Typomorphic characteristics of pyrrhotite as an ore-forming indicator of Heiniudong copper deposit

The contents of iron in pyrrhotite in the Heiniudong copper deposits are in a range of 42.43 similar to 45.58 atom% detected by using the technique of X-ray energy dispersive spectrometry. The compositions of pyrrhotite are plotted onto "pyrrhotite + pyrite" area in the diagram of Fe-S system. All pyrrhotite samples selected from different types of ores are of hexagonal structure determined by X-ray, p energy dispersive spectrometry. According to typomorpbic structural characteristics that the presence of annealing texture in pyrrhotite and the corresponding absence of pyrite take place over the temperature range 550 degrees C to 450 degrees C, the structure and composition of pyrrhotite in the deposit, combined with the characteristic of seldom occurrence of pyrite in ores, indicate that the peak metamorphic temperature should be higher than 450 degrees C. Pyrrhotite may be generated either by precipitating from metal bearing fluid or/and by the reduction of pyrite. The presence of graphite in the ores and wallrocks implies an intensively reductive circumstance in metamorphism, and sulfur has low solubility in reductive circumstance. The association of tourmaline with pyrrhotite and chalcopyrite indicates the existence of middle-high temperature fluid in metamorphism. The existence of fluid, carbonaceous material catalyses reaction and the intensively reductive circumstance are favourable for the generation of pyrrhotite, and for remobilized copper to precipitate in favourable settings which are provided by ductile shear zones.