Preliminary Research of K-feldspar Glasses Synthesis by High Temperature Melting

Laser ablation Quadruple and multiple collector ICP-MS (LA-Q & MC-ICPMS) is one of the most important analytical technique in terms of in situ analysis of trace elements and isotopic compositions. A matrix-matched standard is the principal way to obtain precise measurements by reducing mass fractionation and matrix interferences. Lead isotopic composition of K-feldspar is one of the important proxies to trace the history of rock formation and evolution. However, there is no appropriate external standard for in situ Pb isotope analysis using LA-MC-ICPMS. This paper reports on work done on the synthesis of K-feldspar glass in a high temperature furnace. The final experimental conditions of the synthesis were to melt the 1300 mesh K-feldspar powders at 1680℃ for 2 hours followed by liquid nitrogen quenching. Routine 74 μm (200 mesh) K-feldspar is not good enough to produce homogeneous K-feldspar standard glass. The surface glass is slightly heterogeneous due to lead evaporation at high temperature, while the inside of the glass is homogenous. Results showed that the lead isotopic compositions of the inner glass 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) and 39.888±0.005 (²⁰⁸Pb/²⁰⁴Pb, 2s), and the RSDs were 0.007%, 0.008%, 0.016%, 0.016% and 0.021%, respectively. Therefore, synthesized K-feldspar glass could potentially serve as an external calibration standard for in situ lead isotope measurements.