Mineralogy, geochemistry and geothermometry of chlorite in Malvak area(South of Malayer-Iran)

The chemical composition of chlorite group minerals show that physicochemical condition of crystallization and their formation. The chemical analysis of chlorite from biotite alteration has done based on 30 points of 8 rock samples by electron microprobe. The composition of chlorite samples is located in repidolite- pychnochlorite domain. The mole fraction in the interlayer phase, range from 0.97 to 0.99, indicating a complete lack of smectite layers and purity of chlorite. Calculation of the structural formula of chlorites in Malvak area show that the number of silicon atoms are in the range of 2.64 to 2.91 (apfu) and the sum of the octahedral cations are 6 (apfu). Chlorites of the Malvak area are trioctahedral type. The low titanium content of chlorites, the presence of titanium minerals coexite with chlorite cleavage, and the presence of early biotite crystals are evidence of biotite to chlorite alteration. The mean temperature of chlorites in the Malvak area is 340 ºC, which corresponds to the temperature obtained with the geothermometry of biotite-altered to chlorites. Mesothermal type fluids from the granitoid mass in the study area have been effective in chlorite occurrence. Also, regional metamorphism has played an important role in the chlorite formation.