Determination of Ultra‐Trace Au, Ag, As, Pt and Re Mass Fractions in Volcanic Glasses and Rock Powders by LA‐ICP‐MS

Abstract

Practical methods for determining the ultra‐trace abundances of precious metals in geological materials are needed for research into magmatic and hydrothermal processes and to expand the geochemical footprints of concealed ore deposits. This study presents a new protocol for determining Au, Ag, As, Pt and Re mass fractions in both volcanic glasses and in rock powders prepared as nano‐powder pellets, through the synthesis and refinement of published LA‐ICP‐MS methods. This matrix flexibility allows the method and its limitations to be rigorously assessed for the first time using different volcanic materials. High‐yield laser parameters, interference corrections and low oxide production rates facilitated by laser ablation sampling enabled accurate measurements without chemical pre‐separation. A key finding is that ablation‐remobilised system contamination must be quantified and corrected to make accurate ng g−1‐level Au determinations by LA‐ICP‐MS, resulting in a mean + 2s quantification limit for Au of 0.38 ng g−1. This approach is likely necessary for other ultra‐trace LA‐ICP‐MS analyses of certain elements. Following this correction, the protocol can be usefully applied to both in situ analysis of volcanic materials and efficiently integrated into methods for the determination of major and trace elements in nano‐powder pellets.