Eight methods of ore sterilization, including steam autoclaving, dry heat, tyndallization, cobalt-60 irradiation, thymol (5-methyl-2-(1-methylethyl) phenol) and mercuric chloride additions, were tested using a monzonite porphyry copper ore containing chalcocite, chalcopyrite, pyrite, and minor molybdenite. All treatments were found to effectively eliminate iron-oxidizing bacteria added to the ore. Heating methods were found to be effective sterilization procedures and to have a minimal influence on the leaching characteristics of the ore. However, gamma irradiation and the additions of thymol and mercuric chloride significantly altered the ore and suppressed the abiotic leaching rate. Results suggest that previous bioleaching studies using thymol as a bacterial inhibitor may have overestimated the bacterial role in ore leaching.