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

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 delta S-34(V-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 (Pb-206/Pb-204 = 18.280-18.386, Pb-207/Pb-204 = 15.549-15.588, and Pb-208/Pb-204 = 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 delta O-18(H2O) values (6.4 to 7.7%) of quartz in stages I and II are similar to typical magmatic water values, but the delta D (-142.5 to -125%) and delta O-18(H2O) (-1.1 to 3.4 parts per thousand) 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 degrees 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.

Automated summary

This study investigates the origin and evolution of ore-forming fluids in the newly discovered Xiaokele porphyry Cu (-Mo) deposit in the northern Great Xing'an Range of northeast China. The results suggest a close genetic relationship between the deposit and the granodiorite porphyry, with ore-forming materials likely originating from the porphyry. Furthermore, the deposition of copper in the deposit is primarily controlled by fluid cooling.