Dating the Xiaobaishitou skarn W–(Mo) deposit, Eastern Tianshan, NW China: Constraints from zircon U–Pb, muscovite 40Ar–39Ar, and molybdenite Re–Os system

Abstract

The Xiaobaishitou deposit (36,264 tonnes @ 0.78 wt% WO3) in the Eastern Tianshan orogenic belt is a medium-sized skarn deposit characterized by W–(Mo) ore bodies that developed along contacts between Triassic biotite granite and Mesoproterozoic carbonaceous rocks. Scheelite and molybdenite are the dominant metallic minerals in this deposit and mostly precipitated during the retrograde stage and/or quartz–sulfide stage, respectively. Laser ablation multi-collector inductively coupled plasma mass spectrometry (LA–MC–ICP–MS) zircon U–Pb dating of the mineralization-related biotite granites from underground openings and outcrops yields ages of 247.9 ± 1.7 Ma (1σ; N = 22; MSWD = 0.69) and 252.2 ± 3.0 Ma (1σ; N = 12; MSWD = 1.60), implying they were emplaced in the Early Triassic. A muscovite 40Ar/39Ar weighted plateau age of 247.6 ± 2.3 Ma (2σ; MSWD = 2.03) and molybdenite Re–Os model ages ranging from 235.8 ± 5.7 Ma to 249.6 ± 3.6 Ma (weighted mean age = 251.1 ± 1.6 Ma; 2σ; MSWD = 0.70) are interpreted as the time of the hydrothermal activity mineralization. The excellent agreement among the U–Pb, 40Ar–39Ar, and Re–Os chronometers confirms that the Xiaobaishitou deposit formed in the Early Triassic. The Re contents of the molybdenites range from 18,477 to 130,447 ng/g, suggesting that the ore-forming materials were derived from continental crust together with the involvement of abundant mantle components. As one of the representative Triassic deposit in Eastern Tianshan, the Xiaobaishitou provides important chronological evidence for metallogenic regularity in the Eastern Tianshan and the Central Asian Orogenic Belt. The new ages reported here confirm that the Xiaobaishitou deposit represents one of the magmatic–hydrothermal mineralization events that occurred in the Eastern Tianshan orogenic belt in lithospheric extension during the Triassic. It is suggested that mantle material played a role in producing the Triassic mineralization and associated magmatism.