Contribution discrepancy of two distinct wall rocks to wolframite mineralization from Dongshanwan quartz-vein tungsten deposit, Southern Great Xing’an Range, China

Abstract

The Southern Great Xing’an Range is a significant polymetallic metallogenic belt in Northeast China. The ages of granite related to tungsten mineralization have been well quantified, however, the timing and mechanism of quartz vein-type wolframite deposition remain unclear. Therefore, our study focused on the Dongshanwan tungsten deposit, representing a typical wolframite-bearing quartz vein-type deposit in the Southern Great Xing’an Range. Quartz vein-type tungsten mineralization was mainly contained in the Early Cretaceous granite porphyry, with few exceptions in the Permian tuff. Representative wolframite samples were collected from intragranitic (Wol-I) and intra-tuff (Wol-II) quartz veins for wolframite U–Pb dating, electron probe microanalysis (EPMA), and trace elemental analysis. Wolframite U–Pb dating recognized an Early Cretaceous mineralization event at 139–141 Ma, consistent with the previous Dongshanwan granite’s ages (∼142 Ma) but much younger than tuff (∼260 Ma). All the wolframite samples belonged to the ferberite series (FeO/MnO = 4.0–6.9), which indicates a link to the highly fractionated granite. Wol-I showed high contents of Nb, Ta, Sc, and HREEs and a strongly negative Eu anomaly (0.02–0.29), while these elements in Wol-II were approximately one order of magnitude lower than in Wol-I and the Eu anomaly was highly variable (0.17–1.02). The redox characteristics reflected by the Eu anomaly of wolframite may correspond to the variations in oxygen fugacity. Based on petrology, geochemistry, and element mass migration, this study suggests that the granite porphyry and tuff in the Dongshanwan deposit contributed differently to the wolframite precipitation even if the ore-forming fluids were of a common magmatic-hydrothermal origin. The exsolved fluid reserved in the closed system interacts with granite to achieve continuous enrichment in Nb, Ta, Sn, and REEs and accepts external Fe supply from granite alteration to precipitate Wol-I. In contrast, the fluids in relatively open and non-granitic systems have lower Nb, Ta, Sn, and REEs than the former, and Fe supply depends on the alteration of tuff. The abundance of fluorite and the non-CHARAC (CHArge-and-RAdius-Controlled) behavior of Y/Ho and Zr/Hf in the wolframite suggested that fluorine plays an important role in the migration and enrichment of tungsten and other elements during tungsten mineralization.