Apatite chemistry of Late Triassic granitic rocks from Yidun Terrane: Implications for petrogenesis and mineralization

Abstract

The Yidun Terrane hosts huge amounts of Late Triassic granitic plutons. While the southern Yidun Terrane, also referred to as the Zhongdian arc, mainly includes Late Triassic porphyry and related porphyry Cu-Au deposits, rare mineralization was found related to the contemporary granitic batholiths in the northern Yidun terrane (NYT). This paper has explored the chemical compositions of the apatite from these intrusions, which provide insights into the petrogenesis and the mineralization potential. The higher Mg and V concentrations and La/Sm ratios of the Zhongdian apatite than the Cuojiaoma and Daocheng apatite in the NYT suggestes that the Zhongdian porphyries were derived from a mixed source with both mantle and crustal contributions, while the Cuojiaoma and Daocheng granites are dominantly crustal derived. Compared with the Cuojiaoma and Daocheng apatite, the Zhongdian apatite are characterized by higher Sr, Eu/Eu* [Eu_N/(Sm_N×Gd_N)^0.5], S and Cl, and low Mn and Y concentrations with adakitic affinity, indicating an environment with high oxygen fugacity and S and Cl contents for their parental magmas, which is favorable for the formation of porphyry Cu-Au deposits. By comparing the chemical characteristics of apatite from the ore-bearing porphyries and ore-barren granites in the Yidun Terrane, this study proposes that the apatite from the ore-bearing rocks commonly has relatively high Sr, S and Fe concentrations and low Mn, Y and Si/S ratio. These geochemical characteristics can be good indicators for predicting the metallogenic potential of the rocks.