The processing behaviour of the sphalerites from the Big Syncline deposit, South Africa

Abstract

Abstract Big Syncline is one of the few unexploited deposits of the Aggeneys-Gamsberg Ore District of the Northern Cape Province of South Africa and comprises Zn > Pb > Cu mineralisation. Future exploitation of this deposit requires a good understanding of the mineralisation textures and mineralogy for beneficiation purposes. Two of the most commonly occurring mineralisation types at Big Syncline, the mineralised pelitic schist (PEL) and garnet-magnetite-associated mineralisation (GM), are investigated with regards to sphalerite petrography and mineralogy and their potential impact on Zn flotation recovery and grade. Detailed optical petrographic analyses revealed three colour variations in the sphalerite: the opaque (i.e., black) and ruby-red varieties prevalent in the PEL; and the honey-yellow variety more common in the GM. Scanning electron microscopy with energy dispersive X-ray spectroscopy (EDS) analyses indicated increasing Fe content from the honey-yellow to ruby-red to opaque sphalerite varieties. The latter two varieties were also observed to have elevated Mn contents. Laboratory-scale differential flotation tests were applied on the two mineralisation types to determine their processing behaviour. Despite poor selectivity, the GM produced a bulk Zn concentrate of superior quality to the PEL. However, the latter showed better selectivity with the bulk of the Zn reporting to the Zn concentrate. The reduced overall quality of the PEL concentrate is attributed to the increased dilution. This is due to the high abundance of gangue sulphides in the flotation feeds as well as higher Fe and Mn contents in sphalerite. The higher Mn content in the PEL sphalerites also leads to higher Mn recovery and grade in the Zn concentrates. Although the GM overall has higher Mn contents, it is hosted in silicates leading to substantial Mn rejection to the tailings.