The Geological Features And Genesis Of The Dongjun Lead-Zinc-Silver Deposit In Inner Mongolia, China

Dongjun Pb-Zn-Ag deposit belongs to Dongwuqi-Xingan metallogenic belt in Daxinganling. It is located in the Hailaer Jurassic volcanic rocks. Regional north-eastward Derbugan deep fault pasts from its northwest. This paper is based on the geological conditions, combined with the geochemical behavior, fluid inclusion study. This paper aims at understanding the mineralization of ore deposit, establishing genetic model of ore deposit, at the same time, we use the measures and process of exploration to sum up the model for exploration.The mine area is only outcroped in J2tm basaltic volcanics. The ore bodies are mainly layered on banded. The main minerals holding silver are clinohedrite, eugenite, aftonite and aerositer. The rock alteration have silicate, calcilization, chloritization, kaolinisation.Geochemical studies indicate that the rock pertains to calc-alkaline igneous rock, relatively rich in light rare earths, and large-ion lithophile elements are richer than high field strength elements. The partition model between the ore and volcanic rock is similar. It indicate that they have the congruent source. The trace elements of ore are less than the volcanic rock, which may caused by hydrothermal alteration. Ore of lead, sulfur isotopes indicate that the metallogenic material overall has the character of far reaching magma, and contamination occurred with the surrounding rock. Besides, the Rb, Sr, Sm, Nd isotopes in volcanic rocks and invasive rocks indicate that the magma come from the mantle.The studies of fluid inclusion showed that the ore-forming fluids have characteristics of low salinity and middle-low temperature. Based on the study of C-O isotopic compositions, the writer presumed that the ore-forming fluids are dominated by magmatic water in its early stage while are mixed with a lot of precipitation in the later phase. The age of the volcanic rock by LA-ICP-MS is 166Ma. It is later Middle Jurassic. The writer infers that the age of ore-forming is Late Jurassic to Early Crataceous. The research demonstrates that the Dongjun deposit is controlled by fault, filed along the cracks and faul in volcanic rocks, which is a middle-low temperature hydrothermal lead-zinc-silver deposit generated from volcanic rocks and subvolcanic rocks.