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Article: Mineral chemistry of chromite from the Permian Jinbaoshan Pt-Pd-sulphide-bearing ultramafic intrusion in SW China with petrogenetic implications

TitleMineral chemistry of chromite from the Permian Jinbaoshan Pt-Pd-sulphide-bearing ultramafic intrusion in SW China with petrogenetic implications
Authors
KeywordsChromite
Jinbaoshan Ultramafic Intrusion
Pt-Pd-Sulphide Deposit
Sw China
Yunnan
Issue Date2005
PublisherElsevier BV. The Journal's web site is located at http://www.elsevier.com/locate/lithos
Citation
Lithos, 2005, v. 83 n. 1-2, p. 47-66 How to Cite?
AbstractThe Jinbaoshan ultramafic intrusion is a member of the late-middle Permian (260 Ma) Emeishan Large Igneous Province in Yunnan Province, SW China and hosts an economical Pt-Pd-sulphide deposit. The intrusion consists mainly of wehrlite (92 vol.%), with minor olivine clinopyroxenite and clinopyroxenite (8 vol.%). The ores, defined as rocks having >0.5 ppm Pt and Pd, contain abundant chromite (up to 20 vol.%) and minor sulphide (<3 vol.%). Sulphide aggregates occur along the silicate grain boundaries and thus clearly crystallized after olivine and chromite. Olivine occurs as euhedral, subhedral or rounded crystals, and varies from 0.3 to 4 mm in size. The olivine has almost constant Fo contents (83 wt.%), and variable Ni contents (0.13 to 0.34 wt.%). There are two types of chromite: (1) relatively homogeneous chromite, as euhedral inclusion in olivine; and (2) zoned chromite as interstitial phase between silicate minerals, and occasionally, as inclusion in olivine pseudomorphs. The zoned chromite can be further divided into type 2a with magnetite rim and type 2b without magnetite rim. Primary chromites, including type 1 chromites and the core of type 2a chromites, have relatively high Cr#'s (51 to 70), a relatively wide range of Mg#'s (13 to 57), variable TiO2 (1.55 to 9.39 wt.%) and low Ni (NiO≤0.35 wt.%) and Zn (ZnO≤0.72 wt.%). Type 2 chromites formed during serpentinization and were chemically modified toward magnetite rim. The modified chromites have generally lower Cr2O3 and Al2O3 and higher FeOt (total Fe) than primary chromites. The high Cr contents of the primary chromites and the high MgO/FeO molar ratio (1.47) of the calculated melt composition in equilibrium with olivine in the Jinbaoshan intrusion demonstrated that the Jinbaoshan chromites most likely crystallized from a low-Ti and high-Mg tholeiitic magma derived from a mantle plume in an intra-continental setting. The relatively large amount of chromite in the ores may indicate a direct connection between the chromite crystallization and the ore formation. We infer that the parental magma was S-undersaturated, and remained rich in highly siderophile elements such as Pt and Pd. The parental magma may have experienced early olivine crystallization such that Ir and Os were depleted. This magma intruded the Devonian limestone, sandstone, and slate. Assimilation of the country rocks induced temporary supersaturation of chromites and also triggered S-saturation in the magma. The Jinbaoshan intrusion represents a magma conduit in which magmas deposited excess ultramafic components with Pt-Pd-sulphide enriched horizons due to delayed S-saturation during crystallization. © 2005 Elsevier B.V. All rights reserved.
Persistent Identifierhttp://hdl.handle.net/10722/151153
ISSN
2015 Impact Factor: 3.723
2015 SCImago Journal Rankings: 2.920
ISI Accession Number ID
References

 

DC FieldValueLanguage
dc.contributor.authorWang, CYen_US
dc.contributor.authorZhou, MFen_US
dc.contributor.authorZhao, Den_US
dc.date.accessioned2012-06-26T06:17:43Z-
dc.date.available2012-06-26T06:17:43Z-
dc.date.issued2005en_US
dc.identifier.citationLithos, 2005, v. 83 n. 1-2, p. 47-66en_US
dc.identifier.issn0024-4937en_US
dc.identifier.urihttp://hdl.handle.net/10722/151153-
dc.description.abstractThe Jinbaoshan ultramafic intrusion is a member of the late-middle Permian (260 Ma) Emeishan Large Igneous Province in Yunnan Province, SW China and hosts an economical Pt-Pd-sulphide deposit. The intrusion consists mainly of wehrlite (92 vol.%), with minor olivine clinopyroxenite and clinopyroxenite (8 vol.%). The ores, defined as rocks having >0.5 ppm Pt and Pd, contain abundant chromite (up to 20 vol.%) and minor sulphide (<3 vol.%). Sulphide aggregates occur along the silicate grain boundaries and thus clearly crystallized after olivine and chromite. Olivine occurs as euhedral, subhedral or rounded crystals, and varies from 0.3 to 4 mm in size. The olivine has almost constant Fo contents (83 wt.%), and variable Ni contents (0.13 to 0.34 wt.%). There are two types of chromite: (1) relatively homogeneous chromite, as euhedral inclusion in olivine; and (2) zoned chromite as interstitial phase between silicate minerals, and occasionally, as inclusion in olivine pseudomorphs. The zoned chromite can be further divided into type 2a with magnetite rim and type 2b without magnetite rim. Primary chromites, including type 1 chromites and the core of type 2a chromites, have relatively high Cr#'s (51 to 70), a relatively wide range of Mg#'s (13 to 57), variable TiO2 (1.55 to 9.39 wt.%) and low Ni (NiO≤0.35 wt.%) and Zn (ZnO≤0.72 wt.%). Type 2 chromites formed during serpentinization and were chemically modified toward magnetite rim. The modified chromites have generally lower Cr2O3 and Al2O3 and higher FeOt (total Fe) than primary chromites. The high Cr contents of the primary chromites and the high MgO/FeO molar ratio (1.47) of the calculated melt composition in equilibrium with olivine in the Jinbaoshan intrusion demonstrated that the Jinbaoshan chromites most likely crystallized from a low-Ti and high-Mg tholeiitic magma derived from a mantle plume in an intra-continental setting. The relatively large amount of chromite in the ores may indicate a direct connection between the chromite crystallization and the ore formation. We infer that the parental magma was S-undersaturated, and remained rich in highly siderophile elements such as Pt and Pd. The parental magma may have experienced early olivine crystallization such that Ir and Os were depleted. This magma intruded the Devonian limestone, sandstone, and slate. Assimilation of the country rocks induced temporary supersaturation of chromites and also triggered S-saturation in the magma. The Jinbaoshan intrusion represents a magma conduit in which magmas deposited excess ultramafic components with Pt-Pd-sulphide enriched horizons due to delayed S-saturation during crystallization. © 2005 Elsevier B.V. All rights reserved.en_US
dc.languageengen_US
dc.publisherElsevier BV. The Journal's web site is located at http://www.elsevier.com/locate/lithosen_US
dc.relation.ispartofLithosen_US
dc.rightsLithos. Copyright © Elsevier BV.-
dc.subjectChromiteen_US
dc.subjectJinbaoshan Ultramafic Intrusionen_US
dc.subjectPt-Pd-Sulphide Depositen_US
dc.subjectSw Chinaen_US
dc.subjectYunnanen_US
dc.titleMineral chemistry of chromite from the Permian Jinbaoshan Pt-Pd-sulphide-bearing ultramafic intrusion in SW China with petrogenetic implicationsen_US
dc.typeArticleen_US
dc.identifier.emailZhou, MF: mfzhou@hkucc.hku.hken_US
dc.identifier.authorityZhou, MF=rp00844en_US
dc.description.naturelink_to_subscribed_fulltexten_US
dc.identifier.doi10.1016/j.lithos.2005.01.003en_US
dc.identifier.scopuseid_2-s2.0-20544445124en_US
dc.identifier.hkuros123396-
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-20544445124&selection=ref&src=s&origin=recordpageen_US
dc.identifier.volume83en_US
dc.identifier.issue1-2en_US
dc.identifier.spage47en_US
dc.identifier.epage66en_US
dc.identifier.isiWOS:000230333500003-
dc.publisher.placeNetherlandsen_US
dc.identifier.scopusauthoridWang, CY=34976092700en_US
dc.identifier.scopusauthoridZhou, MF=7403506005en_US
dc.identifier.scopusauthoridZhao, D=36509465000en_US
dc.customcontrol.immutablesml 130308-

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