A method for controlling the extraction of gold from a gold ore by the cyanidation process in which a leaching step including the addition of a lead compound, which is typically lead nitrate or other lead salt, is used. In order to maintain stable conditions in the leaching process, and to use the leaching reagents efficiently, an analysis step is used to monitor the concentration of thiocyanate in the cyanidation step. This value has been found to be directly related to the rate of addition of the lead compound in the pre-leaching or leaching step. Further, the rate of addition of lead compound is also directly related to both the time required for, and the efficiency of, the cyanidation step. By establishing a target value, and a preferred range, for the thiocyanate concentration based on the properties of the ore being processed, optimal extraction conditions can be established in the leaching process and maintained by monitoring the thiocyanate concentration. By the use of an automated potassium permanganate titration procedure as the analysis step, the thiocyanate concentration can be measured on line with only a short delay.