Comprehensive Information Prediction Of Lead-zinc Deposit In Naganchu Inner Mongolia

The study area is located in Wuerqihan-Wunuer Paleozoic upwelling area within Elunchun Variscan fold belt in the medium to north section of Great Khingan,the junction of ancient Asian Plate and Peri-Pacific Plate.Through combined action of the evolution of Paleo-Asian tectonic domain in the early Mesozoic and Peri-Pacific tectonization and magmatism in Mesozoic-Cenozoic,the region evolved to form an extremely complex tectonic setting,which provided favorable ore-forming geological conditions.In this paper,the geological features of the deposit are summarized and the genetic type of the deposit is determined.Based on the comprehensive information mineral prediction theory,the metallogenic regularity and prospecting criteria are summarized according to the existing geological,geophysical and geochemical data,and the comprehensive prospecting information of lead,zinc and copper deposits is extracted,the prospecting target area is delineated and the prospecting direction is put forward.In the study area,the stratum of medium-upper Daminshan Formation in Devonian system is the major ore-bearing horizon,containing rock types as follows: silty slate,fine slilty slate,argillite,argillic-silty slate,sericite slate,metamorphic sandstone,feldspar quartz sandstone,siltstone,dacite lithic crystal tuff lava.Intrusive rocks in the area are complex,which along NE and near EW distribution,intrusively contacting with the lithostratigraphy of Daminshan Formation.There are mainly include subvolcanic rocks(porphyry)and late vein rocks.There are quartz porphyry,fine-grain granite and fine-grain diorite on the surface and biotite plagiogranite and subrhyolite rock in deep drilling holes.The fracture structure is developed,the NNE trending structure has a certain ore guiding effect,and the near East-West structure is the main rock controlling and ore controlling structure.The plumbum-zinc ore(chemical)body mainly comes from the medium-upper Daminshan Formation in the Devonian system outside the beresitization belt,reserved in the structural fracture zone of silty slate,sericite slate,metamorphic siltstone and lithic crystal tuff and the diorite vein.Copper ore(chemical)body is located within the beresitization belt,originating in quartz porphyry and plagiogranite,and closely related to porphyry and relevant hydrothermal activities.In the deposit,metallic minerals include galena,sphalerite,chalcopyrite,limonite,pyrite,magnetite and arsenopyrite,and alteration includes sericitization,silication,chloritization and carbonation.The horizontal zonality of mineral alteration fully indicates the study area is in a close relation with mineralizing subvolcanic rocks and porphyry after multi-stage magmatism and hydrothermal activities.The formation of Naganchu plumbum-zinc deposit includes two stages.In Neopaleozoic,the Devonian system consisting of neritic facies clasolite and carbonatite provided abundant metallogenic materials through neutral-acid volcanic activities.During contact,contraction and closure of Zhongchao ancient plate and Siberian plate,post-orogenic granite rich in cooper,plumbum and zinc was formed to provide sufficient sources of ore and heat for deposit formation.The late-magmatic vein rocks and subvolcanic rocks with metallogenic materials invaded along faulted structure and cracks in layer.With chemical and physical changes,a large amount of gas-water hydrothermal separated out while magma condensed,which formed a convective circulation with meteoric water and interlayer water,leading to large-scale hydrolysis(beresitization).During this period,the copper ore body was formed in the beresitization belt.At the end of lava crystallization,low-temperature ore-forming fluid infused the weak zones on the side and top of beresitization belt to form lean and zinc ore(chemical)body.In Mesozoic era,magma was active in the structure.Rising magmatic temperature activated ore-forming elements.Multi-difference vein rocks and subvolcanic rocks rich in ore-forming materials invaded the mineralized alteration zone,which transformed the ore(chemical)bodies formed in early stage through combined effect.After multi-stage magmatic intrusion,a complex beresitization alteration zone,leading to the deposit containing Pb,Zn,Ag and Cu.Accordingly,Naganchu Pb-Zn deposit is a medium-low temperature hydrothermal deposit associated with subvolcanic rocks and porphyry.According to synthetic studies,prospecting criteria are established.Pb-Zn prospecting criteria: in Daminshan Formation,silty slate,argillite,metamorphic siltstone,crystal tuff are the prospecting criteria for Pb-Zn deposit,while the rock structure fracture zone is the direct prospecting criterium;silication,carbonation,ferritization and pyritization are the signs for mineral alteration;medium-high abnormal polarizability of IP intermediate gradient and resistance is the geophysical indication for prospecting Pb-Zn ore(chemical)body;Pb,Zn and Ag high-value anomaly is the geochemical prospecting criterium.Cu prospecting criteria: in the beresitization belt,the stratum of Damashan Formation and the intrusive position and structural fracture developing position of subvolcanic rocks(porphyry)or vein rocks are the favorable sections for ore prospecting;silication,sericitization,beresitization and pyritization are the signs for mineral alteration;high abnormal polarizability of IP intermediate gradient and low resistance indicating the position where metal sulfide accumulates is the geophysical indication for prospecting;Cu,W and Bi high-value anomaly is the geochemical prospecting criterium.According to ore-forming geological conditions and characteristics of prospecting criteria development,2 Grade I targets and 3 Grade II targets in the study area are set.The prospecting potential of the Nacanchu lead-zinc deposit is evaluated and the prospecting direction is determined,which provides the basis for the follow-up investigation work in the study area.