Advancing exploration hydrogeochemistry using single particle inductively coupled plasma–time-of-flight mass spectrometry at the Bear Lodge alkaline complex, Wyoming, USA

In this study, we demonstrate the use of single-particle inductively coupled plasma–mass spectrometry (spICP–MS) as a new tool for exploration hydrogeochemistry through a case study at the Bear Lodge alkaline complex in Wyoming, USA. Nanoparticulate forms of gold and associated pathfinder elements (Ag, Sb, Bi, Tl and Te) were detected in well waters proximal to rare earth element (REE) and Au mineralization, resulting in stronger geochemical anomalies compared with conventional acidified water analysis. Using the multi-elemental capability of spICP–time-of-flight MS (spICP–ToF-MS) to analyse waters, we detected REE particles that were hypothesized to be nanoscale REE mineral grains originating from the oxidized zone of carbonatite mineralization. For the first time, we present chondrite-normalized REE patterns from individual nanoparticles, allowing for geochemical interpretations based on light rare earth element enrichment and Ce anomalies. This study demonstrates that spICP–MS analysis of waters could be a valuable tool to detect concealed mineralization in environments with weak hydrogeochemical signatures. Moreover, the detection of indicator minerals using spICP–ToF-MS represents a novel use of the technique that may provide additional, previously unattainable information from water samples.