The Ore-controlling Factors And Prospecting Directions Of The Daxiyingzixi Gold Deposit In Chifeng Region,Inner Mongolia

The Daxiyingzixi gold deposit,which is a newly discovered one in the Chifeng-Chaoyang gold concentration area,is situated in the eastern part of the northern margin of the NCC(North China craton),its northern neighbor is Chifeng-Kaiyuan fault and Xing-Meng Orogenic Belt.However,its characteristics of basic geology and ore-forming fluid,regularity of mineralization and enrichment,mineralization age and genesis are lack of systematic research.Based on previous research,this thesis draws on field investigation together with sample testing and analyzing to study the geological characteristics,alteration types and fluid inclusions in an attempt to understand the ore-controlling factors and prospecting directions of the Daxiyingzixi gold deposit.The main strata of this deposit is Manitu formation,which is mainly composed of pyroclastic rock,volcanic lava,volcanic-sedimentary rock and subvolcanic rock.The intrusions are dominated by Paleo-Proterozoic metamorphic intermediate-acid rocks and Late Jurassic fine-grained granite porphyry.This area has well-developed NNE faults and widely distributed structural breccia belts and cataclastic rocks which clearly controlled the gold mineralization.Most mineralization bodies fill the tension-shearing or shearing fractures presenting as fine veins.The main ore minerals in this deposit are galena,sphalerite,chalcopyrite,natural gold and covellite,the main gangue minerals are transparent minerals and minor amounts of pyrite,pyrrhotite,marcasite and arsenopyrite.The hypidiomorphic and xenomorphic granular textures are the main ore textures,and vein,mesh-vein structures are the main ore structures.The wall rock alteration includes potassic(the most common one),silication,sericitization,albitization,carbonation,kaolinitization.The analysis results of the fluid inclusions in quartz indicates that there are two homogenization temperature ranges: 200??225??270??280?,the peak values of the pressure range from 10 bar to 25 bar,which mean a low-medium temperature,low pressure metallogenic condition.Study on the characteristic spectra of altered minerals shows that there are two major altered mineral assemblages,the illite-montmorillonite-kaolinite-halloysite-muscovite association usually appears in the Au enriched area,and the illite-montmorillonite-kaolinite-chlorite association generally appears at the upper part of the Au enriched area.The Late Jurassic Manitu formation is the main ore-hosting rock in the Daxiyingzixi gold deposit,but the mineralization shows no obvious selectivity for the type of surrounding rock.Connecting with previous researches,we infer that the ore-forming fluid was mainly derived from magmatic water formed by deep seated crust-mantle magma mixing process,with part of atmospheric water.The older basement rocks with high Au abundance,strong magmatic activities during Late Jurassic and widely developed faults are the main ore-controlling factors in the study area.Combined with the results of geophysical exploration,geochemical exploration and 3D modeling,we suppose that the NW side of this exploration district,especially the area close to the NNE fault zone,possess of better potentials for prospecting.