Study On Metallogenesis Of Lead-zinc Polymetallic Deposit In Shaolang River Metallogenic Belt, Inner Mongolia

Shaolang River metallogenic belt, as a part of the northern margin of North China plate of the Caledonian fold belt, is situated at the central position of Xar Moron caledonian fold belt that is EW-trending. Its north boundary and south boundary are Xar Moron river and Chifeng-Chaoyang Fault, respectively. The area has the characteristics of complicated, superior metallogenic conditions, mutiple mineralization periods, intensive mineralization and complex and various deposit types due to multiple metallogenic provinces overlying, combining and transforming. North of the Shaolang River metallogenic belt is Huanggangliang-ganzhuermiao-Wulanhaote metallogenic belt where the Pb-Zn polymetallic deposit focused in North China. Though there are some representative Pb-Zn polymetallic deposits(Xiaoyingzi, Aobaoshan, Dongzi, Heerwusu) found, yet study in Shaolang River metallogenic belt was unsystematic and still there are new works expected to be explored. This paper carried out systematic chronology, petrogeochemistry and the other analysis on basis of typical deposits. Studies suggested that the area was mainly influenced by Paleo-Asian Ocean tectonics metallogenic province before Mesozoic and was under a micro continental environment consisting of a number of secondary ocean basins. After Mesozoic, the North China plate and Siberia plate collided and jointed after the closure of the Paleo-Asian ocean, leading to the area with frequent tectonic activities and under a continent/continent collision and post-collisional crustal extension tectonic environment. Paleo-Pacific plate subducted towards Pal-Asia, resulting in regional tectonic framework occurring a great change during Yanshanian, and tectonic-magmatic activities were intensive along with strong polymetallic mineralization generating at that time.Main deposits of Shaolang River metallogenic belt according to its tectonic setting and mineralization characteristics are divided into two types including skarn type(Xiaoyingzi and Aobaoshan) and hydrothermal vein type deposits(Dongzi and Heerwusu). Petrogeochemistry datas revealed that ore-hosting rock ages of Dongzi and Xiaoyingzi Pb-Zn polymetallic deposit were 424.5±4.1Ma, 414.8±2Ma and 404.3±7.8Ma, respectively. While age of the Heerwusu rock was 268.1±2.6Ma. During late Caledonian subduction occurred from Paleo-Asian Ocean to Siberia Plate and during Variscan, Siberia Plate and North China Plate collided, the whole environment belongs to volcanic arc magmatism environment under compressional condition and Yanshanian was the period that tectonic regime changed greatly, regional extension and thinning took place with mass Pb-Zn mineralization generating. Metallogenetic chronology suggested metallogenic ages of Pb-Zn polymetallic deposits in study area belonged to Mesozoic Jurassic: Xiaoyingzi Pb-Zn deposits of 161~171Ma, Aobaoshan Pb-Zn deposit of 125~170Ma, Dongzi Pb-Zn deposit of 153 Ma, Heerwusu Pb-Zn deposit of 135~154Ma, reflecting Shaolang River metallogenic belt was affected by Mesozoic tectonic- magmatic activities, and formed during the time Mesozoic Jurassic thet massive mineralizations broking out. This was closely related to the tectonic regime changing and the rock thinning in North China. Most polymetallic deposits of both sides in Xar Moron River were connected with the magma intrusion activities to some degree.Fluid inclusion and C, H, O, S, Pb isotopes researches revealed that Shaolang River metallogenic belt polymetallic deposit were mainly gas-liquid two-phase types, and belonged to NaCl-H2 O system, at tempertures of 120°C~382°C, salinity of 0.5~25.6%NaCleqv, depth of 0.38~2.60 km. Ore-forming fluid was mainly composed of magmatic water, and inconclusive meteoric waters participated in the mineralizations as well. Ore-forming fluid of Xiaoyingzi Pb-Zn deposit was derived mainly from magmatic water, few meteoric waters participated in the mineralization. The distribution condition was merely influenced by mineralization temperature. Ore-forming fluid of Dongzi and Heerwusu Pb-Zn deposits were derived mainly from waters mixed by magmatic water and meteoric waters and mineralization were controlled by both meteoric waters and mineralization temperature. Source of S of metal sulfide was single, basically coming from deep source magmatic sulfur. Pb isotope analysis showed that source of mineralization materials were not only provided by deep source magmatic sulfur, but a part of the archean basement strata with characteristics of mixed crust-mantle.Metallogenic regularity research suggested that Shaolang River metallogenic belt polymetallic deposit was affected by strata, tectonics and magmatite. As the main ore-controlling factor, the fault tectonics provied channels for mineralization as well as favorable room for the final concentration of the deposit. As the main ore-bearing layer, the Permian strata obviously enriched in metallogenic elements such as Pb, Zn, while the carbonate and fault controlled the distribution position of scarn type and hydrothermal vein type respectively. Metallogenic belt ore body was usually accompanied by Mesozoic intermediate-acidic intrusive rocks, suggesting Pb-Zn polymetallic mineralization had genetic connection with intermediate-acidic magma.This paper based on full collection and analysis results of previous studies, combined with this study on the ore-forming geological conditions and the source of ore-forming materials in the northern margin of the North China plate hyperplasia with Shaolang River metallogenic lead-zinc polymetallic deposit. At the same time, the regularities of distribution of the deposit in time and space are analyzed and summarized, for further exploration work providing certain theoretical basis in this region. Besides, summary of the mineralization and metallogenic regularity for the establishment of prospecting model, has important significance for guide of the deposit prediction.