Integrated Geological And Geophysical Research In Shuangjianzishan Ore Concentration Area,Inner Mongolia

Shuangjianzishan silver-lead-zinc deposit,a typical epithermal magmatic hydrothermal composite superimposed mineralization deposit located in the southeast part of Great Khingan range,an ideal area for superimposed mineralization of three tectonic domains:the Paleo-Asian Ocean,the Mongolian-Okhotsk Ocean and the Paleo-Pacific Ocean.Based on the methods of mineralogy,chronology,geology and petrogeochemistry,the authors defined the mineralization type,metallogenic period,ore-bearing strata and mineralization-related intrusive rock types of shuangjianzishan deposit.However,the above methods mainly rely on the core data collected by drilling,and the detection results are limited to a shallow of 1000 m.The strata,intrusive rock and tectonic system's deep distribution are not clear.It seriously restricts the determination of metallogenic model and the further exploration of deep mineral resources.In order to define the metallogenic related elements' distribution and the metallogenic model of Shuangjianzishan,We carried out a comprehensive geological-geophysical study on the shuangjianzishan ore concentration zone.This paper classifies the geophysical characteristics of the main geological units in the research area based on the test result of 1043 rock samples including resistivity,susceptibility and density.The result shows that:there are great physical differences between intrusive rocks and sedimentary strata which are closely related to mineralization.Porphyritic granite related to mineralization shows high resistivity,high susceptibility and low density.On the contrary,argillaceous and silty slate of the Dashizhai formation shows low resistivity,low susceptibility and high density.Based on these results,we studied five 2D Magnetotelluric profiles passing through Shuangjianzishan ore concentration zone and the 3D inversion result of this area.We also studied the 3D focusing inversion result of 1:200000 gravity data and1:50000 aeromagnetic data in Balinzuoqi area.Based on geophysical inversion data and geological understanding,this paperestablished a shallow 3D geological-geophysical model of 3000 m.The deep distribution characteristics of Metallogenic related elements,mineralization modeland and favorable metallogenic area in Shuangjianzishan ore concentration zone will be discussed in this paper:(1)The Dashizhai formation,which provides the hosting space for magmatic hydrothermal mineralization,is mainly found in Shuangjianzishan deposit and the south area of baiyinnuore deposit.The thickness of Dashizhai formation in Shuangjianzishan deposit is uneven,the maximum thickness is less than1000 m,thinning from south east to north west.But the thickness of dashizhai formation in the south of baiyinnuoer mining area is over 3000 m.In addition,there is a hidden Dashizhai formation's anticline under the quaternary cover area in the south of Shuangjianzishan deposit.There is a large area of high resistance intrusive rock basement in the deep of Shuangjianzishan ore concentration zone.The porphyritic granite related to the mineralization of Xinglongshan ore section is not vertically intrusive and the underlying direction of the bedrock is south-eastern.(2)Shuangjianzishan is a typical epithermal magmatic hydrothermal silver-lead-zinc deposit with two main metallogenic periods in Mesozoic,it is closely related to porphyritic granite and occurs in argillaceous-silty slate of Dashizhai formation.In the late Jurassic,the porphyritic granite under the Xinglongshan ore section was highly emplaced below the shallow dashizhai formation,and the ore-bearing hydrothermal fluid was precipitated,deposited in the shallow ductile NW shear zone;In the early Cretaceous,magmatic hydrothermal fluid upwelling along the NE deep faults in the Shuangjianshan ore section,it was precipitated at the cross section of NE and NW faults,deposited in the shallow NE faults in Dashizhai formation's argillaceous-silty slate;(3)We also found two deep regions favorable for magmatic hydrothermal mineralization:the thick strata of Dashizhai formation located in the south area of baiyinnuore deposit,the hidden anticline of Dashizhai formation under the quaternary cover area in the south of Shuangjianzishan deposit.