Magmatic Activity And Metallogeny Of Dong Ujimqin Banner, Inner Mongolia

Located in the Chaganobo—Aououte—Chaobuleng along the southern edge of the Siberian plate, the study area of northern Dong Ujimqin Banner of Inner Mongolia lies in western of Greater Xing'an Mountains metallogenic belt. Controlled by the multiple subduction, collision and connection of North China platform, the ancient Mongolia section of oceanic crust and Siberia platform, the region is characterized by widely exposed Paleozoic volcanic-sedimentary rock, complex structures, all kinds of intensive magmatic activities, and widespread ore deposits and occurrences. The study area was of special geological structure and context of a favourable environment mineralization.At present, more than 23 deposits and occurrences have been found in northern Dong Ujimqin Banner of Inner Mongolia, including one large deposit, five medium-sized deposits and five small deposit. There were many kinds of ore deposits such as tungsten, iron, copper, lead, zinc, silver, gold, bismuth, and so on. Deposits were the main types of skarn deposits, plutonic intrusions-related deposits and medium-low temperature hydrothermal deposits. In order to study the region of magmatic activity and polymetallic deposits of mineralization, to find out the mineralization and to guide mineral exploration, the paper studied five representative granitoid intrusions and three typical deposits. The research on geological survey, petrology, geochemistry, isotope and SHRIMP U-Pb chronology of the granitoid intrusions and deposits in the study area was the first conducted systematically, and the emplacement setting and age of the major intrusions as well as their relations to deposits were discussed in detail.Most intrusions of the study area were alkali-rich, potassic and alkaline-calc- alkaline granitoids. And there were high content of Al₂O₃ as well as Pb, Zn, Au, Ag etc.. Lead isotope ratios of granitoid intrusions were similar. In plumbotectonic model diagram, the lead isotopic compositions of granitoid intrusions were mainly located around mantle. According to Sr-Nd isotopic analytical results, granitoid intrusions had similar Sr, Nd isotopic characteristics to those of Xing'an-Mongolia orogenic belt such as low (⁸⁷Sr/⁸⁶Sr)_i initial ratios, positiveεNd(t) and lower model ages. SHRIMP U-Pb isotopic ages of Jilinbaolige intrusion is 314±8.8Ma, early stage Aqinchulu intrusion is 299±5Ma, late stage Aqinchulu intrusion is 284.3±9.7Ma, Chagan Obo intrusion is 237±6Ma and Aerhada intrusion is 218±5Ma, respectively. It has been suggested that Jilinbaolige intrusion and Aqinchulu early and late stage intrusions belong to island-arc granite, Chagan Obo quartz diorite is Adakitic rock, Aerhada intrusion belong to A type granite. The later two intrusions formed in an extensional environment of post collision. Metallogenic material of Jilinbaolige silver-gold deposit mainly derived from magma and only a few derived from derived from strata. Isotope analytical results showed that sulfur mainly derived from magma, but a few from sedimentary rock, lead mainly derived from magma. It is considered that hydrothermal ore forming solution mainly moves upward along the fracture and deposits by the process of filling and replacement. Quartz diorite and partial skarn of Chagan Obo iron-zinc deposit showed nearly uniform rare earth element and trace element distribution patterns. Theδ³⁴S value of sphalerite was 10.3‰, and pyrite of quartz diorite compared with 0.8‰. Not only S-Pb but also Sr-Nd isotope analysis results imply that metallogenic material of Chagan Obo deposit derived from magma but was contaminated by crust. Chagan Obo iron-zinc deposit belong to skarn deposit which related to quartz diorite. The article considered that Chagan Obo iron-zinc deposit formed in an extensional environment. During ore-forming process, ore bearing ancient residual oceanic crust melted partly at first, and then intruded shallow depths in the crust after mixed by potassium rich basic mantle, and separated out iron at last most likely to be the result of metasomatism by sodium when magma contacted with marble. By contrast, the Jilinbaolige lead - zinc - silver ore deposit was hydrothermal deposit which related to Indosinian intermediate-acidic magmatism. Tuff which was one of host rock of the deposit was intermediate volcanic rocks belong to potassium and aluminium rich tholeiite series. The values ofδ³⁴S of sulfide from deposit showed sulfur derived from magma and sedimentary rock.. Temperature calculated from sulfide pairs showed two groups values of 399℃—407℃and 194℃—287℃. Lead isotope analysis results imply that metallogenic material of deposit derived from magma and sedimentary rock.The regional ore deposits in the study area formed in three periods, i.e. Hercynian, Indosinian and Yanshanian. They were closely related to granite intrusions in the temporal and spatial distribution. Generally speaking, the intrusions not only provided heat source, part ore-forming fluids and elements, but also caused the long convective circulation of heat water which leached ore-forming elements of into the appropriate spaces to form ore-bodies. Finally, this paper concludes effective prospecting criterias and puts forward favorable prospecting directions in the study area.