2022 年 25 巻 1 号 p. 33-39
The Zone 5 Cu-Ag deposit is the most consistently (for ～4.2 km) mineralized deposit in the Khoemacau district in northwestern Botswana, with an underground mineable resource of ～100 Mt grading 2 % Cu and 21 g/t Ag. The deposit consists of a redox-buffered metal-zoned ore body hosted preferentially by chemically reduced meta-sediments overlying oxidized hematite-bearing arkosic sandstone. Ore-grade mineralization is typically hosted in variably deformed quartz-calcite veins, along metamorphic cleavage, along bedding, in shear fabric, and in folds. Geochemical assay data established during exploration indicates widespread signifi cant concentrations of Ag, correlating positively with Cu. In this study, we apply a Bruker M4 TORNADO micro-X-ray fluorescence (μXRF) scanner for multi-element mapping in selected highgrade drill core samples, with particular focus on Ag partitioning. Collection of μXRF data was followed by microscopic and SEM-EDS observations to validate results. The μXRF data coupled with petrographic results indicate: i) μXRF multi-elemental mapping on the Zone 5 drill core samples was very eff ective and can be applied as a fi rst order geochemical analytical tool for characterizing mineralization and targeting important sections of the core, ii) silicification contributed to cleavage formation, which later became important ore trap site, and iii) Ag is closely associated with Cu and Fe. SEM-EDS results show that native silver and stromeyerite in part co-precipitated with hematite post Cu-(Fe)-sulfi de deposition.
