Case Study – Newmont Gold Quarry

A geophysical case study is presented below, highlighting a successful deployment of HGI’s brand of mining geophysics and our unique toolkit for solving complex problems.

A comprehensive electrical resistivity characterization project was conducted at Newmont’s Gold Quarry mine to understand the distribution of wet and dry areas in a mature gold heap leach pad. Typically, wet areas will exhibit lower resistivity values, whereas dry zones will show high resistivity. The wetting of ore and movement of leachate is controlled by permeability, which is influenced by both micro and macrostructure developed from dumping practices, geology, and ore pre-treatment. Low permeability zones, for example, may cause the leachate to bypass large portions of ore for more accessible regions by way of preferential flow. Preferential flow allows large amounts of ore to be underleached, leaving significant amounts of metal inventory within the heap. Since leachate will flow more easily through zones of highest permeability, these zones will become effectively leached over a short time span and ultimately skewing the pregnant leach solution (PLS) grade lower.

HGI’s core strength is in helping to identify issues related to permeability in a heap. Our brand of mining geophysics and unique toolkit for solving complex problems will bring clarity to issues related to poor recovery

This geophysical case study at Gold Quarry included a set of parallel resistivity survey lines that allowed a 3D model to be generated over an area of approximately 20 acres. The data presented below shows high and low resistivity zones that can be attributed to structure. Borehole samples and assay results within the domain (locations identified as black dots in the figure) showed little to no structure (link to co-kriging paper), making that dataset difficult to obtain relevant spatial characteristics. Our mining geophysics methodology of applying electrical resistivity allowed relevant spatial data to be acquired to give a greater understanding of leached and unleached areas.

The complex structure within a heap is often masked when conducting a drilling program. Electrical resistivity can provide information at a scale that is more easily understood, allowing easier decisions for operation.

The figure below shows a slice through the heap at approximately 50 ft below the pad surface. High and low resistivity features converted to moisture are co-mingled to show how a complex and compartmentalized distribution of moisture. Three-dimensional views are also shown to highlight the wettest (low resistivity) and driest (high resistivity) material.

Electrical resistivity data on a gold heap to highlight complex structure

The characterization work was completed in order to preferentially select suitable borehole locations where additional leach solution could be injected at varying depths. The set of 2D electrical resistivity profiles shown in the figure below illustrate the significant moisture variations that can occur within a leach pad. These results were used to identify and target underleached (low moisture) areas that would benefit from the subsurface injection.

HGI’s mining geophysics with resistivity can help to identify heterogeneities within a heap leach pad.