Propylitic alteration develops chlorite, epidote, and calcite assemblages commonly found in porphyry copper–gold deposits. This study aims to understand the formation temperature, oxygen, and sulfur fugacity of chlorite, a characteristic central element of propylitic-related minerals such as epidote and calcite, using a combination of qualitative and quantitative experimental methods. The propylitic alteration forming condition was analyzed in detail using a superprobe (JXA-iSP100) and Electron Probe Micro Analysis (EPMA) at a voltage of 15.0 kV. The chlorite composition is relatively homogeneous, and displayed as Mg-rich chlorite (Type-I) within AlIV-Mg-Fe, ripidolite with respect to Si vs Fe/(Fe+Mg). The chlorite geothermometer indicates that the crystallizing temperature ranges from 288.30 to 332.82°C. The oxygen and sulfur fugacity log fO2 and log fS2 of chlorite are low ranges (– 70.4 to – 51.85) and (– 32.55 to – 20.65), respectively. The analyses identify the mineral as true epidote, with spatial variations indicating Fe occurs as Fe³⁺ and Mn as Mn²⁺. However, the examined proportion of moles of the significant elements (Mg, Ca, Fe, Mn) indicates that calcite is present in hydrothermal systems.
Por et al. (Fri,) studied this question.