Neoproterozoic W-Sn mineralization and magmatism in the western Jiangnan Orogen: Constraints from geochronology, geochemistry of the Heiwanhe W-Sn polymetallic deposit in Fanjingshan area of Guizhou Province

An increasing number of Neoproterozoic granitoids and associated W-Sn mineralization occurrences have been identified in the Jiangnan Orogen. However, the genetic mechanism and key factors controlling the spatio-temporal link between the granitic magmatism and W-Sn mineralization are yet to be well established. Neoproterozoic granites and associated W-Sn mineralization have been reported in Fanjingshan area, located in the western Jiangnan Orogen, making it an ideal site to investigate the coupling between the Neoproterozoic magmatic evolution and mineralization processes. Here, we integrate petrology, mineralogy, and geochronology to identify W-Sn mineralization events of the Heiwanhe W-Sn polymetallic deposit, which is the largest W-Sn deposit in Fanjingshan area, and elucidate the genetic link between the W-Sn mineralization and the highly fractionated S-type granitic magmatism. LA-ICP-MS U-Pb dating and mineralogical analysis of wolframite and cassiterite from Heiwanhe reveal two distinct mineralization stage: Sn mineralization at 831-822 Ma, and W mineralization at 818-812 Ma. The age data (833-826 Ma) of the Qinglongdong granite pluton, which is spatially closely associated with the Heiwanhe deposit in south Fanjingshan, indicate a close spatio-temporal link between the W-Sn mineralization and the granitic magmatism. These ages, together with those of the Xiaojiahe pluton (822 ±3.6 Ma) in the central, the Taoshulin and Lanchaping plutons in the north of Fanjingshan, constitute a Neoproterozoic granitic complex intrusive event. The Xiaojiahe and Qinglongdong granites are characterized by high SiO₂ (74.5-75.8 wt.%) and Al₂O₃ (13.9-14.7 wt.%), and are strongly peraluminous (molar A/CNK = 1.11-1.97). They have low total REE content (ΣREE = 7-19 ppm) and pronounced negative Eu anomalies. This suggests that they are highly-fractionated S-type, which is conducive to W-Sn mineralization. The wide range of ε_Hf(t) values (-6.9 to +7.4) of these granites indicates they were they were generated by partial melting of Paleoproterozoic lower crustal metasedimentary rocks. This study establishes the spatio-temporal framework for the W-Sn mineralization events in the western Jiangnan Orogen: granitic magmatism within this region was mainly emplaced during ca. 850-810 Ma, whereas W-Sn mineralization is almost exclusively restricted to the narrow time interval of 830-820 Ma. The relatively higher ε_Hf(t) values exhibited by Neoproterozoic granites, in comparison with their Mesozoic analogues in the Jiangnan Orogen, imply that the Neoproterozoic mantle or the ancient crust was pre-enriched in tungsten and tin. These elements were subsequently remobilized during Mesozoic tectono-magmatic events, leading to the reactivation, redistribution and reconcentration of W-Sn metals and the formation of large-scale mineralization.