Molybdenum (Mo) is a high technology metal, which is of economic importance due to its wide range of applications, ranging from high performance lubrication, catalysis, to super alloys, heating elements, or similar technological equipment. Whilst it is well known that Mo-bearing ore deposits are formed by hydrous fluids deep inside the Earth’s crust, little is know about the structure and the chemical composition of the ore forming fluids. Hence we will systematically study the solubility of Mo-minerals in hydrothermal fluids at high pressures and high temperatures using a new hydrothermal apparatus and synchrotron radiation. Furthermore, we will also investigate the stability of various Mo complexes in hydrothermal fluids at a range of pressures, temperatures and in fluids of different chemical composition.