Fluid evolution and metallogenesis of the Meiling Cu‐polymetallic deposit in the East Tianshan, NW China: Constraints from ore geology, fluid inclusions, stable isotope, and U–Pb geochronology

Abstract

The Meiling Cu-polymetallic deposit is located in the Kalatag Cu metallogenic belt of the East Tianshan, Xinjiang, NW China. Multiple-stage hydrothermal activities have resulted in the silicification, chlorite alteration and sericite alteration in this deposit. At least three mineralization stages are recorded: (a) a phase comprising quartz-pyrite veining, (b) a quartz-chalcopyrite-pyrite-sphalerite phase and (c) a quartz-calcite phase, respectively. LA-ICP-MS zircon U-Pb dating yielded 302 ± 2.1 Ma for an orebearing quartz porphyry and 296 ± 3.2 Ma for a post-mineralization diorite porphyry dyke, respectively, indicating that the copper mineralization took place during the Late Carboniferous period (302-296 Ma). Fluid evolution during the three stages of mineralization was determined by a detailed fluid inclusion study: (a) Stage I fluids were trapped under two-phase conditions, as evidenced by the coexistence of vapour-rich (type II) inclusions (T h = 183-242 C, average salinity = 4.8 wt% NaCl equiv.), liquid-rich (type I) inclusions (T h = 171-259 C, average salinity = 5.3 wt% NaCl equiv.), and daughter-bearing (type III) inclusions (T h = 192-208 C, average salinity = 8.6 wt% NaCl equiv.). (b) Stage II fluid inclusions in quartz were also trapped under two-phase conditions (boiling), as identified by the coexistence of V-and Ltype fluid inclusions; L-type inclusions T h between 136 and 218 C (average = 189 C), with salinities of 2.2-7.6 wt% NaCl equiv. (average = 3.8 wt% NaCl equiv.). V-type inclusions homogenized temperatures between 153 and 226 C (average = 192 C), with salinities of 2.4-6.7 wt% NaCl equiv. (average = 3.5 wt% NaCl equiv.). (c) Stage III fluids are represented by inclusions in barren quartz-carbonate veinlets, characterized by homogenization temperatures ranging from 98 to 177 C (average = 135 C) and salinities between 0.5 and 3.2 wt% NaCl equiv. (average = 1.9 wt% NaCl equiv.). The initial hydrothermal fluids are characterized by low-intermediate temperature, low-salinity and near-neutral pH condition, belonging to a H 2 O-NaCl bearing hydrothermal system. The mineralization of the Meiling deposit occurred at a shallow

Palaeozoic tectonic evolution and magmatism in the Kalatag area, East Tianshan, NW China: Evidence from the geochronology and geochemistry of intrusive rocks

“…The Sr–Nd isotope results further reveal that the Late Ordovician–Carboniferous rocks have similar ( 87 Sr/ 86 Sr) i values (0.70380 to 0.70462) and ε Nd (t) values (4.2–10.2) that indicate the characteristics of a mantle source (Figure 10a; Du et al, 2017; Mao et al, 2018; Zheng et al, 2018; Chen et al, 2020). The Lu–Hf isotope data points of Late Ordovician–Silurian plot near the depleted mantle lines on the ε Hf (t) versus t (Ma) diagram, which is similar to the zircons from the Devonian and Carboniferous rocks in the Kalatag area (Figure 9; Sun, Wang, Wang, et al, 2019b; Cheng, Yang, Zhang, Zhang, Li, & Yang, 2020). The Late Ordovician–Carboniferous rocks show high Hf isotope compositions, with 176 Hf/ 177 Hf ratios from 0.282781 to 0.283137, ε Hf (t) values between 12.22 and 18.15, and very young two‐stage Hf model ages (T DM C = 0.19–0.63 Ga), which are consistent with a depleted mantle that is accompanied by limited crustal assimilation.…”

“…However, the Devonian magmatism was relatively weak, as the diorite that is exposed in the Xierqu ore district has zircon U–Pb ages of 378–391 Ma (Chen et al, 2020; Mao et al, 2018; Sun et al, 2019b). Carboniferous magmatism occurred in the Meiling–Hongshan ore district and is composed of diorite with zircon U–Pb ages of 296–334 Ma (Cheng et al, 2020; Mao et al, 2021). The Permian mafic‐ultramafic intrusions in the Yueyawan Cu–Ni ore district are composed of troctolite, olivine gabbro, hornblende gabbro, and gabbro, which have zircon U–Pb ages of 265–282 Ma (Lü, Mao, Guo, Li, & Sun, 2020; Mao et al, 2021; Sun, Wang, Lü, et al, 2019a; Zhou et al, 2019).…”

“…The diorite porphyry from the Meiling ore district was formed at 296 Ma (Cheng, Yang, Zhang, Zhang, Li, & Yang, 2020). The chemical compositions of the diorite porphyry are metaluminous to weakly peraluminous.…”

Geochronology and Geochemistry of the Early Paleozoic Ore‐host Volcanic Sequence in the Kalatag Area, East Tianshan, NW China: Implications for the Tectonic Evolution

“…The Devonian diorite has zircon U-Pb ages of 391-378 Ma in the Xierqu ore district (Mao et al, 2018;Sun et al, 2019b;Chen et al, 2020). The Carboniferous quartz porphyry with zircon U-Pb ages of 334-296 Ma occurred in the Meiling and Hongshan ore districts (Cheng et al, 2020b;Mao et al, 2021b). Permian mafic-ultramafic rocks with zircon U-Pb ages of 282-265 Ma are widely exposed in the Yueyawan ore district (Sun et al, 2019a;Zhou et al, 2019;Lü et al, 2020;Mao et al, 2021a).…”