Research On The Spatial Distuibution Characteristics, Ore-controlling Mechanism And Spatial Information Metallogenic Prognosis Of The Granite Contact-depression Zones In Gejiu Tin Deposit

Gejiu tin-copper polymetallic ore-concentrating district,located in the metallogenic belt of Southeast Yunnan,is famous for its huge Sn reserves,numerous mineralization types and very long exploitation history in China as well as in the world.Guided by the theories of activated tectonometallogeny,metallogenic prognosis and 3D visualization modeling,starting with the geologicalgeochemical features of the different type ore deposit(body),metallogenesis and typical granite depression zones etc,combined with the regional mineralization background,which summarized the spatiotemporal distribution regularities,and spatial distribution characteristics.It has researched of the Ore-controlling mechanism,the geological modeling and spatial information metallogenic prognosis of granite contact-depression zones by adopting the polygenetic compound theory,3D visualization technology, the fractal theory,the BP neural network evaluation mode and spatial information metallogenic prognosis model etc.The main research findings and new viewpoints achieved in this paper are as follows:1.After comparing the granite petrochemistry component evolution rule of the eastern area and the western area,discovered the granite of the eastern area show the poor in K₂O,Na₂O,Al₂O₃,Fe₂O₃ and the rich in TiO₂,FeO,MgO,CaO,P₂O₅ relatived to the granite of the western area. The main reason is that the granite of the eastem area has the assimilation with the surrounding rock generally.2.By using multifractal method,12 mirrorelements have been studied,according to the curve shape,which has been divided into two kind of multifractal patterns.Patternâ… is a simple multifractal pattern with two non-scale areas,the second tangential fit with the curve all-right, Hg,Mn,Sb,Mo,As,Zn have this pattern,which are some non mineralization elements and some associated elements with the mineralization.Patternâ…¡is a high-clustering multifractal pattern,the fitting degree of the second tangential and the curve is bad,obvious deviation,some elements present bigger deviation degree,which has reflected the element of high-content points pile up patternâ… .Sn,Cu,Pb, Ag,W,Bi have this pattern mainly,these elements all have the prodigious local anomaly in this area,in which main mineralization element Sn,Cu, Pb,Ag have formed some different rank deposits.3.By analyzing the orebody spatial distribution rule of depression zone synthetically,the orebody exists mainly about the apophyse,the upper and lower contact strip of the akmolith,depression-midst, depression-root,the contact strip position of depression-bottom.The change of the shape,occurrence,scale of depression zone influence directly the shape,occurrence,scale of orebody.The shape of depression zone is more complex,which is more advantageous to the mineralization. The major axis trend of depression zone orebody is consistent with the trend of depression zone basically.The metallogenic element distribution of depression zone orebody has the obvious zonation in the space.The inner contact strip of granite depression zone distributed tin mineralization mostly,the copper mineralization distributes on the outer contact strip.On the entire vertical of depression zone,the metallogenic elevation is from high to low,the orebody has the metallogenic tendency of tin(lead)ore→tin,copper ore→copper and tin ore→copper ore.4.Through 3D modeling software Surpac,builds the 3D visualization entity model of the granite contact-depression zone,the orebody and metavolcanics.The paper studies the spatial distribution relation among the entity models of Laochang-Zhuyeshan ore block,Kafang-Zhulin ore block,the western depression of Kafang ore block.The research discovered the coherence between the distribution rule of orebody and the granite distribution,as a whole,assuming the belt-shaped distribution along the granite depression zone,there are the affinity between the complex degree of the granite surface and the formation of orebody;the metavolcanics impedes the intrusion of the later period granite,which often forms the granite depression structure,then controls the orebody distribution of the depression zone.5.Guided by the polygenetic compound theory,the formation and ore-controlling mechanism of the Gejiu granite contact-depression zone have been researched.It can be said that the granite contact-depression zone is the production of the late of Yanshanian granite emplacement, which is the synthetical result of many kinds of factor such as Yanshanian granite magmatism,the stratum,the structure and Indosinian volcanics.Granite is the main metallogenic country rock,has the decisive function in the deposit spatiotemporal distribution,supplied with substance or thermal energy and so on;Kafang member of Gejiu Formation are the main ore-controlling and host stratum,make dominant function in the process of rock-forming and ore-forming;The regional tectonic format control Indosinian submarine volcanic activty and hot-water deposit mineralization and become the channel and the space of Yanshanian granite emplacement;The shape of Indosinian volcanics control the granite shape directly,control the formation and distribution of the granite superposition reconstruction orebody indirectly and offer a certain material origin for the deposit formation.6.The space analysis method and the information statistics unit method have been used to research the model establishment of the spatial information metallogenic prognosis in Gejiu granite contact-depression zones,which can compute the mineralization beneficial degree of each grid information unit,according to the mineralization beneficial degree, taking 0.7 and 0.5 as the dividing point of abnormity,the prospecting target has been divided the level of A and B.Level A target is relatively advantageous to the mineralization condition,is the obvious prospecting criteria and has the potential of seeking the large-scale copper-tin polymetallic deposit;Level B target is the poor prospecting criteria and has the potential of seeking the medium and small copper-tin polymetallic deposit.7.In order to confirm the validity in the model of the spatial information metallogenic prognosis,the paper imports the BP artificial neural network to evaluate the mineralization beneficial area,The model inversion result discovers the studied effect of the neural network is good, the output value and the expectation value satisfies the evaluation requirement,which indicated it is feasible using the BP neural network to evaluate the mineralization beneficial area,thus also explained the computed mineralization beneficial degree is correct in the model of the spatial information metallogenic prognosis,the division of the prospecting target is reasonable.