Geochemical and Mineralogical Comparison of XRT-XRF Scanning Technology Versus Traditional Analysis of Drill Core from the Assarel Porphyry Copper-Gold Deposit (Panagyurishte District, Bulgaria)

Abstract: Ongoing, environmental and economic matters related to mining sustainability and its impacts are leading to the search for new ways to asses and extract commodities more efficiently. A key aspect in the shift to more sustainable mining is the rapid, digital characterization of orebody mineralogy and geochemistry to help optimize the extractive process. A novel scanning instrument aligned with this goal is the GeoCore X10 system, presently developed by Orexplore AB (Stockholm), which provides 3D images and geochemical compositions of scanned drill core using integrated XRT/XRF analysis. This study aims to assess this scanning technology on drill core from a porphyry Cu deposit (Assarel mine, Bulgaria) with a focus on the geochemical and mineralogical character of a single selected drill hole (XM001). Scanning results are compared with results derived from other more standard-type used lab techniques such as optical microscopy (transmitted and polarized light microscopy), semiquantitative X-rays diffractometry (XRD) and electron microscope probe analysis (EMPA/EDS). Observed discrepancies between the different methods are assessed and used to provide feedback to improve results for future drill core scanning studies. The mineralogical XRT/XRF output shows that the XM001 includes 53 minerals, which is refined based on the other investigative methods. The minerals include quartz, plagioclases, chlorite, K- feldspars, muscovite, pyrite, magnetite, chalcopyrite, rutile, zircon, and other possible minerals such as gypsum, pyrrhotite, siderite, goethite and bornite, among others. On the other hand, the main chemical elements recognized by all methods used are, in decreasing order: O, Si, Al, K, Mg, Fe, Ca and S, which represent an estimated of ca. 98 wt % of the core. The most relevant trace element defined is Cu and it was possible to define relevant (potentially) economic accumulations of Cu along XM001 considering values > 2 000 ppm. Comparison of microscopy, XRD and EMPA/EDS results for 10 samples collected from XM001 with XRT/XRF scanning results at the same indicate discrepancies of ± 10-20 wt % for the main chemical elements (O, Si, Al, K, Mg, Fe, Ca, S and Cu). Overall, the GeoCore X10 scanning instrument provided geochemical and mineralogical output data from XM001 that is consistent with other more traditional analytical techniques. However, it is suggested scanning results need to be refined, especially the mineral list, which includes mineral phases such as barite, yttrialite and ‘Co-olivine’ which are not occurring. This happens as elements such Ba, Y and Co more likely occur as substituents in other minerals rather than forming independent phases. To treat the geochemical results, it is needed to establish an initial criterion to understand how to analyze such highly detailed scanned information. Here, it is proposed to divide the drill core according to geological features such as lithological, alteration and/or mineralization variations and treat the different zones separately.