Geological Characteristics And Ore-controling Structure Of Daiwangshan Gold Deposit In Aohanqi Of Inner Mongolia

“Gold deposits related to ductileshear zones"become the focus of present research and front field.Its metallogenic mechanism and Ore-forming model are paid more and more attention.Before Mesozoic Northern border area of North China craton experienced cratonization-rifting?archean-paleoproterozoic?,stable sedimentary stages?early Paleozoic?,accretion of arc-continental collision to the northern edge of North China craton?at the end of the early Paleozoic?,continental margin of Anden type?late carboniferous?.Since Mesozoic,Northern border area of North China craton?represented by yanshan area?underwent intracontinental compression orogenic stage,with intense tectonic deformation,multiple stage of magmatic intrusion and the corresponding volcanic activity,along with the corresponding gold polymetallic mineralization.It formed a series of closed folds,schistosition belt and giant ductile shear zones.the regional structural features are mainly NE and EW.Located in the east of chifeng city,Inner Mongolia,Dai wangshan gold deposit isand is in the north margin of north China craton.The formation of gold deposits is closely related to the evolution of regional structure.The gold deposit is formed in the continental?plate?orogenic phase,which is closely related to the large folds and ductile shear in the region.Research area belongs to part of Shijianggou synclinorium???of Aohanqi synclinorium???.Regional gold deposits are control by the folds.Later,tectonic stress is transformed into the right shear,forming a series of NE-ductile and brittle-ductile shear zones.These ductile shear zones play an important role in the formation of the gold metallogenesis.In this paper,through the comprehensive analysis of regional geological data and combination of exploration achievement,based on the field work and the comprehensive geological characteristics of gold ore-body.Meanwhile,the structural styles and distribution rules of the brittle-ductile shear zone were investigated,and the relevant test and analysis were carried out by collecting the relevant optical wafer,probe slice and oriented thin section.This paper studied the deformation of shear zone,analyzed the feature of geometry and kinematics characteristics of shear zone.This paper focuses on the microstructure and the distribution of the veins in the brittle-ductile shear zone.Main progresses and achievements are as follows:1.At present,there are 79 ore bodies in the mining area,among which the?1???2???3?-ore body are the main ore bodies.The ore bodies are controlled by the Bd1 brittle-ductile shear zone and its secondary fractures.Layer-like or lenticular ore bodies occur like a discontinuous north east vein.The individual orebody has the characteristic of wavy bending in the flat and section,and the local swelling contraction phenomenon.The main host rock is mainly composed of metasandstone and sandy slate,and the second is andalusite-slate.and red column petrifaction.The wall rock alterations are not strong,and mainly include:sericitization,limonitization,hematitization,silication,pyritization and carbonation,graphitization and alteration of and andalusite.2.The ore minerals are mainly composed of natural gold,limonite and pyrite.Gangue minerals are mainly mainly composed of quartz and clay minerals.grain size of natural gold is dominated by fine grain-particles,and medium-and coarse-grained mainly in high grade ores.There are two important existing form of gold in the ores:crystal interface-gold and crack-gold,followed by free gold and a small amount of inclusion gold.Ore texture mainly includes cataclastic structure,metasomatic relict texture,hypidiomorphic gra-nular texture and solid solution separation texture.The structure of ores mainly includes vein structure,veinlet disseminated structure and meshvein structure.The grade of gold ore is closely related to pyrite.Pyrite with rich gold is light yellow,yellow,dark yellow,but yellow white with low gold content;the content of pyrite and gold grade was positively related;gold-bearing properities of pyritohedron is better than the cube;the pyrite with complex crystal shape,subidiomorphic and xenomorphic,the fine grain,fracture development are gold enriched.Pyrite or its oxide?limonite?with vesicular,banded,disseminated,stockwork structure are gold enriched.3.The early stage of structural deformation is mainly fold deformation.There are four alternate anticline and syncline,of which the f₃ syncline is closely related to the gold ore body.The direction of the f_3-axis is generally NE.But the direction turn to south in the east of the Baishan valley,and the direction of the f_3-axis is generally EW or NWW.The main orebodies are located in the brittle-ductile shear zone,which locate in the SE-flank and turning point transition of f3-fold.Two brittle-ductile shear bands?Bd₁and Bd₂?are found in the mine area,and the distribution direction is approximately the same as that of the fold.The Bd1 brittle-ductile shear zone controlled the location of the gold ore body.The direction of f3-fold is NE,the width is 40¹00m.The plane distribution pattern of Bd1 brittle-ductile shear zone is slightly wavelike"S".In the west of the Baishan valley,the direction is 30°⁴0°,and the east is about 100°,and the mainly inclination of the shear zone is NW,angle of inclination is 50°⁶0°.4.The high strain zones and low strain zones are alternating distribution in the ductile zone,which is evident in the vertical dimension.NE-trending tectonic schists are maimly in the surface,downward mylonitization-rocks and protomylonites,medium mylonite,and ultramylonites are rich in deep.there is a large amount of directional elongated rhomboid andalusite-porphyroclsats in the tectonic schist,and the local andalusite-microboudin and undulatory extinction and subgrainsof quartz.mylonites and ultramylonites are in the deep level.There are three kinds of dynamic recrystallization grain of quartz?bulding recrystallization,subgrain rotation recrystallization,and grain boundary migration?.A lot of stretching lineation and andalusite-growth lineation,asymmetric rotational augens in deformed limestone,andalusite-porphyroclsats in mylonite,asymmetric andalusite?sericitization?fish,andalusite-bookshelf structure,bookshelf-microfracture of quartz-subgrain,all these macro and micro structures indicates the direction of the ductile is dextral shear.5.gold veins in brittle-ductile shear zone are mainly D-type?parallel to shear zone boundary?and R-type?15°to shear zone boundary?.quartz vein types with higher grade gold throughout are located in the"S"part of the brittle-ductile shear zone.its thickness is generally smaller;The higher thickness of the altered rock vein usually occurs in the area where the trend is same,and its grade is smaller.There is change rule in the vertical direction.Deep-level ductile shear is unsuitable to gold mineralization,where temperature is very high and ultramylonites are rich.So golf-element is generally moved out of the area.In the medium-shallow level,there are rich of mylonites and tectonic schists.ore-forming elements,where can be divided into three subregions,corresponding to three types of gold mineralization:deep under ductile-brittle transition area formed mylonite,easy occurrence mylonite-ype gold vein;for low temperature transformation near ductile-brittle transition area,easy occurrence altered rock type gold vein;The near surface is mainly suitable to quartz vein type deposit.