Multiple-stage tungsten mineralization in the Silurian Jiepai W skarn deposit, South China: Insights from cathodoluminescence images, trace elements, and fluid inclusions of scheelite
Abstract The Jiepai deposit, located in the northeastern part of the Miao’ershan-Yuechengling batholith, South China, is characterized by predominant skarn mineralization that formed near the contact between the Silurian biotite granites and the Upper Cambrian carbonate rocks. Jiepai scheelites are recognized as two main generations based on their occurrences, cathodoluminescence (CL) signatures, and REE systematics. Prograde skarn-hosted scheelite I has uniformly dark CL characteristics and LREE-enriched patterns. Retrograde skarn-hosted scheelite IIa is homogeneously dark under CL, and has a slightly MREE-enriched pattern, whereas quartz vein-hosted scheelite IIb is delineated by fine oscillatory CL zones and a relatively flat REE pattern. Additionally, the CL images reveal that both scheelite I and II were modified by later-stage hydrothermal overprints, which occur as ubiquitous overgrowth rims and cutting veins with bright CL signatures, low REE, but similar REE patterns to their precursors. The compositional variations and fluid inclusions in Jiepai scheelites identify episodic pulses of hydrothermal fluids with different properties. The ore-forming fluids with high Nb/Ta, but low Nb, Ta and REY in the early retrograde stage are featured by moderate to high temperature and low to moderate salinity. Under relatively oxidizing conditions, they interacted with the host rock and underwent boiling to precipitate scheelite I. By contrast, the fluids with higher Nb, Ta and REY, but lower Nb/Ta in the late retrograde stage have slightly lower temperature and higher salinity. We therefore speculate that scheelite II may deposit from later magmatic fluids that have experienced continued boiling in more reducing environment.