U–Pb Dating of Hydrothermal Zircons from the Neoproterozoic Liushanyan VMS Cu–Zn Deposit, Central China: Evidence for a Triassic Deformation Event

Abstract

The Liushanyan deposit is an important volcanic-host massive sulfide (VMS) Cu–Zn deposit in the Qinling-Tongbai-Dabie orogenic belt, central China, with reserve of 2.38 Mt Cu and 16.11 Mt Zn. Orebodies occur in the meta-quartz keratophyre of the Liushanyan formation. In this paper, we present textural features and laser ablation ICP-MS U–Pb dating results of zircons from the ore-bearing mylonitized meta-quartz keratophyre. The hydrothermal zircons are distinct from metamorphic zircons in this rock, showing low cathodoluminescence (CL) response and hydrothermal rims (black in CL images). They have relatively flat light rare earth element patterns and high La content and low (Sm/La)N and Ce/Ce* values. These features are typical of hydrothermal zircons. The cores of metamorphic zircons yield a weighted mean 206Pb/238U age of 900 ± 26 Ma, interpreted as the volcanic and related VMS mineralizing age. Two much younger events are also recorded by zircons in this rock: (i) the Early Silurian amphibolites–greenschist facies metamorphism at 435 ± 26 Ma; and (ii) the growth of hydrothermal zircons at ca. 241 ± 1 Ma, associated with the ductile shear deformation. The Silurian metamorphic event is probably associated with the arc–continent collision, while the Triassic ductile deformation event formed in the final continent–continent collision setting.