Abstract
Porphyry-type molybdenum deposits, many of which are in China, supply most of the World's molybdenum. Of particular importance are the molybdenum deposits located in the Qinling-Dabie region that are responsible for more than half of China's molybdenum production. A feature that distinguishes this suite of deposits from the better-known Climax and Endako sub-types of porphyry molybdenum deposits is their formation from CO(2)-rich magmatic-hydrothermal fluids. The role of CO(2), if any, in the transport of molybdenum by these fluids, however, is poorly understood. We conducted experiments on the partitioning of molybdenum between H(2)O-CO(2), H(2)O-NaCl, and H(2)O-NaCl-CO(2) fluids and a felsic melt at 850 °C and 100 and 200 MPa. Here we show that the exsolution of separate (immiscible) brine and vapor leads to the very high brine D(Mo) values needed for efficient extraction of Mo from the magmas forming Dabie-type porphyry molybdenum deposits.