Standard K-feldspar Synthesis And Pb Isotopic Composition Of It In Situ Microanalysis By LA-MC-ICPMS

The feldspar is one of the common rock forming minerals. The Pb isotopic composition of feldspar could be used as tracer of the rock formation and the history evolution. Based on lead isotope geochemistry research, one may not only determine the metallogenetic epoch or the modle age, but judge the origination of mineralization material metallogenesis. The traditional bulk rock analysis of lead isotopic composition can only obtain the mixed lead isotopes and may not have practical significance. This requires the in situ analytical techniques. The laser ablation coupled with multiple-collector inductively coupled plasma mass spectrometer (LA-MC-ICPMS) is one of the most important in situ micro analytical techniques for lead isotopic coposition measurement. However, all kind of in situ micro analycial techniques need external standard materials to calibrate instrumental fracationation and other obstacles to get elemental and isotopic compositions of samples. The matrix matched external calibration standards are the short cut way to obtain the geochemical information of relative geological samples in most applications. There is no feldspar standards for precise lead isotope analysis of K-feldspar using in situ analytical techniques, such as LA-MC-ICPMS. We tried to synthesize K-feldspar glasses using high temperature furnace with monosilicate lead dopted K-feldspar powder and evaluated the homogeneity of trace elements and lead isotopic compositions.1. The grinding step prior to melting is one of the key step for homogenized glasses synthesion. The K-feldspar need to be grinded to 1300mesh instead of 200mesh to get final homogenized glasses due to high viscosity melt;2. The experimental coditions for K-feldspar glasses synthesion are:heating temperature 1680℃,heating duration time 2 hours and liquid nitrogen quenching;3. The homogeneity of the synthesized K-feldspar glasses are:RSD% of major and trace elements are less than 5% and 10%, respectively. Lead isotopic compositions are 1.90779±0.00009 (208Pb/206Pb,2s),0.75899±0.00004 (207Pb/206Pb,2s),20.909±0.002 (206Pb/204Pb,2s),15.871±0.002 (207Pb/204Pb,2s)和39.888±0.005 (208Pb/204Pb,2s),while the relative RSD of these ratios are 0.007%,0.008%,0.016%,0.016% and 0.021%, respectively.