Pyrite geochemistry reveals the key controlling factors of large gold deposit formation in Jiaodong Peninsula: A comparative study

With an estimated gold reserve of more than 5000 t, the Jiaodong Peninsula is incontestably the largest gold ore belt in China. Dozens of gold deposits developed in the area with variable deposit types, grades, and reserves, and the key controlling factors for these differences are not clear. In this study, the representative Jiuqu (JQ), Canzhuang (CZ), and Sanshandao Northern Sea (SNS) gold deposits located in the NW portion of the Jiaodong district have been comparatively investigated using pyrite geochemistry, to constrain the mineralization sources and grade differences of each deposit. The pyrite from ore samples in JQ, CZ, and SNS deposits display euhedral to sub-euhedral geometries and do not show obvious zonation. The SNS pyrites present higher values for most trace elements (e.g., Cu, As, Ni) than the JQ and CZ pyrites. Moreover, the SNS deposit has the highest delta 34S value (+11.70 %o), followed by the CZ deposit (+10.43 %o) and the JQ deposit (+7.67 %o). This is positively correlated to their ore grade in order. The presence of relatively high contents of Cu, As, Ni as well as delta 34S values in the SNS deposit pyrites may suggest that more mantle materials have been contributed to the gold ores. It can be argued that these high values are associated with high oxygen fugacity in the subducting and stagnant slabs related to the lithospheric mantle metasomatism, which is responsible for the delta 34S enrichment and formation of Au and S reservoirs, serving as the key controlling factor for the formation of large gold deposits in Jiaodong. This study enables us to better describe the evolution of the mineralizing fluids and understand the mechanisms of ore genesis in gold mineralization systems by using pyrite geochemistry.