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MINE DEVELOPMENT common services and sharing a mainte- nance shop. Underground conditions differ somewhat at each operation, however: Meikle is a 'hot' mine, requiring an extensive ventilation and refrigeration system to cool underground air temperatures to about 80°F. Rodeo generally does not have underground heat issues—with one notable exception. An Alternative to D&B; Roadheaders are not commonly used in hardrock mining production. They are gen- erally employed as tunneling or under- ground construction machines, although they and their continuous-miner cousins are used to mine industrial minerals such as potash, gypsum and salt. However, the performance points of these tracked, rotat- ing-drum machines—continuous produc- tion of a fairly uniform fragmented product, simultaneous excavation and muck clear- ing, the ability to cope with variable rock conditions, and general invulnerability to high ambient temperatures—mesh well with conditions commonly encountered in a number of Nevada underground mines, such as blocky, fractured rock that im- pedes efficient drill-and-blast (D&B;) oper- ations, and high temperatures. One such area, in the Lower Rodeo zone of the Meikle underground complex, pres- ents both problems to such a degree that there simply isn't a safe and cost-effective method of mining it using conventional methods; rock temperatures range from 280°–325°F (140°– 160°C) and rock mass ratings (RMR) vary from 20–50 (poor to fair), making the area too blocky to conduct efficient drill-and-blast (D&B;) operations— and even if it could be blasted safely, the rock would be too hot for miners to handle without a cool-down period of several days. A few years ago, a manager at Rodeo became interested in assessing the poten- tial benefits that could be obtained through mechanical mining in certain areas of the mine, and arranged to have an older Dosco roadheader taken underground to assess its performance. Although maintenance prob- lems with the well-used, high-hour machine and another that followed precluded a full evaluation of its potential, the machine's performance in the Lower Rodeo hot zone was sufficient to maintain the mine's inter- est in mechanical-cutting methods. In 2010, Rodeo management approved further evaluation of roadheader mining, leading to negotiations with Sandvik Mining & Construction for temporary use of a newer model—a Sandvik (formerly Voest www.e-mj.com Alpine) MR360 with transverse cutterhead and more power, size and reliability than the previous machines. The MR360, part of Sandvik's MR300 series of roadheaders, is capable of excavating rock with uncon- fined compressive strength up to 100 MPa, according to the company. After a short underground run, the MR360 was removed and delivered to anoth- er site to fulfill a pre-existing rental obliga- tion, but was returned to Rodeo in 2011. By October, the machine was reinstalled under- ground and began mining on a full-shift basis in the Lower Rodeo, gradually gaining effi- ciency as the operating crew became more familiar with its maintenance requirements, characteristics and performance. Making Money from Nothing Asked to gauge the effectiveness of road- header mining in the problem zone, Mining Engineer Drew Wheeler said, "I'd definitely describe it as successful. It's allowed us to mine an area in which we can't blast, giving us access to material we'd never have been able to mine using conventional methods." Wheeler and General Supervisor Patrick Chacon were the originators of the roadhead- er experiment and oversee the ongoing effort. From an economic perspective, early results of the roadheader project were decidedly positive: in October 2011, the machine extracted more than 1,000 oz of gold in a 'hot' heading that would have been difficult, if not impossible, to mine other- wise, generating more than $1.75 million in revenue for the company. In addition, cer- tain operating and material costs were reduced and worker safety was improved. The potential productivity of the machine actually has been constrained by real-world practicalities. Spare haul trucks are scarce at the mine; consequently, the roadheader loads a single, 26-ton-capacity hauler and then must wait for it to return before starting up again. And, although the MR360 has performed adequately, it has occasionally approached the limits of its cutting capacity in the hard rock of the Lower Rodeo zone. One factor that could have been a sig- nificant hindrance never materialized. Whenever new technologies and methods brush up against long-standing business cultures and traditions, there's always fric- tion and the possibility of resistance. In the case of the roadheader approach versus conventional drill-and-blast (D&B;) meth- ods used at the mine, worker and manage- ment 'culture shock' wasn't an issue. "Drill and blast has been around for- ever, and everyone here is familiar with it," said Wheeler. But the [roadheader] crew was quick to see the advantages it could provide, and they've been very involved in keeping the machine running at its best during the tests. In fact, they were down- right unhappy when it was pulled out of the mine the first time." The Mining Sequence During E&MJ;'s visit to the mine in March, the MR360 was working on the 3790 level and during that month advanced at an average rate of 12.3 ft (3.8 m) per shift. It has since been moved to the 3860 level. By early May, the roadheader had cut 928 ft (280 m) of advance in multiple head- ings, all in the ore body. In the most productive environment, the roadheader provided 200 ft (61 m) of advance per month, cutting a 20-ft-wide (6.1-m) by 16-ft-high (4.9-m) profile. It has mined a total of 21,600 tons of ore, according to Wheeler. In the mining sequence, the roadheader advances the heading as it loads the truck— which normally takes 4 to 6 minutes—then powers down while the truck hauls the load several hundred feet to an ore pass and makes the return trip. During the 8- to 10- minute truck haul, the roadheader crew uses the downtime to change cutter picks, wet-down the face for dust suppression and perform other small cleanup and mainte- nance tasks. On average, three picks are replaced per foot of advance. In theory, the roadheader could make a 16-ft (4.8-m) cut before exposing the oper- ator to uncontrolled ground; however, the crew limits the cuts to 14 ft or less to pro- tect the operator as well as the machine's electrical boxes from exposure to rockfalls. As Wheeler explained, "If falling rock dis- abled the machine, we'd have to bolt around the roadheader before we could work on it, or find some way to move it safely out of the area." Not a simple task for a machine that weighs 55 mt and is 34- ft (10.3-m) long. Once the cut is completed, the road- header backs out and usually trams to another heading as the bolter moves in. Cable handling is a constant concern, according to Chacon, but the crew has devel- oped a routine to move it and keep it safely stowed along the rib using hydraulic tuggers. The mine uses 8-ft (2.4-m) inflatable rockbolts on a 4 x 4-ft pattern or 12-ft rockbolts on a 6 x 6-ft pattern, along with JUNE 2012 • E&MJ; 79