Gencor Ltd.

Several titanium placer deposits containing some 42 million tons of ilmenite have been delineated at Moebase in the Zambezia province of Mozambique. The project area is remote and field operations required detailed planning to overcome the lack of infrastructure, especially at the critical start-up phase. A fly-in/fly-out operation with a self-contained base camp and field laboratory was established in 1993. Evaluation methods consisted of detailed photogeol. mapping followed by systematic drilling and sampling. Drill samples were logged and processed in the field laboratory to provide heavy mineral grades. Heavy mineral concentrates were air freighted to Johannesburg for detailed mineralogical analyses. Resource calculations were done using a simple block model at a cut-off grade of 2% heavy mineral. To date some 30,000 m of reverse circulation drilling has identified a resource of 1253 million tons with a grade of 3.8% heavy minerals. The heavy mineral suite contains an average ilmenite content of 75% with byproduct rutile and zircon of 1.8% and 4.5% resp. The titanium content of the ilmenite ranges from 52.6% to 56% TiO₂.

A review with 8 references The 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.

Gencor Limited are pioneers in the commercialization of the bio-oxidation of refractory gold ores. They started developing the bio-oxidation (BIOX process in the late 1970s at Gencor Process Research, and the process is now being used in five com. plants. The paper describes the BIOX plants at Fairview (South Africa), Sao Bento (Brazil), Harbor Lights and Wiluna (Australia), and Sansu (Ghana), giving details of the tests conducted and the results achieved. A sixth BIOX plant is to be constructed in Peru for the Proano Tamboraque project. The plant will treat 60 t of high-arsenic concentrate per day and should be commissioned towards the end of 1996. During the BIOX process, arsenic and sulfur are solubilized before being neutralized with limestone and/or milk of lime in a two-stage process. Results from the five operating plants, as well as from extensive laboratory and pilot-scale testwork, have proved that the basic ferric arsenate precipitate formed during neutralization is stable when the molar ratio of Fe³⁺ to As⁵⁺ exceeds 3:1. The capital cost of a BIOX plant is significantly lower than that of a pressure-oxidation plant of similar capacity. The operating cost compares favorably with that of competing processes.