Fluid origin and migration of the Huangshaping W–Mo polymetallic deposit, South China: Geochemistry and 40Ar/39Ar geochronology of hydrothermal K-feldspars

Abstract

The Huangshaping deposit is a world-class W–Mo–Pb–Zn–Cu polymetallic deposit that formed during the Jurassic magmatic event in the central Nanling region, South China. In order to reveal the three-dimensional development of mineralization and alteration in this complicated fluid-rock system, four typical hydrothermal K-feldspar samples were collected from potassic alteration zones at different elevation levels around main W–Mo ore bodies, followed by precise trace element analysis and 40Ar/39Ar dating. The results show that these K-feldspars have a pronounced lanthanide tetrad effect with high contents of Ga, Ta, Nb, U, Y and HREE but low concentrations of Ba, Sr, Eu and Zr, suggesting a hydrothermal origin. Additionally, correlation between the Ca/Cl/K ratios and the apparent ages suggest that metasomatic fluids played an important role in the formation of the hydrothermal K-feldspars. The plateau 40Ar/39Ar ages which represent the timing of potassic alteration vary from 152.9±0.5 to 154.3±0.6Ma, spatially showing younger trends from north to south and from shallow to deep. These dates correspond to the previous published molybdenite Re–Os data variations in different elevation levels, which record the mineralization event with relatively older ages ranging from 153.8 to 159.4Ma. Combined with the spatial relation analysis among samples, the fluid migration rates associated with the mineralization and alteration are calculated at 10–100mMa−1. Thus, we propose a fluid downward migration model for the Huangshaping polymetallic deposit.