When one tectonic plate sinks beneath another, it generates magmas rich in volatiles such as water, sulphur and chlorine. As these magmas ascend, they release magmatic fluids, in which sulphur and chlorine bind to metals such as gold and copper, and transport these metals towards the surface of the Earth. As the extreme conditions relevant to natural magmas are very difficult to reproduce in the laboratory, the precise role of the different forms of sulphur in metal transport remains highly debated. However, an innovative approach has demonstrated that sulphur, in its bisulphide (HS-) form, is crucial for the transport of gold in magmatic fluids.