Ore from the Rosebery mine is processed in the concentrator where the valuable minerals containing zinc, lead, copper, gold and silver are separated from waste rock. The concentrator uses a number of processes to recover the valuable minerals to form mineral concentrates suitable for sale to smelters and refineries where the pure metals are produced.
Processing begins by crushing ore as it is trucked from the underground workings. The ore passes through three crushers to reduce it to 8mm particles. The ore particle size is further reduced in tumbling mills where water is added and steel balls grind the ore to less than one tenth of a millimetre. At this size the fine grains of valuable mineral are freed from the waste rock.
Gold is the first mineral to be recovered. Fine gold particles are recovered from the ore slurry in a high “G” gravity separator. This gold and some associated silver are melted into bars sold as doré to gold refiners.
Ore is tipped into the crusher
Copper, lead and zinc are recovered next. These metals occur in the ore as sulphide minerals which can be efficiently recovered by a process called froth flotation. Chemicals or reagents are used to make these minerals water repellent so that they attach to air bubbles introduced into the slurry of finely ground ore particles and water. A specific reagent is used for each sulphide mineral so each one is recovered separately. Some of the gold is associated with the copper minerals and most of the silver is associated with the lead minerals so those metals form a part of the copper and lead concentrates. The remaining waste material, referred to as tailings, is pumped to a tailings storage facility.
Tailings generated at Rosebery are currently stored within the Bobadil facility, a side-hill tailings facility adjacent to the operation. The facility design incorporates natural topography and engineered earthfill embankments for containment.
In operation since 1974, the Bobadil facility has sufficient capacity for tailings collection until approximately 2017.
A planning application and Development Proposal and Environment Management Plan (DPEMP) were submitted to the West Coast Council (WCC) and Environment Protection Authority (EPA) in Tasmania for the development of a new facility on the site of three previous tailings storage facilities. These facilities, which are now dry, were used to contain tailings generated from operations between 1955 and 1996.