Age and genesis of the Gangcha gold deposit, western Qinling orogen, China

Abstract

The Gangcha gold deposit in Hezuo, Gansu, China, is a newly discovered medium‐scale (19 tons) epithermal deposit occurring within the western Qinling orogenic belt. The Daguanshan Formation, represented by metamorphosed volcanic–clastic rock suite, is the main ore‐bearing strata. Gold occurs mainly as submicroscopic inclusions in sulphides and quartz. The hydrothermal alteration is characterized by mid‐ to low‐temperature mineral assemblages such as pyrite, arsenopyrite, and fluorspar. We report results from Rb–Sr isotopic dating of pyrites in the main orebody, which yield an isochron age of 225.3 ± 3.4 to 229.9 ± 4.7 Ma suggesting that the mineral deposit formed during the middle Triassic within a collisional orogenic setting. The initial 87Sr/86Sr value of pyrite (0.710326 to 0.710349) is lower than that of the continental crust and higher than that of the mantle. The S isotope data of pyrites from the deposit show a narrow range from 0.6‰ to 1.3‰ with an average of 0.975‰. Their Pb isotopes exhibit characteristics of a crust–mantle mixed source with a μ (238U/204Pb) of 9.39 to 9.53 and a ω (232Th/204Pb) of 36.81 to 38.14. The S and Pb isotopic composition indicates that ore‐forming materials were derived from a magma sourced in the lower crust, which also incorporated mantle components.

The structural deformation characteristics and the control of gold mineralization of the upper Triassic flysch (Langjiexue Group) in Tibetan Plateau

“…For the major orogenic gold deposits in the world that was listed by Goldfarb, Groves, and Gardoll () and Groves, Goldfarb, Gebre‐Mariam, Hagemann, and Robert (), gold mineralization was originally thought to occur in an accretionary orogenic tectonic setting (e.g., Barley & Groves, ; Kerrich, Goldfarb, Groves, Garwin, & Jia, ), especially in the outer converge supercontinent cycle or the edge of the inner converge supercontinent cycle. In recent years, several medium to large orogenic gold deposits have been discovered in collisional orogenic belt (e.g., Chai, Sun, Xing, Chen, & Han, ; Kong et al, ), especially in the Tibetan Plateau in China. At least two important Himalayan period orogenic gold deposit belts have been identified, which are the Ailaoshan orogenic gold belt controlled by lateral shear strike‐slip (~30 Ma; e.g., Deng & Wang, ; Deng, Wang, Li, Li, & Wang, ) and the Yarlung Tsangpo orogenic gold belt controlled by forward collision extrusion (~50 Ma; e.g., Hou & Cook, ; Jiang, Nie, Hu, Lai, & Liu, ; Sun et al, , ; Zhang et al, ).…”

“…In recent years, several medium to large orogenic gold deposits have been discovered in collisional orogenic belt (e.g., Chai, Sun, Xing, Chen, & Han, 2016;Kong et al, 2017), especially in the Tibetan Plateau in China. At least two important Himalayan period orogenic gold deposit belts have been identified, which are the Ailaoshan orogenic gold belt controlled by lateral shear strike-slip (~30 Ma; e.g., Deng & Wang, 2016;Deng, Wang, Li, Li, & Wang, 2014) and the Yarlung Tsangpo orogenic gold belt controlled by forward collision extrusion (~50 Ma; e.g., Hou & Cook, 2009;Jiang, Nie, Hu, Lai, & Liu, 2009;Sun et al, 2015Sun et al, , 2016Zhang et al, 2017).…”

Mineralogy and Geochemistry of Pyrite and Arsenopyrite from the Zaozigou Gold Deposit in West Qinling Orogenic Belt, Central China: Implications for Ore Genesis

“…Therefore, the Zaozigou gold deposit is better defined as an epithermal deposit (Chen et al, ). The Gangcha gold deposit in the West Qinling orogenic belt also belongs to the epithermal deposit (Kong et al, ).…”

Age of theYongxin Audeposit in theLesser Xing'an Range: Implications for anEarly Cretaceousgeodynamic setting for gold mineralization inNE China

“…Basic requirements for the Rb–Sr isochron dating of hydrothermal minerals are that the minerals have been deposited simultaneously, the hydrothermal system has remained closed to Rb and Sr diffusion after the minerals formed, and the ( 87 Rb/ 86 Sr) i ratios of minerals have adequate variation (Liu, Zhan, Shen, Jiang, & Huo, ). In recent years, with the advances in experimental techniques, many workers have defined the age of hydrothermal gold deposits by using Rb–Sr isotopic dating of pyrite (Dong et al, ; Kong et al, ; Li et al, ; Wang, Zeng, & Liu, ; Yang & Zhou, ; Zhai, Liu, Ripley, & Wang, ).…”