Mineralization of the Shangjiazhuang Mo deposit in the Jiaodong peninsula, China: Constraints from S–H–O isotopes and fluid inclusions

Abstract

The Shangjiazhuang Mo deposit is located in the east of Shandong Peninsula, which is tectonically the eastern extends of the Dabie-Sulu orogenic belt. The ore bodies occur in the Early Cretaceous Yashan porphyritic granodiorite, which are stratiform, vein-like and lentoid. The orebodies are controlled by the fractures with NW direction, and have similar orientations, with strike of 337°–344° and dips of 20°–26° to the northeast. The potassic alteration, biotitization, silicification, sericitization, chloritization, and carbonatization are developed in the country rock. According to the relationship of mineral symbiotic assemblage and the cutting relationship of the hydrothermal veins, the hydrothermal metallogenic period of Shangjiazhuang Mo deposit can be divided into three stages: quartz-molybdenite (early stage), quartz-chalcopyrite and molybdenite (middle stage) and quartz-pyrite (late stage). We studied S–H–O isotopes, fluid inclusions and mineralization age of the Shangjiazhuang Mo deposit, aiming to clarify the genesis mechanism for the Mo deposits in the eastern Jiaodong Peninsula. The δ³⁴S value of molybdenite and chalcopyrite in the main metallogenic stage range from 4.5‰ to 5.0‰, which is consistent with magmatic sulfur. The δ¹⁸O_H2O valve decrease gradually from the early metallogenic stage (4.5‰–5.0‰) to the late metallogenic stage (0.39‰–1.48‰), indicating that the ore-forming fluids were mainly magmatic water at the early stage and a mixture of meteoric and magmatic water at the late stage. The ore-forming fluids evolved from moderate temperature, CO₂-rich and high salinity at the early stage to low temperature, CO₂-poor with nearly constant salinity in the late stage. Different types of inclusions with similar temperature and different salinity coexist in the main metallogenic period, indicating that as temperature drops, fluids in the system were either immiscible or boiling, leading to CO₂ escape, and finally leads to the precipitation and enrichment of ore-forming elements.