The Typomorphic Characteristics And Their Genetic Implications Of Pyrrhotite In Saishitang Copper Deposit, Qinghai Province

The Saishitang copper deposit is one of the important deposits constituting the Ela Mountain metallogenic Belt. Pyrrhotite in the deposit which is the most important metallic mineral is in close paragenesis with chalcopyrite,. This paper tries to reveal the mineralogical characteristics of pyrrhotite by means of X-ray diffraction, SEM and electron probe microanalysis combined with microscope observation so as to find the useful information for ore genesis of Saishitang Deposit, Qinghai.The ore types are Pyrrhotite-Copper skarn ores, Pyrrhotite-Sphalerite-Galena skarn ores, Molybdenite-Copper skarn ores, and Magnetite skarn ores, vein Pyrite-Arsenopyrite-Sphalerite-Stannite-Quartz-Calcite ores.The pyrrhotite has 2 occurrences. One is in the Cu-Zn skarn, in paragenesis with Chalcopyrite-Sphalerite, mostly subhedral to xenomorphic-granular with grain size larger than 0.1mm; the other is in veined or disseminated form hosted in quartz diorite and diorite with grain size 0.06-0.2mm. The contents of iron in pyrrhotite in the Saishitang copper deposits are in the range of 45.69～46.92 atom% corresponding to the chemical formula Fe7S8 with very little compositional change even in different occurrences.The contents of Co,Ni in pyrrhotite changes from 1.60% to 0.06%. The content of Ni is a little lower with the average of 0.03%. The cell parameters of pyrrhotite are determined to be ao=0.689, bo=1.189, co=1.286, beta=117.21°, in accord with that of normal monoclinic pyrrhotite, suggesting the mineralization temperature should be below 254℃.