Abstract: The Yulong porphyry copper (molybdenum) deposit in Xizang is the largest one in China and even in Asia. As a representative supergiant porphyry copper deposit comprising varying mineralization types, the nature of magmatic melts may play the most important part in the mineralization of the Yulong copper deposit. The study of physical and chemical properties and evolution of the magmatic melts was made on the basis of the calculated data on the density and viscosity of the magmatic melts to explain the formation of the Yulong copper deposit. Abundant ore-forming elements and volatile components (mineralizers) in the magmas from which the Yulong copper deposit may serve as the principal sources of the ore-forming matter in the deposit. The viscosity (56.43 Pa·s) and density (2.09g/cm³) of the magmatic melts suggest a kind of low viscosity and high density of magmas. The physical and chemical properties of the magmas facilitate the enrichment of ore-forming matter and the generation of abundant mineralizing fluids.