Distribution of REE and other trace elements in the Hetai gold deposit of South China: implications for evolution of an auriferous shear zone

Abstract

The Hetai gold deposit is contained within a shear zone which is hosted by metavolcano-sedimentary units of the Late Proterozoic Yunkai Group. The shear zone, striking northeast and dipping northwest, is over 3 km long and has a thickness of about 20–50 m. The ore occurs in the shear zone as a series of lenticular and vein-type bodies. The auriferous shear zone has undergone three stages of evolution: the early stage was characterized by ductile deformation when auriferous mylonite containing less than 1 ppm Au was formed; the intermediate stage took place in brittle-ductile environments during which the lenticular ores with about 10–100 oom Au were formed; the last stage was developed during brittle deformation resulting in emplacement of auriferous quartz veins with grades of 1–5 ppm Au. REE pattern analysis demonstrates that no significant modification of lanthanide distribution occurred during the ductile deformation stage of the shear zone evolution, which resulted in the formation of mylonite and ultramylonite, although important mineralogical and chemical changes of the original metamorphic rocks have been observed. In contrast, extensive variations of REE patterns occurred in the hydrothermally infiltrated rocks which are products of the brittle-ductile and the brittle deformation stages of the shear zone evolution. This confirms that REE behavior during dynamometamorphism seems to be similar to that during metamorphism and hydrothermal alteration, which is determined both by fluid/rock ratios and by REE patterns and abundances in reacting fluids and rocks.