Investigation of chemistry and the style of formation of calc-silicate minerals in Aghbolagh skarn zone, north of Oshnavieh, West-Azarbaidjan Province, NW Iran

The Aghbolagh area is located about 21 km north of Oshnavieh city, West-Azarbaidjan Province, NW Iran. This study showed that the Fe-Cu skarn deposit in this area can be separated into two zones, (1) Garnet skarn and (2) Garnet-pyroxene skarn. Based upon the results of electron probe micro-analysis, the garnets are chemically of andradite-grossularite type with dominant andraditic component. The pyroxenes are also chemically of diopside-hedenbergite type. The skarnification processes took place in two distinct stages, (1) prograde and (2) retrograde. The lack of wollastonite, intergrowth of garnet and clinopyroxene crystals, and the lack of replacement texture indicate that garnets and pyroxenes were formed  concurrently during prograde stage within the temperature range of 450-500ºC and ƒO2 = 10-23- 10-26. During retrograde stage at temperatures < 430ºC, the anhydrous calc-silicate minerals were altered to hydrous calc-silicates, sulfides (pyrite and chalcopyrite), oxides, chlorite, quartz, and carbonates. During this stage, at temperatures <430ºC, andradite at ƒS2 > 10-6 was altered to assemblages of quartz calcite + pyrite but at ƒS2 < 10-6 to quartz + calcite + magnetite.