Engineering & Mining Journal

SEP 2018

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NARROW VEIN MINING SEPTEMBER 2018 • E&MJ 41 www.e-mj.com Kitchkeesick reported. Afterward, raise development, cable-bolting, production drilling and production blasting each em- ployed two per shift. Equipment included, but was not lim- ited to, the double-drive raise climber, two boom jumbos, a 6-yd 3 scoop, scissor lift, bulk emulsion loader, down the hole drill, grout mixer, small tools and pumps. Specifically, raise development, which employed the double-drive raise climber, started "with a nest and a hanging wall at the bottom of the stope," Kitchkeesick reported. "In this case, we've got the nest at 4.5 m wide, 6 m high, and 18 m long." That allowed mucking access beneath the nest. "The length of 18 m is just to keep us a safe distance away from the raise because the nest also serves as a little maintenance area," she reported. The raise was driven along the hanging wall of the stope. "After the breakthrough at the top level, there is a landing installed and this is for safety reasons, for people ap- proaching, loading or leaving the climber," Kitchkeesick reported. "With this landing in place, the raise is screened from the top down and after that the ore is painted up, surveyed, and it is then cable bolted." The raise was multipurpose and served as a temporary access between levels, a ventilation opening, production access and blast void. The center of the hanging wall was ca- ble-bolted. "With the support, the stable stopes can be the foci of the ore, elimi- nating the need for quite a bit of devel- opment, in this case three sublevels," Kitchkeesick reported. "We included a wagon drill in this purpose because with the wider orebodies we've got some cable bolting going on below in the undercut." Production drilling was oriented 10° to 30° downward from horizontal for optimal toe breakage, making the un- dercut the production slot. "Production drilling is done with the raise production drill that sits on the deck of the unit," Kitchkeesick reported. Blasting entailed one shift per day. "With the electronic caps, we do much larger blasts, up to stopes in their entire- ty, which we refer to as mass blasting," Kitchkeesick reported. With the higher strike length, less re- mote mucking was required. "Generally, we muck the swell from the blast and keep most of the ore in the stope so that it keeps the walls," Kitchkeesick report- ed. "And then we muck it out at the end as quickly as we possibly can and that is followed with paste fill." The Cutoff Mark With the projects sufficiently similar in sta- bility number, initial development, labor per task, tasks per shift, and equipment used, apples could be compared to apples. The total number of man shifts and the resulting metric ton per man shift were cal- culated and plotted "against ore thickness, using the results we got for each different mining method," Kitchkeesick reported. The number of man shifts were deter- mined by taking "the days per task, the crew size per task, and the amount of tasks per number levels," McKirdy report- ed. "This is repeated for each thickness." For LHOS, "we came up with about 18 mt to 50 mt per man shift, depending on the ore thickness," McKirdy reported. For MCRM, the results differed slight- ly. "We did go down a little bit narrower just because we can," Kitchkeesick re- ported. "For 1.2-m-ore-thickness, we had 12.9 mt per man shift up to 45.5 for the 12 m thickness." On the resulting chart, the productiv- ity lines for each method run parallel up- wards, with MRCM slightly above LHOS until the two intersect a bit below 10 m. "Anything under 8 m, assuming the four sublevels, it is more efficient to do the raise mining," Kitchkeesick reported. Additional development and sublevels moved the point upward. "Obviously, the more sublevels you have, the more appli- cable raise mining is," she reported. And the four-sublevel project was more ideal than practical, McKirdy said. "You want to minimize the number of stopes if you can, which generally means making them larger," McKirdy said. Accurate drill- ing, in a perfect world, maxes out at around 25 m and is the limiting factor. Rare are 25-m stopes, he said. "More likely you would do 20 m, five rows of stopes high." That additional row requires additional man shifts, driving down efficiency. "There is an optimum stope size, and then you start adding the number of stopes, so you add ventilation changes, you add backfill dams, you add slot raises," McKirdy said. "So it is the preparation." At five sublevels, the cutoff point climbs to 11 m. At six, it is 13 m, Kitch- keesick reported. MRCM is also more efficient in instanc- es where access is limited and reaches only "isolated little islands of ore," McKirdy said. In those cases, the miner can "either do it blind, or you can drive a sublevel and an extra raise," he said. "Most of those are so short that we (MRCM) then blind and blast them with i-kons." Nonetheless, it is the 8-m cutoff point that McKirdy said is generalizable enough for quick calculations, brainstorming and informal planning. "If you had a tabular, steeply dipping orebody that was less than 8-m thick, you'd look at Alimak raise mining," he said. "If it was thicker, then it might be reason to look elsewhere."

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