Funds are requested in this proposal for support of theoretical studies of the chemical evolution of a magmatic hydrothermal system that was associated with the formation of a major molybdenum porphyry deposit. The deposit has been well characterized through many years of field, laboratory and analytical studies. We will build on these studies to establish, for the first time, water-rock interactions responsible for the hydrothermal alteration assemblages and the precipitation of the molybdenite ore in a magmatic hydrothermal system.