A late Mesozoic Cu mineralizing event in the eastern Central Asian Orogenic Belt, NE China: Implications from geology and geochronology of the newly discovered Zhalageamu deposit

Abstract

The eastern part of the Central Asian Orogenic Belt in NE China is one of the world’s well-known Ag-Pb-Zn-Mo metallogenic provinces, and the late Mesozoic magmas have been considered to supply dominant metals for mineralization. However, Cu mineralization in this belt is relatively rare. The Zhalageamu deposit is a newly discovered copper deposit in this region and could be applied to address the issue of whether the regional late Mesozoic magmatism could have triggered the formation of large Cu deposits. The quartz diorite and granite porphyry in Zhalageamu returned laser ablation−inductively coupled plasma−mass spectrometric (LA-ICP-MS) zircon U-Pb ages of 267.1 ± 2.0 Ma and 255.6 ± 2.2 Ma, respectively. Molybdenite coexisting with chalcopyrite yielded an isotope dilution−negative−thermal ionization mass spectrometric Re-Os age of 141.8 ± 0.8 Ma. This age is almost identical to that of the coexisting arsenopyrite within the analytical uncertainty, which yielded an Re-Os isochron age of 140.7 ± 5.9 Ma. The above ages constrain the timing of Cu mineralization to the late Mesozoic. The fact that the Cu mineralization is >110 m.y. younger than its igneous host rocks precludes a genetic link between them. Instead, the Cu mineralization age indicates that a possible hidden late Mesozoic intrusion likely contributed Cu mineralization. The age of the Zhalageamu deposit is similar to that of the late Mesozoic magmatic-hydrothermal Ag-Pb-Zn-Fe-Sn mineralizing event (140−120 Ma) in NE China. This suggests that the Zhalageamu Cu mineralization was part of this event and implies the broader existence of a late Mesozoic magmatic-hydrothermal Cu mineralizing event in NE China, a discovery that would be of great significance for further Cu exploration.