Textures, fluid inclusions and trace elements of multistage quartz in the Chengba Cu-Zn skarn deposit, Tibet

• Seven generations of quartz have been identified, with Qz-C2 and Qz-S3 being associated with Cu and Zn mineralization, respectively. • Cu precipitation was primarily triggered by fluid boiling, whereas Zn deposition was induced by an increase in fluid pH. • Integrated quartz CL imaging, trace element, and fluid inclusion of quartz analyses constrain the fluid evolution and ore-forming processes. The Cu-Zn skarn deposit represents a distinct subtype of skarn systems, in which Cu mineralization occurs in the proximal zones, whereas Zn orebodies are hosted in locations closely associated with Cu mineralization. However, the evolution of ore-forming fluids and the mechanisms responsible for Cu and Zn precipitation remain poorly constrained. The Chengba Cu-Zn skarn deposit, containing more than 0.6 Mt of ore with average grades of 1.29 wt% Cu and 3.9 wt% Zn, represents the first large-scale Cu skarn deposit formed during the syn -collision stage of the Gangdese metallogenic belt. Here, we integrate scanning electron microscope–cathodoluminescence (SEM-CL) imaging, quartz trace element analysis, and fluid inclusion microthermometry from multiple minerals to reconstruct the fluid evolution and sulfide precipitation processes of the Chengba Cu-Zn skarn deposit. Based on mineral assemblages and crosscutting relationships, four paragenetic stages are distinguished: (I) prograde skarn, (II) retrograde skarn, (III) quartz–sulfide, and (IV) carbonate. Quartz was further subdivided into three sub-stages with seven generations: brecciated quartz (Qz-B), quartz–chalcopyrite veins (Qz-C1, Qz-C2, Qz-C3), and quartz–sphalerite veins (Qz-S1, Qz-S2, Qz-S3). Among them, Qz-C2 and Qz-S3 represent the main fluid stages for Cu and Zn precipitation, respectively. Trace element data show a general decrease in Ti contents from Qz-B to Qz-S. Aluminum and Li exhibit strong coupling in most quartz generations, but in Qz-S3 their relationship differs from earlier generations, possibly indicating that H + in the fluid substituted for Li + in charge-balanced substitution with Al 3+ . Three types of fluid inclusions (S-, B-, and C-type) were identified, with homogenization temperatures progressively decreasing from 547 ± 43 °C (prograde skarn), to 313 ± 43 °C (quartz–sulfide), and 213 ± 42 °C (carbonate). Salinity variations indicate two major boiling events during the prograde skarn (7.0–44.2 wt% NaCl equiv) and quartz–sulfide (0.6–37.4 wt% NaCl equiv) stages. It is inferred that chalcopyrite precipitation was triggered by fluid boiling, whereas sphalerite precipitation was mainly controlled by elevated fluid pH, with progressive cooling acting as an additional factor. These results provide new insights into fluid evolution and metal precipitation mechanisms for the Cu-Zn skarn deposits in the Gangdese metallogenic belt.