The Broken Hill deposits form part of the Bushmanland Group which is a volcano- sedimentary sequence that hosts ore deposits (Reid et al., 1997). This group has metapelitic rocks that are CaNa-Mg depleted. The group’s ore body is divided into two types: a pyrrhotite-galena-sphaleritechalcopyrite ore hosted by quartz-garnet-rich gangue (Black Mountain and Broken Hill) and a pyrite-pyrrhotite-sphalerite ore hosted by quartz- biotite-sillimanite gangue (Big Syncline and Gamsberg). The principal ore minerals are sphalerite, galena and chalcopyrite with garnet and apatite being minor constituents. Barite horizons occur as lateral equivalents of the sulphide ores at Black Mountain and Gamsberg and calcitic marble bands are associated with the Big Syncline and Gamsberg (Moore et al., 1990).

Despite the discovery of Gamsberg zinc deposit in 1972, the ore body continues to be South Africa’s greatest unexploited base metal resource. Regardless of its size, the low zinc and high manganese content of the sphalerite combined with the low zinc price prohibits the development of the deposit. The high manganese content of the sphalerite makes it unsuitable for processing by conventional methods i.e. roasting, leaching/ solvent extraction and/or electrowinning (McClung & Viljoen, 2011). The ore body has two distinct ore types, namely pelitic and garnetmagnetite ore.

Gamsberg is one of the largest known, undeveloped zinc orebodies in the world and comprises an open pit mine and a dedicated processing plant.

During Phase 1, at full production capacity Gamsberg will produce 4 000,000 tonnes of ore from its open pit mine and 250,000 tonnes per annum of zinc-in-concentrate.

Studies into Gamsberg Phase 2 and 3 are underway which will see ore mined increase to 8 million tonnes per annum and production of zinc-in-concentrate to 450,000 tonnes, and, in a modular fashion, ultimately to 600,000 tonnes per annum. It will reflect an additional investment of US$350 to US$400 million.