The primary rock excavation in hard rock mining is dependent on the proper application of the drill-and-blast process. The main purpose of blasting is to break up the solid rock mass into pieces that would be easier to load, haul, and crush. NONEL initiation systems using pyrotechnic delay shock tubes remain popular owing to the simplicity in handling and low unit price. However, pyrotechnic delays have chemical scatter within the range of 3-5% (1% nominal scatter), resulting in improper detonation, excessive fines formation, and poor fragmentation.
Electronic detonators make use of integrated circuit microchips and ceramic clocks in order to overcome these problems. With the help of electronic initiation, the blasters can set up delays on site in 1 ms steps with nearly no scatter (±0.1 ms accuracy). This technical article focuses on the comparison between the electronic and non-electronic initiation systems in terms of rock fragmentation and productivity.
The precise control of delay interval times is important in controlling the explosive energy release rate and, hence, the muckpile size distribution. In bench blasting, the programmed delay helps reduce the burden on each borehole before subsequent detonations. Double-hole bench blasting tests carried out using granite models show that the delay time determines the most dominant rock failure mode.
The use of a short delay time interval of 13.69 to 54.72 µs, where stress-wave superposition occurs, increases horizontal crack propagation and slope failure. When the delay time increases to 180 µs (which corresponds to 9 ms in bench blasting in the field), the dominant failure mode changes from slope breakage to vertical crack propagation. Vertical crack propagation creates new free surfaces for adjacent blast holes and increases rock fragmenting, even without stress-wave superposition. From experimental results, the use of delay interval of 180 µs increases the average fragment size (x50) by 20% to 25%.
Field production data from Gold Fields Ghana Limited (Tarkwa Gold Mine) support these experimental results. At the Tarkwa mine, the primary crushing equipment’s requirements demand that 80% of the muckpile should be below 240 mm so that materials can flow freely. Comparing pit trials shows that blastholes using electronic detonators always achieve the 80% passing requirement compared to those using pyrotechnic NONEL shock tubes. Blasts using pyrotechnic NONEL shock tubes cannot meet the 80% requirement in 33.33% of cases and create a bottleneck in the crusher.
Consistent muck pile fragmentation creates real advantages throughout the loading, hauling, and crushing system stages. Increased consistency of muck sizes improves the efficiency of diggers and loaders. The primary crushing capacity is significantly improved in the absence of oversized boulders, as well as reducing the wear of the crusher liners and secondary crushing cost. Studies show a 20%-25% decrease in the mean size of blocks related to the implementation of electronic systems, thus increasing mining efficiency.
The usage of electronics brings safety measures into effect as well. Electronic detonators are protected against static electricity, stray currents, and radio frequency. There is two-way communication between the bench firing box and each individual detonator, allowing blasters to identify open circuits and malfunctioning detonators before igniting them. The pre-blast electronic diagnostics reduces the rate of misfires from approximately 1% of non-electric systems to under 0.1%. Firing codes are encrypted and prevent using stolen detonators without a decoder.
The control of blast-induced ground vibrations continues to be an issue in close proximity to sensitive pit walls and surface constructions. Electronic detonators enable controlled waveform sequencing that prevents vibration risks in surface bench blasting operations. Yet, research in small-section rock tunnel drilling found some site-dependent drawbacks. For instance, at the Bei-Zhan Iron Ore Mine, segmented simultaneous tunnel blasting has proven that NONEL detonators have lower peak ground vibrations than digital electronic detonators.
The pyrotechnic delay scatter in NONEL (mean error per segment was 75.6 ms) ensured the random interference and damping of waves and led to a reduction of vibration energy by 19.4% per each segment. In its turn, digital electronic detonators had the accuracy of average delay equal to 98.1% (mean error – 2.9 ms), which enabled firing the boreholes simultaneously and the energy concentration in narrow frequency bands (50-200 Hz). Still, the use of electronic detonators resulted in significantly better rock breakage in tunnels, the mean particle size (x50) being 128.7 mm, while for NONEL it was 265.28 mm, and there were fewer oversized boulders.
Price discrepancy is the main factor preventing full adoption of electronic detonators. The unit cost of an electronic detonator is 5-10 times higher than for a conventional non-electric shock tube. Adoption requires dedicated digital loggers, blasting machines, and proper personnel training. Great care should be taken when tieing detonators to ensure safety of micro-circuits from dynamic shocks and water penetration into wet boreholes. Modern-day total-cost analysis shows that often the savings on energy consumption in crushing, fuel economy, and loader efficiency compensate for additional initial costs.
Electronic blasting caps mark a paradigm shift in modern excavation technologies. Microprocessor-controlled delay timing reduces pyrotechnical scatter, maximizes the use of the explosive force, and improves rock fragmentation homogeneity. Electronic detonation field experiments reveal greater loader diggability, better crushing efficiency, and enhanced safety through preblast digital inspection. While non-electronic shock tubes have an initial cost advantage as well as a vibration damping effect in the small tunnel/borehole network system, electronic solutions give better process control. A total cost management approach adopted by operation teams can leverage electronic detonators for optimal hauling efficiency and reduced crushing costs.
