The Study Of The Geological Characteristics And Enrichment Regularities Of Mineralization Of Chiweigou Deposit In Wangqing County, Jilin Province

Chiweigou Gold Deposit is located in Wangqing County of Jilin Province.It is atypical epithermal gold deposit in Yanbian area. The scale of the deposit is small with atotal gold metal quantity of6453kg. It is considered as a small deposit. The tectonicposition is located in the eastern margin in Xingmeng orogenic belt.It locates to the eastof the Dun Mi fault and to the north of Fuer river-Gudong River fault, which belongs tothe active continental marginal of Pacific Rim.Chiqweigou Gold Deposit is located in Yanshannian gold and copper metallogenicbelt of Yanbian area in Jilin province. There are complex and frequent tectonic andmagmatic activities so the metallogenic geological condition is well. Mining area stratumsare mainly simple metamorphic rocks of Kedao group, Tuntianying group and Chiweigougroup of late Jurassic and Jingouling group of early Cretaceous. The main rock types ofKedao group are tuffaceous slate and tabular sandstone; Late Jurassic-Early Cretaceousformation is a set of acid volcanic rocks slag and volcaniclastic rock. The vocanic rocks ofJingouling group have the closely connection with mineralization, and it is the mainbeaing ore rock. The main rock types are andesitic tuff, tuff breccia, andesitic agglomeratebreccia, andesite and andesitic lava. This study finished zircon U-Pb dating in andesitictuff, with a diagenetic age of127.7±6.3Ma, determining the diagenetic age of earlyCretaceous. The tectonics in the ore field is dominated by the faults, mainly for NNE, NEand NW trending.There are three ore veins in the mining area named I, II, III vein and7orebodydelineated. The orebody is strictly controlled by NNE-NE trending faults and exist directly in the quartz-carbonate veins showing its neutral-in reducing environment. Ore bodiesexist in volcanic rock of Jingouling group on the the Permian and early Cretaceousunconformity surface but there is no ore contained in the simple metamorphic rocks underthe unconformity surface in the Permian; the vertical extension of the body is small. Thetrends of the ore bodies are NNE-NE and they are mainly vein and cystic shaped.The ore type is low sulfide quartz-calcite vein type; sulfidition is less than1%. Oreminerals are mainly pyrite, electrum, gold, and Limonite etc., containing a small amountof chalcopyrite, tetrahedrite, and galena minerals. The average grade of ore is4.5×10-6.Ore textures are mainly euhedral to subhedral-granular texture and xenomorphic granulartexture, metasomatic texture, poikilitic structure, crush structure and pseudoform structure;the main ore structures are sparse disseminated structure, disseminated structure, fine (net)vein, drusy and brecciated structure. The wall rock alteration are mainly silicification,orthoclase, sericitization, carbonation, fluoritization, chloritization and propylitization etc..We determined the ore deposits are mainly experienced hydrothermal mineralization andsupergene oxidation metallogenic period, and the hydrothermal stage can be divided into4stages: Ⅰ.Quartz-adularia stage, II. Coarse grained calcite stage, Ⅲ. Fine grainedcalcite-quartz-adularia-gold stage, Ⅳ. Quartz-chalcedony-calcite stage, the Ⅲstage is the main mineralization stage.Fluid inclusion study indicates that, inclusion type of quartz and calcite in ore ismainly the gas-liquid phase type, the gas-liquid ratio is relatively small, mainlyconcentrated in the10-25%. The main mineralization fluid has the characteristics of lowsalinity (1.2-2.4wt%NaCl), low density (0.84-0.90g/cm3);The metallogenic temperature is180-230℃and the forming pressure is15-20MPa, showing the characteristics of lowtemperature and low pressure;The metallogenic depth is1.5-2km, which is characteristichypabyssal. The hydrogen-oxygen isotope study of quartz in ore indicates that theore-forming fluids were mainly derived from meteoric water. Sulfur, lead, strontium,carbon stable isotope studies show that the mineral is mainly derived from upper mantle orlower crust. So we determine the genetic type of Chi Wei Gou Gold Deposit is poorsulfide-low sulfidation-epithermal vein type gold deposit. Mining area stratum is mainly simple metamorphic rocks of Kedao group,tuntianying group and Chiweigou group of late Jurassic and Jingouling group of earlyCretaceous. It does not contain ore minerals in the Permian simple metamorphic rockunder the unconformity surface. Orebodies dip with the unconformity towards north east,the distance between bottom boundaries to the unconformity surface is150-200m, andthey are approximately parallel. The deposit is composed of a series of small ore bodiesand it is difficult to find a large continuous orebody. The direct extension and verticalextension are both not more than500m.The ore body of Chi Wei Gou Gold Deposit is controlled strictly by fracturestructure. The ore controlling faults in mineralization period expression is left normalfaulting. The industrial ore bodies exist in the local extensional parts which deviate fromthe north in the direct extension and have steep tendency (near vertical). The industrialorebody pitch overall the direction of NE with a pitch angle of20°-30°. The orecontrolling fracture no matter in trends direction or in depth is undulating. As a result,favorable structural positions which the industrial orebody exists reproduce in spaceaccording to a certain rule so as to control the gold mineralizational enrichment section.The central and southern area exists3NW trend the faults after mineralization (F4,F5and F6), and the gold veins (body) have different degree of cutting and damage by them.The F5fracture has the largest scale and it is north-west extended and north-east dip. TheNW structure after mineralization has the reversed fault properties.The effect of F5fault-the NW trend after mineralization makes that I and II vein vein plane have been broken onplane in both sides of the fault F5near the21line andⅠ and Ⅱ vein which dipoppositely in the lower plate over F5tend to move to the opposite dip direction. We candetermine that south-west of the fault relatively declined, so there may be concealed orebody in the southern tip deep of veinⅠand Ⅱ with further ore prospecting potential.Study on metallogenic structures provides useful information to find the deep (edge)orebody.With the Au/Ag ratio we can determine the position of the orebody, evaluate deeplyand prospect on the surface.We select ore from I vein in220m,180m,180m under ground to analyse Au/Ag ratio and the results were0.46,0.67,0.60showing that with the increaseof depth, the Au/Ag ratio increased; With the predictial regulation that orebody pitch north,we predict that, there may be concealed orebody and has great potential to the north of the16line and under the180m of vein Ⅰ. Ore from Vein Ⅱ from surface, subsurface downto540m,540m down to500m,500m down Au/Ag ratio get the result:>>1,0.85,0.62,0.61,0.42,0.41, Au/Ag ratio is gradually decreased, we predict that there is noprospecting potential.On the base of the comprehensive analysis of ore controlling structure, the spatialdistribution of ore controlling fracture dynamics characteristics, ore body spatialpositioning mechanism and the lateral trending law mineralization enrichment regularityand concerned with transformation and influence within the mining area, combined withthe post mineralization fracture, and analysis of information and Au/Ag ratio in theextraction of primary halo, we think there are favorable metallogenic section in the southdeep of vein Ⅰ and Ⅱ and the north deep of vein Ⅰ.These position have greatprospecting potential.