Geochemistry, petrogenesis and tectonic implications of granitic plutons at the Liziyuan orogenic goldfield in the Western Qinling Orogen, central China

Abstract

The Liziyuan goldfield is located along the northern margin of the western part of the Qinling Orogen (WQO). The goldfield consists of five gold-only deposits hosted by metavolcanic rocks, and one polymetallic (Au–Ag–Pb) deposit hosted by the Tianzishan Monzogranite. As the Liziyuan goldfield appears to be spatially and temporally related to the Jiancaowan Porphyry, the study of the deposit provides a crucial insight into the relationship between tectonic-magmatic events and gold metallogenesis in the WQO. In this paper, we present whole-rock major and trace element geochemistry, and in situ zircon U–Pb and Lu–Hf isotopic data from the Tianzishan Monzogranite and Jiancaowan Porphyry. The two granitic plutons are enriched in LILEs and LREEs, depleted in HFSEs and have zircon εHf(t) values between −14.1 and −5.1 for the Tianzishan Monzogranite and between −21.0 and −8.4 for the Jiancaowan Porphyry. These characteristics indicate that the granites are derived from the crust. The Tianzishan Monzogranite has LA-ICP-MS zircon U–Pb ages of 256.1 ± 3.7 to 260.0 ± 2.1 Ma, which suggests that it was emplaced in the WQO during the convergence of the North and South (Yangtze) China cratons in the early stage of the Qinling Orogeny. In contrast, the porphyry has a LA-ICP-MS zircon U–Pb age of 229.2 ± 1.2 Ma, which is younger than the peak collision age, but corresponds to the widespread Late Triassic post-collisional granitic plutons in the WQO. The Tianzishan Monzogranite has somewhat higher Sr contents (196–631 ppm), lower Y (2.23–19.6 ppm) and Yb (0.20–2.01 ppm) contents, and a positive Eu/Eu* averaging 1.15. These characteristics suggest the pluton was derived from partial melting of the thickened crust. In contrast, the relatively higher MgO content (0.85–2.08 wt%) and Mg no. (43.4–58.2) of the Jiancaowan Porphyry indicates that insignificant amounts of subcontinental lithospheric mantle-derived mafic melts were involved in the generation of the magma. The Liziyuan goldfield is hosted by faults in greenschist-facies metamorphic rocks. Fluid inclusion studies suggest that gold was precipitated from CO2-rich, low-salinity and medium temperature fluids. This feature is consistent with the other orogenic gold deposits throughout the world. The field relationships and zircon U–Pb ages of the two granitic plutons suggest that gold mineralization is coeval with or slightly younger than the emplacement of the Jiancaowan Porphyry. Therefore, both the porphyry and deposit formed during the post-collisional stage of the Qinling Orogen.

Triassic tectonics and mineral systems in the Qinling Orogen, central China

“…(2) Several workers (e.g. Li et al, 1996;Lu et al, 1996;Zhang et al, 2001;Qin et al, 2007Qin et al, , 2008Qin et al, , 2009Zhou et al, 2008;Zhu et al, 2010;Yang et al, 2013) considered the Triassic Qinling Orogen to be under syn-to postcollisional settings, because they believed that the volcanic rocks at Heigouxia formed in an island-arc setting and were metamorphosed at ca. 242 ± 21 Ma (Sm-Nd isochron age) and thermally disturbed at 221 ± 13 Ma (Rb-Sr isochron age) .…”

“…) and is dated to have formed at 209 ± 5 Ma using a SHRIMP U–Pb method on the xenotime and monazite in the ores (Zhou et al ., ). The Liziyuan Au–Ag deposit and the Ma'anqiao Au deposit are located at the northern margin of the SQL and have been constrained to be of Triassic age (Zhu et al ., ; Yang et al ., , ).…”

“…However, the precise timing of oceanic closure remains controversial, leading to debates over the Triassic tectonics and the geodynamic setting of the Triassic granitoids and mineral systems (Li et al ., ; Lu et al ., ; Zhang et al ., ; B.R. Zhang et al ., ; J. Zhang et al ., ; N. Li et al ., ; Qin et al ., , , ; Liu et al ., , ; Zhou et al ., ; Chen et al ., ; Chen, ; Jiang et al ., ; Zhu et al ., ; Dong et al ., ; Yang et al ., ; Han et al ., ; Mao et al ., ).…”

“…Zhang et al, 2002;N. Li et al, 2007Qin et al, 2007Qin et al, , 2008Qin et al, , 2009Liu et al, 2008Liu et al, , 2011Zhou et al, 2008;Chen et al, 2009;Chen, 2010;Jiang et al, 2010;Zhu et al, 2010;Dong et al, 2012;Yang et al, 2013;Han et al, 2014b;Mao et al, 2014).…”

Mineralogy, Fluid Characteristics, and Re-Os Age of the Late Triassic Dahu Au-Mo Deposit, Xiaoqinling Region, Central China: Evidence for a Magmatic-Hydrothermal Origin

“…Li et al, 2012a), while the Triassic Au-Mo mineralization is related to final collision between the North China craton and the Yangtze craton, and the subsequent postcollisional extensional process. Triassic quartz vein-style Au deposits (e.g., Liba Au deposit, ~216 Ma: Zeng et al, 2012; Liziyuan Au deposit, ~229 Ma: T. Yang et al, 2013), quartz vein-style Au-Mo deposits (e.g., Majiawa Au-Mo deposit, 232 ± 11 Ma: Y.T. Wang et al, 2010; Dahu Au-Mo deposit), quartz vein-style Mo deposits (e.g., Qianfangling Mo deposit, 239 ± 13 Ma, and a number of Mo occurrences in the Songxian County: Gao et al, 2010), carbonatite-related 0361-0128/15/4278/119-27 Hu et al, 1994;Mao et al, 2002;J.…”