Investigation of skarn zoning, minerals chemistry and conditions for formation of exoskarn in Bisheh iron deposit (south of Birjand)

In the Bisheh area, intrusion of hornblende porphyry diorite in limestone and tuffs rocks caused skarn formation. Garnet and pyroxene are the most abundant minerals in prograde exoskarn, respectively. In retrograde processes, epidote, tremolite-actinolite, quartz, calcite and opaque minerals such as magnetite were formed. Electron microprobe analysis shows that the studied garnets are andradite-grossular solid solution. Studied garnets show variations in Fe3+/Al ratio that is related to changing conditions during growth. Studied pyroxenes are very close to diopside end member and lowest diopside content is 64.97%. Based on garnet and pyroxene composition, the average  logarithm of oxygen fugacity is calculated -20.18 megapascal. The presence of magnetite, pyrite and pyrrhotite along with calcite and quartz show that metasomatism fluids probably had ƒS2~10-7 and temperature < 430°C.