Mineralogical study of electrum grain size, shape and mineral chemistry in process streams from the Krumovgrad mine, Bulgaria

The gold ore mined at the Krumovgrad mine, Bulgaria is processed by flotation following grinding and regrinding stages securing the targeted liberation size of the electrum which is the principal precious metal-bearing mineral. The findings from a SEM-based automated mineralogy study aiming to quantify electrum occurrences in the processing scheme are presented and the implications of these characteristics on precious metals recovery are discussed. It has been found that Au/Ag grade ratios in the electrum tend to increase in the concentrate streams and decrease in the tailings. The mineralogical analysis indicated that in comparison to the precious metals grains met in the reground rougher concentrate, those detected in the cleaner concentrate are characterized by about 10 % higher gold content. Moreover, particles possessing zones largely enriched in gold (zones where electrum is detected as having at least 90 % gold grade) are more frequently observed in the cleaner concentrate. Grains morphology suggests that the stirred media detritor (SMD) used in the regrinding circuit does not significantly modify particle shape. Likewise, opting for a staged flotation reactors (SFRs) as the main flotation units seem to be a judicious choice by maintaining conditions favouring the recovery of the ultrafine gold.