Polymetallic Mineralization And Prospecting Direction In The Gaoerqi-Chaobuleng Area,Inner Mongolia

The Gaoerqi-Chaobuleng area from Inner Mongolia is located in the southeast of the junction of the Siberian plate and the North China Craton.A total of more than 20 large and medium-sized copper-lead-zinc-silver polymetallic ore deposits,as well as numerous small polymetallic ore deposits and occurrences,have been discovered in the area,which indicates that the study area has excellent ore-forming geological conditions.Following the metallogenic systems theory,this paper determines three major metallogenic systems based on previous geological data,i.e.the Late Paleozoic copper polymetallic oreforming system from rift environment,the Late Paleozoic copper polymetallic mineralization system from post-collisional extension environment,the Mesozoic leadzinc-silver polymetallic metallogenic system from the intracontinental extension environment,which are further divided into seven metallogenic sub-systems.Typical mineral deposits from the three systems,i.e.the Xibaliang copper polymetallic deposit in the Late Paleozoic rift environment,the Bayan Dulan copper polymetallic deposit in the Late Paleozoic post-collisional extension environment,and the East Wulan Tolgai silver polymetallic deposit,the Chaobuleng iron polymetallic deposit and the Shamai tungsten deposit from the Mesozoic intracontinental extension environment are selected to conduct the detailed mineralisation study.These work are used to summarize the mineralization characteristics,mineral geological conditions,ore-controlling factors,metallogenic regularities of different metallogenic systems.The prospectivity of this area is also evaluated based on this work.The key points of the paper are as follows:1.The Xiaobaliang Cu-Au deposit is closely related to the formation of ophiolite and the spilite-keratophyric series in the area.The zircon LA-ICP-MS U-Pb ages of the host tuff are 314.36 ± 0.42 Ma and 313.8 ± 1.2Ma,indicating that the deposit may form in a rift environment and belongs to the VMS type deposit.2.The ore bodies in the Bayan Dulan copper polymetallic deposit are controlled by faults.The Sm-Nd isotope isochron age of the scheelite is 314±15 Ma,which is consistent with the formation age of the host granite?305-323 Ma?.Fluid inclusions in the early stage of the deposit have a high homogeneous temperature?390-430 °C?,and the sulfide S isotope??34S is +2.3‰⁺3.5‰?and Pb isotopes in the ore have obvious magmatic characteristics.The comprehensive analysis shows that the mineralization of the deposit is related to the magmatic activity under the background of post-collision extension dynamic setting.The magma provides the main ore-forming materials and fluids for the formation of Bayandulan copper deposit after shallow emplacement and differentiation.3.The ore bodies of the East Wulan Tolgay Silver polymetallic deposit are controlled by the faults and the contact zone between intrusion and strata.The mineralization may occur in the Late Mesozoic,which is obviously later than the granites?306.8 ± 2.1 Ma?and rhyolite porphyry?323.8 ± 4.3 Ma?exposed in the mining area.The ore S isotope study indicates that the sulfur in the deposit may derive from magma and strata,and the Pb isotope indicates that the ore-forming material is a mixture of the upper crust and the mantle.Therefore,the deposit is a hydrothermal vein-type polymetallic deposit.4.The Chaobuleng polymetallic deposit belongs to the skarn type deposit formed after the Yanshanian tectonic-magmatic activity.The Re-Os isotope model age of the ore molybdenite sample is 152.9±3.0¹15.7±1.2 Ma,the ⁴⁰Ar-³⁹Ar plateau age of the muscovite is 136.4±1.6Ma,and the zircon U-Pb ages of the granites in the mining area are 138 ± 1.6 Ma and 148 ± 1.4 Ma.Thus,diagenesis and mineralization have a consistent spatial-temporal relationship.The results of multi-isotope studies further indicate that the magmatic rocks and strata in the area provide ore-forming fluids and ore-forming materials.5.The ore bodies of Shamai tungsten deposit are hosted by the biotite granite.It is a typical fault-fracture controlled quartz vein-type tungsten deposit.The previous Ar-Ar age of muscovite and the Re-Os model age of molybdenum ore are nearly the same as the intrusion ages of the fine-grained granite?142.5±1.0Ma?,medium-grained granite?141.9±1.1Ma?,and porphyritic biotite granite?140.2±0.99Ma?obtained in this study,indicating that these intrusions provide material and the fluid basis for mineralization.Further Hf isotope studies indicate that the magmatism in the area is derived from the juvenile lower crust.6.The ore-forming age of the Gaoerqi-Chaobuleng area is concentrated in two major periods,i.e.the Late Paleozoic and Mesozoic?Late Jurassic-Early Cretaceous?.The Paleozoic-Mesozoic multi-cyclonic magmatic-tectonic-fluid system controls the formation of the polymetallic ore-forming system.In addition,the NW-and NE-trending structures control the spatial distribution of ore fields,deposits and ore bodies in this area.According to the summarization and analysis of ore-controlling factors and prospecting indicators of typical deposits,I finally delineated 10 ore targeting areas,of which 3 are well identified and 7 are potential ore targeting areas with certain resource potential.At the end of the thesis,the metallogenic geological conditions,geophysical and geochemical characteristics and prospecting direction of each targeting area are comprehensively reviewed.