Influence of gold mineralogy on its flotation recovery in a porphyry copper–gold ore

Abstract

The present study investigates the implications of gold mineralogy on its flotation recovery, in a typical porphyry copper–gold ore (1.7g/t Au feed grade). Also, flotation strategies to optimise gold recovery and grade without compromising copper recovery and grade were examined. The approach used in this study involves a combination of different mineralogical techniques such as quantitative X-ray diffraction (QXRD) and scanning electron microscopy (QEMSCAN). Based on the mineralogical information obtained, different collector regimes involving sodium iso-butyl xanthate (SIBX), N-butoxycarbonyl-n butyl thionocarbamate (XD5002), mercaptobenzothiazole (MBT) and dithiophosphate (DTP) at different grind sizes (p80, i.e. a nominal product size of 80wt% passing (a) 70µm and (b) 38µm screen) were tested to examine the flotation behaviour of gold in relation to copper recovery. Chalcopyrite and covellite are the principal copper mineral phases in the ore, with pyrite as the main sulphide gangue mineral. Quartz, Fe oxide and carbonates were identified as the main non-sulfide gangue minerals. The identified gold particles occurred as either liberated particles (∼10–22µm) or fine inclusions (∼1–3µm) in pyrite, biotite and sphalerite. Two-stage flotation (copper and pyrite rougher stages) at a p80 of 70µm indicated that high gold (95.2%) and copper (97.4%) recovery can be achieved, but the levels of pyrite in the concentrate are also very high (49.1%). At finer grind (p80=38µm) and without pyrite flotation stage, gold recovery decreased from 95.2% to 73%, but at an improved grade (5.3g/t) compared to 3.5g/t in the baseline. This approach improved gold grade significantly due to a drastic reduction in pyrite recovery. The flotation study indicates that the collector regime, SIBX/XD5002 (at 38µm feed size) gives the maximum gold recovery and grade while rejecting significant pyrite without compromising copper recovery and grade. Further studies are warranted to identify means of recovering Au from the copper flotation tail.