Improved whole rock low detection limit gold analysis by LA-ICP-MS utilizing pressed-powder-pellets

Abstract

Analysis of Au in geological materials has been proven useful for understanding geological processes related to the formation of various Au-rich ore deposits. However, the Au concentration in the related source rocks is extremely low (∼<1 ng g−1) and the methodologies allowing analysis at sub-ng g−1 levels are time-consuming, costly and generally involve the handling of hazardous chemicals. Here we present an improved method for low Au concentration analysis by laser-ablation inductively-coupled-plasma mass-spectrometry (LA-ICP-MS) of pressed-powder-pellets (PPP). Fine instrumental tuning for key parameters such as ICP-MS sample gas flow, torch position, RF power, laser frequency, ablation style and laser gas flow allows increasing the Au sensitivity while keeping oxide production low. The latter is critical when analyzing low Au concentrations as the ICP-MS analysis can be impaired by 181Ta16O and 180Hf16O1H interferences. Reducing oxide production and quantifying interferences by analyses of matrix-matched Ta- and Hf-doped pellets, allow for efficient corrections. The method improves the method limit of detection with values as low as 0.10–0.05 ng g−1 Au and routine analysis of reference materials shows that Au analysis by PPP-LA-ICP-MS is reliable. This contribution highlights that the PPP-LA-ICP-MS method is suitable for investigating Au distribution and behavior in Au-depleted rocks.