Cu-S Isotopes of the Main Sulfides and Indicative Significance in the Qibaoshan Cu-Au Polymetallic Ore District, Wulian County, Shandong Province, North China Craton

With a focus on the Cu isotope geochemistry of chalcopyrite, this paper analyzed the Cu isotope geochemistry of the Qibaoshan crypto-explosive breccia-type Cu-Au polymetallic ore district in Wulian, Shandong Province, North China Craton (NCC). Combined with the results of the in situ sulfur isotope analysis of sulfides, a certain reference and evidence for the study of the genetic mechanism of the epithermal-porphyry Cu polymetallic metallogenic system were provided. The results of the in situ isotope analysis show that the & delta;S-34 values of the main sulfides in the Qibaoshan Cu-Au polymetallic ore district range from -6.81 & PTSTHOUSND; to +3.82 & PTSTHOUSND; and are likely to be attributed to the mixing of the derived mantle with the surrounding sedimentary rock assimilation. The ore-forming mechanism may be related to the progressive cooling and transition of the earliest hydrothermal fluids that were dominated by H2S under relatively reducing conditions, followed by a gradual transition from oxidation to reduction. The Cu isotopic composition of the sulfides in ores (& delta;Cu-65 = +0.169 & PTSTHOUSND;-+0.357 & PTSTHOUSND;) decreases with depth, which is likely caused by the upward transport of heavier Cu isotopes. The upper part of the crypto-explosive breccia pipe in the Qibaoshan area may be relatively more gaseous, resulting in the enrichment of & delta;Cu-65. As the gas phase decreases and the liquid phase increases with depth, the & delta;Cu-65 value gradually decreases. This indicates the transition from a low-temperature phyllic alteration to a high-temperature K-feldspar alteration. Large, concealed pluton intrusions or orebodies may be present at a depth of the Qibaoshan area. The heavy & delta;Cu-65 characteristic is a potential indicator for tracing the fluid activity of the porphyry system and searching for Cu mines. The results provide a reference for the study of the genetic mechanisms of the epithermal-porphyry Cu polymetallic metallogenic system.