The Application Of Integrated Geochemical Exploration Methods For Minerals Prospecting In The Grassland-covered Area Of Xinbaerhuyou County Of Inner Mongolia

Geological prospecting in coverage areas has been a difficult and hot issue of the geological work,and using integrated geophysical and geochemical methods and techniques to obtain the mineralization information laid underneath the depth of the coverage areas would be the key to geological prospecting in the future.Because the rock is less exposed, water system is poorly developed,the covered layer is thick,and aeolian sand is interfered obviously on surface in the grassland-covered areas,using conventional methods such as the stream sediments and soil geochemical surveys to carry out mineral exploration can't get a satisfactory results.The unconventional geochemical methods such as soil heat-released mercury survey, soil electro- conductivity survey, speciation analysis of elements in soils, geogas survey etc are characterized by strongly pertinency, simple and direct measurements among some of them in the field,therefore,they are paid extensively attention and application for geological and exploration sectors in domestic and abroad,and it gets good effects when they were used in covered areas for geochemical prospecting of Au,Ag,U and oil-gas etc.This paper,selected a mineral prospecting area in the grassland-covered area of Xinbarerhuyou county of Inner Mongolia as the test area,carried out the methods of the soil geochemical survey, the soil electrical conductivity survey, the soil heat-released mercury survey and the soil speciation analysis of elements survey in test area,on the basis of condition trail for soil sampling depth,the sample granular to be processed and the feasibility of above methods in a known mine area,and finally portrayed 1 area for the potential prospecting area by the results of various methods and the extent of overlaid of various anomalys.The research methods and some considerations of the paper may have a significance to Xinbarerhuyou county of Inner Mongolia as well as in some other areas.1. Regional characteristics of geography,geology and geochemistryThe research area is located in Xinbarerhuyou county of Inner Mongolia, it belongs to the semiarid grassland-hill landscape and grassland-covered area.The coverage layer of the area is mainly composed of grass and eluvial layer (the calcic-accumulated layer is 30cm to 60cm below the surface). The soil type was chestnut.The area is suited at Manzhouli anticlines in the Da Hinggan Mountains folded belt,and also the west side of Eerguna-Hulun fault zone with striking northeast.The mainly exposed stratum in this area is the Tamulangou Formation and Kuli Formation of Jurassic,and strata of the upper Proterozoic,Paleozoic and Cenozoic are sparsely exposed.The regional magma activity is frequent,igneous rocks can be divided into the stages of late Hercynian, early Yanshannian and late Yanshannian.The main rock types are granite,granitic porphyry, rhyolitic porphyry,and of which the subvolcanic porphyry rocks are closely related to Cu, Ag polymetallic mineralizations.The metallic ore resources in this area are enriched,and many large and medium-sized Cu,Pb,Zn,Ag,Mo ore deposits have been found.The genetic types of the ore deposits mainly are of porphyry, subvolcanic epithermal and skarn ones.2. Soil geochemistry and its geochemical anomaliesThree soil profiles were selected in the mining area to test the soil sampling depth and the soil sample processing granular, and it was confirmed that the depth for soil sampling was 50cm to 60cm below the surface,and the grain size was 80 to 100 mesh.The density of soil samples were collected with 14.71 samples / km². AES,atomic fluorescence spectrometry and ICP were used to analyze the elements of Au, Ag, Cu, Pb, Zn, As, Sb, Bi, Hg, Mo, Sn, Co, Ni, Cr, V, Ti, Mn, Be, B in soil samples,the analytical data were processed with SPSS software. The Pb, Be, Sn, Ag, B, As, Bi etc were enriched in soils, Mn, Au, Hg, Cr, Cu, Ni etc were depleted in soils.Exception to Au, Ag and Mo which were unevenly distributed in soils,the others were evenly distributed,which was basically accorded with the geological fact.Through the factor analysis,the six factors were gained,and different factors represented the geological signifycan -ce.Among the six factors,F1(Cr-Ni-Co-V) and F2(Mn-V-Ti-Zn) were diagenetic factors,F3 (Pb-Zn-Au), F4(Mo-Sn-Ag) and F6(Cu-B) were factors related with mineralizations,F5(As-Sb-Hg) was factor to indicate the mineralizetion.27 anomalies,with the area larger than 0.25km²,of single element were portrayed in the study area.According to the coexisting of elements and the overlaid extent of anomalies of single element,portrayed and graded 3 integrated anomalies.Among of them,the A-1 anomaly was first grade,and its acreage was about 2.05km².The element association was Ag^2.9-Au^1.2-B^1.3- Sb^0.4-As^0.21.The superposition among single element anomalies in the integrated anomaly was good,the distribution of the concentration centre of single element anomalies was basically consistent.The overlaid extent of these elements indicated that the mineralization with the anomaly belonged to Au, Ag hydrothermal mineralization.This anomaly was in the Cu-Ag anomaly previously circled by lithogeochemical survey.The A-2 integrated anomaly was the second grade,and its acreage was about 0.8km2. The element association was Au0.6-Ag0.4-Sb0.4-Mo0.11-Bi0.1.In light of the association and distribution of elements,it was deduced that the mineralization related to the anomaly belonged to Au, Ag hydrothermal mineralization in contact zone,accompanying the weak Mo mineralization. This anomaly was in the Mo-Bi anomaly previously circled by litho- geochemical survey.The A-3 integrated anomaly was second grade too,and its acreage was about 2.1 km². The element association was Bi1.2-Zn0.9-Cu0.6-Mo0.6-Ag0.5-As0.4 -Au0.2.From the characteristics of the elements association, the mineralization belonged to Zn, Cu, Mo, Ag hydrothermal mineralization.This anomaly was also in the Mo-Bi anomaly previously circled by litho- geochemical survey.The major mineral associations in the soil of the study area were feldspar and quartz,and plagioclase was predominated in feldspar.Calcite and cristobalite also existed in some individual samples. The clay minerals were mainly illite, chlorite and kaolinite.Through researching of the relationship between the mineral composition of soil and the elements content, the content of clay minerals in soil samples from the anomalous areas were generally higher than that from the background areas,implying that the absorption of clay minerals had some impact on the enrichment of elements .3. Soil electrical conductivity,the soil heat- released mercury,the speciation analysis and their geochemical anomaliesFour profiles were selected in the mining and non-mining areas for the condition trial before the soil electrical conductivity survey, the soil heat-released mercury survey and the specition analysis survey were carried out, it was got that the grain size of soil samples was 120-140 mesh,the stirring time to test soil electrical conductivity was 1 minute,the optimal temperature for the heat-released mercury was 800℃.On the basis of the conditional experiment,the feasibility study of the soil electrical conductivity survey, the soil heat-releasted mercury survey and the speciation analysis survey was carried out in the mining area.The relation between the soil electrical conductivity,the soil heat-released mercury and the orebody position was very clear.Above the main orebody,the soil electrical conductivity and the soil heat-released mercury were higher,and both anomalies were distinct.While it away from the main orebody,the soil electrical conductivity and the soil heat-released mercury were lower,which reflected that there were no mineralization underground or the degree of mineralization was lower.All these suggested that the soil electrical conductivity and the soil heat-released mercury are possible to reflect the existence of the underground orebody or fault zones,therefore,both can be used to prospect silver polymetallic ores.Through the comparison between the content of the mobile form of elements in mining area and non-mining area,it was suggested that the element content extracted with water and soil adsorbed elements of the soil samples in the mining area were higher than those in non-mining area except to Pb,which indicated that the speciation analysis can be used to distinguish to the mining area from non-mining area.Through the statistical analysis,the correlation coefficient of the soil electrical conductivity and dissolved Cu, Pb, Ag were larger than 0.4. The soil electrical conductivity,the heat-released mercury and most of the speciation analysis had inverse correlation.The correlation between the two mobile forms of elements was also about 0.4.With the lower anomalous limit,3 soil electrical conductivity anomalies were circled, their acreage were all larger,the anomaly zonings were very clear,and the distribution of the concentration centres often along with the fault zones or the contact zones among various rocks. In addition, 7 dissolved anomalies and 10 clay-adsorbed elements anomalies were also portrayed, the overlaid of them was good, and the scale of Cu and Ag anomalies was relatively larger.All the anomalies were mainly located in the granite or monzogranite.The soil heat-released mercury anomaly was negative anomaly,which also was distributed along with the fault zones.According to the superposition of the single element anomalies of soil electrical conductivity , dissolved Cu, dissolved Zn, soil-absorbed Ag, soil-absorbed Cu, soil-absorbed Pb, dissolved Pb, dissolved Ag, soil-absorbed Zn ,one integrated anomaly with exploration potential was portrayed, that is, X-1 integrated anomaly.Its acreage was about 7.5 km2.Through the anatomic analysis for the integrated anomaly, could elicite that the various single element anomalies of the integrated anomaly were generally distributed along with the contact zones among of the rocks,fault zones or in the vicinity of dikes,the degree of the superposition of the concentrated centres were also good,especially near the fault zone,most of the anomalies had a clear zoning,and the high value points were basically distributed in this area too.The extensively distributed soil electrical conductivity anomalies show that a great deal of metal ions were enriched in the anomaly area;the heat-released mercury anomalies was explained that the anomalies was formed on fault zones,the mineralizing possibility was great.The contrast of the speciation analysis were all exceeded 1,which may imply that using the dissolved elements measure and soil-absorbed elements measure can intensify the anomaly,and the mobiled metal ions were generally from the underground orebody,which can also be used to determine ore types.The influence of mineral compositions in soil on the soil electrical conductivity, the soil heat-released mercury,and the speciation analysis was studied.The content of the clay minerals were relatively higher in anomaly areas,and that of clay minerals were generally lower in the background,which also suggested that the content of clay minerals had a certain effect on soil electrical conductivity, the soil heat-released mercury and the speciation analysis.One exploration potential area was confirmed by overlapping among the surveies of soil geochemical, soil clectrical conductivity,soil heat-released mercury and speciation analysis in the study aera. On the basis of summarizing and contrasting the characteristics of the anomalies,it can conclude that it is feasible to get the new approach of fast exploration in semi-arid grassland coverage areas,that is using soil electrical conductivity survey to circle anomaly scope,using speciation analysis survey to intensify anomalies and determine ore types,using the surveies of soil heat-released mercury or soil electrical conductivity or soil geochemical to find faults or mineralizing alteration.