Variability of magmatic sulphide compositions at the Kabanga nickel prospect, Tanzania
Identifieur interne : 001C72 ( Istex/Corpus ); précédent : 001C71; suivant : 001C73Variability of magmatic sulphide compositions at the Kabanga nickel prospect, Tanzania
Auteurs : David M. Evans ; Leopold Byemelwa ; Jon GilliganSource :
- Journal of African Earth Sciences [ 1464-343X ] ; 1999.
Abstract
Magmatic NiCu sulphide deposits are often geometrically and compositionally complex, and it is important to understand this complexity at an early stage of their economic evaluation. The Kabanga Ni prospect in Tanzania consists of two deposits associated with cumulate-textured ultramafic intrusions. The Ni occurs in a typical magmatic sulphide assemblage of pyrrhotite-pentlanite-chalcopyrite-pyrite and magnetite, with net-textured, disseminated and massive textures. The sulphides occur as layers within, and at the lower boundary of small, elongate transgressive olivine-pyroxene cumulate bodies, which were derived from a high Mg basaltic magma. Different layers within the intrusions have distinct sulphide geochemistry, with Ni tenor varying from 0.5 to over 20% in 100% sulphide. Generally, the lowermost layers have higher metal tenors, higher Ni Cu, and lower S Se ratios than the upper ones, suggesting a temporal evolution of sulphide chemistry. These trends suggest that the earliest sulphide melts separated from a primitive basaltic melt with a relatively high ratio of silicate to sulphide melt (R factor). Later sulphides separated from a more fractionated silicate melt with a lower R factor, implying an increasing contribution of sedimentary sulphide by wall rock assimilation during fractionation in a lower magma chamber.
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DOI: 10.1016/S0899-5362(99)00101-3
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Evans</name><affiliation><mods:affiliation>BHP Minerals International Exploration Inc., PO Box 60566, Dar es Salaam, Tanzania</mods:affiliation></affiliation><affiliation><mods:affiliation>E-mail: evans_dave_m@hotmail.com</mods:affiliation></affiliation></author><author><name sortKey="Byemelwa, Leopold" sort="Byemelwa, Leopold" uniqKey="Byemelwa L" first="Leopold" last="Byemelwa">Leopold Byemelwa</name><affiliation><mods:affiliation>BHP Minerals International Exploration Inc., PO Box 60566, Dar es Salaam, Tanzania</mods:affiliation></affiliation></author><author><name sortKey="Gilligan, Jon" sort="Gilligan, Jon" uniqKey="Gilligan J" first="Jon" last="Gilligan">Jon Gilligan</name><affiliation><mods:affiliation>BHP Minerals International Exploration Inc., PO Box 60566, Dar es Salaam, Tanzania</mods:affiliation></affiliation></author></titleStmt><publicationStmt><idno type="wicri:source">ISTEX</idno><idno type="RBID">ISTEX:33EBE26348E145A930DC868A17DD357B6898607B</idno><date when="1999" year="1999">1999</date><idno type="doi">10.1016/S0899-5362(99)00101-3</idno><idno type="url">https://api.istex.fr/document/33EBE26348E145A930DC868A17DD357B6898607B/fulltext/pdf</idno><idno type="wicri:Area/Istex/Corpus">001C72</idno><idno type="wicri:explorRef" wicri:stream="Istex" wicri:step="Corpus" wicri:corpus="ISTEX">001C72</idno></publicationStmt><sourceDesc><biblStruct><analytic><title level="a">Variability of magmatic sulphide compositions at the Kabanga nickel prospect, Tanzania</title><author><name sortKey="Evans, David M" sort="Evans, David M" uniqKey="Evans D" first="David M." last="Evans">David M. Evans</name><affiliation><mods:affiliation>BHP Minerals International Exploration Inc., PO Box 60566, Dar es Salaam, Tanzania</mods:affiliation></affiliation><affiliation><mods:affiliation>E-mail: evans_dave_m@hotmail.com</mods:affiliation></affiliation></author><author><name sortKey="Byemelwa, Leopold" sort="Byemelwa, Leopold" uniqKey="Byemelwa L" first="Leopold" last="Byemelwa">Leopold Byemelwa</name><affiliation><mods:affiliation>BHP Minerals International Exploration Inc., PO Box 60566, Dar es Salaam, Tanzania</mods:affiliation></affiliation></author><author><name sortKey="Gilligan, Jon" sort="Gilligan, Jon" uniqKey="Gilligan J" first="Jon" last="Gilligan">Jon Gilligan</name><affiliation><mods:affiliation>BHP Minerals International Exploration Inc., PO Box 60566, Dar es Salaam, Tanzania</mods:affiliation></affiliation></author></analytic><monogr></monogr><series><title level="j">Journal of African Earth Sciences</title><title level="j" type="abbrev">AESOLD</title><idno type="ISSN">1464-343X</idno><imprint><publisher>ELSEVIER</publisher><date type="published" when="1999">1999</date><biblScope unit="volume">29</biblScope><biblScope unit="issue">2</biblScope><biblScope unit="page" from="329">329</biblScope><biblScope unit="page" to="351">351</biblScope></imprint><idno type="ISSN">1464-343X</idno></series><idno type="istex">33EBE26348E145A930DC868A17DD357B6898607B</idno><idno type="DOI">10.1016/S0899-5362(99)00101-3</idno><idno type="PII">S0899-5362(99)00101-3</idno></biblStruct></sourceDesc><seriesStmt><idno type="ISSN">1464-343X</idno></seriesStmt></fileDesc><profileDesc><textClass></textClass><langUsage><language ident="en">en</language></langUsage></profileDesc></teiHeader><front><div type="abstract" xml:lang="en">Magmatic NiCu sulphide deposits are often geometrically and compositionally complex, and it is important to understand this complexity at an early stage of their economic evaluation. The Kabanga Ni prospect in Tanzania consists of two deposits associated with cumulate-textured ultramafic intrusions. The Ni occurs in a typical magmatic sulphide assemblage of pyrrhotite-pentlanite-chalcopyrite-pyrite and magnetite, with net-textured, disseminated and massive textures. The sulphides occur as layers within, and at the lower boundary of small, elongate transgressive olivine-pyroxene cumulate bodies, which were derived from a high Mg basaltic magma. Different layers within the intrusions have distinct sulphide geochemistry, with Ni tenor varying from 0.5 to over 20% in 100% sulphide. Generally, the lowermost layers have higher metal tenors, higher Ni Cu, and lower S Se ratios than the upper ones, suggesting a temporal evolution of sulphide chemistry. These trends suggest that the earliest sulphide melts separated from a primitive basaltic melt with a relatively high ratio of silicate to sulphide melt (R factor). Later sulphides separated from a more fractionated silicate melt with a lower R factor, implying an increasing contribution of sedimentary sulphide by wall rock assimilation during fractionation in a lower magma chamber.</div></front></TEI><istex><corpusName>elsevier</corpusName><author><json:item><name>David M. Evans</name><affiliations><json:string>BHP Minerals International Exploration Inc., PO Box 60566, Dar es Salaam, Tanzania</json:string><json:string>E-mail: evans_dave_m@hotmail.com</json:string></affiliations></json:item><json:item><name>Leopold Byemelwa</name><affiliations><json:string>BHP Minerals International Exploration Inc., PO Box 60566, Dar es Salaam, Tanzania</json:string></affiliations></json:item><json:item><name>Jon Gilligan</name><affiliations><json:string>BHP Minerals International Exploration Inc., PO Box 60566, Dar es Salaam, Tanzania</json:string></affiliations></json:item></author><language><json:string>eng</json:string></language><originalGenre><json:string>Full-length article</json:string></originalGenre><abstract>Magmatic NiCu sulphide deposits are often geometrically and compositionally complex, and it is important to understand this complexity at an early stage of their economic evaluation. The Kabanga Ni prospect in Tanzania consists of two deposits associated with cumulate-textured ultramafic intrusions. The Ni occurs in a typical magmatic sulphide assemblage of pyrrhotite-pentlanite-chalcopyrite-pyrite and magnetite, with net-textured, disseminated and massive textures. The sulphides occur as layers within, and at the lower boundary of small, elongate transgressive olivine-pyroxene cumulate bodies, which were derived from a high Mg basaltic magma. Different layers within the intrusions have distinct sulphide geochemistry, with Ni tenor varying from 0.5 to over 20% in 100% sulphide. Generally, the lowermost layers have higher metal tenors, higher Ni Cu, and lower S Se ratios than the upper ones, suggesting a temporal evolution of sulphide chemistry. These trends suggest that the earliest sulphide melts separated from a primitive basaltic melt with a relatively high ratio of silicate to sulphide melt (R factor). 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The Kabanga Ni prospect in Tanzania consists of two deposits associated with cumulate-textured ultramafic intrusions. The Ni occurs in a typical magmatic sulphide assemblage of pyrrhotite-pentlanite-chalcopyrite-pyrite and magnetite, with net-textured, disseminated and massive textures. The sulphides occur as layers within, and at the lower boundary of small, elongate transgressive olivine-pyroxene cumulate bodies, which were derived from a high Mg basaltic magma. Different layers within the intrusions have distinct sulphide geochemistry, with Ni tenor varying from 0.5 to over 20% in 100% sulphide. Generally, the lowermost layers have higher metal tenors, higher Ni Cu, and lower S Se ratios than the upper ones, suggesting a temporal evolution of sulphide chemistry. These trends suggest that the earliest sulphide melts separated from a primitive basaltic melt with a relatively high ratio of silicate to sulphide melt (R factor). Later sulphides separated from a more fractionated silicate melt with a lower R factor, implying an increasing contribution of sedimentary sulphide by wall rock assimilation during fractionation in a lower magma chamber.</p></abstract><abstract xml:lang="fr"><p>Résumé: Les gisements magmatiques de sulfures de NiCu montrent souvent une géométrie et une composition complexes et il est important de comprendre cette complexité à un stade précoce de leur évaluation en termes de rentabilité. Le prospect de Ni de Kabanga consiste en deux gisements associésà des intrusion ultramafiques à textures de cumulats. Le Ni se présente dans un assemblage magmatique typique de pyrrhotite-pentlandite-chalcopyrite-pyrite-magnétite, avec des textures en réseau, disséminées et massives. Les sulfures forment des couches à l'intérieur et à la limite inférieure de petits corps cumulatifs allongés de cumulats transgressifs à olivine-pyroxène, dérivés d'un magma basaltique riche en Mg. Les différentes couches dans les intrusions ont des sulfures de compositions chimiques distinctes, avec des teneurs en Ni variant de 0,5 à plus de 20% and 100% de sulfures. En général, les couches inférieures ont de plus fortes teneurs en métal, un rapport Ni Cu plus élevé et un rapport S Se plus bas que les couches supérieures, ce qui suggére une évolution dans le temps du chimisme des sulfures. Les tendances évolutives suggèrent que les liquides sulfureux les plus précoces se sont séparés d'un liquide basaltique primitif ayant un rapport liquide silicaté/liquide sulfureux (facteur R) relativement élevé. Les sulfures plus tardifs se sont séparés d'un liquide silicaté plus évolué avec un facteur R plus bas, ce qui implique la contribution croissante de sulfures sédimentaires par assimilation de l'encaissant, pendant le fractionnement de la chambre magmatique inférieure.</p></abstract></profileDesc><revisionDesc><change when="1998-04-21">Modified</change><change when="1999">Published</change></revisionDesc></teiHeader></istex:fulltextTEI><json:item><original>false</original><mimetype>text/plain</mimetype><extension>txt</extension><uri>https://api.istex.fr/document/33EBE26348E145A930DC868A17DD357B6898607B/fulltext/txt</uri></json:item></fulltext><metadata><istex:metadataXml wicri:clean="Elsevier, elements deleted: tail"><istex:xmlDeclaration>version="1.0" encoding="utf-8"</istex:xmlDeclaration><istex:docType PUBLIC="-//ES//DTD journal article DTD version 4.5.2//EN//XML" URI="art452.dtd" name="istex:docType"></istex:docType><istex:document><converted-article version="4.5.2" docsubtype="fla"><item-info><jid>AES</jid><aid>99001013</aid><ce:pii>S0899-5362(99)00101-3</ce:pii><ce:doi>10.1016/S0899-5362(99)00101-3</ce:doi><ce:copyright type="unknown" year="1999"></ce:copyright></item-info><head><ce:title>Variability of magmatic sulphide compositions at the Kabanga nickel prospect, Tanzania</ce:title><ce:author-group><ce:author><ce:given-name>David M.</ce:given-name><ce:surname>Evans</ce:surname><ce:cross-ref refid="COR1"><ce:sup>∗</ce:sup></ce:cross-ref><ce:cross-ref refid="FN1"><ce:sup>1</ce:sup></ce:cross-ref><ce:e-address>evans_dave_m@hotmail.com</ce:e-address></ce:author><ce:author><ce:given-name>Leopold</ce:given-name><ce:surname>Byemelwa</ce:surname><ce:cross-ref refid="AFF1"><ce:sup>2</ce:sup></ce:cross-ref></ce:author><ce:author><ce:given-name>Jon</ce:given-name><ce:surname>Gilligan</ce:surname><ce:cross-ref refid="AFF1"><ce:sup>2</ce:sup></ce:cross-ref></ce:author><ce:affiliation id="AFF1"><ce:label>a</ce:label><ce:textfn>BHP Minerals International Exploration Inc., PO Box 60566, Dar es Salaam, Tanzania</ce:textfn></ce:affiliation><ce:correspondence id="COR1"><ce:label>∗</ce:label><ce:text>Corresponding author.</ce:text></ce:correspondence><ce:footnote id="FN1"><ce:label>1</ce:label><ce:note-para>Present address: Montrose, Llanddeiniol, Llanrhystud, SY23 5AN, UK</ce:note-para></ce:footnote></ce:author-group><ce:date-received day="30" month="9" year="1997"></ce:date-received><ce:date-revised day="21" month="4" year="1998"></ce:date-revised><ce:date-accepted day="30" month="10" year="1998"></ce:date-accepted><ce:abstract><ce:section-title>Abstract</ce:section-title><ce:abstract-sec><ce:simple-para>Magmatic NiCu sulphide deposits are often geometrically and compositionally complex, and it is important to understand this complexity at an early stage of their economic evaluation. The Kabanga Ni prospect in Tanzania consists of two deposits associated with cumulate-textured ultramafic intrusions. The Ni occurs in a typical magmatic sulphide assemblage of pyrrhotite-pentlanite-chalcopyrite-pyrite and magnetite, with net-textured, disseminated and massive textures. The sulphides occur as layers within, and at the lower boundary of small, elongate transgressive olivine-pyroxene cumulate bodies, which were derived from a high Mg basaltic magma. Different layers within the intrusions have distinct sulphide geochemistry, with Ni tenor varying from 0.5 to over 20% in 100% sulphide. Generally, the lowermost layers have higher metal tenors, higher <math altimg="si1.gif"><rm><fr shape="sol"><nu>Ni</nu><de>Cu</de></fr></rm></math>, and lower <math altimg="si2.gif"><rm><fr shape="sol"><nu>S</nu><de>Se</de></fr></rm></math> ratios than the upper ones, suggesting a temporal evolution of sulphide chemistry. These trends suggest that the earliest sulphide melts separated from a primitive basaltic melt with a relatively high ratio of silicate to sulphide melt (<ce:italic>R</ce:italic> factor). Later sulphides separated from a more fractionated silicate melt with a lower <ce:italic>R</ce:italic> factor, implying an increasing contribution of sedimentary sulphide by wall rock assimilation during fractionation in a lower magma chamber.</ce:simple-para></ce:abstract-sec></ce:abstract><ce:abstract xml:lang="fr"><ce:section-title>Résumé</ce:section-title><ce:abstract-sec><ce:simple-para>Les gisements magmatiques de sulfures de NiCu montrent souvent une géométrie et une composition complexes et il est important de comprendre cette complexité à un stade précoce de leur évaluation en termes de rentabilité. Le prospect de Ni de Kabanga consiste en deux gisements associésà des intrusion ultramafiques à textures de cumulats. Le Ni se présente dans un assemblage magmatique typique de pyrrhotite-pentlandite-chalcopyrite-pyrite-magnétite, avec des textures en réseau, disséminées et massives. Les sulfures forment des couches à l'intérieur et à la limite inférieure de petits corps cumulatifs allongés de cumulats transgressifs à olivine-pyroxène, dérivés d'un magma basaltique riche en Mg. Les différentes couches dans les intrusions ont des sulfures de compositions chimiques distinctes, avec des teneurs en Ni variant de 0,5 à plus de 20% and 100% de sulfures. En général, les couches inférieures ont de plus fortes teneurs en métal, un rapport <math altimg="si3.gif"><rm><fr shape="sol"><nu>Ni</nu><de>Cu</de></fr></rm></math> plus élevé et un rapport <math altimg="si4.gif"><rm><fr shape="sol"><nu>S</nu><de>Se</de></fr></rm></math> plus bas que les couches supérieures, ce qui suggére une évolution dans le temps du chimisme des sulfures. Les tendances évolutives suggèrent que les liquides sulfureux les plus précoces se sont séparés d'un liquide basaltique primitif ayant un rapport liquide silicaté/liquide sulfureux (facteur <ce:italic>R</ce:italic>) relativement élevé. Les sulfures plus tardifs se sont séparés d'un liquide silicaté plus évolué avec un facteur <ce:italic>R</ce:italic> plus bas, ce qui implique la contribution croissante de sulfures sédimentaires par assimilation de l'encaissant, pendant le fractionnement de la chambre magmatique inférieure.</ce:simple-para></ce:abstract-sec></ce:abstract></head></converted-article></istex:document></istex:metadataXml><mods version="3.6"><titleInfo><title>Variability of magmatic sulphide compositions at the Kabanga nickel prospect, Tanzania</title></titleInfo><titleInfo type="alternative" contentType="CDATA"><title>Variability of magmatic sulphide compositions at the Kabanga nickel prospect, Tanzania</title></titleInfo><name type="personal"><namePart type="given">David M.</namePart><namePart type="family">Evans</namePart><affiliation>BHP Minerals International Exploration Inc., PO Box 60566, Dar es Salaam, Tanzania</affiliation><affiliation>E-mail: evans_dave_m@hotmail.com</affiliation><description>Corresponding author.</description><description>Present address: Montrose, Llanddeiniol, Llanrhystud, SY23 5AN, UK</description><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">Leopold</namePart><namePart type="family">Byemelwa</namePart><affiliation>BHP Minerals International Exploration Inc., PO Box 60566, Dar es Salaam, Tanzania</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">Jon</namePart><namePart type="family">Gilligan</namePart><affiliation>BHP Minerals International Exploration Inc., PO Box 60566, Dar es Salaam, Tanzania</affiliation><role><roleTerm type="text">author</roleTerm></role></name><typeOfResource>text</typeOfResource><genre type="research-article" displayLabel="Full-length article"></genre><originInfo><publisher>ELSEVIER</publisher><dateIssued encoding="w3cdtf">1999</dateIssued><dateModified encoding="w3cdtf">1998-04-21</dateModified><copyrightDate encoding="w3cdtf">1999</copyrightDate></originInfo><language><languageTerm type="code" authority="iso639-2b">eng</languageTerm><languageTerm type="code" authority="rfc3066">en</languageTerm></language><physicalDescription><internetMediaType>text/html</internetMediaType></physicalDescription><abstract lang="en">Magmatic NiCu sulphide deposits are often geometrically and compositionally complex, and it is important to understand this complexity at an early stage of their economic evaluation. The Kabanga Ni prospect in Tanzania consists of two deposits associated with cumulate-textured ultramafic intrusions. The Ni occurs in a typical magmatic sulphide assemblage of pyrrhotite-pentlanite-chalcopyrite-pyrite and magnetite, with net-textured, disseminated and massive textures. The sulphides occur as layers within, and at the lower boundary of small, elongate transgressive olivine-pyroxene cumulate bodies, which were derived from a high Mg basaltic magma. Different layers within the intrusions have distinct sulphide geochemistry, with Ni tenor varying from 0.5 to over 20% in 100% sulphide. Generally, the lowermost layers have higher metal tenors, higher Ni Cu, and lower S Se ratios than the upper ones, suggesting a temporal evolution of sulphide chemistry. These trends suggest that the earliest sulphide melts separated from a primitive basaltic melt with a relatively high ratio of silicate to sulphide melt (R factor). Later sulphides separated from a more fractionated silicate melt with a lower R factor, implying an increasing contribution of sedimentary sulphide by wall rock assimilation during fractionation in a lower magma chamber.</abstract><abstract lang="fr">Résumé: Les gisements magmatiques de sulfures de NiCu montrent souvent une géométrie et une composition complexes et il est important de comprendre cette complexité à un stade précoce de leur évaluation en termes de rentabilité. Le prospect de Ni de Kabanga consiste en deux gisements associésà des intrusion ultramafiques à textures de cumulats. Le Ni se présente dans un assemblage magmatique typique de pyrrhotite-pentlandite-chalcopyrite-pyrite-magnétite, avec des textures en réseau, disséminées et massives. Les sulfures forment des couches à l'intérieur et à la limite inférieure de petits corps cumulatifs allongés de cumulats transgressifs à olivine-pyroxène, dérivés d'un magma basaltique riche en Mg. Les différentes couches dans les intrusions ont des sulfures de compositions chimiques distinctes, avec des teneurs en Ni variant de 0,5 à plus de 20% and 100% de sulfures. En général, les couches inférieures ont de plus fortes teneurs en métal, un rapport Ni Cu plus élevé et un rapport S Se plus bas que les couches supérieures, ce qui suggére une évolution dans le temps du chimisme des sulfures. Les tendances évolutives suggèrent que les liquides sulfureux les plus précoces se sont séparés d'un liquide basaltique primitif ayant un rapport liquide silicaté/liquide sulfureux (facteur R) relativement élevé. Les sulfures plus tardifs se sont séparés d'un liquide silicaté plus évolué avec un facteur R plus bas, ce qui implique la contribution croissante de sulfures sédimentaires par assimilation de l'encaissant, pendant le fractionnement de la chambre magmatique inférieure.</abstract><relatedItem type="host"><titleInfo><title>Journal of African Earth Sciences</title></titleInfo><titleInfo type="abbreviated"><title>AESOLD</title></titleInfo><genre type="journal">journal</genre><originInfo><dateIssued encoding="w3cdtf">199908</dateIssued></originInfo><identifier type="ISSN">1464-343X</identifier><identifier type="PII">S0899-5362(00)X0035-8</identifier><part><date>199908</date><detail type="issue"><title>Geology and Mineral Resources East Africa</title></detail><detail type="volume"><number>29</number><caption>vol.</caption></detail><detail type="issue"><number>2</number><caption>no.</caption></detail><extent unit="issue pages"><start>281</start><end>428</end></extent><extent unit="pages"><start>329</start><end>351</end></extent></part></relatedItem><identifier type="istex">33EBE26348E145A930DC868A17DD357B6898607B</identifier><identifier type="DOI">10.1016/S0899-5362(99)00101-3</identifier><identifier type="PII">S0899-5362(99)00101-3</identifier><recordInfo><recordContentSource>ELSEVIER</recordContentSource></recordInfo></mods></metadata></istex></record>Pour manipuler ce document sous Unix (Dilib)
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