Development of a viable process for the recovery of zinc from oxide ores by

The whole-ore-leaching concept applied at Skorpion Zinc in Namibia relies on the economical leaching of zinc minerals with sulphuric acid solutions under atmospheric conditions. Economic viability is premised on the selective mining of the zinc oxide ore from a limestone pit shell. Subsequent to the successful commissioning of Skorpion Zinc in 2003, a number of deposits, historically considered to be similar to Skorpion, have been investigated in greater detail and exploration activities stepped up. Green Team International (Pty) Ltd (GTI) has been involved in the development of two such projects for Metalline Mining and Zincore Metals Inc., respectively. In both cases, it was found that whole-ore-leaching is unlikely to be economically viable due to the presence of sulphuric acid consuming gangue minerals, which in contrast to Skorpion, are present throughout the deposits. Metalline’s Sierra Mojada (SM) Project is located in the state of Coahuila, Mexico and was discovered in 1879 as a silver deposit. Later, silver-copper deposits in the area gained importance, and finally lead was also discovered as a lead-carbonate (cerussite) manto. Oxide zinc was discovered in the 1920s. Without exception, exploitation of these deposits has always been through selective mining with shipping of high grade zinc ore directly to customers, such as smelters and fertilizer producers. The Accha-Yanque property covers over 30 000 hectares and consists of 41 concessions over a 30 kilometre distance in Southern Peru. Accha is 70 km from the Andean town of Cuzco at the north end of the property with Yanque at the south. A number of zinc prospects, with limited exploration, occur between these two deposits. Zincore Metals are currently prioritizing the development of Accha and Yanque, for which a greater body of knowledge exists. Metallurgical design and test work carried out to date was aimed at developing viable flowsheets for the treatment of run of mine (ROM) ore from these deposits, using proven technology. Test work comprised both mineralogy and bench-scale metallurgical test work. Although considerable work has been done on the SM and Accha deposits, test work on Yanque commenced recently and is not dealt with here.