<p>This work is focused on the effect of the ultrafine grinding (UFG) of a refractory ore (RO) on the gold and silver leaching. The UFG was performed at 60 (UFG60) and 120 min (UFG120). The d₈₀ for RO was 27.95 µm while for the samples UFG60 and UFG120, were 15.07 µm and 13.64 µm, respectively. The leaching of the RO and the UFG samples was performed by cyanide solution (1 and 2 g/L at pH 11), 10% of solids, 240 min. The gold and silver concentrations in leaching solutions increase with the leaching time and cyanide concentration; the highest gold and silver concentrations were obtained for the UFG samples. UFG for 60 min, increases the gold and silver leaching rate due to a diminution of the particle size, improving the contact between refractory ore and leaching solution at 2 g/L, reaching leaching efficiency of gold 22.34% and silver 81.85%.</p> Graphical Abstract <p></p>