Apatite geochemistry as an indicator of petrogenesis and uranium fertility of granites: A case study from the Zhuguangshan batholith, South China

Abstract

To explore the potential of apatite geochemistry as an indicator of petrogenesis and uranium fertility of granites, we analyzed the major and trace elements of apatites from U-bearing (Changjiang and Youdong) and barren (Jiufeng and Fuxi) granites in the Zhuguangshan batholith, South China. All the investigated apatites are identified as fluorapatite that is typical for igneous apatite. Apatites from the U-bearing plutons have higher concentrations of Mn, Fe, Na, and Y, and lower Sr, (Eu/Eu*)N, and (La/Yb)N than those from the barren ones. The compositional variations are interpreted to be related to whole-rock parameters such as SiO2 abundance, oxidation state, and aluminum saturation index. In addition, the presence of other REE-Th-rich minerals such as monazite and allanite can affect REE and Th concentrations in apatites by competing for these elements during apatite crystallization. Concentrations of Sr, Y, and Mn in the studied apatites can serve as a proxy of whole-rock compositions. Apatite compositions indicate that magmas of the U-bearing plutons have higher degrees of magmatic differentiation and lower oxygen fugacity than those of the barren ones. Our results suggest that Sr, Mn, Y, Na, Fe, (La/Yb)N and (Eu/Eu*)N in apatites are effective in distinguishing U-bearing granites from the barren ones. This study highlights the potential of apatite geochemistry to assist in deciphering petrogenesis and uranium fertility of granites.