Abstract:
Good support design is of paramount importance in a bid to mitigate rockfalls. Most platinum mines using room and pillar method have failed to reach the target milestones of zero harm due to the presence of geological discontinuities. Geological discontinuities along the Great dyke of Zimbabwe comprise of shear zones, sympathetic joints together with dykes. The prevailing geological structures have led to a decrease in productivity and challenges of support failure. Virtuous mining practices together with good support design will lead to an improved productivity, less operating costs and improved safety. The need to improve the key performance indicators led to the compulsion for this research to be conducted based on support design and mining practices in bad ground conditions. Geological data and geotechnical data were obtained from a Zimbabwean platinum mine. It was clinched that the presence of shear zones deteriorated the rock mass which have led to the unpredictable unravelling of the rocks. The current support systems as well as the mining practices were analyzed and benchmarked. Empirical support designs together with numerical modelling were used to design optimum support system. Support design encompasses regional support of pillars and local support of roofbolts. Various rock mass classification methods were used to get the quality of the rock. From the analysis of the current support systems used, it was noted that the current support systems together with mining practices need to be adjusted for sustainable operations. Furthermore, the current mining practices need to be revised since the use of ANFO explosive results in excessive bad hangings, stoping overbreak and increased costs. The bords currently mined gave a shorter stand-up time which again compromises safety. Pillars need to be redesigned together with the implementation of a new roofbolt system to improve both productivity and safety. Optimum pillar design which gave the prime extraction ratio without compromising safety was proposed.
Introduction
Upright support design and sound mining practices warrants economic and sustainable mining operations. This research makes a crucial review of the current support systems used in bad ground conditions at a Zimbabwean platinum mine. The area of research is sited on the Great Dyke of Zimbabwe and is infested by faults and sympathetic joints. Platinum Group Elements (PGEs) are the primary metals exploited and base metals are also recovered. The orebody is shallow having a maximum depth of 250m. The Zimbabwean Great Dyke is the second leading reserve of PGEs following the South African Bushveld complex (Oberthür et al [7]). The comprehensive section of the Great Dyke is virtually a bowl shaped which encompasses strata that are dipping towards the axis. The Dyke encompasses for about 550km having a maximum width of 11km (Prendergast [8]). The Mineralized Sulphide Zone (MSZ) contains the minerals of interest and the economic thickness averages 2m. The host rock of minerals is pyroxenite which is sandwiched by bronzitite and websterite. The average dip of the reef is 11 degrees. Figure 1 shows the cross sectional view of the strata.
