Genesis of the Fuxing porphyry Cu deposit in Eastern Tianshan, China: Evidence from fluid inclusions and C-H-O-S-Pb isotope systematics

摘要

The Fuxing porphyry Cu deposit is a recently discovered deposit in Eastern Tianshan, Xinjiang, northwestern China. The Cu mineralization is associated with the Fuxing plagiogranite porphyry and monzogranite, mainly presenting as various types of hydrothermal veins or veinlets in alerted wall rocks, with potassic, chlorite; phyllic, and propylitic alteration developed. The ore-forming process can be divided into four stages: stage I barren quartz veins, stage II quartz-chalcopyrite-pyrite veins, stage III quartz-polymetallic sulfide veins and stage IV quartz-calcite veins. Four types of fluid inclusions (Fls) can be distinguished in the Fuxing deposit, including hypersline (H-type), vapor-rich two-phase (V-type), liquid-rich two-phase (L-type), and trace amounts of pure vapor inclusions (P-type), but only the stage I quartz contains all types of Fls. The stages II and III quartz have two types of Fls, with exception of H- and P-types. In stage IV quartz minerals, only the L-type inclusions can be observed. The Fls in quartz of stages I, II, III and IV are mainly homogenized at temperatures of 357-518 degrees C, 255-393 degrees C, 234-322 degrees C and 145-240 degrees C, with salinities of 1.9-11.6 wt.% NaCl equiv., 1.6-9.6 wt.% NaCl equiv., 1.4-7.7 wt.% NaCl equiv. and 0.9-3.7 wt.% NaCl equiv., respectively. The ore-forming fluids of the Fuxing deposit are characterized by high temperature, moderate salinity and relatively oxidized condition. Carbon, hydrogen and oxygen isotopic compositions of quartz indicate that the ore-forming fluids were gradually evolved from magmatic to meteoric in origin. Sulfur and lead isotopes suggest that the ore-forming materials were derived from a deep-seated magma source. The Cu mineralization in the Fuxing deposit occurred at a depth of similar to 1 km, and the changes of oxygen fugacity, decompression boiling, and local mixing with meteoric water were most likely critical for the formation of the Fuxing Cu deposit. (C) 2016 Elsevier B.V. All rights reserved.