Fault-controlled fluid evolution in the Xitian W–Sn–Pb–Zn–fluorite mineralization system (South China): Insights from fluorite texture, geochemistry and geochronology

Abstract

Fluorite is one of the most common minerals in the granite-related hydrothermal systems, and widely distributed in the Xitan W–Sn polymetallic ore field (South China). It existed from the early W–Sn stage to the middle Pb–Zn stage and then to the late fluorite stage, thus responsible for the Xinggao and Guangming fluorite deposits in the region. In this research, textural, geochemical and geochronological analyses of fluorites were used to reconstruct the fluid evolutionary history and its bearings on fault activities in the ore field. The fluorites from the ore field yielded a Sm–Nd isochron age of 153.3 ± 8.0 Ma (initial 143Nd/144Nd = 0.511871 ± 0.000013, MSWD = 1.5) which is consistent to the timing of the W–Sn ore-forming stage within the error. This suggests that the fluorites were formed in the same time with the W–Sn ores. And the average value of εNd(t) is similar to those of the Jurassic granites (εNd(t) = −9.2 to −7.3) in the ore field. This indicates that fluorite mineralization is mainly related to the Jurassic granites, and the basement rocks could be the source for the ore-forming materials. From the early stage fluorites (coexisting with wolframite) to the late fluorite-only veins, the total amount of rare earth elements (∑REE) in the fluorites substantially decreases (average values vary from 174 to 37.2 ppm), especially the LREE (La/Lu values decrease from 80.0 to 16.6). In addition, the ore-forming elements (e.g., W, Sn, Mo) in the fluorites also decrease significantly with time. And the low δ18OH2O values (−4.30‰ to −3.90‰) and moderate δD values (−63.8‰ to −59.6‰) in the fluorites suggest that the late fluorite stage was contributed largely from meteoric water. Combined with previously reported fluid inclusion data in the ore field, we propose that the W–Sn mineralization was related to fluid boiling and mixing, the Pb–Zn ore was formed from the changing of the redox environment from oxidizing to reducing, and the fluorites were formed due to rapid cooling. The formation of the W–Sn, Pb–Zn, and fluorite ore-forming zones belong to a single magmatic-hydrothermal system but was controlled by the fault evolutionary processes from the early granite plutons intrusion to the large-scale crustal extension in the Xitian ore field.