Applications of synchrotron X-ray techniques to orogenic gold studies; examples from the Timmins gold camp

Abstract

Understanding the association between precious metals and trace elements in ore minerals is integral to ore deposit research and exploration. In situ characterization of ore minerals is now at the forefront of this field. The power of in situ element mapping and characterization is the ability to combine geochemistry with mineralogical and broader geological context. Synchrotron radiation (SR) X-ray techniques such as X-ray Fluorescence (XRF) and X-ray Absorption Near Edge Spectroscopy (XANES) are incredibly powerful tools for studying ore systems with applications in exploration, geometallurgy, and remediation. We provide examples of these applications to gold-bearing samples from across the world-class Timmins gold camp in Canada. Analysis of thin sections, billet offcuts, as well as cut rock slabs highlights the versatility of SR-XRF and XANES analysis at multiple stages of deposit investigation and for multiple sample types. SR-XRF mapping of large areas at 20 μm resolution is very effective for quickly identifying and characterizing gold and trace element associations with gold, even in low grade and nuggety samples. Large area mapping is integral to quickly providing key geochemical information within the sample context as well as for improving efficiency and mitigating bias in grain selection for higher resolution analyses. High-resolution SR-XRF mapping and XANES analysis of individual mineral grains are compared to conventional EPMA mapping and reveals micrometer scale associations with trace metals, Au, and As. The characterization of trace element associations with different fluid events and gold mineralization styles is integral to understanding mineralizing systems and developing exploration vectors. Point XRF and XANES identified and characterized the presence and nature of refractory gold in pyrite as well as grain scale variability in As speciation. An early understanding of the distribution and redox state of gold, trace metals, and deleterious elements at the exploration stage has implications for mitigating future geometallurgy and remediation issues. The examples presented highlight the potential for the application of synchrotron studies early in the mine cycle for characterizing gold mineralization in orogenic systems.