Geochronology, Geochemistry, and Lu-Hf Isotopic Compositions of Monzogranite Intrusion from the Chang’anpu Mo Deposit, NE China: Implications for Tectonic Setting and Mineralization

Abstract

The Chang’anpu Molybdenum deposit occurs in the monzogranite intrusions in the Lesser Khingan Mountains-Zhangguangcai Mountains metallogenic belt. Previous work focused on the study of deposits, including geological characteristics, mineralization time, S-Pb isotope, etc. However, systematic petrogeochemical study of monzogranite intrusion and comparative analysis with other porphyry deposits in the region are lacking. Three monzogranite dating samples yield LA-ICP-MS zircon weighted mean 206Pb/238U ages of 174.7 ± 1.3 Ma, 174.9 ± 1.4 Ma, and 174.3 ± 1.8 Ma, respectively, indicating that the magmatism occurred in the middle Jurassic of Mesozoic. The 14 monzogranite samples show alkali rich and relatively high silica content (up to 84.39%) with the differentiation index (DI) ranges from 86 to 96, showing that monzogranite have been subjected to fractional crystallization during its evolution; the depletion of Ba, Sr, P, Nb, Ti, and Eu also indicates that the rock has undergone crystallization fractionation, the monzogranite belong to the highly fractionated I-type. Positive εHf(t) values (6.72–8.85) and young TDM2 (551–673 Ma) of the monzogranite indicate that the formation of Chang’anpu monzogranite intrusion is related to the partial melting of juvenile lower crust, originated from the Mesoproterozoic depleted mantle. The magmatism and related Mo mineralization in the Chang’anpu deposit occurred in an active continental margin setting associated with westward subduction of the Paleo-Pacific plate beneath the Eurasian plate.