In the present investigation the influence of ferric ion concentration and agitation time during the biooxidation process as a pretreatment was studied to increase the gold and silver recovery rate of a refractory mineral from Sayapullo by means of experimental tests in bioreactors. The sample consisted of 27 bioreactor tests, which were subjected to three different concentrations of ferric ion (8,8; 10,2 and 13) g / L and three different stirring times during the biooxidation process (24, 48 and 72) Hours , making use of two replicates for each test and then analyzing the degree of gold recovery using the fire test method or also called fire assay. The results show that, for a concentration of ferric ion of 8,8 g / L and at a time of 24, 48 and 72 hours the% gold recovery are respectively: 18,64%; 30,45% and 20,91%. For a ferric ion concentration of 10,2 g / L at a time of 24, 48 and 72...