By: Ray Reece
Skillfully managing tailings in today’s mines requires both careful planning and ongoing monitoring to make sure risk is contained and profit is maximized. The right drilling technology can help you do both. Utilizing the wrong technology in a tailings application can create an inaccurate environmental risk profile and may even leave money on the table by washing away valuable minerals previously processed unsuccessfully.
Where conventional drilling methods chronically struggle to obtain a continuous core sample—in soft and unconsolidated ground—sonic drilling thrives. Sonic drilling is a vibratory drilling method where rotating eccentric weights from the rig’s rotation unit impart a vibration into the rod string and core barrel assembly. Drillers then reach optimum drilling speeds by matching the frequency of vibration to the natural frequency of the ground. Efficiently penetrating the formation, sonic drills can consistently obtain close to 100% core recovery in mine dumps and heap leach pads, particularly when operated by a seasoned drill crew.
Heap leach pads are often susceptible to incomplete flow distribution within the pad, where leaching solution collects around an impermeable zone and is unable to extract the mineral. Sonic drilling can be used first to evaluate the effectiveness of the initial leaching process and remaining mineralization, and then to install injection points to redistribute the flow net. Using surface geophysics to identify the “dry zones,” contractors reach them precisely using sonic technology to install solution injection wells and capture the leached mineral fluid. Sonic technology can also be utilized to produce a core sample that is useful in evaluating effectiveness of new biological methods for accessing minerals.
Sonic is also utilized to maximize value in tailings impoundments and in waste dump piles. In established mines where older processing techniques were used, minerals were processed with less efficient technologies available and pumped to a storage location with a valuable mineral concentration still remaining. In other situations, market conditions cause mineral value to rise above the profit threshold, and drilling contractors can effectively deploy sonic drilling technology to return an accurate core sample and confirm exact mineral concentration without fluid dilution. In some cases mine companies have found a higher concentration of minerals in tailings than what they were currently mining.
The sonic method of drilling also creates an extremely straight borehole, making it an optimal technology for installing instrumentation and monitoring equipment. Drilling contractors use sonic technology to install inclinometers that monitor the formation and help mining operations know if the ground is subsiding or moving so they can catch dam failure before it occurs. In the event of an earthquake or other large geologic event, mining companies can quickly gain an understanding of the impact to the tailings dam. But contamination and toxic leak monitoring is perhaps one of sonic drilling’s most important contributions, enabling drillers to efficiently return precise samples of ground surrounding tailings impoundments and heap leach pads to determine if it’s been contaminated. Installation of ground water monitoring wells provides further information, like determining water-flow direction and chemical levels.
Ray Reece is the environmental and infrastructure business development manager for Boart Longyear.