No abstract

Blasting is the dominant method of breaking rock for the purposes of mining. When used underground, blasting is part of a batch process. If rock can be cut rather than blasted, mining can become continuous, leading to process and efficiency improvements.Coal produced from underground mines is now predominantly excavated using mechanical means, but underground hard rock is still broken primarily by explosives.This paper traces the history of rock cutting, reviews the main physical processes that are or could be used, and comments on the future. It is written from the perspective of narrow-stope hard-rock mining typical of South African gold and platinum mines.This review is not definitive, but covers the most important experiences in rock cutting that are applicable to the South African hardrock environment, and discusses the future of practical techniques, as well as briefly examining some more speculative methods. The issue of the mining system is not a primary consideration -it is a topic for another paper.Rock cutting offers a number of advantages over drill-and-blast mining. Possibly the most significant is that cutting offers the opportunity for continuous operations. Blasting introduces a cycle into mining, which then forces a batch mode on the process: drill, blast, clean, support. Particularly on larger mines, where all blasting occurs at about the same time, the mining process must fit into the defined time between blasts. If the drilling, cleaning, and supporting take less than the allocated time, then time is wasted. If they take longer, then the next blast is missed. In both cases, the rigid timing leads to system inefficiency. The move to continuous processes is now considered the key to improved productivity in industry, as part of the Lean philosophy (Womack and Jones, 2003), and offers the same benefits for mining.Mechanical methods of tunnelling have the potential to be significantly faster than drilland-blast methods. In the context of mining, earlier access to the orebody considerably increases the net present value of the mine.Rock cutting has a number of other advantages:® In tunnelling and other applications that might be close to human settlements, cutting generates significantly lower vibration and noise levels than the use of explosives ® The cutting process affects the rock surrounding the excavation less than explosives, thus the rock stronger is and safer (or easier to support)A review of rock cutting for underground mining: past, present, and future by D. Vogt* Rock has been cut in the process of mining since before the invention of explosives. Today, we seek to return to cutting to reap the benefits of continuous operations for South African underground hard-rock mines, to improve speed of access to the orebody, and to improve the efficiency of mining operations. Development of new technology fits within a framework of engineering knowledge. By understanding the characteristics of the rock, the tools we use to cut it with, and the history of mining and rock cutting, we can see the g...

Borehole radar is an electromagnetic tool that can be applied to assist in the delineation of orebody geometry, ideally using routinely drilled cover and exploration boreholes. Successful trials of borehole radar for delineating reef horizons on South African gold and platinum mines have led to the development of a borehole radar system specifically designed for routine application in those environments. The radar design includes novel elements, including a receiver with instantaneous sampling down the borehole, and it is implemented in probes that can operate in 48 mm boreholes, with development planned for 38 mm boreholes. The radar is known as the Aardwolf BR40.The need for information about dislocations of 3 m to reefs determines the desirable radar resolution while available access geometry determines the range requirement. The electrical properties of typical gold and platinum rocks show that the range/resolution trade-off is feasible for the majority of economically important reef horizons. Boreholes drilled horizontally or upwards are accessed using a borehole crawler.Trials of the radar show that it meets its performance specification. The radar is robust enough for routine work underground and is easy to use. The borehole radar is a useful addition to the toolbox of the mining geoscientist because it can give information about the reef plane along a line, rather than the single point information about the reef given by a borehole.

No abstract

Radio Tomography (RT) has proven itself as an imaging tool for base metal orebody delineation. To date, theoretical considerations of the imaging technique and inversion algorithms have concentrated on the propagation of energy from the transmit antenna to the receive antenna, while ignoring the antennas themselves.The Finite-Difference Time-Domain technique for modelling antennas has been extended to efficiently model antennas embedded in arbitrary media such as rock. The model is set up with body-of-rotation symmetry to produce models that have three dimensional accuracy, while only having two dimensional computational cost. Wire dipole antennas are efficiently modelled by the addition of a subcell extension for a thin wire coated with a thin layer of insulation.The extended code is used, both to aid in the design of an improved antenna, and to investigate how the performance of the antenna affects the imaging of RT data in particular circumstances. A completely insulated antenna is preferred because its performance is more independent of the surrounding rock. The numerical model aids in the design of an improved antenna, with the optimum combination of performance features in a physically realizable antenna. If the electronics package is placed at the end of the dipole, the electronics package can be housed in a bare metal pressure casing without significantly affecting antenna performance as a function of rock type.The model also shows how the use of RT can be influenced by the geometry of the system and particularly by the use of conductors to suspend the RT antenna: wire cable support is not recommended until full waveform inversion techniques can take into account the presence of the wire. Antenna arrays appear to be viable, but if antennas without insulation are used, the spacing between the antennas should be at least as great as the length of each antenna.