Tracking cobalt, REE and gold from a porphyry-type deposit by LA-ICP-MS: a geological approach towards metal-selective mining in tailings

Abstract

High-resolution mineral characterization performed on mine material from a giant porphyry copper deposit shows that critical and precious metals, such as cobalt, lanthanum, gold, silver, and tellurium, are concentrated in pyrite in the form of visible micro-inclusions, invisible mineral nano-inclusions, and trace metals in the mineral lattice. Visible and invisible inclusions consist of Ag-Au-Te sulfosalt and monazite-(La) particles. Trace metal concentrations grade up to 24,000 g/t for cobalt, up to 4000 g/t for lanthanum, and up to 4 g/t for gold. Pyrite, considered a waste material, is removed from the valuable copper ore material and sent to the tailings. Thus, tailings with high contents of pyrite can represent a prime target to explore for critical metals in the porphyry copper mining operations, transforming it into a new source of supply for critical metals. We propose that high-resolution mineral characterization is the key to evolve from a quasi-single-metal (copper) operation to a multi-metals business by developing metal-selective mining. To address this challenge, we coined the Metal-Zone concept to identify zones enriched in a specific metal within a mineral deposit, instead of zones enriched in an ore mineral.