• Microwave roasting self-leaching achieves 96.18% gold extraction from high-sulfur refractory gold ore without cyanide.
• Response surface methodology identifies CuSO4 and NH3·H2O as critical factors influencing the self-leaching process.
• XPS analysis reveals that sulfide, polysulfides, and thiosulfate act as key ligands in gold complexation.
• The copper–ammonia complex catalyzes self-leaching, but improper ratios cause copper–sulfur precipitates that lower recovery.