Mineralization events in the Xiaokele porphyry Cu (-Mo) deposit, NE China: Evidence from zircon U-Pb and K-feldspar Ar-Ar geochronology and petrochemistry

The Great Xing'an Range (GXR), Northeast (NE) China, is a major polymetallic metallogenic belt in the eastern segment of the Central Asian Orogenic Belt. The newly discovered Xiaokele porphyry Cu (-Mo) deposit lies in the northern GXR. Field geological and geochronological studies have revealed two mineralization events in this deposit: early porphyry-type Cu (-Mo) mineralization, and later vein-type Cu mineralization. Previous geochronological studies yielded an age of ca. 147 Ma for the early Cu (-Mo) mineralization. Our 40Ar/39Ar dating yielded 40Ar/39Ar plateau ages of 124.8 +/- 0.4 to 124.3 +/- 0.4 Ma on K-feldspar in altered Cu-mineralized diorite porphyrite dikes that represent the overprinting vein-type Cu mineralization, consistent with zircon U-Pb ages of the diorite porphyrite (126.4 +/- 0.5 to 125.0 +/- 0.5 Ma). The Cr and Ni contents and Mg-# of the Xiaokele diorite porphyrites are high. The diorite porphyrites at Xiaokele are enriched in light rare-earth elements (REEs), and large-ion lithophile elements (e.g., Rb, Ba, and K), are depleted in heavy REEs and high-field-strength elements (e.g., Nb, Ta, and Ti), and have weak negative epsilon(Hf)(t) values (+0.29 to +5.27) with two-stage model ages (T-DM2) of 1,164-845 Ma. Given the regional tectonic setting in Early Cretaceous, the ore-bearing diorite porphyrites were likely formed in an extensional environment related to lithospheric delamination and asthenospheric upwelling induced by subduction of the Paleo-Pacific Plate. These tectonic events caused large-scale magmatic activity, ore mineralization, and lithospheric thinning in NE China.