Geological Characteristics And Prospecting Prediction Of Erdui Exploration Area,Nenbei Farm,Heilongjiang Province

The study area is located in the south margin of Zhalantun-Duobaoshan island arc belt of the Greater Khingan basin system in Xing'an massif,which belongs to the ore-forming subbelt of Cu,Au,Mo and W in Duobao Mountain.It is one of the areas which show a greater potential of ore-prospecting among the ore-forming belts in Heihe tectonic plate of Hegen Mountain.The author reorganized the existing geological,geophysical prospecting and geochemical prospecting data in the exploration area,analyzed the ore-forming background and ore-forming geological conditions and summarized ore-forming characteristics and ore-prospecting indicators on the basis of previous ore exploration and research works.A ore-forming model and a ore-prospecting model were purposed to delineate the ore-forming prediction area and illustrate the deployment scheme of additional prospecting works.The results of this thesis indicate the following,The gold mineralization in this area is characterized by gold-bearing polymetallic sulfide alterated rocks and altered belts,which are mainly hosted in the diorite-porphyrite vein and its contact zone with mylonitize granite,mylonite or sericite schist of Dawangzi formation.The ore-forming is mainly controlled by dioritic porphyrite,sericite schist of Dawangzi formation,NE-trending ductile shear belt and brittle structures,which constitute the major geological conditions for the gold ore formation together.The gold ores mainly are the gold-bearing polymetallic sulfide alteration rock type,and the gold-bearing sulfide altered quartz dioriteporphyrite type and the sulfur compound quartz vein type take the second place.The metallic minerals in ore are mainly composed of pyrite and chalcopyrite,followed by sphalerite,bornite and magnetite.The gangue minerals are mainly composed of quartz,anorthose,potassium feldspar,chlorite and calcite.The texture of ores are mostly euhedral-subhedral granular and metasomatic,and the disseminated structure dominates.The wall rock alteration mainly consists of silicification,ferritization,low muscovitization,chloritization,carbonatation and pyritization,and silicification and pyritization are the major prospecting indicators.The field observations along with the microscopic identifications indicate two epoches and four stages of mineralization.The hydrothermal period includes pyrite-quartz stage,quartz-sulfide stage and carbonate-quartz stage,and the quartz-sulfide stage is the primary ore-forming stage.The geochemistry characteristics of the rocks show that dioritic porphyrite,diorite and granite are all high-K calc-alkaline rocks or calc-alkaline rocks,which indicates that the magmatic source contains high-and middle-maturity continental materials.Moreover,the granite shows characteristics of mantle-crust migmatite,and the diorite and dioritic porphyrite show characteristics of mantle-derived rocks.The diagram for discriminating tectonic settings indicates characteristics of syn-collision volcanic arc granite.The rock-forming age and ore-forming age analyses indicate that the ore-forming within the study area occurred in the late early Cretaceous(~116Ma),which could be a sign that the ore-forming was closely related with the subduction of Pacific plate in the early Cretaceous.The ductile shearing in the early Jurassic had prompted the preliminary enrichment of ore-forming matters in this area.Thereafter,the mantle-derived magmatic fluid in the early Cretaceous epoch had carried abundant ore-forming matters into the study area,and the ore-forming gradually developed.In addition,previous studies indicate a typical medium-low temperature hydrothermal gold deposit in the study area.The geochemical fields of Au,Ag,Pb and other elements in the study area are high,moreover,there are strong variations in Au and Ag.The results of cluster analysis and factor analysis indicate two stages of Au mineralization.The anomalies of multiple metallic elements,such as Pb,Zn,Mo and W,could be applied as the soil geochemical prospecting indicators for the corresponding elements in this area.In the light of soil geochemical characteristics,sixty-nine single element anomalies were identified in total.Eleven anomalies of Au were included,among which six were high value anomalies,three were secondary anomalies and two were low value anomalies.The evident high-contrast high value anomalies of Au in the concentration centers form the most immediate indicators for Au deposit.Five composite anomalies were identified,among which the anomalies of HT-1 and HT-5 were provided with better matching and stronger anomaly.The author performed reduction to the pole analysis,extension and resolution of the high magnetic measurements,and twenty-eight lineaments,eleven circular tectonics were interpreted.The results indicate that the NW-trending and the NE-trending tectonics form the fundamental tectonic settings in the ore-forming area;C1 and the central parts of,C8,C10 and C11 circular tectonics are the most probable ore-forming areas,in particular the conjunction areas between lineaments and circular tectonics.The results of IP intermediate gradient measurements indicate that high resistivity and high polarization and local low resistivity and high polarization are the major ore-prospecting indicators for gold deposit in the study area.On the basis of analysis of deposit geology and geochemical characteristics,deposit formation factors were indentified.Moreover,a ore-forming mode and a prospecting model were purposed to delineate two first-level ore-forming prediction areas(?a and ?b)and one second-level ore-forming prediction area(?a).Meanwhile,the results of this thesis illustrate the deployment scheme of additional prospecting works.