In Situ Analysis Of Pb Isotopic Composition In Chalcopyrite Using Femtosecond Laser Ablation Multiple-collector Inductively Coupled Plasma Mass Spectrometry

Chalcopyrite (CuFeS2) is a common sulfide mineral containing trace amounts of gold and silver. Chalcopyrite is one of the major minerals of porphyry copper deposit and formed in a variety of geological conditions. Lead isotopic composition can be used to trace rock formation and evolutionary history. However, the traditional bulk rock analysis of the lead isotopes can only obtain the mixture of lead composition of a small amount of minerals, and may not reveal the actual geological process since most of the minerals exist zones with different lead isotopic compositions. The laser ablation coupled with multiple-collector inductively coupled plasma mass spectrometer (LA-MC-ICPMS) is a powerful technique for in situ micro analysis of lead isotopes. Nevertheless, the laser ablation technique requires matrix matched standards for external calibration due to elemental fractionation during laser ablation and measurement using mass spectrometer. There are no chalcopyrite standards available for in situ micro measurement in terms of lead isotope. This work attempts to find a suitable chalcopyrite standard for this purpose from fifteen existing national chalcopyrite standards using femtosecond laser ablation MC-ICPMS which is installed in the State Key Laboratory of Continental Dynamics, Northwest University. The femtosecond laser ablation MC-ICPMS can measure the Pb isotopes precisely due to its ultra-short pulse duration, finer aerosol (<0.2μm) and enhanced sensitivity. A lead isotopic contents analysis method of chalcopyrite using femtosecond laser ablation MC-ICPMS is setup after carefully comparing lead isotopic compositions between in situ analysis using the laser ablation and solution work after chemical chromatography separation. Following conclusions are obtained:1) Lead isotope compositions of sulfide minerals can be measured precisely using femtosecond laser ablation MC-ICPMS.2) NIST SRM610/612glasses are not suitable for external calibration of chalcopyrite due to the extraordinary matrix difference between sulfide and NIST glasses and different ablation behavior. One of the fifteen copper based standards is picked up as a candidate external calibration standard for lead isotopic contents measured by fsLA-MC-ICPMS. Accurate lead isotopic composition can be achieved using T1(aspirate by Aridus â…¡) as internal standard which is mixed with laser ablated aerosol using a three way.3) CUPB12(GBW02137, No.ZQSn6-6-3) is one of the most suitable candidate standard among15national chalcopyrite standards due to its homogeneity of lead isotopes. The isotopic compositions of CUPB12are37.9621±0.0018(208Pb/204Pb,2s),15.57873±0.0006(207Pb/204Pb,2s),17.74998±0.0008(206Pb/204Pb,2s)å'Œ2.13882±0.0001(208Pb/206Pb,2s),0.877729±0.000027(207Pb/206Pb,2s) and relative standard deviation (RSD) are0.0087%,0.0067%,0.0079%,0.0078%,0.0057%, respectively. These results agree well with the ratios obtained after chemical separation in2s, and reveals that the CUPB12can be applied in in situ Pb isotope analysis for external calibration and quality control purposes.