Heap Leach Pad Surface Moisture Monitoring Using Drone-Based Aerial Images and Convolutional Neural Networks: A Case Study at the El Gallo Mine, Mexico

An efficient metal recovery in heap leach operations relies on uniform distribution of leaching reagent solution over the heap leach pad surface. However, the current practices for heap leach pad (HLP) surface moisture monitoring often rely on manual inspection, which is labor-intensive, time-consuming, discontinuous, and intermittent. In order to complement the manual monitoring process and reduce the frequency of exposing technical manpower to the hazardous leaching reagent (e.g., dilute cyanide solution in gold leaching), this manuscript describes a case study of implementing an HLP surface moisture monitoring method based on drone-based aerial images and convolutional neural networks (CNNs). Field data collection was conducted on a gold HLP at the El Gallo mine, Mexico. A commercially available hexa-copter drone was equipped with one visible-light (RGB) camera and one thermal infrared sensor to acquire RGB and thermal images from the HLP surface. The collected data had high spatial and temporal resolutions. The high-quality aerial images were used to generate surface moisture maps of the HLP based on two CNN approaches. The generated maps provide direct visualization of the different moisture zones across the HLP surface, and such information can be used to detect potential operational issues related to distribution of reagent solution and to facilitate timely decision making in heap leach operations.

Monitoring and Controlling Saturation Zones in Heap Leach Piles Using Thermal Analysis

This manuscript describes a method that is based on the implementation and setup of a mechatronic system that can recognize and detect, through thermal analysis, the zones where heap leaching piles may become locally saturated. Such a condition could trigger the potential of liquefaction, generating local or general collapse in the pile. In order to reduce this potential danger, and therefore achieve full stability in the pile, the irrigation system must be properly controlled; for instance, in potentially saturated zones, the irrigation flow can be reduced or eliminated until the saturation has disappeared. The mechatronic system consists of a hexacopter, equipped with a thermal infrared camera mounted on its structure and pointing down to the ground, which is used to obtain the temperature information of the heat transfer between the heap pile and the environment. Such information is very useful, as the level of saturated zones can then be traced. The communication between the operator of the irrigation system and the mechatronic system is based on a radio-frequency link, in which geo-referenced images are transmitted.

Management of Copper Heap Leach Projects: A Geologist’s Perspective

Editor’s note: The Geology and Mining series, edited by Dan Wood and Jeffrey Hedenquist, is designed to introduce early-career professionals and students to a variety of topics in mineral exploration, development, and mining, in order to provide insight into the many ways in which geoscientists contribute to the mineral industry. Abstract Copper production by heap leaching, coupled with solvent extraction and electrowinning (SX-EW), is a well-established technology, with an annual output of about 3.7 million tonnes (Mt) of copper metal. Ores presently amenable to copper heap leaching include copper oxides and secondary copper sulfides. Most copper deposits amenable to acid sulfate heap leaching result from supergene processes within porphyry copper systems, although copper heap leaching has been applied to sandstone and shale-hosted deposits, among others. Copper heap leaching is a rate-dependent process sensitive to copper mineralogy (copper oxides > secondary sulfides > hypogene sulfides), driven by the pH of the leach solution, the activity of ferric iron (Fe3+ (aq)) dissolved in the leach solution, and temperature. Acid consumption, a principal operating cost item, depends on the pH of the leach solution; the presence of reactive gangue minerals, notably carbonates, Ca plagioclase, pyroxene, Fe-rich amphibole, and olivine; and the cumulative surface area of material in the heap. There are three basic approaches to commercial copper heap leaching—run-of-mine, dedicated pad, and on-off pad leaching, with variables that include crushing, acid/ferric agglomeration, solution application rate, and leach solution pH. These approaches affect copper leach kinetics, overall copper recovery, acid consumption, and capital and operating costs. A successful copper heap leach evaluation program requires a systematic approach, beginning with geologic mapping, then drilling and hydraulic and metallurgical testing, and concluding with financial analysis, engineering, and permitting. As geologists are the unique party in the process, with a thorough understanding of the overall deposit geology, including ore and gangue mineralogy, the domains that comprise the deposit, and the geochemistry of leaching, they must remain fully involved in the project throughout the evaluation. At the outset, geologists must manage the drilling program and define the grade-mineral domains. Later, they must participate in the metallurgical and hydraulic testing programs, including the evaluation of test results; then, during financial modeling, they must collaborate with all of the other specialists.