Characterization of gold deportment and thiosulfate extraction for a copper‑gold concentrate treated by pressure oxidation

Gold extraction from porphyry copper‑gold ore is challenging due to the presence of copper and sulfide minerals. In this study, pressure oxidation (POX) was used for copper extraction and gold liberation from the sulfide mineral matrix. The POX residue was investigated for gold mineralization and leaching study. Gold deportment study was conducted using a series of techniques, including X-ray diffraction (XRD), optical microscope, scanning electron microscope with energy dispersive X-ray spectroscopy (SEM-EDX), and dynamic secondary ion mass spectrometry (D-SIMS). Cyanidation was compared as a baseline for gold extraction; ammoniacal thiosulfate ((NH₄)₂S₂O₃) and non-ammoniacal thiosulfate (Na₂S₂O₃) were investigated as alternative leaching conditions. In this work, POX achieved a high copper removal percentage and left 0.66% copper in the residue. Undestroyed sulfide minerals such as chalcopyrite, pyrite, and molybdenite presented with 2.7%. Hematite formed during POX and accounted for 66% of the total mineral phases. Meanwhile, hematite was the major sub-microscopic gold carrier, containing 64.7% of the total gold as colloidal gold. Visible gold was identified as 24.4%. Gold extraction tests revealed that the maximum gold extraction achieved by cyanidation was 85% using 250 mg/L NaCN, consistent with the gold deportment study. Similar gold recovery was observed using 0.03 M (NH₄)₂S₂O₃, but it reduced drastically in Na₂S₂O₃ leaching solution due to the absence of ammonia.