Metallogenic Mechanism And Location Prediction Of The Aobaotu Lead-zinc-silver Polymetallic Deposit In The Southern Great Xing’an Range,Inner Mongolia

The thesis takes the Aobaotu survey area（about 80km²）as the research scale.For deep and peripheral prospecting in the Aobaotu deposit,the research includes the metallogenic mechanism and the extraction of geological,geophysical,geochemical information of ore prospecting and aims to evaluate the prospecting potential of deep porphyry mineralization,to conduct deep location prediction on the vein-shaped ore body which is controlled by structure,and to evaluate the prospecting potential of the outside known ore body.The main understandings and achievements are as follows:（1）The Aobaotu deposit is a hydrothermal vein deposit which is controlled by faults.It is closely related to the late Jurassic I-type granitic rocks,the sulfur originated from deep magma,and the ore lead is of the mixed source of crust and mantle,which is closely related to magmatism.The ore-forming fluids is characterized by medium temperature and almost originated from magmatic hydrothermal fluids with the addition of atmospheric precipitation in late stage.The granodiorite porphyry,ore-forming parent rock,formed in 140.0-155.7 Ma,which experienced full crystallization and differentiation.Both the ore-forming parent rock and the supporting fault structural system played a decisive role in the mineralization.It is speculated that there is a large-scale granodiorite porphyry basement in the deep,and the possibility of"upper vein lower body"metallogenic structure can not be ruled out.The rhyolite porphyry formed at 169.9 Ma is an important source rock in the study area.（2）The geophysical information is extracted as follows:（1）The electric characteristics of ore body is medium-high polarizability with low resistance,and the mineralized rock is high resistance with high polarization.The gradient zone in which the apparent resistivity and apparent polarizability of conventional IP sounding correspond well with the vein-like ore（chemical）body.（2）A total of 4 types,6 major anomalies and 10sub-anomalies were resolved by the 1:10,000 ground high-precision magnetic survey.The magnetic survey ofⅠ/Ⅱore belts have obvious abnormal reflection,and then,transformation and processing of magnetic measurement data by various methods:the position ofⅡore belt,which is a high positive anomaly area,has a clear gradient,and the output part of the ore body is NW-beaded shaped and banded positive anomalies are accompanied by beaded and clustered negative magnetic anomaly mosaics,and intervals appear.TheⅠore zone is located between low and slow clustered positive magnetic anomalies and clustered negative magnetic anomalies,and the gradient is slower.The upward extension is reflected in the existence of large strong magnetic geological bodies in the deep part of the eastern end of theⅠ/Ⅱore belts,which is a reflection of deep intrusions.（3）A total of 4 high-density anomalous bodies and 7low-density anomalous bodies were surveyed with a 1:10,000 gravity sweep.The range of high-gravity anomaly G-4 coincides with the known height ofⅠ/Ⅱore belts,So it is speculated that the four high-density anomalies are ore-causing anomalies,and the seven low-density anomalies are local geological units of hidden intrusions or rhyolite porphyry.（3）The geochemical information was extracted as follows:（1）In terms of the primary halo-vertical domain:Hg-Sb-As-Cd-Cu-Bi-In-Sn are important element assemblages for ore-prospecting;The primary halo axial zoning sequences ofⅠ/Ⅱore belts indication of reverse zoning with multi-stage hydrothermal superposition.There are two upper and lower mineralization enrichment belts inⅠ₆ ore body,the second mineralization enrichment belt exists below the elevation of 260m,and the dizziness of the lower mineralization enrichment belt is superimposed on the tail halo of the upper mineralization enrichment belt;Ⅱ₁ ore body has two upper and lower mineralization belts,the second mineralization enrichment belt metallogenic center is below 260m.The scale of no（weak）ore between the second mineralization enrichment belt and the first mineralization enrichment belt is about 160～180m.（2）Secondary halo-plane domain aspects:W,Sn,Mo,Bi,Cd,Cu,Sb,As,Au and so on are important indicator elements.Principal component analysis yields 4 principal components,the main load factors Bi,Sn,Pb,W,Sb,Ag,Mo of second principal component is an effective index to evaluate the mineralization of intrusive rocks;The main load factors Au,As,Sb of third principal component are effective indices for evaluating the hydrothermal vein mineralization,which is controlled by the structure,belongs to the leading edge halo element.The two principal component anomaly centers can be used as one of the location prediction bases for the source rock rhyolite porphyry and ore-forming parent granite diorite porphyry.Geochemical high-value anomalous center of third principal component is one of the basis for positioning prediction of shallow ore-controlling structures.Two mines can thus be screened for anomalies.（4）The ore controlling factors in the study area include:tectonic control over mineralization（EW structure plays a role of ore guiding and ore holding;NW ore bearing structure;ore controlling system with NW direction derived from EW direction echelon fault structure group,ore controlling system with fault bridge formed by NW direction fault structure in EW direction echelon fault structure group,ore controlling system with diamond structure and ring formed by EW direction structure and NW direction structure）,the control of ore-forming parent rock to ore-forming（Jurassic to early Cretaceous granodiorite porphyry is closely related to mineralization,the magmatic activity of granodiorite porphyry stage is an important factor of mineralization）,the control of ore source rocks on mineralization（the rhyolite porphyry formed at（169.9±0.8）Ma was extracted by magmatic hydrothermal solution intruded by the granodiorite porphyry stage at（155.7±1.0）Ma in the later stage,which provided a certain degree of mineralization.Material is an important source rock in the study area）.The control of surrounding rock lithology to mineralization（light color rock series is favorable for ore hosting,black rock series leads to ore dispersion）four categories.The prediction criteria extracted in the study area include:geological criteria（structural criteria,metallogenic parent rock criteria,ore source rock criteria and surrounding rock lithology criteria）,geophysical criteria（the results of geophysical information extraction is about electrical anomaly criteria,magnetic anomaly criteria,gravity anomaly criteria）,geochemical criteria（the results of geochemical information extraction is about geochemical prediction criteria of primary halo and the geochemical prediction criteria of secondary halo）.（5）Innovative economic thinking has been introduced in this study.The comprehensive grade and mineralization intensity of Pb,Zn and Ag in the samples were calculated according to the economic indices,such as mineral recovery rate,metal price,processing cost and pricing coefficient.It is considered as means of studying the spatial mineralization information of ore bodies,and participation in deep positioning prediction research.（6）Positioning predictions have been made in the known depths ofⅠ₆ andⅡ₁ ore body,and there are multi-stage hydrothermal superimposition mineralization inⅠ₆ andⅡ₁ore belt,a second mineralization enrichment zone exists in the depth,the ore body has obvious lateral regularity,which delineates the deep prospecting target area.The deep target area ofⅡ₁ ore body has been successfully verified,while,theⅠ₆ ore body has not been verified.（7）The location prediction is carried out on the periphery of knownⅠ/Ⅱore belts,and a total of 9 target areas in four categories were delineated.The A1 and A2 target area have been successfully verified.The A1 target area has obtained 122+333 mineable stone resources of 120.47 million tons,and the A2 target area has obtained 122+333mineable stone resources of 85.24 million tons.