Granite-related hydrothermal veins typically have high ore grades and tonnages and thus are an excellent target in the search for such commodities as tin, tungsten, silver, copper and many other metals.Although the geology of these deposits is well described, a considerable debate persists about key issues related to their genesis, such as the timing of fluid separation from crystallizing magmas, the controls on ore-metal ratios, and the mechanism of ore deposition.This study proposes to improve our under standing of these topics by investigating the magmatic and hydrothermal processes, which formed the world-class San Rafael cassiterite-sulfide deposit (Peru) and by establishing parallels with other deposits of this type.The core of the project will consist of a detailed study of melt and fluid inclusions from the host rocks and ores of the deposit. First, careful petrographic studies will establish the paragenetic sequence of inclusion types and microthermometric measurements will be conducted.Then, using state-of-the-art analytical techniques (principally laser-ablation ICP-MS analysis) we will quantitatively characterize the microchemistry of individual inclusions.This will constrain the composition of the evolved silicate melts and exsolving fluids and, in conjunction with studies of mineral equilibria, the subsequent evolution of the ore fluids in terms of composition, temperature, pressure, pH, fO2, and fS2.On this basis, we will identify the main controls on high-grade cassiterite deposition at San Rafael and develop a comprehensive genetic model for the deposit. Ultimately, the research project will establish the factors underlying the formation of unusually rich hydrothermal tin-tungsten resources and the controls on their ore-metal ratios.It will combine academic advancement and the development of new ore-deposit models with direct applications in the exploration for new metal sources on a global scale.