Abstract

DONG, Qian et al. Composition of biotite within the Wushan granodiorite, Jiangxi Province, China: Petrogenetic and metallogenetic implications. Earth Sci. Res. J. [online]. 2014, vol.18, n.1, pp.39-44. ISSN 1794-6190.  https://doi.org/10.15446/esrj.v18n1.40830.

The Wushan skarn copper deposit is genetically associated with the Wushan granodiorite. In this study, we investigate the petrography and mineralogy of biotites within the Wushan granodiorite. We also determine the formation conditions of these biotites and discuss the significance of these minerals in terms of petrogenesis and mineralization. Electron microprobe analysis shows that biotites within the Wushan granodiorite are Magnesio-biotites that contain relatively high Mg and Ti concentrations and low Fe and Al concentrations. The ionic coefficient of Al^VI in these biotites ranges from 0.03 to 0.19, with ∑FeO/(∑FeO + MgO) ratios that range from 0.531-0.567 and MgO concentrations that range from 12.80-14.06 wt%. These results indicate that the Wushan granodiorite is an I-type granite. The Wushan biotites crystallized at temperatures (T) of 720°C-750°C, with oxygen fugacity (fO2) conditions of -11.6 to -12.5 and pressures (P) of 0.86-1.03 kb. These conditions are indicative of a crystallization depth (H) of 2.84-3.39 km. These data also indicate that the Wushan granodiorite developed under conditions of high temperature and high oxygen fugacity, suggesting that the Wushan granodiorite is prospective for magma-hydrothermal mineralization and that this granodiorite probably contributed to the formation of the Wushan skarn copper deposit.

Keywords : biotite; granodiorite; mineral chemistry; petrogenesis and mineralization; Wushan skarn copper deposit.

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