3D Prediction Of Pulang Copper Deposit In Yunnan Based On Geospatial Weighting

Copper mine as a strategic mineral resource is deficient in China,and its external dependence has been high for a long time.In recent years,with the rapid development of industry,the demand for copper is becoming higher and higher.Therefore,it is of great practical significance to further accelerate the exploration process of copper resources,comprehensively improve the guarantee degree of copper resources in China,and continuously reduce the external dependence of copper resources.Pulang porphyry copper deposit is located in the east of Diqing Tibetan Autonomous Prefecture,Yunnan Province.Its tectonics is located in the Zhongdian Island arc at the southern end of Yidun Island arc belt,which is the largest Indosinian porphyry copper polymetallic deposit in China.With the development of exploration and research,the mineral resources of the deposit are increasing,and the prospect of the deposit shows super-large scale.However,the known 7 ore bodies of Pulang deposit have not been completely controlled by exploration engineering.According to the analysis of the current exploration results,the Pulang copper deposit still has great prospecting potential in the deep and the edge of the mining area.Therefore,it is of great significance to use the modern 3D modeling technology and spatial data mining method to carry out metallogenic prediction in the study area.Based on the study of regional geological background analysis,this paper comprehensively collected and sorted out the geological,exploration,geochemical and geophysical data of Pulang copper deposit,and used the three-dimensional digital mine modeling software of Geovia Surpac to conduct 3D models of geological objects,and established a multi-source 3D geological spatial database of the deposit.The integrated management of multi-source geospatial data in a unified 3D visualization environment is realized.Then,3D spatial analysis methods such as geological body distance field and morphological characteristics analysis method are used to analyze the characteristics of ore-controlling geological bodies of rock mass,fault and alteration zone in the mining area,to determine the hidden spatial distance and morphological correlation between ore-controlling elements and ore bodies,obtain quantitative indexes,and establish a scientific prospecting index system.The sequential Gaussian simulation(SGS)and concentration volume(C-V)multifractal model are used to quantitatively simulate the intensity of different alteration zones of the deposit.Fractal and multifractal are used to quantitatively describe the three-dimensional spatial distribution characteristics of copper,which provides a new basis for further understanding the mineralization alteration zones and enrichment mechanism of copper.The three-dimensional geological prospecting information model is constructed,the prospecting indexes are extracted quantitatively,the multi-source prospecting information is integrated and fused by using the three-dimensional geographical weighted regression model,and the two deep orebody prospective sections of the deposit are delineated,thus the three-dimensional metallogenic quantitative prediction of the deposit is studied.Finally,the influence of various 3D prediction factors on the uncertainty of the prediction results is measured and evaluated by using the index of prediction ability,and the influence of different prediction factors on the 3D metallogenic prediction results is analyzed,so as to provide a basis for the next prospecting and exploration work.The classification and characteristics of the geological data of the Pulang copper deposit are studied,combined with the actual work,the digitization of multi-source 3D geological spatial data and the construction of the geological spatial database of the Pulang copper deposit are studied.The organizational structure of the model is constructed based on the three-dimensional geological spatial database,and the three-dimensional geological models of the strata,rock mass,fault and alteration zones in the study area are constructed.Because of the singularity of magmatic mineralization,the fractal model can be used to study the enrichment of ore-forming elements and the spatial distribution of ore bodies.In this paper,different mineralization zones in the first mining area of Pulang copper deposit are interpolated,characterized and divided quantitatively by C-V fractal model and Cu content data in borehole cores.The results show that the distribution of Cu element is not uniform in the porphyry bodies.The non-mineralized areas are mainly distributed around the porphyry bodies and hornfels,while the mineralized areas(rich mineralized areas)with moderate and high grade are mainly distributed in the porphyry bodies,mainly located in the central and southern parts of the deposit.In order to better reflect the characteristics of inhomogeneous mineralization in the Pulang deposit,the singularity indexαand multifractal spectrum f(α)are used to quantitatively describe the enrichment and distribution characteristics of ore-forming elements.In this paper,the Cu element grade of 19 exploration lines in Pulang mining area is selected to calculate the multifractal spectrum.The results show that the multifractal spectra of different exploration lines show great differences in graphic pattern,spectrum width and height difference,which reflects that the spatial distribution of ore-forming elements is very uneven,and the non-stability is an external manifestation of the internal structural differences of ore-forming systems.By comparing the spectral width and height difference characteristics of multifractal spectrum of each exploration line,it can be seen that the high-grade mineralization of exploration line 03～28 is relatively enriched.However,in line 07,line 24,line 32,line36 and line 40,low-grade areas are dominant,and the degree of mineralization enrichment is relatively weak.On the basis of geological background analysis,3D spatial analysis methods such as geological body distance field and morphological characteristics analysis method are used to analyze the characteristics of ore-controlling geological bodies of rock mass,faults and alteration zones in the mining area.Factors such as the fault distance field through the analysis computation,the Z-axis height difference between the rock mass and the ore body,the morphological factors of the degree of uplift and depression on the top surface of the rock mass,alteration factors,and geochemical anomalies are used to determine the hidden spatial distance and morphological relationship between each ore-controlling element and the ore body,obtain quantitative indicators and improve the scientific nature of the establishment of the prospecting index system.On the basis of the three-dimensional modeling of Pulang porphyry copper deposit,sequential Gaussian simulation(SGS)and concentration-volume(C-V)multifractal model were used to effectively fit the drillhole data,and quantitative simulation was carried out to delineate different alteration zones of Pulang copper deposit,including potassic alteration zone,phyllic alteration zone and propylitic alteration zone.The results show that the range of Cu<0.218%determined by sequential Gaussian simulation and fractal model has a better spatial correspondence with the propylitic alteration zones.The range of 0.631%<Cu<1.259%determined by the simulation has a better relationship with the phyllic alteration zones.The range of Cu>1.4120%determined by the simulation has a better spatial correlation with the potassic alteration zones.Through the quantitative simulation of different alteration zones of the deposit,the uncertainties in spatial position and boundary of deep alteration zones caused by the limitation of engineering controlled are reduced.The three-dimensional geological prospecting information model of Pulang copper mine is constructed,the prospecting indexes are extracted quantitatively,and the multi-source prospecting information is integrated and fused by using the geographical weighted regression model,so as to study the three-dimensional metallogenic quantitative prediction of the deposit.According to the regression coefficient of each ore controlling factor obtained from statistics,each three-dimensional unit has a set of local parameter estimates,and the influence of different ore controlling geological factors on copper grade shows obvious spatial difference.By comparing and analyzing the multiple linear regression model of mineralization variables and the three-dimensional geographically weighted regression prediction model,it is found that the adjusted R~2of the three-dimensional geographically weighted regression model is significantly higher than that of the multiple linear regression model,and its fitting effect and estimation accuracy are significantly better than that of the multiple linear regression model.It can be seen that the three-dimensional geographically weighted regression model can obtain more reliable three-dimensional metallogenic prediction results.Based on the listed various ore prospecting information variables,with missing single element as the rule,5 sets of data sets with different missing prediction elements were constructed.The data integration and calculation of metallogenic favorable degree were carried out for the above combinations using three-dimensional geographically weighted regression model.Finally,the prediction ability of the known metallogenic facts in Pulang copper deposit is calculated,and the influence of various prospecting information variables on the uncertainty of the prediction results is measured and evaluated.The results show that the absence of different 3D predictive variables has different effects on the uncertainty of prediction results.The data sets that missing three predictive variables,the alteration zone,Z-axis height difference between rock mass and ore body,and fault distance field factor,have significantly low predictive ability,indicating that the three predictive variables have a strong influence on the predicted results.Therefore,it is of great significance to enhance the reliability and effectiveness of the above three prediction variables and reduce the uncertainty of three-dimensional prediction elements.Among them,different alteration zones,including the potassic alteration zone and phyllic alteration zone,are of great significance to determine of the core part of metallogenic prospective area.Therefore,the uncertainty of the core part of prediction area can be further reduced by further analysis and research on the alteration zoning in the study area.Considering the prediction results database obtained by the three-dimensional geographically weighted regression prediction model,combined with the geological characteristics of the study area and the existing prospecting facts,the deep ore body prospective sections were delineated.The visualization of predict results was expressed by using the three-dimensional geological modeling software.On this basis,considering the favorable geological conditions for mineralization,two prospective zones of deep ore bodies are delineated in the study area.Prospective zone 1 is located in the western part of the central part of the study area,between exploration line 03 and line 20,with a north-south length of about 875m,an east-west width of about 310m,an elevation range of 3210-3780 m,a total of 14910 predicted ore bearing units,the predicted average copper grade of about 0.325%,and copper resources of about 119684.60 t.Prospective zone 2 is located in the east part of the main ore body KT1,between exploration line 00and line 04,with a north-south length of about 195m,an east-west width of about 180m,and an elevation range of 3550-3985 m.There are 1226 predicted ore bearing units,with a predicted average copper grade of about 0.325%and copper resource of about9841.27 t.