Solutions For A Complex World:
Pinpointing Heap Leach Seepage with Electrical Resistivity Tomography
Article by: Dr. Dale Rucker | Chief Technical Officer | hydroGEOPHYSICS
Adverse hydraulic conditions within leach pads can lead to seep formation on side slopes. The formation of seeps and their continuous flow will erode the ore’s cohesive deposition, potentially causing slip or failure. Geophysical tools such as Electrical Resistivity Tomography (ERT) is part of a set of value-driven technologies that can quickly provide an unprecedented level of understanding over large areas of a leach pad’s slope. Using ERT can help uncover unfavorable solution movement within heaps and dumps, which can be a significant factor leading to the development of seeps and slope failures. The origin of slope failures can often be traced back to the formation of side slope seepage. ERT provides an excellent value for early detection of these adverse hydraulic conditions inside a heap and frequently allows a first look to track seep origins.
Insufficient understanding of subsurface flow regimes can lead to disastrous consequences such as slope failure.
The hydrodynamics near slopes of heaps and dumps is critical for mining engineers and leach pad supervisors to understand. This knowledge feeds into sound design, enabling safe stacking methods, minimizing failure risk, and maximizing ore throughput and profit. On the other hand, an insufficient understanding of subsurface flow regimes can lead to disastrous consequences such as slope failure. The origin of slope failures can often be traced back to the formation of side slope seepage. ERT provides an excellent value for early detection of these adverse hydraulic conditions inside a heap and frequently allows a first look to track seep origins.
The image above shows seepage exciting a slope on a heap leach pad. The plot below shows a resistivity profile of contrasting resistive and conductive subsurface features. The blue and purple area in the plot represents a perched water table leading to a seep formation exciting at the side slope
The ERT survey method is one of the most widely used exploration techniques in the mining industry. In recent years ERT investigations have increased on mining heaps to uncover and define adverse hydraulic conditions that may give rise to seep formation. Examples of adverse hydraulic conditions include compacted ore that prevents drainage or perched water tables that create excess pore pressures.
ERT is an electrically-based sub-surface imaging method that measures the electrical field strength during current flow into the ground. The ERT electrical field strength is proportional to the resistivity of the earth, which is affected by the saturation of the ore. Thus, highly saturated ore on or near slopes, indicative of a seep, can easily be mapped with ERT technology.
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Safe
Because there is no need for heavy equipment, ERT is inherently safer than other more invasive characterization techniques such as drilling and CPT. All work is performed on foot using portable gear.
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Fast
ERT, by its nature, is extremely fast when compared to other forms of subsurface characterization. ERT is a type of remote sensing technology where information about subsurface areas is obtained from a distance rather than directly through physical observations such as drilling.
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Straightforward
ERT data acquisition is conducted strictly from the surface with a minimal footprint using a small field crew. Equipment installation is straightforward, using electrodes and cables laid out linearly.
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Data analysis & presentation
ERT data analysis and presentation give a broad, holistic view of subsurface environments. Plots show contrasts between resistive and conductive features, revealing telltale signs of unseen hydrodynamic variability.
The bottom line is that project decisions are made based on safety, time, and cost. ERT is an extremely valuable diagnostic tool for mining operators to define, track, and mitigate seepage problems in heap leach piles, dumps, and tailings. The method gives broad actionable information safely, quickly and costs less than more invasive characterization programs.
HGI can acquire, process, interpret and present ERT data providing heap operators with actionable deliverables within a cost and timeline that meets the rigorous needs of your schedule and budget.
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About the Author: Dr. Dale Rucker | hydroGEOPHYSICS
Dr. Dale Rucker currently acts as the Chief Technical Officer (CTO) for HGI. He is a geophysicist and hydrogeologist with a strong background in engineering and publishing. As CTO, Dr. Rucker has been instrumental in bringing to HGI new geophysical-based technologies to solve complex problems involving water resource, mining, engineering, and geotechnical issues.
Dr. Rucker is also the editor-in-chief of a well-regarded geophysical journal, the Journal of Environmental and Engineering Geophysics (JEEG). Over the past 15 years, he has published over 40 peer reviewed papers and book chapters in subjects of mining, karst, hydrogeology, and geophysics. Dale holds a BS in Mechanical Engineering, MS in Civil Engineering, and a Doctorate in Hydrology and Water Resources from the University of Arizona.
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