Timing and ore formation of the Xiaokele porphyry Cu (–Mo) deposit in the northern Great Xing’an Range, NE China: Constraints from geochronology, fluid inclusions, and H–O–S–Pb isotopes

Abstract

The Xiaokele Cu (–Mo) deposit is a newly discovered porphyry deposit in the northern Great Xing’an Range (GXR) of northeast China. The multiphase hydrothermal superposition on the Xiaokele Cu (–Mo) deposit obscures temporal relationships between quartz veins/veinlets in different mineralization stages, and consequently limits the understanding of the origin and evolution of the ore-forming fluids and metal precipitation mechanism. In this study, we document detailed descriptions of alteration and vein mineral paragenesis in the Xiaokele Cu (–Mo) deposit, present LA–ICP–MS zircon U–Pb and molybdenite Re–Os geochronology, the microthermometry and laser Raman spectroscopy of the fluid inclusions (FIs), and H–O–S–Pb isotope compositions. Four mineralization stages are identified, with stage II being the main Cu mineralization stage. The molybdenite Re–Os dating yielded a weighted average age of 148.7 ± 0.9 Ma (MSWD = 0.52), which is similar to the LA–ICP–MS zircon U–Pb age of 149.3 ± 0.9 Ma (MSWD = 0.15) yielded by the granodiorite porphyry. The δ34SV–CDT values of the sulfides (–1.2 to 2.4‰) conform the recognized magmatic sulfur values, indicating that the sulfur may have a magmatic origin. The Pb isotope compositions of the sulfides (206Pb/204Pb = 18.280–18.386, 207Pb/204Pb = 15.549–15.588, and 208Pb/204Pb = 38.153–38.359) coincide well with those of the Xiaokele granodiorite porphyry. These results indicate that the Xiaokele Cu (–Mo) deposit has a close genetic relationship with the granodiorite porphyry, and the ore-forming materials likely originated from the granodiorite porphyry. Petrographic/compositional characteristics of FI assemblages suggest that the ore-forming fluids belong to an H2O–NaCl–CO2 system in stage I and an H2O–NaCl system from stages II to IV, and fluid boiling occurred from stages I to III. The FI homogenization temperatures show a decreasing trend from stages I to IV. The δ18OH2O values (6.4 to 7.7‰) of quartz in stages I and II are similar to typical magmatic water values, but the δD (–142.5 to –125‰) and δ18OH2O (–1.1 to 3.4‰) of quartz in stages III and IV are significantly lower than magmatic water values, indicating that the ore-forming fluids were magmatic in origin and gradually mixed with meteoric water from stages III to IV. Microthermometric data show that Cu-bearing sulfides in stage II were mainly deposited at a temperature below 400 °C, indicating that fluid cooling was the primary factor that controlled Cu precipitation in the Xiaokele Cu (–Mo) deposit. Our research on the Xiaokele porphyry Cu (–Mo) deposit will help to provide a scientific basis for future prospecting of this deposit and even the Late Jurassic porphyry deposits in the northern GXR.