Heap Leach Investigations Could Lead to Big Payback
Article by: Dr. Dale Rucker | Chief Technical Officer | hydroGEOPHYSICS
Heap Leach Investigations Could Lead to Big Payback – If someone were to say that they could tell you where ore is being leached, where it was compacted and underleached, and where potential trouble spots were, would you be interested?
Since the advent of the modern leaching operation, there have been many questions and much research centered on understanding the internal hydraulics of heaps. Traditionally, mine operators have relied on point source information from boreholes to give them a glimpse of the leaching process and gain some actionable information to increase production. However, because of the unique heterogeneity and complex flow regimes of these large systems, a holistic understanding of these internal processes has remained a mystery.
Recent advances in subsurface imaging with geophysics, especially electrical resistivity and induced polarization, is helping to shed light on what is happening in the internal environment of a leach pad, waste rock pile, tailings dam, and other engineered structures. These advances heap leach investigations include rapid acquisition hardware, improved software modeling, and most importantly a large set of case studies from which to draw. The geophysical industry is getting to a point where data, image, and interpretation are converging to a cogent toolset for increased knowledge and production.
Recent advances in geophysical heap leach investigations is helping to shed light on the internal environment of a leach pad.
Consider the example below. An electrical resistivity geophysical survey or heap leach investigation was conducted over a copper heap comprising run-of-mine material, but with significant fines. Low permeability has historically caused low recovery and the geophysical survey was meant to help identify the size of the problem. The survey was conducted from the surface of the heap, meaning no drilling was necessary to get the geophysical information. The data, presented as a color contoured slice of high and low resistivity values, indicate drier material near the liner (high resistivity values) and a mid-layer of pooled solution (low resistivity values).
A follow-up drilling campaign revealed that the high resistivity areas were representative of high-density ore and high copper values. It was also evident that surface irrigation alone was not going to be effective at extracting the metal locked up in the lower lifts. The raffinate was simply not able to penetrate the compacted ore. Instead, it was suspected that the solution was making its way to the reclaim pond via preferential flow channels.
In response, the mine took up a comprehensive subsurface leaching program to increase recovery and drawdown those extra pounds. The subsurface leaching included a number of rinse wells whose depths were completed approximately 20ft above the liner. A short screened interval allowed the wells to focus flow to the areas of the highest grade. The subsurface leaching was accompanied by a broad monitoring campaign to ensure a proper water balance, safe operations, well efficiency, optimal recovery, and payback. In the last year of operation, it is estimated that approximately 2.5 million lbs of copper have been recovered. And it all started with a simple investigation.
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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