The Late Mesozoic granodiorite and polymetallic mineralization in southern Anhui Province, China: A perspective from apatite geochemistry

Abstract

The region of southern Anhui Province (SAP) is one of Late Mesozoic magmatic belts and copper-molybdenum-gold-tungsten polymetallic ore districts in China, but the relationship of polymetallic mineralization and related granodiorite remains unclear. Previous studies indicate that apatite can be an indicator for magmatic evolution and mineral exploration. In this study, apatites from the SAP ore-bearing granodiorites were investigated using observations from the electron microscope, electron probe microanalysis (EPMA), laser-ablation inductively-coupled plasma-mass spectrometry (LA-ICP-MS). The studied apatite samples identified as fluorapatite, show high F (2.69–4.13 wt.%) and low Cl contents (mainly<0.2 wt.%). These apatites also have high La/Y (0.41–4.69) and δEu (0.13–0.70) values, and low (Sm/Nd)N values (0.34–0.81), indicating that the SAP magma was derived from mafic I-type melt. The REE patterns, negative Eu anomalies, the negative δEu and δCe correlation, and high logfO2 values (−10.5 to −13.8) of apatites studied, further indicate that the SAP granodiorites had originated from mantle-derived magmas mixing with the lower crustal components in high oxygen fugacity environment. The results indicate that the Sr/Y and δEu values of apatite can be a good indicator to distinguish adakitic rocks from non-adakitic rocks. Moreover, the δEu value and Cl content in apatite can be effectively used to discriminate the unmineralized rocks and ore deposit types. Keywords: In-situ geochemistry of apatite, Granodiorite, Polymetallic mineralization, Late Mesozoic, Southern Anhui Province