sr) similar to the MBM cumulates. Modelling their crystallization produces cumulus mineral compositions similar to those in the Musongati ultramafic rocks, which suggests a broadly picritic parental magma. On the other hand, finegrained rocks from the Nyabikere area are not related to the Nyabikere cumulates. Nd and Sr isotope ratios show that the MBM magmatism is related to an enriched source, possibly an old subcontinental lithospheric mantle. The Nyabikere dykes, as well as the Waga dykes, come from a depleted mantle source, as do the A-type granitoids occurring in the same boundary zone. Several lines of evidence point to two types of parental magmas, a picritic magma, and a more evolved magma, broadly similar to the Bushveld Main Zone magma.

show abstract

“…As an example, the occurrence of basal reversals, upper picrite units and especially a relatively sharp contact between picritic and gabbroic units in the mafic sills of the Noril'sk region, Russia, are usually taken as evidence for their formation by Figure 1a, b and c. Data are from the following sources: Basistoppen mafic sill: Naslund (1989); Bushveld Complex: Naldrett (1989); Rum Complex: Renner & Palacz (1987). See text for discussion.…”

Section: Introductionmentioning

confidence: 98%

Phase equilibria testing of a multiple pulse mechanism for origin of mafic–ultramafic intrusions: a case example of the Shiant Isles Main Sill, NW Scotland

Latypov

Chistyakova

2009

Geol. Mag.

View full text Add to dashboard Cite

In this paper we examine the role of multiple emplacement of sills into partly solidified rocks (an intrusive mechanism 'liquid into solid') as a possible explanation for some textural and compositional 'anomalies' of single-cyclic mafic intrusions. As a case study we used the Shiant Isles Main Sill that is widely regarded as a classical example of a multiple, picrite-picrodolerite-crinanite alkaline sill. This sill is currently interpreted as having been formed by several olivine phenocrystrich pulses of magma, which were successively emplaced into their almost solidified predecessors. Such an intrusive mechanism is a random process in which many parameters vary independently and unpredictably. Among them are: the number, relative volume and bulk composition of magma pulses, and their place, sequence and timing of emplacement, as well as modal abundance, phase composition and distribution of intratelluric phenocrysts in magmas upon emplacement. In terms of these variables, one can envisage countless different profiles through alkaline sills produced from only three randomly intruded magma pulses of picritic, picrodoleritic and crinanitic composition. Such multiple sills can readily be distinguished from simple ones formed from a single pulse of magma by anomalous compositional profiles with several prominent breaks in crystallization and compositional sequences. The compositional profile of the Shiant Isles Main Sill is remarkably similar to an M-shaped profile expected from fractional crystallization of a single pulse of olivine-saturated magma along a crystallization path Ol+Sp+L (picrite), Ol+Pl±Sp+L (picrodolerite = troctolite), Ol+Pl+Cpx+L (crinanite). The probability of the accidental formation of such a compositional profile by multiple intrusion 'liquid into solid' is exceedingly small, even for the single case of the Shiant Isles Main Sill. The probability approaches zero when considering that exactly the same sequence of intrusive events must have been repeated in about 20 neighbouring alkaline sills with similar compositional profiles. This can only be achieved by some universally operating differentiation process. The best candidate for this is the classical fractional crystallization of magma constrained by liquidus phase equilibria. This suggests that the Shiant Isles Main Sill can be best interpreted and modelled as a simple sill that crystallized from one large pulse of magma, with possible involvement of minor refilling events. Further progress in our knowledge of intrachamber magma fractionation processes will probably enable us to interpret many 'anomalous' textural and compositional features of mafic-ultramafic intrusions in the frame of a single magma pulse model.

show abstract

The Formation of Stratiform PGE Deposits in Layered Intrusions

Cited by 49 publications

References 50 publications

Solubility of Pt in sulphide mattes: Implications for the genesis of PGE-rich horizons in layered intrusions

Solubility of Pt in sulphide mattes: Implications for the genesis of PGE-rich horizons in layered intrusions

Petrogenesis of the Kabanga–Musongati layered mafic–ultramafic intrusions in Burundi (Kibaran Belt): geochemical, Sr–Nd isotopic constraints and Cr–Ni behaviour

Phase equilibria testing of a multiple pulse mechanism for origin of mafic–ultramafic intrusions: a case example of the Shiant Isles Main Sill, NW Scotland

Contact Info

Product

Resources

About