Lithological discrimination of altered volcanic rocks based on systematic portable X-ray fluorescence analysis of drill core at the Myra Falls VHMS deposit, Canada

摘要

Portable X-ray fluorescence (pXRF) analyzers can rapidly and inexpensively provide chemical concentrations of a range of geologically significant elements, often with instrument detection limits below 10?s of ppm. We compiled conventional XRF lithogeochemical data from Myra Falls to assess Ti/Zr discrimination criteria for volcanic-hosted massive sulfide (VHMS) host rocks at Myra Falls. Robust and discrete Ti/Zr trends for coherent volcanic rock types were identified from this dataset. To test if pXRF analysis could reproduce these trends, two experiments were designed. Single-spot pXRF analyses of pressed powdered drill core samples and three-spot pXRF analyses measured directly on the flat, cut surface of drill core samples were compared to conventional XRF results from the same sample sets. Our results indicate that both pXRF sampling methods reproduce the laboratory based XRF results for Ti and Zr, and that there is no significant improvement in accuracy or precision between drill core powders and unprepared drill core samples. We propose a calibration, estimation of total measurement uncertainty, and data reduction procedure for systematic three-spot pXRF analysis of drill core samples to improve lithological logging of altered volcanic rock types. We suggest that pXRF analysis become a routine part of lithology logging providing, for some key elements, robust and time-efficient chemical analyses with results that can be used to define important, often cryptic, lithological boundaries at Myra Falls. Portable XRF therefore has the ability to improve geological and stratigraphic interpretations, which are vital for developing mineral exploration models, for VHMS deposits and other economic mineral systems.