Genesis of the Talate Pb–Zn (–Fe) deposit in the Altay, Xinjiang, NW China: Evidence from fluid inclusions and stable isotopes

Abstract

The Talate Pb–Zn (–Fe) deposit, located in the Kelan volcanic-sedimentary Basin, Chinese Altay (part of Central Asian Orogenic Belt, NW China), is hosted in the second unit of the lower member of the Lower Devonian Kangbutiebao Formation. This deposit has undergone two periods, including submarine exhalative-sedimentary period (I), and magmatic hydrothermal (skarn) period (II), and period II can be further divided into three stages: prograde skarn stage (II-1), retrograde skarn stage (II-2), and quartz–sulfide stage (II-3). Electron microprobe analyses data show that garnet from II-1 stage is consists of solid solutions of almandine, spessartine, pyrope, and grossularite, with small fraction of andradite and uvarovite. Chlorite forming temperature ranging from 163 to 169 °C. L-type fluid inclusions in period I sphalerite has two total homogenizing temperature of 259 °C and 286 °C, respectively. The ore-forming fluids in the II-1 and II-2 stage belong to the H2O–NaCl system with moderate to high temperatures (mainly at 206–368 °C and 202–416 °C, respectively) and moderate–low salinities (7.17–17.34 wt% NaCl eqv. and 6.45–19.21 wt% NaCl eqv., respectively). The II-3 stage ore-forming fluids belong to H2O–CO2 (±CH4/N2)–NaCl system, their temperature and salinity varies widely (193–445 °C, 0.42–37.40 wt% NaCl eqv., respectively). The garnet and quartz samples from II-1 and II-3 stages yield δDV-SMOW and δ18Ofluid values (–79.8 to –64.9‰ and 4.14 to 6.17‰, respectively) and (–80.7 to –67.0‰ and –0.15 to 3.05‰). The microthermometry data combined with stable isotope data indicate ore-forming fluids in II-1 and II-3 stages are derived from primary magmatic water, but in II-3 stage is mixed with more meteoric water. In addition to meteoric water, it is supplied by carbon-rich, high-temperature and high-salinity fluid in II-3 stage. The δ34S values of the period I sulfides range from –11.7‰ to 2.4‰. Sulfur source in Talate deposit derived from the deep magmatic hydrothermal fluid. The Talate Pb–Zn (–Fe) deposit belongs to the volcanogenic massive sulfide (VMS) + skarn type, thus a genetic model is proposed to explain the metallogenic process of the Talate deposit.