An amenability test is conducted in a reactor that is stirred and aerated. The reactor contains a sample of milled ore and a sample of microbe culture. Some ores contain elements, generally in the host rock, that may be harmful to the microbes in high concentrations. The microbes themselves do not produce the toxins. As well as checking for toxins in the ore during amenability testing, the ‘worst case’ acid consumption of the ore is also determined as all acid consuming minerals are exposed during milling. Heap leaching takes place on coarse crushed ore and hence there is less exposure of the acid consuming ores than in tank leaching.