Genesis and hydrothermal evolution of the Zhazigou skarn W (Mo) deposit, East Qinling, China: Constraints from fluid inclusions and H–O–S–Pb isotopes

Abstract

Abstract The Zhazigou is a typical redox-intermediate skarn W (Mo) deposit, located in the Luanchuan ore district within the East Qinling orogenic belt, central China. Skarn and W (Mo) orebodies are hosted mainly in the contact zones between the Yuku porphyritic granite and carbonaceous sedimentary rocks of the Luanchuan and Guandaokou groups. This paper presents detailed fluid inclusion (FI) and isotope data that are used to reconstruct the hydrothermal processes and explore the role of CO2 during scheelite precipitation at the Zhazigou. Four mineralization and alteration stages are recognized: anhydrous skarn (I), hydrous skarn (II), quartz–sulfide (III), and carbonate (IV). Systematic analysis of the FIs elucidates the evolution of hydrothermal fluids through these stages. Four primary types of FIs are recognized: two-phase liquid-rich inclusions (L-type), two-phase vapor-rich inclusions (V-type), halite-bearing (hypersaline) inclusions (H-type), and two- or three-phase CO2-bearing inclusions (C-type). In stage I, coexisting H-type (36.19–46.37\xa0wt% NaCl equiv.) and low salinity V-type FIs have similar homogenization temperatures, indicating that fluid boiling during the formation of anhydrous skarn minerals occurred at 500–550\xa0°C and 550–700\xa0bar (2.0–2.5\xa0km lithostatic depth). In stage II, coexisting V- and L-type FIs in quartz and scheelite within quartz–scheelite\xa0±\xa0actinolite\xa0±\xa0tremolite veins have different salinities but similar homogenization temperatures, indicating they were also trapped in the boiling process at 350–380\xa0°C and ~240\xa0bar (1.8–2.8\xa0km hydrostatic depth). In stage III, L-, V-, and minor H-type FIs have homogenization temperatures indicating continued fluid boiling at 300–340 °C and