New calibration standard for LA-ICPMS analysis of sulphides

Abstract:

Currently available calibration standards for LA-ICPMS analysis for a wide range of trace elements in sulphide minerals include hydrothermally-precipitated Fe-Cu-Zn-S powder doped with trace metals MASS-1 [1] and Li borate glass STDGL-2 [2]. Both of them are not ideal due to a limited range of elements they contain and/or non-homogenous distribution and low concentrations of elements. MASS-1 suffers from a limited range of elements and poor homogeneity, whereas STDGL-2 has low and/or unevenly distributed volatile elements and precious metals (e.g. Se, Te, Tl, Pt, Au). In order to produce a better calibration standard, we have experimented with fusing sulphide mineral mixes in a variety of borate-based fluxes. A range of flux compositions, heating and cooling regimes and times at high temperatures have been tested in order to produce a homogeneous glass disk with an appropriate proportion of sulphide, while retaining volatile elements.

Best results were achieved with using Li tetraborate as a flux with Na nitrate as an oxidizing agent by fusing with an LPG fluxer (M4 by Claisse). Selenium, tellurium and tin were added in the elemental form, whereas thallium was added as carbonate (Tl₂CO₃). A range of elements was added to provide capability for detecting known common interferences on chalcophile and siderophile elements (e.g. Gd, Hf, Ta, W, Zr, Sr). New standard glass STDGL-3 contains homogeneously distributed volatile elements (Se, Te, Tl, Sn) and precious metals (Au, Pt). A larger proportion of volatile elements was retained (100% Ge, 80% Re, 70% Te, 60% Sn, 20% Tl, 20% Se). Most problematic elements turned out to be Se and Tl, which volatilize together through a network of narrow zones, and Pt and Au, which form micro inclusions. Suitability of the new standard for LA-ICPMS analysis of sulphide minerals for trace element concentrations and Pb isotopes will be demonstrated.

[1] Wilson et al., 2002. JAAS, v.17, pp.406–409

[2] Danyushevsky et al., 2011. GEEA,. v.11, pp. 51-60