Engineering & Mining Journal

SEP 2018

Engineering and Mining Journal - Whether the market is copper, gold, nickel, iron ore, lead/zinc, PGM, diamonds or other commodities, E&MJ takes the lead in projecting trends, following development and reporting on the most efficient operating pr

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Page 41 of 75

NARROW VEIN MINING 40 E&MJ • SEPTEMBER 2018 Size matters. Longitudinal data reveals that the thickness of a vein can determine whether the mechanized raise-climber mining (MRCM) method will be more ef- ficient than the long hole open-stoping (LHOS) method. This is according to research by Ken McKirdy, chief engineer, and Tracy Kitch- keesick, technical services manager, Manroc Developments Inc., and reported at the 2018 Canadian Institute of Mining, Metallurgy and Petroleum (CIM) confer- ence. Afterward, the former sat down with E&MJ to elaborate. The research crunched almost two de- cades of data collected by the company. And it was shared at CIM and elsewhere in part as a parting gift from McKirdy, who is closing out a career at perhaps the world's foremost Alimak mining proj- ect firm. "We've been doing this mining method since the early 1990s and peo- ple don't seem to know a lot about it," he said. "Definitely one of the things we wanted to solve was that cutoff line." Specifically, the research looked at data from "a couple projects per year since 2000, roughly 5.5 million to 6 million metric tons (mt) of production ore," McKirdy said. Those projects employed either method. The data was organized on a spread - sheet. The result was "an amalgam of several projects," amounting to a model, McKirdy said. Kitchkeesick reported the model to be "a make-believe" orebody. It represented simi- lar projects that differed mainly by mining method. "We used a 100-meter (m) strike mine, a 100-m vertical extent with a 65° dip, meaning there is 110 m of dip length," she reported. The orebodies considered ranged in thickness, she reported. Each was "a uniform thickness throughout, but we looked at ranges from 1.2 m narrow up to 12 m thick," she reported. Additionally, the orebodies considered were "dry and under a medium-stress environment," she added. McKirdy emphasized the importance of the last spec. "I just wanted them com- parable on the stope stability method," he said. "One of the things that affects these opening sizes is stress and what I wanted to do was set it up so that the stress was pretty similar between the two types of mining." When filtered by method, the amal- gam produced two hypothetical projects, enabling a comparison "based on tons produced per man shift," McKirdy report- ed. That number, for most miners, trans- lates to efficiency, he said. Each project was based on some gen- eral assumptions. Both were assumed to have all the required services, "ventilation, processed water, compressed air, electri- cal power and base fill" and access from the main ramp, McKirdy reported. Each was assumed to tap the parent mine's trucking, supervision and maintenance. Other assumptions were more specific to ensure an accurate comparison. The Model LHOS Project The hypothetical LHOS mine plan called for "an even number of stopes over 100 m, 11.1 m each for a nine-stope level," McKirdy reported. "The zone strike line, strike length and dip length were distrib- uted evenly among the stopes and levels." No major structure in the zone is as- sumed, and "all diamond drill holes in this scenario are grouted," McKirdy re- ported. "The stability number is in the range of 1.9 to 7.1." Of three stope sizes analyzed, "the 23-m x 11-m long-hole open size was chosen to minimize the number of stopes, it being the least costly of the options," McKirdy reported. The result was 36 stopes, nine wide and four high. "That is less than what we would have had if we went a little wider along the strike or with lower levels face-side," McKirdy reported. An access was driven parallel to strike and offset 18 m from the ore. Draw points were driven from the hanging wall access to the ore. In general, lateral development was followed by slot drilling, cable bolting, production drilling, production blasting, mucking and filling. Specifically, the primary stope was un- dercut, and the secondary stope was left until the primary stopes were backfilled. The hanging wall portion of the under- cut, being the new critical face, was then drilled and cable bolted. "A similar se- quence is repeated for the next level up, and the slot raise can be drift divided or drilled once the stope has been undercut and overcut," McKirdy reported. Manpower included a leader and two miners per shift for lateral development, and then a leader and a miner per shift per active raise for slot drilling, for cable bolting, for production drilling, and for production blasting, McKirdy reported. Equipment used included a two-boom jumbo drill rig, a 6-yd 3 scoop, a scissor lift, a bulk emulsion loader, miscella- neous handheld drills and pumps. Cable bolting employed the wagon drill, scissor lift, mixer, pump and small tools. Production drilling employed the top- hammer drill. "It could be the one mount- ed on the wagon drill," McKirdy reported. "Stope production drilling was completed before the final slot raise blast had taken any one stope," McKirdy said. "This is to minimize exposure to open holes." Production blasting employed the scissor lift and bulk emotion loader "be- cause we are loading both upholes and downholes," he reported. The Model MRCM Project The initial development work for the MRCM project was assumed to be similar. The stopes, however, were bigger, with the supported side of the raised stope at 18.3 m x 110 m high. "The induced stresses were not modeled, but we as- sumed they would be comparable in the later stages of mining for each of the dif- ferent methods," Kitchkeesick reported. In general, raise development was fol- lowed by cable bolting, production drilling, blasting, mucking and then paste-filling. The manpower assumed was the same as for LHOS. For initial development, "we have a leader and two miners per shift," Matching Method to Orebody Two narrow-vein project experts reveal when the mechanized raise-climber mining method is more efficient than the long hole open-stope mining method, and when it is not By Jesse Morton, Technical Writer

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