Quantitative Workflow for the Occurrence State of Gold, Cobalt, and Critical Metals in Porphyry Deposits: A Case Study of the Shaxi Deposit, Middle–Lower Yangtze River Metallogenic Belt

Quantifying gold occurrence in low-grade ores is challenging because gold minerals are sparse and fine-grained, limiting their detection in conventional polished sections. This study developed an integrated geometallurgical workflow using the Shaxi porphyry Cu–Au deposit in the Middle–Lower Yangtze River Metallogenic Belt as a case study. Representative ores containing 0.282 g/t Au were subjected to gravity pre-concentration and Superpanner enrichment, followed by resin-mount preparation. TIMA Integrated Mineral Analyzer (TIMA) analysis, electron probe microanalysis (EPMA), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) were combined with mineral mass-balance calculations to characterize gold mineralogy, grain size, liberation, and distribution among mineral hosts. Visible gold accounts for 98.78% of the total gold, whereas submicroscopic gold in sulfides contributes only 1.22% and is hosted predominantly by pyrite. The identified gold minerals are dominated by native gold, with minor electrum and calaverite, and gold grains predominantly range from 15 to 40 μm. At a grind size of 80% passing 150 μm, most gold can be liberated, with an estimated maximum theoretical flotation recovery of 86.53% under the assumed recovery conditions. The workflow links the characterization of discrete gold minerals with the quantification of submicroscopic gold, providing mineralogical constraints for processing low-grade porphyry Cu–Au ores. Its extension to cobalt and other critical metals warrants further evaluation, particularly where discrete mineral phases can be concentrated.