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Scheelite Sm-Nd dating and quartz Ar-Ar dating for Woxi Au-Sb-W deposit,western Hunan

Chinese Science Bulletin 2003年第23期48卷 2640-2646页

作者： PENGJiantang huruizhong ZHAOJunhong FUYazhou LINYuanxian InstituteofGeochemistry ChineseAcademyofSciencesGuiyang550002China TianjinInstituteofGeology&MineralResources ChineseMinistryofLandandResourcesTianjin300170China

Scheelite Sm-Nd and quartz Ar-Ar dating were accomplished for the Woxi Au-Sb-W deposit in western hu-nan. The results show that the Sm and Nd concentrations of scheelite are relatively high, and Sm/Nd ratios are usually high and variable. In the 147Sm/144Nd vs. 143Nd/144Nd diagram, the disseminated scheelites show a good linear array, which corresponds to an isochron age of 402 6 Ma and an initial 143Nd/144Nd ratio of 0.510544 9 (2s ) with a e Nd(t) value of -30.7. The Ar-Ar age spectra for 2 quartz samples display the saddle shape. The minimum apparent age, plateau age and isochron age of each quartz sample generally overlap within errors; and both the minimum apparent ages of 420 20 and 414 19 Ma coincide well with the scheelite Sm-Nd age. Both Sm-Nd and Ar-Ar dating results reveal that the Au-Sb-W mineralization at Woxi district took place in the Late Caledonian. This is in good agreement with the tectonic evolution of the Xuefengshan district and with some geo-chronological data available for Au, Sb and W deposits in this area. The low initial Nd isotope ratio of scheelites sug-gests that the fluid responsible for Au-Sb-W mineralization at the Woxi is of deep crustal origin and probably originated from the underlying Archaean continental basement rather than the host Proterozoic strata in western Hunan. The con-straints on the mineralization time and on the fluid source provide insight into the genesis of the Woxi deposit.

关键词：白钨矿钐钕石英氩金锑湖南

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Organic Geochemistry of the Early Jurassic Oil Shale from the Shuanghu Area in Northern Tibet and the Early Toarcian Oceanic Anoxic Event

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Acta Geologica Sinica(English Edition) 2005年第3期79卷 392-397页

作者： CHENLan YIHaisheng huruizhong ZHONGHong ZOUYanrong OpenLaboratoryofOreDepositGeochemistry InstituteofGeochemistryChineseAcademyofSciencesGuiyangGuizhou550002 OpenLaboratoryofOreDepositGeochemistry InstituteofGeochemistryChineseAcademyofSciencesGuiyangGuizhou550002／／GraduateSchoolofChineseAcademyofSciencesBeijing100039 InstituteofSedimentaryGeology ChengduUniversityofTechnology Chengdu Sichuan610059 StateKeyLaboratoryofOrganicGeochemistry GuangzhouInstituteofGeochemistryChineseAcademyofSciencesGuangzhouGuangdong510640

This paper presents new geological and geochemical data from the Shuanghu area in northern Tibet, which recorded the Early Toarcian Oceanic Anoxic Event. The stratigraphic succession in the Shuanghu area consists mostly of grey to dark-colored alternating oil shales, marls and mudstones. Ammonite beds are found at the top of the Shuanghu oil shale section, which are principally of early Toarcian age, roughly within the Harplocearas falciferrum Zone. Therefore, the oil shale strata at Shuanghu can be correlated with early Toarcian black shales distributing extensively in the European epicontinental seas that contain the records of an Oceanic Anoxic Event. Sedimentary organic matter of laminated shale anomalously rich in organic carbon across the Shuanghu area is characterized by high organic carbon contents, ranging from 1.8% to 26.1%. The carbon isotope curve displays the δ 13C values of the kerogen (δ 13Ckerogen) fluctuating from –26.22 to –23.53‰ PDB with a positive excursion close to 2.17‰, which, albeit significantly smaller, may also have been associated with other Early Toarcian Oceanic Anoxic Events (OAEs) in Europe. The organic atomic C/N ratios range between 6 and 43, and the curve of C/N ratios is consistent with that of the δ 13Ckerogen values. The biological assemblage, characterized by scarcity of benthic organisms and bloom of calcareous nannofossils (coccoliths), reveals high biological productivity in the surface water and an unfavorable environment for the benthic fauna in the bottom water during the Oceanic Anoxic Event. On the basis of organic geochemistry and characteristics of the biological assemblage, this study suggests that the carbon-isotope excursion is caused by the changes of sea level and productivity, and that the black shale deposition, especially oil shales, is related to the bloom and high productivity of coccoliths.

关键词： oil shales Early Toarcian organic carbon isotope organic atomic C/N ratios Oceanic Anoxic Events northern Tibet

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Geological and Geochemical Characteristics of Early Cretaceous Mafic Dikes in Northern Jiangxi Province, SE China and Their Geodynamic Implications

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Acta Geologica Sinica(English Edition) 2005年第2期79卷 201-210页

作者： XIEGuiqing huruizhong MAOJingwen LIRuiling CAOJinjian JIANGGuohao QILiang InstituteofGeochemistry ChineseAcademyofSciencesGuiyangGuizhou550002 InstituteofGeochemistry ChineseAcademyofSciencesGuiyangGuizhou550002／／InstituteofMineralResourcesChineseAcademyofGeologicalSciencesBeijing100037 InstituteofMineralResources ChineseAcademyofGeologicalSciencesBeijing100037 EarthScienceDepartment SunYat-SenUniversityGuangzhouGuangdong510275

The development of Early Cretaceous mafic dikes in northern and southern Jiangxi allows an understanding of the geodynamic setting and characteristics of the mantle in southeast China in the Cretaceous. Geological and geochemical characteristics for the mafic dikes from the Wushan copper deposit and No. 640 uranium deposit are given in order to constrain the nature of source mantle, genesis and tectonic implications. According to the mineral composition, the mafic dikes in northern Jiangxi can be divided into spessartite and olive odinite types, which belong to slightly potassium-rich calc-alkaline lamprophyre characterized by enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE), large depletion in high strength field elements (HSFE) and with negative Nb, Ta and Ti anomalies, as well as 87Sr/86Sr ratios varying from 0.7055 to 0.7095 and 143Nd/144Nd ratios varying from 0.5119 to 0.5122. All features indicate that the magma responsible for the mafic dikes was derived mainly from metasomatic lithosphere mantle related to dehydration and/or upper crust melting during subduction. Differences in geochemical characteristics between the mafic dikes in northern Jiangxi and the Dajishan area, southern Jiangxi were also studied and they are attributed to differences in regional lithospheric mantle components and/or magma emplacement depth. Combining geological and geochemical characteristics with regional geological history, we argue that southeast China was dominated by an extensional tectonic setting in the Early Cretaceous, and the nature of the mantle source area was related to enrichment induced by asthenosphere upwelling and infiltration of upper crust-derived fluids responding to Pacific Plate subduction.

关键词： Jiangxi Province Early Cretaceous geochemical characteristics northern Jiangxi southeast China tectonic implications rare earth elements mineral composition nature of geodynamic setting tectonic setting uranium deposit copper deposit Pacific Plate mantle source high strength belong to in order

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