Enhanced Recovery Techniques For Heap Leach Mining

In the world of industrial open pit metal mining, heap leach pads are a mine site’s most valuable asset. These assets need to be maintained and monitored to continue to produce throughout their lifecycle. However, not all heap leach pads are equal, and adverse hydraulic conditions can arise during their operational lifetime resulting in lower production that leaves valuable inventory behind. Meeting life of mine challenges is essential in today’s mine planning. Adding enhanced recovery metal extraction technology can extend the mine’s lifecycle, especially as traditional extraction methods become constrained by uncontrollable factors in the leaching process. Surface leaching is effective and successful for initial metal recovery but can become an ineffective tool in the long term to remove the remaining inventory.

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Enhanced recovery has proven to be a beneficial addition in extracting precious metals from heap leach mines.

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In recent years, enhanced recovery coupled with a geophysically- and metallurgically-based monitoring program has proven to be beneficial in extracting the last bit of metals from heap leach pads. The technology is used in two ways. First, the internal structure of the pad is characterized using electrical resistivity tomography (ERT). This process is performed because stacking methods, ore properties, and adverse hydraulic conditions create under-leached areas by constraining leachate flow to small flow areas during the traditional leaching process. These underleached regions of the subsurface pad will be dryer, potentially containing vast quantities of metal. ERT can distinguish between the subsurface wet and dry areas as they will have different electrical properties: conductive for wetter areas and resistive for dry locations. The second phase of the process is injecting into the dry areas of the leach pad. Once we have characterized the subsurface and mapped regions of interest (suspected mineral sources), targets are drilled and injection wells installed.

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Electrical resistivity tomography can distinguish between subsurface wet and dry areas because they have different electrical properties. Conductive wet areas in this image are represented as blues and greens, and resistive dry areas show up as red and yellows. The resistive areas are potential regions of high precious metal content.

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HGI designs injection wells and wellfields to suit the specific heap environment. We use geophysically monitored injection techniques to surgically target the remaining ore, liberating the metal through our focused well field design. Each well can target leaching at specific depths, and multiple injection wells coupled with geophysical monitoring help optimize lateral spread making sure the complete area is leached. Additionally, HGI works within the heap constraints to optimize the secondary mineral recovery process using piezometers, monitoring wells, and a full sampling programs. By altering injection flow rates, cycling flow between wells, and monitoring heap chemistry, HGI can deliver the optimal solution for most heap leach pads. HGI has nearly a decade of experience optimizing injection variables for these enhanced recovery projects.

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This is an example of installed injection wells (gray) and monitoring wells (green). The 3-well injection array provides focused leachate distribution at depth throughout the zone of interest. Monitoring wells within the area of influence help optimize the secondary mineral recovery process using piezometers and sampling programs to understand heap chemistry during the entire recovery process.

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Extending the life of a heap leach pad improves mine sustainability for all stakeholders, from community members to employees and business partners. Enhanced recovery can extend the life of a heap leach pad by years and, in some cases, even decades. HGI has experience in most types of metal mines, including gold, silver, and copper in many parts of the world, providing injection monitoring solutions to mines.

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A composite image of three typical piping setups to wells for a heap leach injection program. Each well is fitted with a pressure gauge to ensure adequate flow is reaching the subsurface of this gold ore heap.

?About HGI?| hydroGEOPHYSICS

hydroGEOPHYSICS, Inc. (HGI) has over 30 years of experience providing geophysical services to the environmental, engineering, groundwater, mining, oil & gas, and natural resource exploration industries. We represent value and reliability in a geophysical service provider – our geophysicists, geologists, hydrologists and engineers are dedicated to finding solutions using industry-best equipment and custom-tailored geophysical services with a focus on safety, quality, and innovation. We specialize in the application of 2D & 3D geophysical methods in complex environments, time lapse subsurface monitoring of fluid flow through geologic materials, leak detection & leak location, subsurface characterization, plume mapping, and buried infrastructure detection and mapping.