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Diffusion of Sm-Nd in Scheelite and its Significance to Isotopic Dating and Tracing

Acta Geologica Sinica(English Edition) 2023年第2期97卷 651-661页

作者： ZHANG Dongliang ian mcoulson PENG Jiantang LI Shijie WANG Guoqiang Key Laboratory of Metallogenic Prediction of Nonferrous Metals Ministry of EducationSchool of Geosciences and InfophysicsCentral South UniversityChangsha 410083China Solid Earth Studies Laboratory Department of GeologyUniversity of ReginaReginaSaskatchewan S4S OA2Canada Lunar and Planetary Science Research Center Institute of GeochemistryChinese Academy of SciencesGuiyang 550081China Xi'an Center of Geological Survey CGSXi'an 710054China

As the principal ore mineral in various tungsten(-gold)deposits,scheelite(CaWO_(4))plays an important role in directly dating the timing of ore formation,and in tracing associated material sources through the study of its Sm-Nd geochronology and Nd isotopic *** the retention of Sm-Nd systematics within scheelite is presently unconstrained,equivocal interpretations for isotopic data resulting from this method have occurred quite often in previous studies that apply these isotopic *** order to better elucidate the closure of Sm-Nd in scheelite,the kinetics of Sm and Nd within this mineral lattice were investigated through calculation of diffusion constants presented *** following Arrhenius relations were obtained:D_(Nd)=4.00exp(-438 kJ·mol^(–1)/RT)cm^(2)/s D_(Sm)=1.85exp(-427 kJ·mol^(–1)/RT)cm^(2)/s showing diffusion rate of Nd is near identical to Sm in scheelite when at the same ***,compared to other rare earth elements(REEs),which have markedly different atomic radii to either Nd or Sm,these are shown to exhibit a great variation in *** observed trends in our data are in excellent agreement with the diffusion characteristics of REEs in other tetragonal ABO4 minerals,indicating that ionic radius is a key constraint to the diffusivity of REEs in the various crystal *** this in mind,the same substitution mechanism and a very slight discrepancy in radii will allow us to infer that significant Sm/Nd diffusional fractionation in scheelite is unlikely to occur during most geological *** upon the diffusion data determined herein,Sm and Nd closure temperatures and retention times in scheelite are discussed in terms of diffusion *** results suggest that closure temperatures for Sm-Nd within this mineral are relatively high in contrast to the temperature ranges of ore-formation responsible for scheelite-related deposits,and any later thermal *** is likely,therefore,that rel

关键词： Sm-Nd system diffusion scheelite closure temperature isotopic dating

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Zinc, copper, and strontium isotopic variability in the Baiyangping Cu–Pb–Zn–Ag polymetallic ore field, Lanping Basin, Southwest China

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Acta Geochimica 2021年第4期40卷 557-574页

作者： Caixia Feng Shen Liu Guoxiang Chi Xianwu Bi Ruizhong Hu ian mcoulson State Key Laboratory of Continental Dynamics Department of GeologyNorthwest University229 Taibai RoadXi’an 710069China Departments of Geology University of Regina3737 Wascana ParkwayReginaSK S4S 0A2Canada Institute of Geochemistry Chinese Academy of Sciences99 Lincheng RoadGuiyang 550002China

The Baiyangping Cu-Ag polymetallic ore district is located in the northern part of the Lanping-Simao foreland fold belt,between the Jinshajiang-Ailaoshan and Lancangjiang faults,and the deposit can be divided into eastern and western ore *** upon microscope observation of ore minerals and analysis of zinc,copper,and strontium isotope composition,we conclude that:(1)the zinc isotopic compositions of sphalerite from the eastern and western ore belt of the Baiyangping polymetallic ore deposits are enriched in both the heavy(-0.09‰ to+0.15‰) and light(-0.19‰ to-0.01‰)zinc *** fractionation is likely the additional factor controlling the observed temporal and spatial variations in zinc isotopes in the two studied ore *** zinc isotopic composition in the Baiyangping polymetallic Pb-Zn deposits may have the same fractionation as that of magmatic-hydrothermal,VHMS,SEDEX,and MVT deposits,as demonstrated by geological and other geochemical evidence;(2) the range of δ^(65)Cu in massive tetrahedrite is from-0.06‰ to+0.12 ‰ that relates to the early stages of ore-formation,which are higher than that of venial chalcopyrite(from-0.72‰ to-0.07‰)formed at a late ore-forming stage in the western ore *** ore-forming stages and alteration or leaching processes are likely the main factors controlling the observed variations in copper isotopes in the western ore zone;(3) the ^(87)Sr/^(86)Sr value of hydrothermal calcite in eastern(0.7080-0.7093) and western(0.7085-0.7113) ore belt suggested that mineralization of early calcite,with^(87)Sr/^(86)Sr values much higher than in ancient Late Triassic seawater,may be related to recrystallization from a radiogenic Sr-rich or silicifying fluid,either from the strata that the ore-forming fluid flows through or from other fluids.

关键词： Zn-Cu-Sr isotopic variation Cu-Pb-Zn-Ag poly-metallic ore deposit Baiyangping Lanping Basin

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Zircon U-Pb geochronology,whole-rock geochemical,and Sr-Nd-Pb isotopic constraints on the timing and origin of Permian and Triassic mafic dykes from eastern North China Craton

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Acta Geochimica 2020年第6期39卷 862-886页

作者： Shen Liu Caixia Feng Yan Fan Xiaoqing Chen Yuhong Yang Huibo Zhao ian mcoulson State Key Laboratory of Continental Dynamics and Department of Geology Northwest UniversityXi'an 710069China College of Earth Sciences Jilin UniversityChangchun 130061China Solid Earth Studies Laboratory Department of GeologyUniversity of ReginaReginaCanada

This work reports an important episode of extensional,mafic magmatism that impacted the North China Craton(NCC)during the Permo-Triassic and influenced the evolution of this *** sampled 30 representative mafic dykes cropping out in eastern NCC,within the Hebei Province,*** zircon LA-ICP-MS U-Pb ages,geochemical,and Sr-Nd-Pb isotopic data for these mafic dykes identified them as typical dolerites formed between 211.9±1.3 and 263.9±2.6 *** mafic rocks fall into the alkaline and calc-alkaline *** are enriched in light rare earth elements,some large ion lithophile elements(e.g.,***,and Sr),K,and Pb,and depleted in Nb,Ta,and *** dykes have high initial 87Sr/86Sr ratios(0.7034-0.7178),negative eNd(t)values(—2.2 to—5.9),and relatively constant initial Pb isotopic ratios,that are EMI-like:(206Pb/204Pb)i=16.39-16.74,(207pb/204pb)j=15.22-15.24,and(208Pb/204Pb)i_=36.66-36.86,*** results indicate that the Hebei Province dolerites were likely derived from magma gen erated through low-medium degree partial melting(3.0-20%)of an EMI-like garnet-lherzolite mantle *** parental magmas fractionated olivine,clinopyroxene,and Ti-bearing phases with obvious crustal contamination during rapid ascent and dyke *** the possible influence of subduction of the Yangtze Plate has been excluded,we propose a model for the origin of the investigated mafic rocks,involving the Pennian collision between the Siberian Block and the *** mafic dykes of eastern NCC within Hebei Province formed during a period of crustal thinning in response to extension after the early Permian collision.

关键词： Permo-Triassic Dolerite Origin NCC Siberian block

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