Heap leach pad mapping with drone-based hyperspectral remote sensing at the Safford Copper Mine, Arizona

Abstract

Mapping the distribution of minerals, pipes, ponded lixiviant, and other surficial features on heap leach pads is a continuing challenge for hydrometallurgy operations, maintenance, and design. Recently, commercial drone technology has enabled remote sensing techniques to be deployed for some leach pad mapping and surveying applications, but applications to hydrometallurgical operations are still emerging. This project tested one potential mapping technology, drone-based hyperspectral remote sensing, for mapping leach pads, using the Safford mine as a test site.The results show that hyperspectral remote sensing can acquire information about mineral distribution, piping system, and lixiviant ponding. The main minerals detected on the leach pads are kaolinite, muscovite, and gypsum, although the detection of gypsum is probably due to the widespread sulfate precipitating from agglomerating acid and lixiviant. The path of the stacker loading rocks, lixiviant ponding, and drip lines can also be seen in the spectral images. Chlorite and biotite, long-term acid consumers, were not detected in the results, but are on the leach pads. Best practices for hyperspectral remote sensing in mapping leach pads include: building a reference library from ground-truth samples, using high spatial resolution for mapping piping systems and low spatial resolution for mapping minerals, scanning leach pads in sunshine, and scanning before leaching starts.