Geochronological and geochemical constraints on the formation of Chizhou Cu-Mo polymetallic deposits, middle and lower Yangtze metallogenic belt, eastern China

Abstract

The Cu-Mo polymetallic deposits are widespread in the Chizhou region, the Middle and Lower Yangtze River metallogenic belt, eastern China, but the formation of Cu-Mo polymetallic deposits remains unclear. Geochronological, geochemical and Sr-Nd-Hf isotopic compositions of the Cu-Mo polymetallic deposits in the Chizhou region are systemically investigated to reveal the formation of Cu-Mo polymetallic deposits and petrogenesis of the granodiorite (porphyry). The geochronological dating results show the formation ages of Cu-Mo polymetallic deposits (molybdenite Re-Os age, 151–148 Ma) and the granodiorites (porphyries) (zircon U-Pb age, 150–146 Ma) in the Chizhou region are simultaneous (within error). The Chizhou granodiorites (porphyries) (SiO2 = 62.9–65.7 wt%) are high-K calc-alkaline peraluminous I-type granodiorites. They have high Mg# (mainly >40) values and low Na2O (<4.3 wt%) contents, negative whole-rock εNd(t) (−5.83 to −5.71) and zircon εHf(t) (−12.7 to −3.03) values, high apatite Cl contents (>0.2 wt%), and high log fO2 values (−28.3 to −6.22). The distinctly chemical and isotopic compositions indicate that the Chizhou granodiorites formed from metasomatized mantle-derived magmas mixing with Neoproterozoic crustal components. The results indicate that the formation of the Cu-Mo polymetallic deposits in the Chizhou region may depend on the slab-derived Cl-enriched fluids, an oxidizing environment and a mantle-crust mixed source.