Case Study – Gold Mine in Nevada

In this geophysical case study, a gold mine in Nevada was experiencing issues of acid rock drainage (ARD) seeping alongside slopes and onto haul roads below a waste rock dump. The amount of solution was troublesome for road maintenance as well as with the general environmental concerns of unmitigated hazardous solution. This particular mine had been operating for several decades, but the waste rock pile began construction in the late 90s and was used on and off by the time the geophysical survey took place. Regardless, the pile had reach several 100s of feet in height. Understanding the source and scope of the issue would have been challenging for anything other than electrical resistivity, a mining geophysics method well suited for mapping the solution distribution within rock piles.

HGI routinely operates in complex site conditions and are able to collect high quality data

Many of the areas in which we have conducted geophysical surveys are austere, remote, and difficult to traverse. Especially when dealing with mining environments, the site conditions are less than ideal and normal data acquisition can be a challenge. Fortunately, HGI has the experience and knowledge to overcome these challenges to acquire robust and high quality data to solve these complex problems. Our tool box includes a large equipment inventory to make sure we get the detail, depth, and resolution that maximizes subsurface information, acquisition expertise to make sure we only collect the highest quality data, and processing advantage for creating the best representation of your site.

HGI has the experience and knowledge to overcome difficult site conditions. We have a robust set of tools for solving complex problems that includes a large equipment inventory, specialized acquisition, and processing advantages for creating the best representation for your site.

Electrical resistivity on a waste rock pile to find source of seep formation

For the geophysical case study of the waste rock problem, 15 lines of electrical resistivity were acquired around the site. What we observed, as shown in the upper two sections in the graphic below, was a thin veneer of highly conductive material near the surface of the waste rock pile. ARD is known for having high total dissolved solids from ionic constituents (iron, sulfate, other ions), therefore it was hypothesized that the conductive veneer was mine impacted waters being held close to the surface. This solution was not allowed to be more evenly distributed through the pile, where higher resistivity in the sections suggested compacted and dense material. Instead, the solution cascaded over the edge along the topography, where it eventually daylighted on the haul road below the waste rock pile. Low resistivity values that were at the surface were coincident with seeps and ponding along the lines. In the end, we showed the mine that the lack of percolation and internal storage of their waste rock was creating the adverse flow conditions and either internal drains to move the ARD downward or horizontal drains to move the solution forming seeps to more manageable locations would need to be installed.

Through our years of experience, we have seen that adverse hydraulic conditions can prevent the even distribution of solution in rock piles. Our mining geophysics methods allow for a greater understanding of the problem and the formation of resolutions that can solve these complex issues.