The Habo alkaline intrusion, which is located in the south of the Sanjiang area, Yunnan Province, China, is a typical Cenozoic alkaline intrusion. There are a series of small to medium-sized Au and Pb-（Zn） deposits ...The Habo alkaline intrusion, which is located in the south of the Sanjiang area, Yunnan Province, China, is a typical Cenozoic alkaline intrusion. There are a series of small to medium-sized Au and Pb-（Zn） deposits around this intrusion. Those deposits are spatially associated with the Habo alkaline intrusion. （1） The δ^34S values of sulfides from Au deposits range from -1.91‰ to 2.69 ‰, which are similar to those of Pb-（Zn） deposits （-3.82 ‰ to -0.05 ‰） and both indicate a much greater contribution from magma. （2） The Habo alkaline intrusion has relatively homogeneous Pb isotopic compositions with ^206pb/^204pb ranging from 18.608 to 18.761, ^207pb/^204pb from 15.572 to 15.722 and ^20spb/^204pb from 38.599 to 39.110. These Pb isotope ratios are similar to those of Au deposits, whose ^206pb/^204pb range from 18.564 to 18.734, ^20Tpb/^20apb from 15.582 to 15.738 and ^208pb/^204pb from 38.592 to 39.319. Pb ratios in both the intrusion and Au deposits suggest that Pb mainly derived from the depth, probably represents a mixture of mantle and crust. Pb-（Zn） deposits, however, show a decentralized trait, and most of them are similar to that of the alkaline intrusion with ^206pb/^204pb ranging from 18.523 to 18.648, ^207pb/^204pb from 15.599 to 15.802, and ^20spb/^204pb from 38.659 to 39.206. （3） In the plumbotectonic diagram ^20Tpb/^204pb versus ^206pb/^204pb, almost all of Au and Pb-（Zn） deposits have the same projection area with the Habo alkaline intrusion, which indicates that those deposits almost share the same source with the alkaline intrusion. （4） Isotopic age of the Habo alkaline intrusion is 36-33 Ma, which is similar to that of Beiya, whose ore- related alkaline porphyries age is 38-31 Ma and molybdenite Re-Os age is 36.9 Ma. Therefore, along with S-Pb isotope traits, we suggest that the Habo Au and Pb-（Zn） deposits should be typically Ailaoshan-Red RiverCenozoicalkaline-related deposits and ore-forming ages of these deposits should be later than that of the Habo alkaline intrusion.展开更多
Magnetite separates from the Shaquanzi Fe-Cu deposit in the eastern Tianshan are used for Re-Os geochronological study. Re-Os data show that magnetite separates contain ca. 0.7 to 50.9 ppb Re and ca. 16 to 63 ppt Os. ...Magnetite separates from the Shaquanzi Fe-Cu deposit in the eastern Tianshan are used for Re-Os geochronological study. Re-Os data show that magnetite separates contain ca. 0.7 to 50.9 ppb Re and ca. 16 to 63 ppt Os. Eight samples yield a model 3 isochron age of （303 ±12） Ma （2or）, which is within uncertainty consistent with of the Re-Os date （295±7 Ma） of associated pyrite. Tectonic evolution shows that the Late Carboniferous Aqishan-Yamansu belt was a back-arc rift. Therefore, the Re-Os age of ca. 300 Ma indicates that the Shaquanzi Fe-Cu deposit may have formed in a back-arc extensional environment and was closely related to mantle-derived magmatism. The successful application of Re-Os magnetite geochronology in the Shaquanzi Fe-Cu deposit suggests that the purity of magnetite, relatively high Re and Os contents, and the closure of Re-Os systematic are base factors for a successful Re-Os geochronology. There would be a good prospect for Re-Os geochronology for magnet- ite.展开更多
文摘橄榄岩的 Re-Os 同位素体系作为探讨岩石圈地幔形成年龄的重要手段已受到人们越来越多的重视。然而,Re-Os体系是否会受到橄榄岩的低温蚀变如蛇纹石化和地幔交代作用或橄榄岩—熔体相互作用的影响并不十分清楚。本文在总结国际上典型造山带橄榄岩剖面研究和地幔橄榄岩捕虏体研究的基础上,发现橄榄岩的 Re-Os 同位素体系基本不受蛇纹石化等低温蚀变作用的影响;但橄榄岩—熔体相互作用会造成橄榄岩的 Re-Os 体系的变化即 Re 或 Os 的带入。当熔体/岩石比例较小时(≤1),橄榄岩—熔体相互作用会造成橄榄岩的 Re 含量显著增加,而放射成因的 Os 同位素即^(187)Os 增量有限。但当熔体/岩石比例很大时(≥1),会造成^(187)Os 同位素显著增加。同时,橄榄岩的 Re 含量与中等程度不相容主、微量元素如 Al、Ti、Yb 的正相关关系可以通过橄榄岩的两阶段演化模式来解释,即早期的部分熔融残留和后期的橄榄岩—熔体相互作用共同影响的结果。橄榄岩的 Re 含量与 Cr 含量的正相关关系进一步说明了这一问题。上述结果对华北东部岩石圈地幔的演化过程有重要的启示作用。因为华北东部古生代时期的确存在太古宙岩石圈地幔,然而新生代时期地、橄榄岩捕虏体普遍具有元古宙而非太古宙的事实证明橄榄岩—熔体的相互作用的确广泛存在,从而造成岩石圈地幔橄榄岩变年轻。因此,新生代地幔捕虏体的 Re-Os 同位素年龄并不是岩石圈地幔的形成年龄,而是混合作用的结果。汉诺坝地幔橄榄岩的 Re 含量和 Sr、Nd 同位素组成符合橄榄岩—多元熔体相互作用的混合趋势,其橄榄岩的全岩 Al_2O_3含量和橄榄石 Fo 的反相关性能够通过橄榄岩—熔体相互作用来解释。
文摘The Habo alkaline intrusion, which is located in the south of the Sanjiang area, Yunnan Province, China, is a typical Cenozoic alkaline intrusion. There are a series of small to medium-sized Au and Pb-（Zn） deposits around this intrusion. Those deposits are spatially associated with the Habo alkaline intrusion. （1） The δ^34S values of sulfides from Au deposits range from -1.91‰ to 2.69 ‰, which are similar to those of Pb-（Zn） deposits （-3.82 ‰ to -0.05 ‰） and both indicate a much greater contribution from magma. （2） The Habo alkaline intrusion has relatively homogeneous Pb isotopic compositions with ^206pb/^204pb ranging from 18.608 to 18.761, ^207pb/^204pb from 15.572 to 15.722 and ^20spb/^204pb from 38.599 to 39.110. These Pb isotope ratios are similar to those of Au deposits, whose ^206pb/^204pb range from 18.564 to 18.734, ^20Tpb/^20apb from 15.582 to 15.738 and ^208pb/^204pb from 38.592 to 39.319. Pb ratios in both the intrusion and Au deposits suggest that Pb mainly derived from the depth, probably represents a mixture of mantle and crust. Pb-（Zn） deposits, however, show a decentralized trait, and most of them are similar to that of the alkaline intrusion with ^206pb/^204pb ranging from 18.523 to 18.648, ^207pb/^204pb from 15.599 to 15.802, and ^20spb/^204pb from 38.659 to 39.206. （3） In the plumbotectonic diagram ^20Tpb/^204pb versus ^206pb/^204pb, almost all of Au and Pb-（Zn） deposits have the same projection area with the Habo alkaline intrusion, which indicates that those deposits almost share the same source with the alkaline intrusion. （4） Isotopic age of the Habo alkaline intrusion is 36-33 Ma, which is similar to that of Beiya, whose ore- related alkaline porphyries age is 38-31 Ma and molybdenite Re-Os age is 36.9 Ma. Therefore, along with S-Pb isotope traits, we suggest that the Habo Au and Pb-（Zn） deposits should be typically Ailaoshan-Red RiverCenozoicalkaline-related deposits and ore-forming ages of these deposits should be later than that of the Habo alkaline intrusion.
基金financially supported by the National Basic Research Program of China(Grant No.2012CB416804)the ‘‘CAS Hundred Talents’’ Project from the Chinese Academy of Sciences(Grant No.KZCX2-YW-BR-09)to Qi Liang
文摘Magnetite separates from the Shaquanzi Fe-Cu deposit in the eastern Tianshan are used for Re-Os geochronological study. Re-Os data show that magnetite separates contain ca. 0.7 to 50.9 ppb Re and ca. 16 to 63 ppt Os. Eight samples yield a model 3 isochron age of （303 ±12） Ma （2or）, which is within uncertainty consistent with of the Re-Os date （295±7 Ma） of associated pyrite. Tectonic evolution shows that the Late Carboniferous Aqishan-Yamansu belt was a back-arc rift. Therefore, the Re-Os age of ca. 300 Ma indicates that the Shaquanzi Fe-Cu deposit may have formed in a back-arc extensional environment and was closely related to mantle-derived magmatism. The successful application of Re-Os magnetite geochronology in the Shaquanzi Fe-Cu deposit suggests that the purity of magnetite, relatively high Re and Os contents, and the closure of Re-Os systematic are base factors for a successful Re-Os geochronology. There would be a good prospect for Re-Os geochronology for magnet- ite.
