Bewick, R, Brzovic, A, Rogers, S, Griffiths, C & Otto, SA 2022, 'Benchmarking framework for porphyry copper-gold rock masses for caveability and fragmentation decision-making', in Y Potvin (ed.), Caving 2022: Proceedings of the Fifth International Conference on Block and Sublevel Caving
, Australian Centre for Geomechanics, Perth, pp. 1303-1318, https://doi.org/10.36487/ACG_repo/2205_91
Caveability and fragmentation are two important aspects in a caving project; being very high risks or fatal flaws if they are not properly assessed. There is evidence from historic and current caving mines that there has been significant failure of revenue recovery because the rock mass characterisation process did not properly determine the key elements that control rock mass behaviour.
The main rock mass characteristics of porphyry copper-gold orebodies are the networks of vein systems where most of the ore is located which are super imposed by faults systems. At depths greater than about 500 m, in these massive, competent and multimineral orebodies, joints are typically sparsely occurring or almost nonexistent. The main structural features that control strength in these rock masses are faults and the subset of veins that are infilled with minerals of weak strength such as gypsum, calcite, chlorite, and, in some cases, chalcopyrite. Traditional caveability and fragmentation assessments use classification schemes and tools that are not designed for a rock mass without joints (except for the in situ rock mass rating system). Rock masses that match these structural characteristics have been shown to range in fragmentation and caving performance from good to not so good.
This paper presents the benchmarking framework that focuses on the key porphyry rock mass characteristics of fault/open structure and weak vein system intensity. A matrix has been developed to allow for consistent benchmarking of rock masses in porphyry deposits so that caveability and fragmentation challenges may be better forecasted in the future and engineering design decision making improved.
Keywords: block cave, caveability, fragmentation, discrete fracture network, rock mass characterisation, rock mass strength
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