LA-ICP-MS zircon U-Pb age and petrochemical characteristics of magmatite from the Dadonggou gold deposit in east Liaoning

The Dadonggou gold deposit is located in the east of the northern margin of North China craton.In this paper, zircon UPb chronology and petrochemistry of magmatite from the Donggou gold deposit were studied. The LA-ICP-MS method was used and the ages of zircon in granodiorite and quartz diorite are 2147±10Ma(²⁰⁷Pb/²⁰⁶Pb age-weighted mean, n=17, MSWD=0.59) and 140.8 ±1.2Ma(²⁰⁶Pb/²³⁸U age-weighted mean, n=22, MSWD=0.48) respectively; nevertheless, the granite diorite experienced late hydrothermal events of 1874 ±18Ma.Elemental geochemical test results show that both granodiorite and quartz diorite are high potassium calc-alkaline I type granite. Quartz diorite is a right-dipping model with weak negative Eu anomalies, but granodiorite is a relatively flat right-dipping model with obvious positive Eu anomalies; they both show characteristics of relatively rich light rare earth elements. As for trace elements, they are all enriched in large ion lithophile elements Rb, Ba and K. Quartz diorite is characterized by depletion of high field strength elements such as Nb, Ta, Zr, Hf and Ti, but the granodiorite shows the depletion of high field strength elements such as Th, Nb, Ta and Ti. Combined with regional tectonic evolution and related studies, the authors have reached the conclusion that granodiorite was formed in the tectonic background of continental back-arc basin, mainly caused by partial melting of the lower crustal igneous rocks due to the magmatic heating action of ~2.2Ca. However, quartz diorite was formed in the tectonic background of the oblique subduction of Izanagi plate to the North China plate, which had the feature of crust-mantle mixing.It was the fluid metasomatic mantle in the subduction zone, and the basic magma formed by partial melting was mixed with the crust molten material.