Origin of high Ba-Sr granitoids at Chigou in central China and implications for Cu mineralization: Insights from whole-rock geochemistry, zircon U–Pb dating, Lu–Hf isotopes and molybdenite Re–Os systematics

Abstract

The Chigou copper deposit is situated in the southern part of the Qinling orogenic belt, central China, where quartz diorite and quartz diorite porphyry are associated with porphyry-type copper mineralization. Copper generally occurs as veins, veinlets, and disseminations within-host porphyries. The zircon dates tightly constrain the timing of host porphyries to ca. 149–146 Ma, in agreement with the age of porphyry copper mineralization (146.1 ± 2.8 Ma) constrained by using molybdenite Re–Os dating. The calculated zircon ΔFMQ values for quartz diorite are −9.4 to +9.9 (averaging +4.3). The Chigou granitoids show similar geochemical compositions to high-Barium-Strontium (high Ba-Sr) granites, with high Ba (2256–3717 ppm) and Sr (737–1345 ppm), low Rb (86.2–129 ppm), U (1.9–4.7 ppm), Th (16.2–31.2 ppm), and Nb (11.4–19.1 ppm) concentrations, as well as lack of negative Eu anomalies. The concentrated εHf(t) values (−3.0 to +1.4), moderate Mg# values (41–52), and high (Hf/Sm)PMN and La/Sm ratios, but low Ba/Th, U/Th, and (Ta/La)PMN ratios indicate that ore-forming magmas derived from an enriched lithospheric mantle that had been metasomatized by subducted sediment-derived melts with a minor crustal contribution. Combined with previous studies, we suggest that the Chigou deposit formed in a post-collisional tectonic setting during the Late Jurassic.