Au analysis by pressed-powder-pellets (PPP)-LA-ICP-MS

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 source rocks is extremely low and the methodologies allowing analysis at sub-ng/g levels are time-consuming, costly and generally involve handling of dangerous chemicals. Here we present a new, faster, cheaper and safer method for low Au concentration analysis by Laser-Ablation Inductively-Coupled-Plasma Mass-Spectrometry (LA-ICP-MS) of pressed-powder-pellets (PPP), which has been developed in the Laboratory for Environmental and Raw Materials Analysis (LERA) at Karlsruher Institut für Technologie (KIT). 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 us to increase the Au sensitivity while keeping oxide production low. Indeed, the latter is critical when analysing low concentration Au samples as the ICP-MS analysis is generally impaired by Ta181O16 and the Hf180O16H1 interferences. Reducing the oxides allows the PPP-LA-ICP-MS method for better quantification and correction of these interferences. The new method improves the detection limit down to 0.05-0.1 ng/g Au. Routine analysis of reference materials shows that Au analysis by PPP-LA-ICP-MS is both accurate and precise. This contribution highlights that the method is suitable for investigating Au distribution and behaviour in Au depleted rocks.