Heap Characterization

Large engineered rock piles are composed of complex and interrelated metallurgical, geochemical, geomechanical, hydrogeological, and geothermal systems, each influencing the other (see model below). Predicting this complexity is impossible and trying to capture in situ information can be difficult unless there is an appreciation for the complexity controlling subsurface hydrology. HGI’s heap characterization services are a set of geophysical, hydrological, drilling, and metallurgical applications which can help provide a more holistic understanding of your site at a scale that is meaningful. This ‘Big Picture’ approach enables mining operators the opportunity to gain new and actionable information, positively affecting heaps.

Heap characterization enables mining operators to gain new actionable information detailing the complexity of subsurface hydrology.

It’s Your Greatest Asset

 A heap, or stockpile is the number one economic resource of any heap leach operation and their counterparts, waste rock piles, and tailings piles can be major economic liabilities if not managed correctly.   These economic factors are important considerations for mine operators and a major reason for characterizing and monitoring them, ensuring long-term viability and reducing environmental damage and economic loss. The most critical information is the internal hydraulic structure and how that structure may be inhibiting uniform solution flow. If uniform flow does exist, then the mechanisms controlling flow, stability, and metal recovery can be regulated strictly from the surface through application rate and drip line or sprayer density. However uniform flow is impossible to predict and likely never exists simply because of the complexity and size of surface mining operations. Therefore, having actionable information for the ‘big picture’ of subsurface heap and stockpile hydrologic schemes becomes essential for any mining operation.

The most critical information gained from heap characterization is an understanding of internal hydraulic structure and how that structure may be inhibiting uniform solution flow.

Structure within a man-made rock pile can be characterized as a spectrum, from completely random (no structure) to completely predictable. Our work has shown that rock piles are actually somewhere in the middle, what we call ‘Unpredictably Structured’.  This means that there exists structure that can be used to understand the internal hydraulic and metallurgical processes, but that structure must be measured.

HGI’s heap characterization services provide significant information through state of the art geophysical technologies providing essential information that highlight the main structural components that give rise to heterogeneity and nonuniform flow. Fortunately, the structure is not completely random, but it cannot be predicted based on operating conditions alone. The structure is unpredictable, but it can be measured once the geophysical investigation has been conducted. Below are a few examples showing typical structure as measured with electrical resistivity. In many cases, we followed up with drilling to validate the findings.