Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/562664
Underground Processing OPERATIONS A n underground aggre- gate mine is a different world than a surface operation, presenting unique challenges that surface mining does not. It can be a costly undertaking, requiring special engineering of tunnels, rooms, and pillars that are dependent on the geology of the site. It is dark, even with extensive lighting installed. And underground mining requires Part 48 training, which is more specialized and time intensive than traditional Part 46 training for surface mines. Underground mining also requires a different type of worker than a sur- face operation, and it can be diffi cult to fi nd and maintain experienced operators and mechanics. According to Paul Smith, in- ternational marketing manager for the Astec Aggregate & Mining Group, despite of its challenges, an underground aggregate mine affords benefi ts that can't be duplicated at the surface. For instance, because the mine operates at a uniform temperature and isn't affected by rain or snow, it is operational year round. Additionally, the equipment always starts up warm. "And possi- bly the biggest benefi t producers are considering today is the fact that, for neighbors, an underground oper- ation is comparatively out of sight and out of mind," Smith says. Whether a producer is seeking additional reserves in an existing operation or opening a greenfi eld site, there are considerations that must be made about how and where to process the material. Most underground aggregate operations will blast and then truck or convey material to the surface for processing. Others will conduct primary process- ing underground, and then move the material to the surface. However, if the geology is appropriate, notes Smith, any process that can be conducted at the surface may also be brought underground — limited only by imagination and money. Bob Schmidt, executive vice president and chief operating offi cer of New Enterprise Stone and Lime, agrees. "You can use any of the same equipment underground for the same stages that you would process on the surface," he says. "It would depend on the thickness of the strata; you would have to have wide tunnels — 40 to 45 feet wide; and you'd also have to take 50 to 60 feet out of the fl oor for the necessary depth to add equipment. Other than that, venti- lation and dust control are the only equipment decisions you would have to make that are any different than you would make at the surface." Schmidt offers some caveats with this statement. "You could put the entire plant underground, but access to product inventory becomes prob- lematic. It is not practical for delivery trucks to enter the underground mine. Inventory of fractionated aggregate sizes could be stored un- derground, conveyed to the surface, and combined on demand to create the fi nished aggregate products." AGGREGATES MANAGER Depending on the thickness of the strata in an un- derground aggregate mine, a producer can use any equipment underground that he would use for the same stages in processing on the surface — limited only by imagination and money. Processing beyond the prima- ry, however, typically requires wide tunnels of at least 40 to 45 feet, with room height of at least 50 to 60 feet in order to add secondary and even tertiary equipment. An underground mine is a diffi cult environment where equipment and processes that would be used above ground are more complex to replicate beneath the surface. For instance, if the seam of stone is vertically narrow, the mine height will be limited. A specially de- signed loader can work beneath a low ceiling, directly loading into a stationary or tracked crusher, with sized material dumping to channel conveyors to move it out of the mine. 1 Mine the strata 4 Special conditions, special equipment