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Unconventional gold recovery process from hard rock, in opposition to alluvial gold, using neither gravity nor leaching processes but only comminution and flotation are very rare, although they allow a cost-effective concentration of precious metals. The main problem faced by this type of operation in case of low gold and silver grade such as the Khan Krum deposit near Krumovgrad town in south Bulgaria is the ability to recover a sufficient amount of precious metals that are finely disseminated (95% finer than 100µm). The present work aims to investigate the effect of ore mineralogy on this recovery by focusing on gold occurrences (mainly electrum) and clay minerals impact on plant flotation performances. The study is based on characterization of plant stream samples in order to comment their size distribution, mineralogy and precious metals grains characteristics with SEM analysis. Unfortunately, the low samples grade implied a small number of precious metals grains observed per polish section making statistical analysis of electrum particles irrelevant. However, it was possible to demonstrate that Au:Ag grades ratio increases in concentrate streams, because the more gold is contained in the electrum the better its flotation. Flotation tests were performed on crushed run of mine samples to test new collector mixture and evaluate the impact of fines particles on flotation metallurgical answer. Low silver grade (<1ppm) in flotation tailings did not provide accurate silver recovery calculation. Kaolinite presents mainly in slimes play an important role on froth stability and concentrate grade but has almost no impact on precious metals recoveries. The use of AERO MAXGOLD 900 which has an affinity for precious metals stronger than xanthate could be a way to enhance concentrate grade but do not allow significant recovery amelioration.

Gold --- Silver --- Flotation --- Recovery --- Clays --- Ingénierie, informatique & technologie > Géologie, ingénierie du pétrole & des mines