<p>Processing of high-grade gold ores is uncommon, so extraction is currently carried out using conventional methods, with cyanide as the agent due to its high selectivity and stability. Despite its popularity, this process presents environmental risks, which have led to the implementation of alternative lixiviants such as thiourea, which allows gold extraction in less time than cyanide. Gold leaching with thiourea is an interesting alternative; however, it can degrade irreversibly if the system’s potential is not controlled. This study examines the effect of oxalate as an additive to control the oxidation potential and improve gold recovery by regulating Fe and Cu ions that consume thiourea during acidic leaching at room temperature. While oxalate enhanced gold extraction, it interfered with the determination of thiourea concentration by iodate titration. The use of Zn²⁺ reduces this interference by masking oxalate as a ZnC₂O₄ in an acidic medium.</p> Graphical abstract <p></p>