Deposit geology, geochronology and geochemistry of the Gongpengzi skarn Cu-Zn-W polymetallic deposit, NE China

Abstract

The Gongpengzi Cu-Zn-W polymetallic deposit is a typical skarn deposit located in the Lesser Xing'an-Zhangguangcai Range, NE China. Although the deposit was first discovered in the 1950s, the timing of mineralization, source of the ore-forming materials, and geodynamic setting of the deposit, remain unclear. We present whole-rock geochemical and zircon U-Pb geochronological data for granitoids, molybdenite Re-Os geochronological data, and S-Pb isotopic analyses of sulfide minerals and feldspars from granitoids within the deposit. The results of molybdenite Re-Os and zircon U-Pb dating of biotite granites and granodiorite from the Gongpengzi polymetallic deposit suggest that ore formation occurred at 176.7 ± 5.9 Ma, and that the granodiorite hosting the mineralized zone were emplaced at 173.6 ± 1.0 and 173.9 ± 1.0 Ma, respectively. The granites and granodiorites have high SiO2 and Na2O + K2O contents, are enriched in Rb, Th, U, Ta, and Pb, and depleted in U, P and Ti, and therefore classify as I-type granitoids. One granodiorite sample yielded a (87Sr/86Sr)i value of 0.70444, εNd(t) value of 2.30, and two-stage model age (TDM2) of 785 Ma. The biotite granite samples yielded (87Sr/86Sr)i values of 0.70433–0.70445, εNd(t) values of 2.34–2.54, and TDM2 of 785–765 Ma. These observations suggest that the granites were probably derived by partial melting of both mantle and juvenile crustal material, and that these partial melts underwent fractional crystallization. The ore-forming elements were magmatic source, and may have been derived by mixing between crustal and mantle sources. We interpret granitoid relating to skarn mineralization in the Lesser Xing'an-Zhangguangcai Range to have resulted from subduction of Paleo-Pacific oceanic crust toward the Eurasian continent.