Mineralization potential of the Permian Houdaomu intrusions in the Lesser Xing’an Range, northeastern China

Abstract

Abundant porphyry Mo systems with concentrated Jurassic ages are developed in the Lesser Xing’an Range, northeastern China. The Houdaomu Mo deposit is one of the typical porphyry deposits in this region, and several barren intrusions occur in the mining area. In this study, magmatic apatite and zircon geochemical analyses, zircon U-Pb age dating, and apatite Nd isotope measurement were carried out on the barren intrusions, including the biotite granite, monzodiorite, and biotite diorite. The aims are to obtain the physical and chemical characteristics of the magmas and explore the reasons behind the differences in the ore-forming potential between ore-bearing and barren intrusions. The zircon U-Pb ages of the biotite granite, monzodiorite, and biotite diorite in the Houdaomu deposit are 255.9 ± 0.7 Ma, 255.9 ± 0.9 Ma, and 254.5 ± 1.3 Ma, respectively. The Nd isotopic compositions of magmatic apatite grains are homogeneous, with ε_Nd(t) values ranging from 1.1 to 3.5, corresponding to T_DM2 ages between 938 and 743 Ma, revealing that these intrusions were mainly originated from partial melting of mantle materials (74 %–85 %) with a small amount of lower crustal materials. The calculated zircon Ce anomalies (Ce/Ce* = 1.54–43.2), estimated ΔFMQ range (−1.7 to 1.6) and magma oxygen fugacities (ƒ_O2 = -16.8 to −13.8) are lower than other typical Mesozoic ore-forming intrusions in the region, all of which indicate that these Permian barren magmas in Houdaomu were relatively reduced. From diorite to granite, the Sr/Y ratios of apatite and the Eu/Eu* ratios of zircon decrease, and the Dy/Y ratios of apatite and zircon increase, indicating that the magma water content gradually decreases, and the more evolved the magma, the lower the water content. This is consistent with the significant Eu anomaly in the magmatic apatite and whole-rock samples. The results from this study indicate that the magmas forming these Late Permian intrusions in Houdaomu are characterized by a low magmatic oxidation state and a low water content, which can explain the reason why there was no Mo (or Cu) mineralization temporally and genetically associated with these intrusions.