Temporal and spatial relationships of granitic magmatism and W mineralization: Insights from the Xingguo orefield, South China

Abstract

In South China, extensive multi-phase magmatism was accompanied by W-dominated, polymetallic mineralization. The Xingguo orefield of southern Jiangxi Province in the eastern part of the Nanling region is one of the most important W-dominated mineralized regions in South China. There are more than ten W deposits within or surrounding the Jiangbei complex, including the Huamei’ao quartz vein-type W deposit (WO3 67,400 tons at a grade of 1.344%), the Yanqian skarn-type W deposit (WO3 16,000 tons at a grade of 0.365%), and the Zhangjiadi quartz-vein- and greisen-type Mo-W deposit (Mo 31,806 tons at a grade of 0.1% and WO3 1746 tons at a grade of 0.353%). The orebodies all occur at the contact between the Jiangbei complex and the Sinian metasandstone or Carboniferous-Permian limestone. The Jiangbei complex consists of three lithologies: medium- to coarse-grained, biotite granite (Jγ1), medium- to fine-grained, biotite monzonitic granite (Jγ2), and fine-grained, biotite monzonitic granite (Jγ3), which have zircon U-Pb ages of 160.7 ± 1.1 Ma, 156.3 ± 0.9 Ma, and 153.3 ± 0.8 Ma, respectively. The associated Yanqian, Huamei’ao, Wangnipai, and Liujiazhuang deposits have molybdenite Re-Os ages of 159.2 ± 2.3 Ma, 157.1 ± 1.3 Ma, 157.7 ± 1.4 Ma, and 157.9 ± 1.6 Ma, respectively. A summary of available age dates of intrusions in the Xingguo orefield indicates that the granitic magmatism lasted for ∼8 m.y (ca. 160–153 Ma), whereas the W mineralization occurred in a relatively short period (159–155 Ma), corresponding in age to the episode of large-scale, Mesozoic (165–150 Ma) mineralization in South China. Low εNd(t) values (−10.2–−13.0) of the Jiangbei granitic rocks and low Re contents of the molybdenite suggest that the W-dominated ores and associated granites in the Xingguo orefield were derived mainly from crustal magmas. All three lithologies of the Jiangbei complex have similar geochemical characteristics, and are classified as high-K, calc-alkaline and peraluminous, S-type granites. The Zr/Hf, Nb/Ta, δEu, Rb/Sr, and LREE/HREE ratios all correlate positively with the W contents of the rocks and reach their highest level in the phase II granites. We propose a magmatic-metallogenic model in which W was concentrated by fractionation of crustally derived magmas of phase I and then deposited in skarn-, greisen-, and quartz vein-type ores by both magmatic and hydrothermal processes.