Three-dimensional electrical resistivity imaging of a gold heap

Abstract

A case study is presented for an electrical resistivity geophysical survey, conducted on a gold leach pad of low-grade ore. The electrical resistivity method maps the spatial distribution of electrical resistivity, which is an intrinsic property of material that measures the resistance of electrical current flow through a medium. The property is influenced by moisture content, ionic strength of the porewater, and mineralization. The geophysical method was applied to the leach pad to discern patterns of high and low moisture from past infiltration into the heap. A total of 12 survey lines were run in parallel over an 8 ha portion of the pad. The results showed that the high electrical resistivity areas, which are likely related to low moisture, could be explained by the physics of unsaturated fluid flow or evapotranspiration. The low electrical resistivity areas were thought to be related to high moisture from preferential flow along highly permeable regions of the heap. Validation of electrical resistivity was accomplished by correlating co-located geophysical data and rock samples of moisture content and total gold concentration. On an individual point-by-point basis, the correlation between the two datasets was low, due to the mismatch in measurement scales of the two characterization methods. Averaged resistivity data within discrete bins of the independent variable (rock sample), however, produced high correlations and empirical models were developed from a linear regression of averaged behavior.