As the Witwatersrand Basin of South Africa loses its dominance in world gold production, and production from hydrothermal resources continues to increase so there is an upward trend in the exploitation of the so-called refractory zones associated with these deposits.These ores are pyritic in nature, often containing appreciable quantities of arsenic as arsenopyrite.Much of the gold is occluded in the crystal structure of the sulfide minerals, particularly the arsenopyrite.As a consequence, a much higher level of processing is required when compared to conventional "oxidized" ores, with greater pressure on the environment.Together with this trend in gold production, significant advancements have been made in the development of alternative recovery technologies.From the environmentally hazardous Edwards roasters through the more sophisticated fluosolids system, to second generation hydrometallurgical processes of pressure and biol. oxidationThe paper demonstrates how technol. developments have not only been driven by the normal quest for lower costs and higher recoveries, but in this case by consideration for plant safety and the environment.The modern plant is considered "environmentally safe" with respect to current discharges.However, will they be just as safe in the long term.

Journal of the South African Institute of Mining & Metallurgy

Summary of present knowledge on the representative sampling of ore in the mining industry

作者: Assibey-Bonsu, W.

A review with 8 referencesThe paper discusses some theor. aspects of Gy's sampling theory and provides reasons as to why it has found limited use in the mining industry, particularly for ores with low concentrations of values such as gold.These types of ores are referred to as low-grade ores in the paper.It is shown that the misuse of the a priori liberation factor proposed by Gy is the main reason for the implementation limitation of Gy's model for low-grade ores.In addition, results of a case study done at the Gencor Geostatistics Department based on the new implementation of Gy's theory are provided.

South African Journal of Geology

The geology of the Upper Critical Zone, northeastern Bushveld Complex, South Africa

作者: Lea, S. D.

An eight year drilling program on the farms Doornvlei 456 KS, Voorspoed 458 KS, and Zebediela's Location 123 KS in the northeastern Bushveld Complex has yielded new stratigraphic information in a poorly exposed and relatively little known section of the Rustenburg Layered Suite.Within the Upper Critical Zone, close similarities are evident with the stratigraphy previously reported at the Impala Platinum and Karee Mines, some 250 km away across the central hub of the Bushveld Complex.These comparisons extend to the lateral variation of this stratigraphy over several kilometers.The stratigraphy at the Atok mine, 30 km to the east, is more contrasting due to its location across a sector boundary.On the basis of Platinum Group Element (PGE) value distribution, the Merensky Reef on Doornvlei corresponds to the Western Plats-type described in the Western Bushveld.Further west on Voorspoed and Zebediela's Location, there is a transition to a Marikana-type reef with the inclusion of a pegmatoidal layer in the mining width.Similarity, stratigraphic strike variation is reported for the UG2 Chromitite Layer, Bastard Pyroxenite, and footwall units of the Merensky Pyroxenite.Chromitite layers within the Upper Critical Zone are markedly enriched in base-metal sulfides, particularly segments of the UG1 and UG2 Chromitite layers where unusual textural variation occurs.Platinum group mineral (PGM) assemblages in the Merensky Reef on Doornvlei are dominated by intermetallic compoundsBase-metal sulfide and silicate assemblages indicate deuteric or metasomatic modification.Further west such modification is less evident and PGE sulfides are the commonest PGM.Intermetallic compound assemblages also dominate the UG2 reef.The reef includes a well mineralized footwall pegmatoidal layer which also shows metasomatic/deuteric alteration.

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