Insights into the formation of the Dasuji porphyry Mo deposit (North China Craton) gained from mineral chemistry data

Abstract

The Dasuji Mo deposit is located within the northern margin of the North China Craton. Based on vein cross-cutting relationships, mineral assemblages and alteration characteristics, the formation of the deposit can be divided into four stages: stage 1, consisting of two vein types developed in deep, is characterized by K-feldspathization with minor molybdenum mineralization; stage 2, containing four distinct vein types, is the main stage of molybdenum mineralization accompanied by sericitization and silicification; stage 3 is involved in lead-zinc mineralization associating with carbonatization and fluorination; and stage 4 is characterized by no mineralization. This paper presents new mineral (magnetite, rutile, molybdenite, and pyrite) chemistry data that provide new insights into the formation of this deposit. The magnetites within veins in the deposit have chemical compositions that are indicative of a magmatic origin, suggesting that these magnetites hosted in quartz were captured from syn-mineralization granites in the area. Molybdenite W, Pb, Zn, and Cu concentrations increase with the decreasing temperature of formation, suggesting the initiation of W, Pb, Zn, and Cu precipitation at the end of the second stage of mineralization. The stage 3 pyrite within the deposit contains the highest concentrations of Pb, Zn, and Cu, consistent with the Pb–Zn–(Cu) mineralization that formed during this stage. The majority of the F ion deposition occurred at the end of stage 3, and the fluids associated with stage 4 were meteoric water dominated.