Rhenium (Re) is one of the rarest elements on Earth (average abundance < 1 ppb) and is of fundamental importance for our modern high-tech industry due to its high thermal stability (melting temperature beyond 3100 °C). Yet the enrichment process of Re in ore deposits is little understood mainly due to the difficulties to perform experiments at extremely high dilution levels and simultaneously at high P/T conditions. The new ESRF-extremely brilliant source capabilities and several recent technical developments at the ESRF beamlines FAME and BM23 allow overcoming these limitations. We therefore propose to study systematically the solubility and speciation of Re in fluids as a function of P/T and fluid composition using X-ray fluorescence spectroscopy and High-Energy Resolution Fluorescence Detection (HERFD) X-ray spectroscopy. The new data will improve our understanding of Re mobilization in magmatic systems and its enrichment process with implications for the exploration of Re.