Genesis of the Shaquanzi Zn–Pb deposit in the Eastern Tianshan, NW China: Constraints from geology, fluid inclusion and isotope geochemistry

Abstract

The Shaquanzi Zn–Pb deposit, located in the Central Tianshan Terrane, is mainly hosted by siliceous slates and carbonaceous marbles of the Mesoproterozoic Kawabulake Group, and its mineralization / alteration can be divided into skarn period (I: early skarn stage, II: late skarn stage), quartz-sulfide period (III: early sulfide stage, IV: late sulfide stage and V: quartz-calcite stage) and supergene period (VI: supergene alteration stage). The W-type fluid inclusions (FIs) were identified in the garnet, chlorite, quartz, and calcite in skarn and quartz-sulfide periods. Detailed fluid inclusion study shows temperature of fluids decreased from Stage I (510–520 °C) through, Stage III (481–507 °C), Stage IV (248–417 °C, peak at 280–400 °C) to Stage V (148–260 °C, peak at 200–220 °C), with salinities of 20.8–22.2 wt% NaCl eqv., 19.8–29.1 wt% NaCl eqv., 10.6–27.8 wt% NaCl eqv. (peaks at 20–23 wt%), and 21.6–29.9 wt% NaCl eqv. (peak at 23–27 wt%), respectively, indicating that the ore-forming fluids consisted of a high-medium salinity and Na-Mg-Fe-Ca-rich fluid system, and may have evolved from high-medium temperature to medium temperature. The H–O isotopic compositions varied from Stage III (δ18OH2O = 7.7 ‰–9.0 ‰ and δDH2O = − 105 ‰ to − 91 ‰) through Stage IV (δ18OH2O = 2.6 ‰ to 4.3 ‰ and δDH2O = − 114 ‰ to − 111 ‰) to Stage V (δ18OH2O = − 4.2 ‰ to − 3.7 ‰ and δDH2O = − 119 ‰ to − 96 ‰), suggesting that the ore-forming fluid sources may have evolved from magmatic fluids to meteoric water. The average δ34SH2O values of the early sulfide, late sulfide, and quartz-calcite stages are 5.7 ‰, 8.5 ‰ and 14.0 ‰, respectively, indicating that the sulfur in the early stage was mainly derived from magmatic hydrothermal sulfur, while the increase of the δ34SH2O values in the late stages is likely to be sourced from the Kawabulake Group through water–rock reaction. Above all, we propose that the Shaquanzi may have been a skarn-type Zn–Pb deposit.