Fill support systems for deep-level gold mines

The use of fill in deep-level gold mining presents the possibility of achieving considerable economic and operational benefits if conventional support can be eliminated. Unfortunately, the combination of the properties of tailings from gold reduction plants and the narrow, flat, tabular reefs being exploited make conventional hydraulic filling very unpractical. Laboratory tests indicate that, with careful control of water content, these tailings can provide an adequate fill material. A variety of bonding agents have been investigated, and the most practical seems to be ordinary Portland cement. Even at very low cement contents some cohesion is achieved. The design and layout for a complete fill support system using hydraulic transport, dewatering, and pneumatic placement are discussed, and a surface field trial indicated that the principles involved are correct and that acceptable results can be achieved. This system and material would completely eliminate conventional timber and brick support, and a preliminary economic analysis indicates that filling is cost competitive on a direct replacement basis. All the operations for a full-scale operation are available or have been developed to a stage sufficient to indicate that the system is practical, although certain operations require further refinement.