Constraints on the timing of Fe–(Cu) metallogenesis in the eastern Aqishan–Yamansu–Shaquanzi metallogenic belt, Eastern Tianshan, NW China

Abstract

The Aqishan–Yamansu–Shaquanzi belt is a well-known Fe–Cu–Au metallogenic belt located in the Central Asian Orogenic Belt, NW China. Numerous Fe-rich ores as well as polymetallic mineralization (including Cu, Pb, Zn, and Co) and related magmatic–hydrothermal alteration are hosted in volcanic rocks, especially those in the eastern part of this metallogenic belt. The complex geology of the belt and the divergent geochronological data obtained by different investigators and analytical methods have led to contrasting opinions on the deposit types and metallogenesis of the belt. The present study focuses on the Shaquanzi, Yamansu, and Heifengshan Fe–(Cu) polymetallic deposits in the eastern part of the belt. These deposits display Fe-dominated metallogenesis related to volcanic–sedimentary exhalative processes and polymetallic metallogenesis related to volcanic–hydrothermal metasomatism and skarnization caused by subsequent intrusion processes. The Shaquanzi, Yamansu, and Heifengshan deposits have undergone multiple periods of metallogenesis and contain late Fe–Cu–Pb–Mo, Fe–Cu–Zn–(Co), and Fe–Cu mineralization, respectively. Using zircon U–Pb dating by laser-ablation–multi-collector–inductively coupled plasma–mass spectrometry, two rhyolite samples (at the base and lower-middle part of the Tugutubulak Formation) and a basaltic andesite and a diorite dyke in the Shaquanzi ore district yield concordant ages of 327.9 ± 2.6 Ma (mean square of weighted deviates or MSWD = 0.015), 327.8 ± 1.4 Ma (MSWD = 1.03), 285.9 ± 2.0 Ma (MSWD = 0.81), and 276.3 ± 1.4 Ma (MSWD = 0.21), respectively. Basaltic andesite from the Upper Yamansu Formation in the Yamansu deposit area yields a concordant age of 327.6 ± 6.4 Ma (MSWD = 0.54), whereas rhyolite, diorite dyke, and granite stock from the Heifengshan deposit give concordant ages of 285.7 ± 1.3 Ma (MSWD = 0.01), 273.7 ± 1.6 Ma (MSWD = 1.2), and 274.4 ± 2.5 Ma (MSWD = 0.20), respectively. Hydrothermal molybdenite in the Shaquanzi deposit yields a weighted mean Re–Os age of 314.6 ± 1.7 Ma (MSWD = 0.29) and an isochron age of 316 ± 6 Ma (MSWD = 0.46). A collation of previously reported ages and our new age data show that extensive magmatism occurred during the Carboniferous–early Permian (ca. 350–270 Ma) in the Aqishan–Yamansu–Shaquanzi belt, with a peak period between ca. 335 and ca. 305 Ma. The Yamansu Formation and Tugutubulak Formation volcanic rocks formed at ca. 348–334 Ma (early Carboniferous) and between ca. 328 and ca. 303 Ma (late early Carboniferous to late Carboniferous), respectively. In the eastern part of the belt, Fe-dominated mineralization resulting from volcanic–sedimentary exhalative processes (e.g., ca. 334, ca. 322, and ca. 286 Ma) and polymetallic mineralization resulting from volcanic–hydrothermal metasomatism (e.g., ca. 334–323 Ma), as well as skarnization and magmtic-hydrothermal caused by intrusions occurred at different stages (e.g., ca. 322–316, ca. 299, and ca. 274 Ma), leading to the superimposition of polymetallic mineralization between ca. 334 and ca. 273 Ma.