Regional Metallogenic System And Prediction Of The Western Segment Of The Erlian-Dongwuqi Metallogenic Belt,Inner Mongolia

The Erlian —Dongwuqi Cu-Mo -Pb-Zn-Ag metallogenic belt belongs to the Late Paleozoic epicontinental accretionary zone in southeast continental margin of the Siberian plate, which also locates in the western segment of the Great Hinggan Range Mesozoic volcanic-magmatic belt in the Circum-Pacific tectonic domain. The Paleozoic strata,magmatic rocks and ore deposits are widespread in the region, which are associated with complex structures. The studied area is located in west of the Erlian —Dongwuqi metallogenic belt. Numerous ore deposits have been discovered in recent years, i.e., the Wulandele Cu-Mo, Zhunsujihua Cu-Mo and the Gaoerqi Pb-Zn ore deposits, showing a well exploration potential.Utilizing regional metallogeny and metallogenic system as theoritical guides, and the collection of avaiable geological and scientific results, several typical ore deposits with different genetic types have been selected for field investigations and comprehensive study.The regional metallogenic system has been established, and the metallogenic geodynamics have been discussed. On the basis of summarizing the geological, geophysical and geochemical anomalies for regional ore deposits, an exploration model has been established to transform metallogenic system to practical exploration works for more effective prospecting.Field investigations, petrochemistry, zircon U-Pb geochronology and Lu-Hf isotope of ore-bearing granites in the Gaoerqi lead-zinc deposit reveal that granites belong to the A2 type formed in the extensional setting after plate collision and their magma mainly derive from the partial melting of young crust from depleted mantle. Zircon LA—ICP—MS U-Pb results show that monzogranite and syenogranite formed at 306.8±1.9Ma and 310.4±2.3Ma, respectively. With a combination of ore deposit geology, it is considered that Pb-Zn mineralization is synchronous with or later than granite. In addition, these age data show that the closure of Paleo-Asian ocean in north side is Late Devonian-Early Carboniferous, and the main collision between the North China plate and the Siberian plate has been ended in Late Carboniferous, and the period has entered the post-collision extensional stage.The ?98/95Mo and ?97/95Mo isotopic values of molybdenite samples from the Wulandele Cu-Mo deposit range from -0.09 to -0.04‰ and -0.06 to -0.03‰, respectively, which are consistent with those reported for other porphyry deposits. The Mo isotopic compositions are also similar to those of intrusive rocks (e.g., granite) worldwide, indicating a dominant magmatic origin for Mo in the Wulandele Cu-Mo deposit.Systematic studies of petrochemistry, geochronology and ore-forming material source for typical ore deposits with different genetic types in the region, i.e., the Gaoerqi Pb-Zn,the Zhunsujihua Cu-Mo, the Hadatetaolegai Pb-Zn and the Wulandele Cu-Mo deposits,demonstrate that these ore deposits formed in the extensional setting after plate collision in Variscan period and post-orogenic intraplate rift setting in Yanshan period. Ore deposits are dominated by porphyry and hydrothermal vein types. The ore-forming elements are dominated by Cu, Pb, Zn, Ag, W and Mo. A clear spatial distribution of ore-forming elements in the region has been identified, i.e., W, Mo?*Cu, Mo?Pb, Zn?Ag, Pb,Zn?Cu, Sn?Cu and Bi from west to east. The regional metallogenic systems can be divided into two magmatic-hydrothermal types, one is formed under the extensional setting after plate collision in Variscan period and the other under the post-orogenic extensional setting in Yanshan period.Ore-forming material sources, migration of ore-forming fluids, ore enrichment,variation and preservation after mineralization for different metallogenic systems are summarized. Evolution of different metallogenic systems and their tectonic dynamics are discussed, and the regional metallogenic models in Yanshan and Variscan periods are established, respectively.Comparisons and analysis of ore-prospecting practices of the Gaoerqi and Hadatetaolegai ore deposits result in a summary of the exploratory methods and workflows in the shallow covered areas. Exact delineating prospecting scope and the main minerals should be done first by means of the geo-electrochemical or geochemical prospecting measurement with different proportional scales meanwhile shallow drilling can be chosen for samples. After that, 1:10000 IP (induced polarization) intermedient gradient prospecting coverage can be done for further understanding the deeper distribution of IP bodies (ore bodies) and speculating the basic features of ore-controlling structures. Utilizing the resistivity methods (i.e., CSAMT and TDEM), beginning at seeking ore-bearing space (i.e., fracture zones or different lithologic contact zones),following is SIP works done directly for seeking indicating area with mineralized anomalies in the key area where is favourable for mineralization. Finally,the prospecting goal can be achieved.Based on the studies of metallogenic system, comparisons and analysis on metallogenic potential for the studied area have been done to put forward the forecasting methods and principles for metallogenic predictions. The Class-IV metallogenic prospect areas have been delineated to provide scientific basis for future exploration.