Analysis of platinum-group elements (PGEs) and Au in geological materials at ultra-trace levels: Technique development and applications

Platinum group elements (PGEs) and Au have important applications in terrestrial and planetary geochemistry but because of their low abundances (≤ng/g—parts per billion), they are inherently difficult to quantify. A cation exchange-standard addition technique in combination with ultrasonic nebulization-inductively coupled plasma-mass spectrometry (USN-ICP-MS) is developed to quantify accurately and precisely low- to sub-ng/g PGE and Au abundances in geological samples. This technique now allows quantification of Ir and Pt in samples containing elevated abundances of Hf and Ta, which form polyatomic oxide interferences. This was not possible using the previous USN-ICP-MS method (O'Neill, 1996). The cation exchange-standard addition technique has superior detection limits and generally lower procedural blank levels than other current techniques. Reproducibility in small sample sizes (≤250 mg) is demonstrated using a rehomogenization procedure on reference material UMT-1.; Abundances of PGEs and Au were determined in a variety of geological samples to demonstrate the robustness of the technique and the diversity of PGE applications. This technique has been applied to a variety of samples to solve the following geological problems: (1) Establishing a core-mantle boundary origin for basalts from a large igneous province—the Ontong Java Plateau; (2) An investigation of a fraudulent mining claim in Nevada; (3) An investigation of potential Rh, Pd and Pt pollution from the breakdown (attrition) of automotive catalytic converters; (4) A study of the Cretaceous-Tertiary boundary in Montana; (5) Determination of PGE abundances in Martian meteorites to investigate planetary differentiation processes and evaluate the effects of a late veneer of meteoritic material on planetary composition and evolution; (6) A brief look at PGE abundances in lunar basalts.