Geochemistry and chronology of the biotite granite in the Xiaobaishitou W-(Mo) deposit, eastern Tianshan, China: Petrogenesis and tectonic implications

Abstract

The Xiaobaishitou W-(Mo) deposit (Central Tianshan Massif, eastern Tianshan, northwestern China) is a skarn-type tungsten-molybdenum deposit associated with a biotite granite intruding the Mesoproterozoic Kawabulag Group. Here we present the results from zircon U-Pb geochronology, whole-rock geochemical, and Sr-Nd-Hf isotopic analyses of the biotite granite. Zircon U-Pb dating shows that the biotite granite crystallized at 246.4 ± 1.7 Ma, suggesting that the Xiaobaishitou deposit formed during the Early Triassic. Bulk rock geochemistry shows that the biotite granite has high Si, Rb, K, and light rare earth element contents, but low Ba, Nb, Sr, P, and Ti. Moreover, the rocks have mostly positive εHf(t) values (−0.06 to 4.60), negative εNd(t) values (−3.87 to −2.40), and corresponding Hf isotope TDM2 ages (1.29–1.71 Ga) and Nd isotope TDM2 ages (1.23–1.36 Ga). These geochemical and isotopic data imply that the Xiaobaishitou biotite granite derived from both mantle- and crustal-derived magmas. By comparison of the Xiaobaishitou biotite granite to nearby granites from the Donggebi and Baishan Mo deposits, we show that Triassic granites of the eastern Tianshan likely formed in an intra-continental tectonic setting, and magmatism and metallogenesis were probably associated with regional extension.