Oxygen fugacity, temperature and pressure estimation from mineral chemistry of the granodiorite porphyry from the Jilongshan Au-Cu deposit and the Baiguoshu prospecting area in SE Hubei Province: A guide for mineral exploration

The Jilongshan Au-Cu deposit is located in the Jiurui district of the Middle-Lower Yangtze River Metallogenic Belt in the south-eastern part of Hubei Province and close to the northern border of Jiangxi Province. This study focuses on mineral chemistry of biotite, amphibole and plagioclase in the ore-related granodiorite porphyry at the Jilongshan deposit and similar porphyry rock from the nearby Baiguoshu prospect, in an attempt to investigate the mineralization potential in the Baiguoshu area. The biotites from the Jilongshan and Baiguoshu granodiorite porphyries all belong to magnesian-biotite but the Jilongshan contains higher Mg. The calculation of Fe3 + and Fe2 + of the biotites indicated that the Jilongshan pluton shows higher oxygen fugacity that is favorable for Cu-Au mineralization, whereas the Baiguoshu pluton shows lower fO2. The Jilongshan amphiboles show higher Mg / (Mg + Fe) and lower Si which mainly belong to magnesiohornblende, whereas the Baiguoshu accommodates mainly the tschermakite. The plagioclases of the Jilongshan and Baiguoshu plutons show no compositional difference and both belong to andesine. The calculated temperatures and pressures by the coexisting amphibole-plagioclase pairs indicate that average crystallization temperature of the Jilongshan pluton is 624-736 °C and the pressure is low at 0.5-0.9 kbar, in contrast the Baiguoshu pluton shows higher temperature of 724-832 °C and higher pressure of 3.2-6.3 kbar. These data suggest that the Baiguoshu pluton has less mineralization potential than the Jilongshan pluton, therefore the Baiguoshu prospect shows less economic importance and further exploration should be carried out at depth in the Jilongshan area.