REE behavior during formation of strata-bound skarn and related deposit: a case study of Dongguashan skarn deposit in Anhui province, China.

Systematic studies have been carried out on REE compositions of hydrothermai alterated marbles, massive garnet skarns and ores, as well as garnet and quartz formed in multi-stage skarn and deposit formation. The results show that strata-bound skarn and its related Cu deposits were formed in a complex hydrothermai system during multi-sage infiltration metasomatism. The REE characteristics of skarns, however, are similar to those of the marbles. They were not simply inherited from the marble protolith, but were controlled by garnets, and the latter's were determined by the hydrothermai solutions participating infiltration metasomatism. The related hydrothermai fluids characterized with slightly right-hand dip REE patterns, are enriched in LREE and have strong negative Eu anomalies. The uptake of REE from hydrothermai fluid during garnet crystallization resulted in that garnet shared the similar REE patterns. REE in skarns were provided mainly by hydrothermai fluids associated with the emplacement of granodiorite plutons in the mining district. Based on the dimensional variation of REE in skarns combining with the structures of hosting strata, the transporting route and pattern of fluids involved in the formation of skarns and related deposits can be better understood. The present study demonstrates that extensive REE metasomatism can occur in hydrothermai system at shallow to intermediate depths and REE geochemistry are useful in discerning the origin of skarns and skarn-related deposits.