Superimposed mineralization at the Suoerkuduke Cu–Mo skarn Deposit, North Xinjiang, China

Abstract

The Suoerkuduke Cu–Mo skarn deposit is located in Fuyun County, Xinjiang Uygur Autonomous Region in NW China, within the northern margin of the East Junggar block. Comprehensive studies of ore deposits demonstrate that the deposit features two episodes of skarn mineralization: the first (Episode A) skarn is stratiform or lenticular and is characterized by predominantly disseminated Fe–Cu–Mo ores, whereas the second (Episode B) skarn occurs as veins or stockworks and contains predominantly Cu–Mo–Zn ores.Episode A mineralization formed in the Late Devonian (379.2 ± 2.8 Ma), whereas Episode B mineralization formed in the Early Permian (296.6 ± 1.9 Ma). Episode A skarn was genetically linked to dacite/syenite porphyries and may have occurred in an island arc setting, whereas Episode B skarn was genetically linked to granite porphyry (295.3 ± 3.8 Ma) and may have developed in a postcollisional setting.Based on mineral paragenesis and crosscutting relationships, the hydrothermal mineralizing event of Episode A is further divided into three stages, i.e., the prograde (A1), oxide (A2), and retrograde (A3) stages, while that of Episode B is divided into four stages, i.e., the prograde (B1), retrograde (B2), quartz-sulfides (B3) and quartz-carbonate (B4) stages. Three types and seven subtypes of fluid inclusions (L-, V- and S1- to S5-types) are distinguished based on fluid compositions and phase assemblages.Episode A ore-forming fluid (H2O–NaCl) system involved two major mineralizing events: (1) the first fluid boiling (stage A1) at 530–560 °C and lithostatic pressures of 550–800 bar and (2) the second fluid boiling (stage A3) at 370–420 °C and hydrostatic pressures of 200–300 bar. Episode B ore-forming fluid (H2O–NaCl–KCl) system involved four major mineralizing events: (1) the first fluid boiling (stage B1) at 530–580 °C and lithostatic pressures of 600–850 bar, (2) the second fluid boiling (stage B3) at 320–360 °C and hydrostatic pressures of 100–200 bar, (3) overpressure trapping; brine inclusions homogenized by halite dissolution can be explained as a result of entrapment under overpressure condition, and (4) mixing with meteoric water (stage B4). Fluid boiling was the predominant ore-forming mechanism, while mixing between magmatic and meteoric fluids may also have contributed to ore mineral precipitation (mainly for sphalerite) in Episode B to a lesser extent.