Hyperspectral response to hydrothermal gold mineralisation
integration of Geochemical & Hyperspectral Data
It has become common place within the resource industry to obtain mineralogical information at different stages of mineral exploration and metallurgical investigations using a variety of methods. These include hyperspectral analysis (thermal-, near- and short-wave infrared), quantitative X-ray diffraction (XRD), thin section petrography, and quantitative scanning electron microscope (SEM) analysis. Modern analysis of these datasets allows quantification of mineralogical parameters that can be useful for tracing hydrothermal alteration patterns and for geometallurgical studies. Similarly, suitable lithogeochemical data can be used to infer mineralogical parameters and define trace element enrichment patterns associated with hydrothermal alteration. Less common is the integration of these two data sets to provide cross validated interpretations of alteration patterns in 1, 2 and 3 dimensions. Telemark Geosciencesprovides integrated geochemical services that incorporate diverse data types to optimize the interpretation of geochemical and mineralogical data for integration into exploration and geometallurgy.
White Gold District Example
An example of this approach is provided by integrated hyperspectral and geochemical analysis of diamond drill core from the VG Zone discovery on the QV property of Comstock Metals Ltd in the White Gold District of the Yukon Territory of Canada. Selected major and trace elements from drill core samples reflect mineralogical changes in the felsic orthogneiss host rock during hydrothermal alteration associated with gold mineralisation. The core samples were analyzed using a near-total 4-acid digestion in order to obtain data that will detect changes in silicate mineralogy during hydrothermal alteration, as well as information on important pathfinder elements known to be enriched (or depleted) at the same time that gold was introduced into the rocks. A split of coarse (<2 mm) material from most core samples was also analysed using short-wave and near-infrared radiation on a HyLogger operated by Bureau Veritas Minerals Pty Ltd in Australia. Rather than interpret the hyperspectral data simply in terms of mineralogy, spectral parameters that characterize changes in mineral composition within hydrothermally altered rocks have been plotted in order to demonstrate the correlation of the hyperspectral response with the lithogeochemical data. Trace element data extend the observed downhole width of the hydrothermal alteration halo by an additional 80 % compared to gold data alone, and the hyperspectral data increase the downhole width of the halo by as much as 50 %. While this case study is relatively straight forward to interpret (ie. intercept of interest encompasses a single uniform lithology), complications introduced by lithological variations and structure require an integrated interpretation of multiple data types in order to produce a rigorous interpretation.
The applicability of field portable technologies such as X-ray fluorescence, X-ray diffraction and hyperspectral analysis can be assessed once the characteristic geochemical and hyperspectral parameters have been identified in orientation surveys such as the one described here. These data allow the recognition and definition of hydrothermal alteration patterns in the field and provide rapid targeting aids for exploration programs. Such aids will become more important as mineral exploration shifts increasingly towards drilling buried exploration targets
Summary of Hyperspectral and Geochemical Data from the VG Deposit, Yukon, Canada
The mineralised zone is evident in the wavelength of the AlOH absorption peak in white micas, which is an indication of a shift to more muscovitic compositions