Yali Sun

Quasi-simultaneous determination of U-Pb and Hf isotope compositions of zircon by excimer laser-ablation multiple-collector ICPMS

A method for quasi-simultaneous determination of U-Pb ages and Hf isotope compositions on a single zircon spot is developed, by use of a multiple-collector ICPMS coupled with an excimer laser-ablation system. The ICPMS used in this study is equipped with variable zoom lens to change the dispersion of the analyzer and bring ion beams into the collector coincidentally. This feature allows rapid switching between U-Pb and Hf collector configuration, which is used to quasi-simultaneously determine the zircon U-Pb and Hf isotope compositions. The analytical results on three reference zircon standards, 91500, CZ3 and Plesovice and one nature zircon sample, agree with literature/known values, thereby demonstrating feasibility of the method.

A practical method for determination of molybdenite Re-Os age by inductively coupled plasma-mass spectrometry combined with Carius tube-HNO3 digestion

A simplified method for the determination of molybdenite Re-Os ages using inductively coupled plasma-mass spectrometry (ICP-MS) is presented. By the means of Carius tube method, molybdenite and pyrite were digested using concentrated HNO3, and were then changed into MoO3 and Fe(NO3)3 precipitates, respectively. Rhenium was determined directly by ICP-MS after removal of Os by heating for the molybdenite supernatant or by cation-exchange purification for the pyrite supernatant. Osmium distilled as OsO4 from the supernatant was trapped using pure water and could be directly analyzed by ICP-MS. This method was validated using two molybdenite reference materials, GBW 04435 and GBW 04436, and their Re-Os ages obtained are 220.3 ± 1.1 Ma (1.0%, 2s), and 140.5 ± 0.9 Ma (1.2%, 2s), respectively, consistent with literature values. The proposed Re-Os dating method was applied to molybdenite and pyrite sampled from a porphyry Mo-deposit. The results show that this deposit is the oldest Mo-deposit so far found in China.

Accumulating characteristics of platinum group elements (PGE) in urban environments, China

The three-way catalytic converters [mainly using platinum, palladium and rhodium of platinum group elements (PGE)] have been widely used to reduce the pollution arising from vehicular traffic. Since the late 1990s, the Chinese government has implemented measures for new vehicles, equipped with the three-way catalytic converters in metropolitan cities. However, the PGE spreading on environments has not been strongly concerned in developing countries. This study investigated the accumulation characteristics of PGE in urban environments in China. A few samples from India were also analyzed and compared with those from China. The collected soil, aerosol and plant samples were determined for PGE by inductively coupled plasma-mass spectrometry (ICP-MS) after nickel sulphide fire assay preconcentration. The results have shown higher PGE contents in the samples from the cities where vehicles were fitted with autocatalysts for longer time periods. The highest values are 160 ng/g for Pt, 107 ng/g for Pd and 34.5 ng/g for Rh in Hong Kong soils, whereas the lowest values are 2.59 ng/g for Pt, 1.31 ng/g for Pd and 0.40 ng/g for Rh in Kolkata soils. In Beijing and Guangzhou aerosol samples, the PGE concentrations are 6.22 to 24.3 pg/m(3) for Pt and 1.16 to 8.60 pg/m(3) for Rh and 7.68 to 12.2 pg/m(3) for Pt and 2.15 to 5.15 pg/m(3) for Rh, respectively. The levels of PGE abundances in the urban environments of China have been significantly elevated with increasing number of vehicles equipped with autocatalysts.

An Improved Fe—Ni Sulfide Fire Assay Method for Determination of Re, Platinum Group Elements, and Os Isotopic Ratios by Inductively Coupled Plasma- and Negative Thermal Ionization—Mass Spectrometry

An improved Fe–Ni sulfide fire assay method has been developed for determination of Re, the platinum group elements (PGE), and Os isotopic ratios using inductively coupled plasma–mass spectrometry (ICP-MS) and negative thermal ionization–mass spectrometry (NTI-MS). Recovery of Re using the neoclassical NiS fire assay technique is very low, but recoveries of up to 75% can be achieved by using Fe–Ni sulfide as a collector and Na2B4O7 as a flux. Using isotope dilution for determination of Re, a number of standard reference materials were analyzed for PGE and Re, and the results are consistent with their certified values. Multiple analyses of the reference standard GBW 07290 produced precisions ranging from 2.2% for Os to 5.9% for Ir. The detection limits are 2 pg g−1 for Ru, 1.5 pg g−1 for Rh, 25 pg g−1 for Pd, 23 pg g−1 for Re, 0.7 pg g−1 for Os, 1 pg g−1 for Ir, and 6 pg g−1 for Pt. The low procedural blank of Os (1.3 pg g−1) makes the Fe–Ni sulfide fire assay suitable for analysis of Os isotopic compositions. Using NTI-MS, the 187Os/188Os ratios were measured for WPR-1 and they are consistent with literature values.

Influence of seawater Sr content on coral Sr/Ca and Sr thermometry

The Ca content of a Porites coral from Xisha, South China Sea is quite uniform along its 18-year growth axis. A comparison with previously published data shows that the Ca content of corals from different sites varies by only 0.4%. This is much smaller than the variation of Ca in seawater (2.2%), indicating that Ca variations in seawater do not significantly affect the Ca compositions of coral skeletons. The variation in skeletal Ca contents results in only ±0.6°C of uncertainty in SST calculations, which is much smaller than the large disparities observed for previously established coral Sr/Ca thermometers. In contrast, Sr in tropical seawater varies spatially by as much as 2.4%, corresponding to ~4°C offset for coral Sr/Ca calibrations. The effect of seawater Sr variations on coral Sr/Ca thermometers is evaluated and we demonstrate that the content of seawater Sr is the major factor responsible for disparities in these coral Sr/Ca thermometers. The disparities can be significantly reduced when seawater Sr contents are included in the Sr/Ca thermometers.

Shapinggou: the largest Climax-type porphyry Mo deposit in China

Shapinggou porphyry Mo deposit is the largest Climax-type Mo deposit in China and probably also in the world, with total proven Mo reserves of over 2.2 million tonnes at an average grade of 0.17%. It is located in the western Dabie Mountains, along the eastern extension of the East Qinling Mo mineralization belt. Similar to the majority of Mo deposits in the Qinling Mo belt, it is located north of the Triassic suture between the north and south China blocks. The orebody is mainly hosted in Cretaceous high-K granitic porphyry and explosive breccia, with potassic, silicification, and sericite-pyrite alterations. Fluorite is common in Shapinggou, indicating high-F content. The porphyry is closely associated with a large quartz syenite intrusion. Re–Os dating of molybdenite yielded an isochron age of 111.1 ± 1.2 Ma for the mineralization. Zircon U–Pb ages are 111.7 ± 0.8 Ma and 111.9 ± 0.6 Ma for the granitic porphyry and quartz syenite, respectively. Shapinggou is similar to the well-known Climax and Henderson Mo deposits in terms of geochemical characteristics and alterations, etc. We propose that Mo-rich ore-forming materials accumulated underneath the Shapinggou region during the convergence of the North and South China blocks, whereas the final mineralization was triggered by asthenosphere upwelling induced by Pacific Plate subduction.

Determination of 42 Trace Elements in Seawater by Inductively Coupled Plasma Mass Spectrometry After APDC Chelate Co‐precipitation Combined With Iron

Abstract A method was developed for seawater analysis by inductively coupled plasma‐mass spectrometry. To a seawater sample with 1 mg Fe, 2 ml 1% ammonium pyrrolidinedithiocarbamate was added at pH 2 or pH 4 for coprecipitation of Co, Ni, Cu, Nb, Mo, Cd, Sn, In, Te, and Pb or Be, Sc, Ti, Cr, V, Co, Ni, Cu, Zn, Ga, Ge, As, Zr, Nb, Sn, In, Te, rare earth elements, Hf, Ta, W, Tl, Pb, Bi, and Th. The procedural recovery and reproducibility are ∼96% and ∼4.4%, respectively. This method was validated with seawater references, and the results were consistent with their certified values.

Detailed study on simultaneous separation of rare earth elements by capillary electrophoresis

Separation of all rare earth elements (REEs) by capillary zone electrophoresis was investigated in a system of alpha-hydroxyisobutyric acid (HIBA) as a main complex reagent and acetic acid (HAc) as an assistant complex reagent. In the combined system, ligand Ac- plays an important role in improving separation of Eu and Gd, and Y and Dy. The calculated ratio of Ac- to HIB- concentrations was compared and demonstrated that Eu and Gd, and Y and Dy tend to be separated at lower, and higher ratio of the two free ligands, respectively. An operational buffer system was developed for a complete separation of all REE ions.

Determination of ultra-trace rare earth elements in ultramafic and sulfide samples by quadrupole inductively coupled plasma-mass spectrometry

A method has been developed for the determination of rare earth elements (REE) in ultramafic and sulfide samples by quadrupole inductively coupled plasma-mass spectrometry (ICP-MS). After Na2O2 fusion, REE analytes are separated and preconcentrated by inorganic coprecipitation combined with triethanolamine. By addition of REE standards to unknown samples, the procedural recovery was evaluated, and the mean value is 96.7%. Detection limits for this method are 4.46 ng g−1 for Ce to 0.02 ng g−1 for Ho. This method was validated using ultramafic standard samples, and the results are comparable to the accepted values.

Platinum-group element geochemistry of Cenozoic basalts from the North China Craton: Implications for mantle heterogeneity

Forty-two Cenozoic (mostly Miocene) basalt samples from Jining, Chifeng, Fansi, Xiyang, and Zuoquan areas of the North China Craton (the NCC basalts hereafter) were analyzed for platinum-group elements (PGE, including Os, Ir, Ru, Rh, Pt, and Pd). Most of them are alkaline basalts and tholeiites and all of them display little crustal contamination. The total PGE contents of the NCC basalts vary from 0.1 to 0.9 ppb, much lower than those of the primitive mantle values of 23.5 ppb. Primitive mantle-normalized PGE patterns of these basalts define positive slopes and Pd/Ir ratios vary from 1.2 to 25. In terms of both PGE contents and Pd/Ir ratios, they are quite similar to the mid-ocean ridge basalts. There are no obvious negative correlations between PGE vs. MgO, Ni, and Cu in the NCC basalts, indicating that fractional crystallization of olivine, pyroxene, and/or sulfides during magmatic process cannot be the controlling factor for the observed PGE variation. The observed Pd/Ir variations of the NCC basalts require involvement of non-chondritic heterogeneous mantle sources. Based on Sr-Nd-Pb-Hf isotopic systematics and incompatible-element signatures, a mixing of partial melts from both asthenospheric peridotites and enclosed mantle eclogites at the top of asthenosphere was proposed for the origin of these NCC basalts. The lenses of eclogites are derived from upwelling of recycled continental crust during the westward subduction of the Pacific plate from the ∼600 km discontinuity zone. The PGE geochemistry of these basalts provides independent evidence to support this conclusion and the observed Pd/Ir variations may reflect variations in proportions of tapped peridotitic and eclogitic melts.