Abstract:

 Geochemical study of metasedimentary rocks in the Lala copper deposit was conducted to better constrain their provenance, chemical weathering condition and tectonic environment. These rocks have relatively low CIA values (4465) and K2O/Al2O3 values (002043) with high ICV values (144511), suggesting that they underwent relatively weak chemical weathering and were derived from an immature source with minor clay minerals and alkali feldspar. Compared to PAAS, the samples mostly have relatively lower large ion lithophile element (LILE) contents (Cs, Rb), lower transitional element contents (V, Cr, Zn) and relatively higher high field strength elements (HFSE) contents (Y, U, Zr, Hf, Nb, Sc). The rightslope REE ((La/Yb)n(av)=257) pattern, low Cr/Zr (001042) and Th/Sc (037114) ratios, and Sm and Nd isotopic characteristics, indicate that these rocks were deposited in a continental back arc environment and derived from a felsicdominated provenance. Furthermore, in combination with the results of tectonic setting discrimination of sodic metavolcanic rocks, we conclude that the Lala copper deposit may also have been formed in a continental back arc environment.

Key words: Lala copper deposit, metasedimentary rocks, provenance, weathering condition, tectonic setting