Trace elements in magmatic and hydrothermal quartz: Implications on the genesis of the Xingluokeng Tungsten Deposit, South China

Abstract

The Xingluokeng deposit is the largest granite-related tungsten deposit within the Wuyi metallogenic belt in South China. The Xingluokeng intrusion primarily consists of porphyritic biotite granite, biotite granite, and fine-grained granite. The deposit is represented by veinlet-disseminated mineralization with K-feldspathization and biotitization, alongside quartz-vein mineralization with greisenization and sericitization. This study investigates in-situ analyses of quartz compositions from both the intrusion and hydrothermal veinlets and veins. Trace element correlations indicate that trivalent Al³⁺ and Fe³⁺ replace Si⁴⁺ within the quartz lattice, with monovalent cations (such as Li⁺, Na⁺, and K⁺) primarily serving as charge compensators. Low Ge/Al ratios (< 0.013) of quartz from granites suggest a magmatic origin. The low Al/Ti and Ge/Ti ratios, accompanied by high Ti contents in quartz, suggest that the porphyritic biotite granite and biotite granite are characterized by relatively low levels of differentiation and high crystallization temperatures. In contrast, the fine-grained granite exhibits a higher degree of fractionation, lower crystallization temperatures, and a closer association with tungsten mineralization. Ti contents in quartz from quartz veins indicate Qz-I formed at temperatures above 400 °C, while Qz-II to Qz-V formed at temperatures below 350 °C. Variations in different generations of quartz, as indicated by Al content and (Al + Fe)/(Li + Na + K) ratio, suggest that Qz-I precipitated from a less acidic fluid with a stable pH, whereas Qz-II to Qz-V originated from a more acidic fluid with notable pH variations. Consequently, alkaline alteration and acidic alteration supplied the essential Ca and Fe for the precipitation of scheelite and wolframite, respectively, highlighting a critical mechanism in tungsten mineralization at the Xingluokeng deposit.