LA-ICP-MS zircon U-Pb dating and geochemistry of the metallogenic gabbrodiorite intrusion in the Liudaowaizi iron-copper deposit of eastern Yanbian, Northeast China

The Liudaowaizi iron-copper deposit is located in Yanbian area and belongs to the east part of the Xing'an-Mongolia Orogenic Belt. The major orebodies occur along the contact zone between the Early Yanshanian gabbrodiorite and the Permian marble. The ore-hosting rock in the ore deposit is dominated by the garnet skarn. Based on the ore-forming geological factors and mineralization characteristics, it can be concluded that the deposit belongs to the contact-metasomatic type. Using the LA-ICP-MS U-Th-Pb dating method of isotopes of zircon grains from gabbrodiorite in northern mining area and analysis of the geochemical characteristics of the intrusion, the authors obtained the U-Pb ages, which vary from 196Ma±2Ma to 213Ma±1Ma with an average value of 204Ma±2.3Ma. Both the gabbrodiorite and the associated iron-copper mineralization were formed at the beginning of the Jurassic period. Major elements in the gabbrodiorite are characterized by low SiO2 (55.56%~56.45%), high alkali (3.43%~3.66%), sodium (3.43%~3.66%) and aluminum (17.34%~18.33%), indicating that the metallogenic gabbrodiorite belongs to the metaluminous high-sodium calc-alkaline series. Meanwhile, the rocks are featured by low REE content ((77.43~88.76)×10-6), high LREE and LREE/HREE ratios, and low positive or negative Eu anomalies. Such geochemical features as relative enrichment of large ion lithophile elements, depletion of high field strength elements, low Sr, high Yb and ratios of trace elements between the crust and the mantle show that the gabbrodiorite was derived from the crust-mantle mixed source. In combination with the evolution of tectonic background of Northeast China, the authors hold that both the gabbrodiorite and the associated iron-copper mineralization in the Liudaowaizi deposit were formed in island-arc environment resulted from the subduction of the Paleo Pacific plate to the Eurasian plate at the beginning of the Jurassic period.