Abstract: A method of selectively leaching zinc from a source material containing zinc in sulphide form and iron, comprises the steps of subjecting the source material to bioleaching with a strict sulphur oxidizing micro organism or a mixed culture of sulphur oxidizing and iron oxidizing micro organisms, in the presence of a nutrient solution containing less than about 15 mg/L phosphate ions. In another embodiment, the source material is in the form of a slurry having a solids concentration of at least about 25% on a weight per volume basis and a nutrient solution containing from about 1 mg/L to less than about 100 mg/L ammonium ions, from about 0.5 mg/L to less than about 40 mg/L magnesium ions and from about 2 mg/L to less than about 60 mg/L phosphate ions.