Composition, formation and leaching behaviour of supergene, polymetallic ores from the Sanyati deposit (Zimbabwe)

En savoir plus sur le livre

Copper is extracted from the supergene ore of the Sanyati deposit in north-western Zimbabwe using a heap leaching-solvent extraction-electrowinning (HL-SX-EW) process, yet recovery rates are disappointing. To investigate this issue, the composition, formation, and leaching behavior of the supergene ore were analyzed through mineralogical, geochemical, and experimental methods. The ore bodies, formed in a warm humid climate since the Miocene, are characterized by an immature and heterogeneous oxidation zone, with rudimentary secondary sulphide lenses at their base. Factors contributing to poor recovery include unfavorable grain size distributions and high compaction of the heap leach pad, alongside the ores' textural and mineralogical traits that lead to metal retention during leaching. Significant copper and other base metals are trapped by iron oxides and iron oxy-hydroxides, particularly goethite and haematite, which are prevalent in the supergene ore. The base metal distributions in these iron-rich textures lack geochemical fingerprints of their precursor sulphide phases. Goethite-rich areas show enrichment in copper, zinc, and arsenic, while being depleted in lead compared to haematite-rich areas. Experiments reveal that a substantial portion of copper and zinc is fixed within the lattices of limonite phases, remaining undissolved under leaching conditions, leading to further losses during the extraction process.