In this study, a detailed characterization of a refractory arsenical gold ore by using scanning electron microscopy (SEM), X-ray diffraction (XRD), and diagnostic leaching is presented. The mineralogical analysis of the ore indicates mainly the presence of arsenopyrite, pyrite and quartz. The conventional cyanidation tests showed that the gold extractions with grain size of P90 = 38 μm were limited to 10.77 ± 0.32%, during a leaching period of 24 hours. This fact reveals the high degree of refractoriness of the mineral. Diagnostic leaching tests together with the mineralogical analysis suggest that the refractory gold is primarily associated with pyrite and arsenopyrite. The cyanidation of the leached mineral with nitric acid shows an increase in the gold recovery of 62.03 ± 1.57 %; which is due to the high dissolution of pyrite and arsenopyrite. About 92 % of the gold can be recovered by means of the selective dissolutions of the minerals, the remaining percentage of gold stay associated to the silicates, mainly the quartz. The SEM results show that the refractory ore has a high percentage of both arsenic and iron, which confirms its refractoriness. XRD analyzes determined that the mineral is composed mainly by arsenopyrite, pyrite and quartz. The combination of both SEM and XRD techniques in combination with diagnostic leaching allow the good characterization of the gold-bearing phases, in addition to the identification of possible pretreatment options to overcome their refractoriness before cyanide leaching.