Genesis, Magmatic Process and Metallogenic Constraints on the Wudaoliuhe Intrusive Rocks in the Jiapigou Gold Mining District, Jilin Province: Evidence From Zircon U–Pb Geochronology and Element and Hf Isotope Geochemistry

Abstract

The Jiapigou area is a world-famous gold mining district. Recent studies have revealed that large-scale mineralization occurred between 180 and 172 Ma, which is temporally associated with the Wudaoliuhe intrusive rocks. The Wudaoliuhe intrusive rocks are mainly divided into two stages, including Early Jurassic monzogranite (stage I) and small amounts of Middle Jurassic diorite, granodiorite and monzogranite (stage II), which are present as stocks in the stage I monzogranite and Archean supracrustal rocks. Zircon U–Pb ages suggest that the magma emplacement of the stage I monzogranite occurred at 186.1 ± 1.2 Ma, whereas stage II diorite, granodiorite and monzogranite were emplaced at 176.3 ± 2.4 Ma, 175.0 ± 1.4 Ma and 174.4 ± 1.1 Ma, respectively. The geochemical characteristics reveal that stage I and monzogranite and stage II granodiorite and monzogranite have high SiO₂ and Al₂O₃ contents, low MgO, and CaO contents, A/CNK ratios (1.01–1.10), are enriched in LILEs and LREEs, depleted in HFSEs and HREEs and exhibit moderate negative Eu anomalies. The stage II diorite has high SiO₂, Al₂O₃, CaO and MgO contents, A/CNK ratios (0.93–0.96), is enriched in LILEs, lacks HFSEs and has significant Eu anomalies. The εHf(t) values of the stage I monzogranite are −5.5 to −11.3. The εHf(t) values of stage II diorite, granodiorite and monzogranite are −5.7 to −4.7, −6.9 to −9.7, and −7.7 to −10.4, respectively. These geochronology and geochemistry characteristics indicate that the deep geological process in the Early Jurassic was large-scale partial melting of the crust. With the evolution of the magma chamber and the addition of mantle-derived materials, some residual magma transformed into intermediate–basic magma. The magma intruded upwards and formed the stage II diorite, granodiorite and monzogranite. The large-scale mineralization in the Jiapigou mining district (JMD) coincided with an extensional-transition process triggered by the subduction of the palaeo-Pacific Ocean. The metallogenic process coincided with partial melting of the continental lower crust, and mantle-derived magma participated in the late stage of magma chamber evolution. These findings highlight that crustal partial melting and mantle-derived material input were critical factors controlling the large-scale Au mineralization in the JMD.