Trace element chemistry of hydrothermal quartz and its genetic significance: A case study from the Xikuangshan and Woxi giant Sb deposits in southern China

Trace element concentration and distribution in hydrothermal quartz from the giant Xikuangshan and Woxi Sb deposits in southern China have been investigated in order to discuss the trace element differences between Sb deposits and shed new insights into their genetic processes. The LA-ICP-MS data reveal that Al, Sb, Li, Na, and K are the most important elements in quartz with concentrations of > 10 ppm, which may primarily occur as solid solution within the crystal lattice in quartz, and are probably controlled by the coupled substitution of (Al3+, Sb3+) + (Li+, Na+, K+) <-> Si4+. However, the significant differences in trace element composition are sug-gestive of different precipitation mechanism of hydrothermal quartz at two giant Sb deposit. The higher and relatively homogenous Al concentrations suggest that quartz from the Xikuangshan deposit may have precipitated from more acidic fluids at presumably relative stable pH compared to the Woxi deposit. In contrast, the lower but variable Al concentration in quartz at Woxi is suggestive of a less acidic fluid with significant fluid pH fluctuations that may have driven metal-sulfide precipitation from ore fluids. Moreover, the higher and relatively variable Ti and Ge concentrations in quartz at Woxi are indicative of a higher and dramatic change of fluid temperature during precipitation processes; whereas quartz at Xikuangshan has lower and homogeneous Ti and Ge concentrations, reflecting smaller temperature fluctuations during quartz formation. Additionally, the quartz from the Xikuangshan deposit contains higher Li, Na, K, and Ca concentrations compared to that of the Woxi deposit, suggesting that the quartz-precipitating fluids at Xikuangshan are more enriched in alkali metals. The significant difference in trace element composition of hydrothermal quartz is good evidence for different precipitation mechanisms for two giant Sb deposits: quartz precipitation at Woxi deposit may have resulted from fluid mixing that would lead to dramatic changes of the fluid pH and temperature; whereas fluid boiling is likely the primary mechanism of quartz and sulfide-metal precipitation at Xikuangshan, which caused a smaller fluctuation of fluid temperature during quartz precipitation, and the stable fluid pH was buffered by interaction of boiling ore fluids with wall-rock carbonates.