Engineering & Mining Journal

NOV 2012

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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OPERATING STRATEGIES Boart Longyear Crew Sets Sonic Drilling Depth Record at Bingham Canyon Boart Longyear Drilling Services set up an SR-121 sonic drill rig atop a waste dump at Bingham Canyon to obtain a continuous sample stream that would provide reliable information about the dump's depth and contents. Waste rock dumps are often placed adja- cent to pit areas, and as mining expands more room is needed for the waste rock. Knowledge of certain physical and chemical characteristics of the waste rock dumps is often needed to better understand the geo- technical and geochemical behavior of the dumps—and to evaluate potential mineral value. Sonic drilling, because of its capabil- ity to provide accurate samples along with a high rate of sample recovery, has frequently been used for re-exploration drilling of dumps, tailings and heap leach pads. Sonic drilling employs the use of high- frequency, resonant energy to advance a core barrel or casing into subsurface for- mations. During drilling, the resonant ener- gy is transferred down the drill string to the bit face at various sonic frequencies; simultaneously rotating the drill string evenly distributes the energy and impact at the bit face. When the sonic energy coin- cides with the natural frequency of the drill string, resonance occurs. This results in the maximum amount of energy being delivered to the face. At the same time, friction of the soil immediately adjacent to the entire drill string is substantially mini- mized, resulting in very fast penetration. The sonic drilling method advances a casing as the borehole is drilled. Exact drilling methods are dependent on site conditions and project objectives, with the 120 E&MJ; • NOVEMBER 2012 most common being advancing a core bar- rel, which is then overridden by a larger diameter drill string that cases the open borehole and prevents collapse. Waste rock dumps mainly consist of unconsolidated material, which can lead to challenges in drilling—it's often difficult to know how deep they are or what types of material they contain. However, drilling serv- ices and equipment provider Boart Longyear says its TRUSONIC sonic drilling technology provides a solution by being able to produce 100% accurate in-situ core samples in var- ied ground conditions. Recently, Boart Longyear Drilling Ser- vice took on the challenge of drilling core samples from an unconsolidated waste rock dump at Rio Tinto's Kennecott Utah Copper Bingham Canyon open-pit mine. The intent of drilling was to characterize the contents of the waste rock dump, which comprised mainly blasted porphyry-deposit (granite- like) rock material ranging from 254 to 305 mm (10 to 12 in.) in diameter. An impor- tant goal was to provide a detailed continu- ous sample of the waste rock dump materi- al and confirm bedrock depth. Boart Longyear also needed to install piezometers (water level monitors) and lysimeters (mois- ture content monitors). Geotechnical sam- ples would also need to be taken at fre- quent intervals to confirm stability and moisture content for the first 61 m of the targeted 213-m (700-ft) borehole depth. Sonic drilling, according to Boart Longyear, is the 'perfect' method for drilling in unconsolidated material, such as the waste rock dump at the Bingham Canyon mine, because of the technology's The crew achieved a company-record borehole depth of 900 ft (~275 m) in four drilling stages, using progressively smaller-diameter bits to reach the final target. The project took 16 12-hour shifts to complete. www.e-mj.com

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