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The concentrations of the noble metals in Southern African flood-type basalts and MORB : implications for petrogenesis and magmatic sulphide exploration

Maier Wolfgang D., Barnes Sarah-Jane et Marsh Julian S.. (2003). The concentrations of the noble metals in Southern African flood-type basalts and MORB : implications for petrogenesis and magmatic sulphide exploration. Contributions to mineralogy and petrology, 146, (1), p. 44-61.

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Concentrations of the platinum-group elements have been determined in several suites of southern African flood-type basalts and mid-ocean ridge basalt (MORB), covering some 3 Ga of geologic evolution and including the Etendeka, Karoo, Soutpansberg, Machadodorp, Hekpoort, Ventersdorp and Dominion magmas. The magmas cover a compositional range from 3.7 to 18.7% MgO, 26–720 ppm Ni, 16–250 ppm Cu, and <1–255 ppb total platinum-group elements (PGE). The younger basalts (Etendeka, Karoo) tend to be depleted in PGE relative to Cu, while most of the older basalts (Hekpoort, Machadodorp, Ventersdorp, Dominion) show no PGE depletion relative to Cu. Further, the younger basalts tend to have lower average Pt/Pd ratios than the older basalts, and the MORBs have lower average Pt/Pd than the continental basalts within the broad groupings of ‘‘old’’ and ‘‘young’’ basalts. This may reflect (1) a decreasing degree of mantle melting through geologic time, and (2) source heterogeneity, in that the MORBs are derived from predominantly asthenospheric mantle, whereas the continental basalts also contain a lithospheric mantle component enriched in Pt. In addition to these factors, some PGE fractionation also occurred during differentiation of the magmas, with Pd showing incompatible behaviour and the other PGE variably compatible behaviour. The examined southern African flood-type basalts and MORB appear to offer limited prospects for magmatic sulfide ores, largely because they show little evidence for significant chalcophile metal depletion that could be the result of sulphide extraction during ascent and crystallization.

Type de document:Article publié dans une revue avec comité d'évaluation
Pages:p. 44-61
Version évaluée par les pairs:Oui
Sujets:Sciences naturelles et génie > Sciences naturelles > Sciences de la terre (géologie, géographie)
Département, module, service et unité de recherche:Départements et modules > Département des sciences appliquées > Unité d'enseignement en sciences de la Terre
Mots-clés:absolute age, Africa, Archean, basalts, Botswana, Bushveld Complex, chemical composition, chemical ratios, dates, Dominion Suite, East Africa, Etendeka Group, flood basalts, fractional crystallization, geochemistry, greenstone belts, Hekpoort Basalt, igneous rocks, Jurassic, Karoo Basin, Machadodorp Suite, magmas, Mesozoic, metal ores, metals, metamorphic belts, mid-ocean ridge basalts, mineral composition, mineral exploration, Mozambique, Namibia
Déposé le:08 juin 2016 18:40
Dernière modification:09 déc. 2016 14:32
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