Genetic mineralogy of pyrrhotite from the Liwu copper deposit in western Sichuan

The Liwu copper deposit is a medium-sized copper-rich copper deposit hosted in the Jianglang metamorphic core complex dome in Jiulong, western Sichuan. The present paper deals with the chemical compositions and structural types of pyrrhotite from the Liwu copper deposit based on the microscopic examination, energy spectrum analysis and X-ray diffractional analysis. The analytical results show that there occurs only hexagonal pyrrhotite in the inner part of the copper deposit, with the Fe atomic percentages ranging between 48.63% and 47.99% and metallogenic temperatures higher than 304℃. On the contrary, both the hexagonal and monoclinic pyrrhotite are observed in the outer part of the copper deposit, with the Fe atomic percentages ranging between 45.97% and 47.54% and metallogenic temperatures lower than 254℃. It is inferred from the typomorphic characteristics of pyrrhotite and geological characteristics of the copper deposit that the Liwu copper deposit resulted from the activation caused by deformation and metamorphism in original source beds, and superimposed reworking of moderate-to high-temperature hydrothermal solutions during the Yanshanian.