The refractory behavior of a sulfide-zone copper-rich gold ore from the Mastra deposit (Gümüşhane, Türkiye) was investigated by diagnostic leaching to quantify the deportment of gold and silver and to identify the controls on cyanidation performance. Gold extraction of only 18.4% was obtained by direct cyanidation of the as-received ore, confirming its highly refractory behavior. Sequential pre-treatments with HCl and HNO₃, each followed by cyanidation, increased the cumulative Au extraction to 88.5%. The largest increment, 47.6% of the total Au, was obtained after the HNO₃ stage, indicating that this fraction is associated with a sulfide-bearing matrix. The remaining 11.5% of the Au is reported as an unresolved residual refractory fraction. Silver behaved differently from gold in that 52.9% of the Ag was dissolved directly by the HCl and HNO₃ stages, mainly as chloride species in the HCl stage, and cyanide extracted a total of 38.0%. The high cyanide consumption in direct cyanidation (6.75 kg/t) is largely attributed to the dissolved copper (22.7% of the Cu). The study demonstrates that diagnostic leaching provides a quantitative basis for identifying the causes of gold refractoriness and for selecting appropriate pre-treatment strategies for refractory gold ores that are not amenable to conventional cyanidation.