Petrology and temperature determination of skarn formation in Dezg area, southwestern of Hajiabad, north of Birjand

The study area is located north of Dezq village in southwestern of Hagiabad. Mineralogical and geochemical investigations are showing two main stages of prograde and retrograde metamorphism in formation of skarn in study area. In prograde stage, has formed skarn with anhydrous silicate- calcium mineral assemblage (andradite – grossular and diopside-hedenbergite) in temperature range of 328° to 599° which has similar composition with garnets from Cu- Fe and Au skarns. Formation of anhydrous calcium silicate minerals like andradite, grossular, and clinopyroxene proves the temperature range between 756 and 776ºC and XCO2=0.1-0.6. In retrograde stage,a part of these anhydrous silicates at temperatures lower than 756ºC are affected by retrograde metamorphism and changed to hydrous and anhydrous silicate minerals with less calcium(epidote, tremolite-actinolite) and finally hydrous and anhydrous calcium assemblage has altered to fine grain minerals including chlorite, calcite, quartz and clay minerals in temperature range of less than 300°. The presence of intergrowth texture and absence of replacement texture in andradite and pyroxene, is showing that these minerals are formed as contemporaneous. This mineral assembelage has crystallized in high partial water pressure which is between 0.8 to 0.9 whole pressure. High partial water pressure has been certainly result of water fluid seepage from granitic body to country rock.