The origin of chromitites and related PGE mineralization in the Bushveld Complex: new mineralogical and petrological constraints

Naldrett, A. J.; Wilson, A. H.; Kinnaird, Judith A.; Yudovskaya, Marina A.; Chunnett, Gordon

doi:10.1007/s00126-011-0366-3

Cited by 169 publications

(82 citation statements)

References 75 publications

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“…This mineralization phase has characteristic PGE patterns with high IPGE contents compared to PPGE (samples MA 226, 400 and 422; Fig. 15) which fits relatively well with that of chromitites from ophiolites, komatiites and layered intrusions (Cabri, 2002;Naldrett et al, 2012;Pagé et al, 2012). Chromite crystallized in komatiitic and tholeiitic melts concentrates IPGE.…”

Section: Pgm Crystallization and Pge Fractionationsupporting

confidence: 56%

Petrogenesis of Archean PGM-bearing chromitites and associated ultramafic–mafic–anorthositic rocks from the Guelb el Azib layered complex (West African craton, Mauritania)

Berger¹,

Diot²,

Lô³

et al. 2013

Precambrian Research

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a b s t r a c tThe Archean Guelb el Azib layered complex (GAC) in the West African craton of Mauritania is composed of an association of serpentinites, chromitites, amphibolites and anorthosites with few fine-grained amphibolite dykes. The complex forms tectonic slices in 2.9-3.5 Ga TTG gneiss terrains in close association with supracrustal rocks (BIFs, impure marbles, amphibolites). It was affected by a main granulite-facies grade metamorphism (up to 900• C at 5-6 kbar) with subsequent retrogression in amphibolite and greenschist facies conditions.The preserved igneous macrostructures, the mineral compositions and the nature of relic magmatic assemblages have been used to constrain the composition of the parental melts and the conditions of crystallization. According to petrological observations and to comparison with experimental data, the formation of the complex can be explained by fractionation of a slightly hydrous high-alumina basaltic melt at low pressure. The early fractionation of olivine and the absence of massive clinopyroxene fractionation before plagioclase saturation led to crystallization of highly calcic plagioclase with Fe-, Al-rich but Cr-poor chromite from a hydrous tholeiitic parental magma, similar to worldwide Archean tholeiites.The complex shares many similarities with Archean anorthosite layered complexes, possibly formed in a supra-subduction zone environment according to results obtained on similar 2.9-3.0 Ga complexes from Greenland and India (namely Fiskenaesset and Sittampundi). Three phases of PGE mineralization affected the GAC chromitites: (i) igneous crystallization of laurite; (ii) formation of late magmatic IPGE sulpho-arsenides (irarsite-hollingworthite) and (iii) hydrothermal Pt-Pd mineralization represented by sperrylite and rustenburgite.

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Section: Pgm Crystallization and Pge Fractionationsupporting

confidence: 56%

Petrogenesis of Archean PGM-bearing chromitites and associated ultramafic–mafic–anorthositic rocks from the Guelb el Azib layered complex (West African craton, Mauritania)

Berger¹,

Diot²,

Lô³

et al. 2013

Precambrian Research

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“…Cr/(Cr + Al) or Mg/(Mg + Fe 2+ )), which has been cited as support for in situ growth and settling of chromite from the magma chamber (e.g. Wilson 1982;Campbell and Murck 1993;Naldrett et al 2012). In other cases, clear stratigraphic trends in the composition of chromite and the surrounding cumulate minerals are not observed (Mondal and Mathez 2007).…”

Section: Formation Of Chromitite Layersmentioning

confidence: 92%

“…The apparent excess volume of chromite requires involvement of much larger magmatic systems than is usually considered, with influx of partially crystallized, chromite-bearing magmas from deeper staging chambers (e.g. Eales and Costin 2012) or removal of large volumes of residual liquids from the top of the chamber (Naldrett et al 2012). However, neither of these scenarios alone can fully explain the formation of stratigraphically coherent cumulate layers consisting mostly of chromite (Cawthorn 2005;Cawthorn et al 2005).…”

Section: Formation Of Chromitite Layersmentioning

confidence: 99%

“…In particular, the length-scales and mechanisms of chromite transport and remobilization prior to solidification remain debated (in-situ settling, with or without subsequent thickening, or long distance transport of chromite-laden slurries; e.g. Voordouw et al 2009;Naldrett et al 2012). All these suggest that chromitite formation needs not be restricted to a single mechanism; it is conceivable, and even likely, that a range of different processes are conducive to forming chromitite.…”

Section: Formation Of Chromitite Layersmentioning

confidence: 99%

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Igneous Layering in Basaltic Magma Chambers

et al. 2015

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PrefaceLayered intrusions have received continuous interest since the publication of the treatise on 'Layered Igneous Rocks' by Lawrence Wager and Malcolm Brown, updated in books edited by Ian Parsons in 1987 and Grant Cawthorn in 1996. The study of these fossilized magma chambers keep inspiring a number of scientists with a range of interests including petrology and igneous differentiation, geochronology, geochemistry, mineralogy, rock textures and fabric, fluid dynamics, and ore deposits. The goal of this book is to further our understanding of magma chamber processes and crystal-liquid relationship during magma cooling magma. Physical and chemical processes are now better quantified thanks to the development analytical and computing tools such as compositional mapping, 3D X-ray computed tomography, in situ analyses for trace elements and isotopes, development of new experimental facilities, and progress in instrument sensitivity.The book is subdivided into two parts. The first includes reviews and new views on chronological, textural, mineralogical, geochemical, and magnetic characteristics of layered igneous rocks. The second part reviews recent progress in the study of layered intrusions. A newcomer on the layered intrusions scene is the Panzhihua intrusion (SW China) that has been intensively studied recently. Reviews of recent findings for Sept Iles, Bushveld, Kiglapait, Ilímaussaq, and layered rocks in ophiolites are also presented. Interest in layered intrusions is also driven by their natural resources. Many intrusions host world-class ore bodies of chromium, platinum group elements (PGE), vanadium, titanium and phosphorous. Ore-forming processes and important deposits associated with layered intrusions are described and their origin is discussed.The objective of this book is to outline the most recent ideas and challenges in the study of layered igneous bodies. It has also the purpose to aid in teaching, and to encourage new studies to tackle major issues in the understanding of magma chamber processes and associated ore-forming processes.The book has benefited from detailed comments by a many reviewers, who are greatly acknowledged:

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“…Current theories for the formation of the Cr ores call on contamination of the magma with siliceous wall rocks, or magma mixing, which produce hybrid magmas that crystallise chromite alone, combined with crystal sorting during flow into the magma chamber to concentrate the chromite in layers (Maier et al, 2013). The PGE-and V-rich magnetite deposits also form through accumulation of magmatic phases, with PGE partitioning mainly into sulphide phases; the exact mechanisms of formation of PGE ores is complex and subject to much discussion (e.g., Naldrett et al, 2011).…”

Section: Orthomagmatic Ore Depositsmentioning

confidence: 99%