Resumen
Over the years the theft of material from platinum producers has mainly taken place from high-grade areas such as the precious- and base-metal refineries and the converter and smelting operations. At some concentrators, the metallic stream, which concentrated the larger platinum group mineral (PGM) grains using shaking tables (a gravity process), was also at risk due to its high grade. However, the processing of metallics was discontinued many years ago. The relative low grade of concentrator products has led to the belief that the concentrators are a low-risk area for theft. The final products are still very diluted by the gangue minerals, and to recover and purify the various metals contained in these products requires costly processing techniques (i.e., smelting and refining). High-grade stolen products are generally offered to small refineries who either further process, and package, or directly ship the material overseas for refining. In the case of stolen concentrates, the volume and value of the material would make that an unprofitable option. This assumption, as well as the risk the thieves run of being caught while removing large quantities of material from the concentrators, has resulted in management considering theft from concentrators of lesser importance than theft from the smelters or refineries. However, over the past few years investigations by protection services at concentrators have shown that high-grade platinum products are smuggled off-site. These products have been found on the concentrator as well as at illegal smelthouses where these type of products are processed further. Forensic investigations indicated that these upgraded products are much higher in grade than the normal concentrator products, characterised by high platinum contents, and contain high-density minerals such as galena (lead sulphide) and chromite. This suggests that these materials are significantly upgraded prior to smuggling these out of the operations. The method used by the perpetrators results in much of the value minerals being discarded, giving rise to concentrates that are atypical of Bushveld products. To better understand the process of upgrading these products and to get more information for the ?fingerprinting? database on the ?at-risk products?, concentrator products were obtained from areas where material is stolen for further upgrading. This paper describes the upgrading process used by the illegal ?processors? and discusses the mineralogy and chemistry of the various products down the illegal processing chain. The study indicates that products containing coarse, liberated platinum-group minerals are the most favorable for upgrading. Flotation products with high precious metal grades and low chromite contents are preferred by the syndicate members. These are typically the first cells of the rougher banks, final concentrates, and the various cleaners and re-cleaners feeding into the final concentrates.