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Article: Selective crustal contamination and decoupling of lithophile and chalcophile element isotopes in sulfide-bearing mafic intrusions: An example from the Jingbulake Intrusion, Xinjiang, NW China

TitleSelective crustal contamination and decoupling of lithophile and chalcophile element isotopes in sulfide-bearing mafic intrusions: An example from the Jingbulake Intrusion, Xinjiang, NW China
Authors
KeywordsIsotope decoupling
Jingbulake
Mafic intrusion
Re-Os
Selective crustal contamination
Sr-Nd
Issue Date2012
PublisherElsevier BV. The Journal's web site is located at http://www.elsevier.com/locate/chemgeo
Citation
Chemical Geology, 2012, v. 302-303, p. 106-118 How to Cite?
AbstractThe Jingbulake mafic-ultramafic intrusion in the South Tianshan orogenic belt, Xinjiang, NW China, is a zoned intrusive body composed of gabbro-diorite, olivine gabbro and wehrlite, locally intruded by pyroxenite, within a major W-E structure. Both olivine gabbro and wehrlite contain disseminated Ni-Cu sulfides, whereas pyroxenite hosts an ore body containing massive, net-textured and disseminated sulfide ores. Both silicate rocks and sulfide ores from the Jingbulake intrusion have low Pd/Ir ratios (10-63). The silicate rocks contain Ni-poor olivine (generally <0.1wt.% NiO) and have low Pt (0.48-2.3ppb) and Pd (0.52-4.8ppb) contents and high Cu/Pd ratios (128,000 to 200,000), indicative of significant chalcophile element depletion. The disseminated sulfide ores from No. 1 and 2 mineralization zones have 0.28-1.5ppb Pt and 2.8-8.1ppb Pd, and Cu/Pd ratios (200,000-300,000). The disseminated and net-textured sulfide ores from No. 8 mineralization zone have Pt (39-315ppb) and Pd (76-1100ppb), and intermediate to high Cu/Pd ratios (6850-138,000). The variably high Cu/Pd ratios indicate that the parental magma may have reached earlier sulfide saturation and removal. The low Os contents (0.0146 to 0.276ppb) and high Re/Os (29 to 292) and 187Os/ 188Os(i) ratios (0.277 to 0.916) of the silicate rocks are consistent with a major contribution of Os from crustal materials. On the other hand, the net-textured sulfide ores from No. 8 mineralization zone have high Os contents (15.1 to 32.6ppb), low Re/Os (2.0 to 2.3) and low 187Os/ 188Os(i) ratios (0.125 to 0.141), indicating a mantle-derived origin. Modeling indicates that >30% crustal contamination is required to explain the radiogenic Os isotopic composition if average upper crust is adopted as the crustal contaminant, or 5%-25% if sulfide-rich crustal rock is used as the crustal contaminant. However only 5-10% crustal contamination is required to explain the Nd and Sr isotopes. We propose that the decoupling of Os from Sr-Nd isotopes in the silicate rocks was due to selective crustal contamination. Addition of external sulfur from a crustal source may be the key factor triggering sulfide saturation. The silicate magma that underwent sulfide extraction before emplacement to shallow depth preserved a crustal Os isotope signature. Continued reaction of sulfide melts with new pulses of mantle-derived magma increased the Os content and decreased the 187Os/ 188Os(i) ratios, effectively masking the crustal Os contribution in the sulfides. © 2011 Elsevier B.V.
Persistent Identifierhttp://hdl.handle.net/10722/151364
ISSN
2015 Impact Factor: 3.482
2015 SCImago Journal Rankings: 2.346
ISI Accession Number ID
References

 

DC FieldValueLanguage
dc.contributor.authorYang, SHen_HK
dc.contributor.authorZhou, MFen_HK
dc.contributor.authorLightfoot, PCen_HK
dc.contributor.authorMalpas, Jen_HK
dc.contributor.authorQu, WJen_HK
dc.contributor.authorZhou, JBen_HK
dc.contributor.authorKong, DYen_HK
dc.date.accessioned2012-06-26T06:21:11Z-
dc.date.available2012-06-26T06:21:11Z-
dc.date.issued2012en_HK
dc.identifier.citationChemical Geology, 2012, v. 302-303, p. 106-118en_HK
dc.identifier.issn0009-2541en_HK
dc.identifier.urihttp://hdl.handle.net/10722/151364-
dc.description.abstractThe Jingbulake mafic-ultramafic intrusion in the South Tianshan orogenic belt, Xinjiang, NW China, is a zoned intrusive body composed of gabbro-diorite, olivine gabbro and wehrlite, locally intruded by pyroxenite, within a major W-E structure. Both olivine gabbro and wehrlite contain disseminated Ni-Cu sulfides, whereas pyroxenite hosts an ore body containing massive, net-textured and disseminated sulfide ores. Both silicate rocks and sulfide ores from the Jingbulake intrusion have low Pd/Ir ratios (10-63). The silicate rocks contain Ni-poor olivine (generally <0.1wt.% NiO) and have low Pt (0.48-2.3ppb) and Pd (0.52-4.8ppb) contents and high Cu/Pd ratios (128,000 to 200,000), indicative of significant chalcophile element depletion. The disseminated sulfide ores from No. 1 and 2 mineralization zones have 0.28-1.5ppb Pt and 2.8-8.1ppb Pd, and Cu/Pd ratios (200,000-300,000). The disseminated and net-textured sulfide ores from No. 8 mineralization zone have Pt (39-315ppb) and Pd (76-1100ppb), and intermediate to high Cu/Pd ratios (6850-138,000). The variably high Cu/Pd ratios indicate that the parental magma may have reached earlier sulfide saturation and removal. The low Os contents (0.0146 to 0.276ppb) and high Re/Os (29 to 292) and 187Os/ 188Os(i) ratios (0.277 to 0.916) of the silicate rocks are consistent with a major contribution of Os from crustal materials. On the other hand, the net-textured sulfide ores from No. 8 mineralization zone have high Os contents (15.1 to 32.6ppb), low Re/Os (2.0 to 2.3) and low 187Os/ 188Os(i) ratios (0.125 to 0.141), indicating a mantle-derived origin. Modeling indicates that >30% crustal contamination is required to explain the radiogenic Os isotopic composition if average upper crust is adopted as the crustal contaminant, or 5%-25% if sulfide-rich crustal rock is used as the crustal contaminant. However only 5-10% crustal contamination is required to explain the Nd and Sr isotopes. We propose that the decoupling of Os from Sr-Nd isotopes in the silicate rocks was due to selective crustal contamination. Addition of external sulfur from a crustal source may be the key factor triggering sulfide saturation. The silicate magma that underwent sulfide extraction before emplacement to shallow depth preserved a crustal Os isotope signature. Continued reaction of sulfide melts with new pulses of mantle-derived magma increased the Os content and decreased the 187Os/ 188Os(i) ratios, effectively masking the crustal Os contribution in the sulfides. © 2011 Elsevier B.V.en_HK
dc.languageengen_US
dc.publisherElsevier BV. The Journal's web site is located at http://www.elsevier.com/locate/chemgeoen_HK
dc.relation.ispartofChemical Geologyen_HK
dc.subjectIsotope decouplingen_HK
dc.subjectJingbulakeen_HK
dc.subjectMafic intrusionen_HK
dc.subjectRe-Osen_HK
dc.subjectSelective crustal contaminationen_HK
dc.subjectSr-Nden_HK
dc.titleSelective crustal contamination and decoupling of lithophile and chalcophile element isotopes in sulfide-bearing mafic intrusions: An example from the Jingbulake Intrusion, Xinjiang, NW Chinaen_HK
dc.typeArticleen_HK
dc.identifier.emailZhou, MF: mfzhou@hkucc.hku.hken_HK
dc.identifier.emailMalpas, J: jgmalpas@hku.hken_HK
dc.identifier.authorityZhou, MF=rp00844en_HK
dc.identifier.authorityMalpas, J=rp00059en_HK
dc.description.naturelink_to_subscribed_fulltexten_US
dc.identifier.doi10.1016/j.chemgeo.2011.10.019en_HK
dc.identifier.scopuseid_2-s2.0-84858161160en_HK
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-84858161160&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume302-303en_HK
dc.identifier.spage106en_HK
dc.identifier.epage118en_HK
dc.identifier.eissn1872-6836-
dc.identifier.isiWOS:000302833000009-
dc.publisher.placeNetherlandsen_HK
dc.identifier.scopusauthoridYang, SH=49261330000en_HK
dc.identifier.scopusauthoridZhou, MF=7403506005en_HK
dc.identifier.scopusauthoridLightfoot, PC=7102963749en_HK
dc.identifier.scopusauthoridMalpas, J=7006136845en_HK
dc.identifier.scopusauthoridQu, WJ=8982620500en_HK
dc.identifier.scopusauthoridZhou, JB=35185831100en_HK
dc.identifier.scopusauthoridKong, DY=7202350158en_HK
dc.identifier.citeulike9994006-

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