Abstract:Techniques for high_precision measurements of Fe isotope ratios using MC-ICP-MS at both low-and high_resolution modes have been reported in detail, which includes assessments of isobaric inferences, matrix effects, concentration effects and long_term repeatability. The external precision for the methods established at both low-and high-resolution modes are better than 0.5 ε/amu, and the results obtained under the two modes are consistent with each other. Using the techniques developed, the Fe isotope compositions of national geological reference materials GBW 07105 (basalt powder) and GBW 07111 (grano-diorite powder) have been measured. Relative to IRMM-14, the Fe composition for GBW 07105 is: ε57Fe＝1.9±0.3(2σ)，ε56Fe＝1.3±0.2(2σ)，ε57/56Fe＝0.6±0.1(2σ)； and ε57Fe＝1.8±0.4(2σ)，ε56Fe＝1. 2±02(2σ)，ε57/56Fe＝0.6±0.1(2σ) for GBW 07111.

Abstract:A proper reference material is crucial for accurate measurement of isotope ratios. This paper deals with the preparation of a new reference material with basaltic matrix for Cu, Fe and Zn isotope measurement, which is named CAGSR-1. The substanceselected for preparation of CAGSR-1 is a certified primary standard for analysis of rock and minerals, which is named GBW07105 and composed of basaltic powder. The preparation of the new reference material was carried out strictly in accord with the stipulation of the State Metrological Technical Standard for primary reference material, which includes homogeneity and stability tests, and certification analyses. The certificated values and uncertainty at 95% confidence level are as follows: δ65CuSRM976（‰）=0.10±0.02δ56FeIRMM014（‰）=0.12±0.02；δ66ZnRomil（‰）=745 ±0.01.This newly certified reference material can be used in such aspects asthe assessment of isotope fractionation during chemical separation of geological and environmental samples, the instrumental calibration for Cu, Fe and Zn isotope measurement, and the data quality evaluation in the whole process of sample preparation and isotope measurement. 

Abstract:Fe isotope compositions, major and rare earth elements (REE) of Archaean banded iron formations from Anshan_Benxi area, Liaoning Province have been studied. The average bulk compositions of banded iron formations (BIFs) are rich in total Fe and SiO2, but the Al2O3 and TiO2 contents are very low. These chemical features show that they are chemical sediments devoid of detrital input. REE concentrations in BIFs are very low; the shale-normalized REE+Y patterns display distinct positive anomalies of Eu, Y, and La, and depletion of light REE relative to heavy REE. This demonstrates that the BIFs are the products of chemical sedimentation from paleo_seawater with significant input of volcanic hydrothermal fluids. The Fe isotope compositions of the bulk samples are not only enriched in heavy Fe isotopes relative to IRMM-014, but also strongly correlated with Eu/Eu*, providing direct evidence for the first time that the Fe in the BIFs originate from hydrothermal fluids

Abstract:We present in this paper Fe isotope compositions for magnetite and pyrite mineral separates from banded iron formations in the Anshan-Benxi area, where green schistlower amphibolite facies metamorphism has occurred. Both pyrite and magnetite show heavy Fe isotope enrichment relative to IRMM014; furthermore, Fe isotope compositions of pyrite are systematically heavierthan those of corresponding magnetite from the same samples (Δ57Fepyrite－magnetite＝2.23～5.13). These features cannot be explained if they represent the primary signatures inherited from their sedimentary precursors, but can be reconciled if Fe isotope exchange reequilibrium have been taking place duringregional metamorphism. The equilibrium mass fractionation factor of 57Fe/54Fe in green schist-to lower-amphibolite facies conditions is αpyrite－magnetite≈1.000?4‰±0.06‰(2σ). This study represents a significant advance in understanding the behaviour of Fe isotopes during metamorphism. 

Abstract:Cu isotopes are a new geochemical tracer. A prerequisite for using this tracer to constrain some important geochemical processes is an adequate understanding of the processes and mechanism of Cu isotope fractionation. This paper reports the experimental results of Cu isotope fractionation during CuSO4·5H2O cry stallizing at room temperature, and reviews the current status of our understand ing of mass fractionation processes at low-temperature environments, including precipitation, reduction, adsorption, and biological process.

Abstract:A prerequisite for using the new geochemical tracer—Fe isotope—to constrain some important geochemical processes lies in the adequate understanding of the process and mechanism of Fe isotope fractionation. This paper presents a review of the current situation of people's understanding of mass fractionation processes at low-temperature environments, which include precipitation, dissolution, reduction, oxidation, adsorption, and biological processes. During the precipitation, the resultant is depleted in heavy Fe and the heavier Fe(Ⅱ) is preferentially adsorbed on the surfaces of Fe(Ⅲ)(hydr)oxides. When different kinds of valencestatecoexist, heavy isotope is preferentially enriched in high-valence state.

Abstract:Suspended particulate materials (SPM) were investigated for their iron isotope composition so as to assess their isotope behaviors during the iron biogeochemical cycle in summer in the Aha Lake of Guizhou Province. All the samples were purified with the anion exchange chromatography (Bio_Rad AGMP_1 resin, 100～200 mesh) and the iron isotope composition was analyzed on Nu Plasma MC_ICP_MS. δ56Fe alues of SPM sampled in the lake and the rivers display statistically a negative shift compared with IRMM_014. The values of lake samples vary from －136‰ to －010‰, while those of river samples range from －088‰ to -016‰. Besides,the average iron isotope composition of aerosol sampleses+006‰±002‰.Theoplankton was also sampled and analyzed for the iron isotope composition of the whole sample including intracellular and extracellular iron, which yielded a value of +0.08‰. It is suggested that the complex biogeochemical process plays an important role in changing the δ56Fe values of SPM in the lake apart from various inputs. During stratification in summer, it is the organically bonded iron particles that make the iron isotope composition of SPM in the epilimnion light, with an average value of －0.29‰. An iron cycle is established near the redox boundary where the upwardly diffusing Fe(Ⅱ) is oxidized and the iron particles formed will continuously sink back to the reducing zone, with which the cycle is completed and the δ56Fe values of SPM reach the minima－0.88‰ (DB) and －1.36‰ (LJK), just below the redox boundary. Due to random transportation and diffusion, the profiles of δ56Fe values of the SPM near the redox regions develop to an approximate Gaussian shape. Besides, the formation of ferrous sulfides may be another reason for the light iron isotope composition of the SPM near the water-sediment interface. Moreover, there is a good negative correlation of the δ56Fe value with the Fe/Al ratio especially for DB location, which further indicates that the transformation and diffusion of reactive iron play an important role in modifying the δ56Fe value of the SPM near the redox boundary, and also suggests that the iron isotope and the Fe/Al ratio can serve as indicators of hydro-biogeochmical conditions.

Abstract:The Zn isotopic compositions of SPM (suspended particulate materials)and biological samples from the Hongfeng Lake and the Aha Lake as well as theirmain branches were analyzed with multiple collector inductively coupled plasma-mass spectrometry. The results show that the variations in Zn isotopic composition of SPM in the Aha Lake and in its main branches are -0.18‰～0.27‰ and -0.17‰～0.46‰ respectively, while the variations in the Hongfeng Lake and in its main branches are -0.29‰～0.26‰ and -0.04‰～0.48‰ respectively, indicating that the heavy zinc isotopes are enriched in the SPM in their branches. The zinc isotope compositions in biological material show a larger variation from -0.35‰ to 0.57‰, suggesting that different materials from the lacustrine ecosystem have their respective unique isotopic signatures. It is shown that the zinc isotope composition in the Aha Lake is mainly controlled by the water inputs from the catchment, and hence the zinc isotope composition can be used as a good tracer of source materials. It is also found that δ66Zn variation versus chlorophyll contents shows positive correlation (R=0.97) in the Hongfeng Lake in summer, which can be probably ascribed to the process of adsorption or absorption of zinc onto algae. In addition,the zinc isotope ratio of SPM in the Hongfeng and Aha Lakes in summer is lower than that in winter, implying that the atmospheric deposition might have served as another significant source of lighter zinc isotopes. Moreover, the variation of δ66Zn values in biological material is wider than that in SPM, indicating that inorganic processes controlling zinc isotope fractionation should be of subordinate importance compared with biological factor

Abstract:Accurate determination of Cu and Zn isotopes using MC-ICP-MS requires an adequate separation of the elements from bulk samples. Two methods for accumulator dissolution have been investigated through assessments of the purity of Cu and Zn solutions after ion exchange chromatography using AG MP-1 resin, the repeatability of the chromatographic columns, and the consistency of Cu and Zn isotope determination for samples dissolved and purified using different procedures. The results show that: ① Both methods are effective to destroy the organic matter of plant samples; ② The AG MP-1 resin can been used to separate Cu and Zn from the organic sample after effective dissolution, and it is enough for thesample to get the accurate value of isotope composition after one exchangeusing AG MP-1 resin; ③ The standard error of Cu and Zn isotope composition is smaller than the repeatability over a long time, it shows that whole chemical procedure,the separation of resin and the condition of instrument are suitable.

Abstract:A Ni-Mo sulfide bed occurs in the lower portion of the lower Cambrian Niutitang Formation in south China. Lehmann et al.(2007) reported data of Mo-isotopic compositions of the Ni-mo sulfide ores and host black shales, and suggested aseawater origin for the Mo. The Ni-Mo sulfide ores show very limitedMo-isotopic variation with δ98/95MoMOMOvalues of -1.24‰±0.10‰, whereas the host black hales show larger Mo-isotopic variations with δ98/95MoMOMO values from ～1.82‰ to－0.40‰. Those with low-Mo content black shales show a linear relationship between Mo contents and Mo-isotopic compositions. We suggest that this correlation may reflect a two end-member mixing of seawater Mo and clastic sedimentMo. The sources of Mo in the Ni_Mo sulfide ores were probably from submarine hydrothermal fluids. Further work is needed both on the Ni-Mo ore bed bearing and the barren black shales of the Niutitang Formation in south China, in order to better estimate the Mo-isotopic compositions of the early Cambrian seawater, and to better constrain the ore genesis.

Abstract:In the end of past century, with the advent of analytical instruments such as TIMS and MC-ICP-MS, the non_traditional stable isotopes, including Fe, Cu, Zn, Se, Mo, Cr, Hg, Ca, Mg etc., are developing rapidly, and have becamea very important research frontier in isotope geochemistry. Because of the special feature with the multivalences, multi-mass number and larger isotopic fractionation, Se isotopes have caused more attention. Se isotope research to date has confirmed these measurements, developed new measurement techniques, and investigated Se isotope fractionation during several other critical processes. In this paper, we summarize the chemical preparation (TCF), on-line hydride generation system,massspectrometry, scaling of standard reference materials concerning Se isotopes, and review the isotopic compositions and fractionation mechanism in natural and the experiments.

Abstract:In recent years, multiple_collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has been increasingly used for precise and accurate measurement of transitional metal isotopes, which has greatly improved precision, accuracy, and efficiency of molybdenum isotope analysis of geological samples, andalso made Mo isotopic geochemistry a new frontier in Earth science. This paper presents a review of the recent progress in the systematics of Mo stable isotopeand its application in geology. The natural range of δ98/95Mo is from－1.35‰ to 2.6‰. The fractionation of Mo isotopes in an oxidizing environment is mainly attributed to the adsorption of dissolved Mo on Mn-oxides, whereas that in an suboxic-euxinic environment is controlled by the content of H2S dissolved in water. Mo isotopic signatures in sediments can be used as an indicator for redox conditions of paleo-environment and corresponding paleo-oceanography. Therefore, molybdenum isotopes can be used as a powerful tool for understanding the redox conditions of local or regional depositional environment, the biogeochemical cycle of sulfur or carbon, and the geochemical evolution of ancient oceans. It is believed that, with further studies of the molybdenum isotope fractionation mechanism, molybdenum isotopes will certainly be applied to more and more areas in earth and environment sciences.

Abstract:Black shale of the Lower Cambrian Niutitang Formation is widely distributed in the Yangtze Platform of South China, and there is regionally developed a typical conformable polymetallic sulfide horizon. A lower profile of the black shale enriched in Se, Mo and other metal elements in Xiaozhu of Zunyi area was selected for Se isotope determination so as to investigate the probable source of Se and its depositional environment. The results show that remarkable variation of δ82/76SeSRM 3149 exists in the studied black shale sequence. The middle carbonaceous shale, Ni-Mo layer and carbonaceous carbonate have a narrow range of δ82/76SeSRM 3149, from +0.65‰ to +1.15‰ with a mean of 0.91‰±0.23 ‰ (n=4); the upper carbonaceous shale has a value of －1.24‰; the bottom k-bentonite and phosphorite have a wide range of δ82/7SeSRM 3149 between －4.35‰ and +4.11‰. Combined with the publishedδ98/95MoJMC data of Ni-Mo layer in the Huangjiawan section, it is held that the middle black shale was deposited in an anoxic/euxinic environment,but an uncertain mixing process between basin seawater and oxic ocean water or hydrothermal fluid must have happened at that time. The bottom K_bentonite experienced a strong weathering and alteration, and the oxidization-reducing process probably occurred near the boundary between oxidizing water and anoxic water. Se in seawater might have been leached from the Se-rich bottom K-bentonite or tuff or from submarine hydrothermal fluid. Se isotopes indicate that the depositional environment of black shale in the Niutitang Formation of Zunyi area waspossibly situated on the continental margin of a stricted basin and experienced different evolution stages from dizing-suboxic-anoxic/euxinic to suboxic.

Abstract:Magnesium has three stable isotopes: 24Mg,25Mg and 26Mg. Available data show that the largest Mg-isotopic variation occurs in meteorites, with δ26Mg values of -0.71‰ ～ 11.92‰ (relative to DSM3 standard), whereas the terrestrial rocks show smaller Mg-isotopic variation. For example, mantle rocks show a δ26Mg variation of -3.01‰～1.03‰; sedimentary carbonates display a δ26Mg variation from -4.84‰ to -1.09‰; and loess has a δ26Mg value of -0.60‰. At present, many laboratories use MC-ICPMS for the precise measurement of Mg-isotopic composition. Because of the isotopic heterogeneity of the standard SRM980 produced by NIST, the new standard DSM3 has been recommended as the reference material to report Mg-isotopic compositions. At present the research on magnesium isotope geochemistry is focusing on the following aspects: ① cosmochemistry and star formation processes; ② tracing mantle metasomatism; ③ variation of seawater δ26Mg value through geologic history; ④ estimates of the Mg flux during continental weathering. Study on Mg-isotope geochemistry in China is just starting and the application of Mg isotopes to solving various geological problems will be enhanced in the near future both at home and abroad. 

Abstract:A method for high_precision measurement of Zn isotope composition has been estab lished，which includes correction of instrumental mass discrimination, assessment of isobaric interferences, investigation of matrix effect, and exami nation of long-term repeatability.It has been shown that the instrumental mass discrimination can be corrected with the standard-sample-bracketing method. Theassessment of isobaric interferences was carried out using three approaches, i.e ., ① the direct measurement of the interference signals in the high-resolution mode; ② the examination of correlation between Zn isotope ratios of the raw dat a in a low-resolution mode; ③ the investigation of the deviation of the measured Zn isotope values relative to the “real value". The matrix effect was examined by using the mixed solution of Fe and Zn relative to pure Zn solution. It is found that the content of Fe has no detectable effect on the measured values of Zn isotope when the Fe/Zn ratio is lower than or equal to 0.2.The repeatability as sessed over a period of 7 months is better than 0.06‰ (2sd) per amu. The Zn iso tope composition of a national standard reference material of sphalerite (GBW 7270) was analyzed with the techniques established, and the results are δ66Zn =6.71‰±0.03‰( 2σ)δ67Zn = 10.08‰±0.05‰(2σ)，andδ68Zn=13.37‰±.07‰(2σ).