Point, Map, or Traverse Mode for LA-ICP-MS Analyses: Evaluation using Auriferous Arsenian Pyrite

Abstract

Laser ablation inductively coupled mass spectrometry has become a widely used analytical method in the Earth sciences. Among its many applications, it is extensively used to produce elemental maps and collect in situ point data for sulfides in a variety of ore-deposit settings, with orogenic and intrusion-related gold among the most prominent. There has, however, been little attention given to protocol to ensure the data collected best reflects the varied degree of metal enrichment and elemental associations in the target material, which is paramount to assessing and interpreting the significance of relevant geochemical signatures. Using auriferous, arsenian-poor pyrite from the Neoarchean Magino intrusion-related gold deposit setting (Ontario, Canada), we evaluate three methods—point, mapping, traverse—to assess which of these provides the most representative data in a timely and cost effective manner. The results suggest that traverse mode best addresses these latter two issues when the derived data are processed using the time slice dataset method in binary element plots (e.g., Au versus As and Ag) whereby the content of a third element is also evaluated. Additionally, the chemical profiles from traverses allow one to document, evaluate, and scrutinize better the presence of micro-inclusions and better assess their relevance in regards to how Au is mobilized and upgraded in ore samples.