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Article: Ore geology, fluid geochemistry and genesis of the Shanggong gold deposit, Eastern Qinling Orogen, China

TitleOre geology, fluid geochemistry and genesis of the Shanggong gold deposit, Eastern Qinling Orogen, China
Authors
KeywordsCmf (Collisional Orogeny, Metallogenesis And Fluid Flow) Model
Fluid Geochemistry
Ore Geology
Orogenic-Type Au Deposit
Qinling Orogen
Issue Date2006
PublisherBlackwell Publishing Ltd. The Journal's web site is located at http://www.blackwellpublishing.com/journal.asp?ref=1344-1698&site=1
Citation
Resource Geology, 2006, v. 56 n. 2, p. 99-116 How to Cite?
AbstractThe Shanggong Au deposit in the Xiong'er Terrane, East Qinling, has reserves of about 30 t Au, making it one of the largest orogenic-type Au deposits hosted in volcanic rocks in China. The deposit is hosted in the andesitic assemblage of the Xiong'er Group of 1.85∼1.4 Ga. Three stages of hydrothermal ore-forming processes are recognized, Early (E), Middle (M) and Late (L), characterised by quartz-pyrite, polymetallic sulfides and carbonate-quartz, respectively. Homogenization temperatures of fluid inclusions are between 380-320°C for the E-stage, 300-220°C for the M-stage and 200-120°C for the L-stage. The composition of fluid inclusions changed from CO2-rich in the E-stage to CO2-poor L-stage. The M-stage fluid has the highest contents of cations and anions (e.g., SO4 2-, Cl-, K+), the highest (K+Na)/(Mg+Ca) and lowest CO2/H2O ratios, which probably resulted from CO2 phase separation. This, together with the alkaline and reducing conditions, as indicated by highest pH and lowest Eh values, is most conducive to the deposition of polymetallic sulfides and native elements such as Au, Ag and Te. H-O is otope systematics indicate that ore fluids evolved from deep-sourced through to shallow-sourced, with the M-stage being a mixing phase of these two fluid-systems. Nineteen δ18 OW values, from 4.2 to 13.4 ‰, averaging 8.1 ‰, suggest that the E-stage fluids derived from metamorphic devolatilization of sedimentary rocks at depth. Comparison of the H-O isotope systematics between the Shanggong deposit and the main lithologies in the Xiong'er Terrane, shows that neither these nor the underlying lower crust and mantle, or combinations thereof, could be considered as the source of ore fluids and metals for the Shanggong Au deposit. Instead, a source which meets the isotopic constraints, is a carbonaceous carbonate-sandstone-shale-chert (CSC) sequence, which is present in the Guandaokou and Luanchuan Groups in the south of the Xiong'er Terrane. This conclusion is supported by thirteen high δ18O values of the Meso-Neoproterozoic strata south of the Machaoying fault, and the high δ18OW values calculated for their possibly metamorphic fluids. It can be also supported by previous observation that the Guandaokou and Luanchuan Groups were underthrust beneath the Xiong'er Terrane, during the Mesozoic collision between the Yangtze and Sinokorean continents. Available isotope ages, together with geological field data, constrain the timing of the Au metallogenesis between 250∼110 Ma. This metallogenesis and associated granitic magmatism, can be related to the Yangtze-Sinokorean continental collision that resulted in the formation of the Qinling Orogen. This collision event progressed from early compression (Triassic to Early Jurassic), through middle compression-to-extension transition (Late Jurassic to Early Cretaceous), to late extension (Cretaceous). These three stages in the evolution of the Qinling Orogen form the basis of an ore genesis model that combines collisional orogeny, metallogeny and fluid flow (CMF model). These three evolutionary stages correspond to the three-stages of ore-forming fluids of the Shanggong Au deposit. We conclude that the formation of the Shanggong Au deposit is a result of the Mesozoic northward intracontinental A-type subduction along the Machaoying fault during Yangtze-Sinokorean continental collision, which led to the metamorphic devolatilization of the CSC sequence, thereby providing both fluids and metals.
Persistent Identifierhttp://hdl.handle.net/10722/92150
ISSN
2015 Impact Factor: 0.857
2015 SCImago Journal Rankings: 0.657
ISI Accession Number ID
References

 

DC FieldValueLanguage
dc.contributor.authorChen, Y-Jen_HK
dc.contributor.authorPirajno, Fen_HK
dc.contributor.authorQi, J-Pen_HK
dc.contributor.authorLi, Jen_HK
dc.contributor.authorWang, H-Hen_HK
dc.date.accessioned2010-09-17T10:37:33Z-
dc.date.available2010-09-17T10:37:33Z-
dc.date.issued2006en_HK
dc.identifier.citationResource Geology, 2006, v. 56 n. 2, p. 99-116en_HK
dc.identifier.issn1344-1698en_HK
dc.identifier.urihttp://hdl.handle.net/10722/92150-
dc.description.abstractThe Shanggong Au deposit in the Xiong'er Terrane, East Qinling, has reserves of about 30 t Au, making it one of the largest orogenic-type Au deposits hosted in volcanic rocks in China. The deposit is hosted in the andesitic assemblage of the Xiong'er Group of 1.85∼1.4 Ga. Three stages of hydrothermal ore-forming processes are recognized, Early (E), Middle (M) and Late (L), characterised by quartz-pyrite, polymetallic sulfides and carbonate-quartz, respectively. Homogenization temperatures of fluid inclusions are between 380-320°C for the E-stage, 300-220°C for the M-stage and 200-120°C for the L-stage. The composition of fluid inclusions changed from CO2-rich in the E-stage to CO2-poor L-stage. The M-stage fluid has the highest contents of cations and anions (e.g., SO4 2-, Cl-, K+), the highest (K+Na)/(Mg+Ca) and lowest CO2/H2O ratios, which probably resulted from CO2 phase separation. This, together with the alkaline and reducing conditions, as indicated by highest pH and lowest Eh values, is most conducive to the deposition of polymetallic sulfides and native elements such as Au, Ag and Te. H-O is otope systematics indicate that ore fluids evolved from deep-sourced through to shallow-sourced, with the M-stage being a mixing phase of these two fluid-systems. Nineteen δ18 OW values, from 4.2 to 13.4 ‰, averaging 8.1 ‰, suggest that the E-stage fluids derived from metamorphic devolatilization of sedimentary rocks at depth. Comparison of the H-O isotope systematics between the Shanggong deposit and the main lithologies in the Xiong'er Terrane, shows that neither these nor the underlying lower crust and mantle, or combinations thereof, could be considered as the source of ore fluids and metals for the Shanggong Au deposit. Instead, a source which meets the isotopic constraints, is a carbonaceous carbonate-sandstone-shale-chert (CSC) sequence, which is present in the Guandaokou and Luanchuan Groups in the south of the Xiong'er Terrane. This conclusion is supported by thirteen high δ18O values of the Meso-Neoproterozoic strata south of the Machaoying fault, and the high δ18OW values calculated for their possibly metamorphic fluids. It can be also supported by previous observation that the Guandaokou and Luanchuan Groups were underthrust beneath the Xiong'er Terrane, during the Mesozoic collision between the Yangtze and Sinokorean continents. Available isotope ages, together with geological field data, constrain the timing of the Au metallogenesis between 250∼110 Ma. This metallogenesis and associated granitic magmatism, can be related to the Yangtze-Sinokorean continental collision that resulted in the formation of the Qinling Orogen. This collision event progressed from early compression (Triassic to Early Jurassic), through middle compression-to-extension transition (Late Jurassic to Early Cretaceous), to late extension (Cretaceous). These three stages in the evolution of the Qinling Orogen form the basis of an ore genesis model that combines collisional orogeny, metallogeny and fluid flow (CMF model). These three evolutionary stages correspond to the three-stages of ore-forming fluids of the Shanggong Au deposit. We conclude that the formation of the Shanggong Au deposit is a result of the Mesozoic northward intracontinental A-type subduction along the Machaoying fault during Yangtze-Sinokorean continental collision, which led to the metamorphic devolatilization of the CSC sequence, thereby providing both fluids and metals.en_HK
dc.languageengen_HK
dc.publisherBlackwell Publishing Ltd. The Journal's web site is located at http://www.blackwellpublishing.com/journal.asp?ref=1344-1698&site=1en_HK
dc.relation.ispartofResource Geologyen_HK
dc.subjectCmf (Collisional Orogeny, Metallogenesis And Fluid Flow) Modelen_HK
dc.subjectFluid Geochemistryen_HK
dc.subjectOre Geologyen_HK
dc.subjectOrogenic-Type Au Depositen_HK
dc.subjectQinling Orogenen_HK
dc.titleOre geology, fluid geochemistry and genesis of the Shanggong gold deposit, Eastern Qinling Orogen, Chinaen_HK
dc.typeArticleen_HK
dc.identifier.emailChen, Y:ychenc@hkucc.hku.hken_HK
dc.identifier.authorityChen, Y=rp1318en_HK
dc.description.naturelink_to_subscribed_fulltext-
dc.identifier.doi10.1111/j.1751-3928.2006.tb00272.xen_HK
dc.identifier.scopuseid_2-s2.0-33747014911en_HK
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-33747014911&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume56en_HK
dc.identifier.issue2en_HK
dc.identifier.spage99en_HK
dc.identifier.epage116en_HK
dc.identifier.isiWOS:000238165300001-

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