Evaluation of the PAD re-leaching method for improving gold recovery at Newmont Yanacocha, Cajamarca - Peru

Abstract

Gold mining is a fundamental activity for the Peruvian economy; however, the progressive depletion of high-grade ore forces mining companies to seek innovative alternatives to maximize the extraction of residual metal from previously exploited resources. One such alternative is the Injection Leaching (IL) method, a technique based on the pressurized injection of cyanide solution directly into exhausted heap leach pads to enhance gold recovery. This research evaluated the implementation of Injection Leaching as a re-leaching strategy in the Newmont Yanacocha Mining Unit, specifically in the Carachugo 10 (CA10), La Quinua 8 (LQ8) and La Quinua 1-7 (LQ1-7) leach pads. The study was carried out through a pilot test supported by geophysical monitoring using electrical resistivity, geodetection systems and nuclear magnetic resonance (NMR), which allowed understanding the distribution and behavior of cyanide solution inside the heap. The results showed a rapid increase in the gold concentration in the pregnant solution, stabilizing between 0.5 and 0.6 ppm in CA10 (Figure 15), similar to fresh ore conditions. Additionally, the project generated approximately 350,000 additional ounces of gold, extending the mine’s productive life. Therefore, Injection Leaching proved to be a technically, economically, and environmentally viable method for the recovery of remnant gold, overcoming the limitations of conventional drip and sprinkler leaching systems.