| Porphyry copper deposits are often located at plate convergence boundaries,where usually have complex geological backgrounds with deep valleys and steep mountains,developed structure,thick vegetation.Pulang porphyry copper deposit located in this complex geological background area and is one of the three main potential areas in China to improve the guarantee degree of copper resources.Complex geological background area is an important area of ecological civilization construction in China.Under the background of national strategy of ecological civilization construction,it is an urgent scientific problem in the field of prospecting and exploration that how to carry out the weak information prospecting with the new technology and method of environmental protection.Pulang porphyry copper deposit has poor climatic conditions and thick vegetation cover,the prospecting clues are weak and hidden,so the traditional ground survey is time-consuming,inefficient and costly,and it is difficult to reach some areas with complicated terrain and inconvenient transportation.Remote sensing technology,as a new technique and method of prospecting and exploration with the characteristics of environmental protection,can play an important role in prospecting and exploration.The research on how to use remote sensing technology to extract mineralization remote sensing alteration information and guide ore prospecting has been relatively mature.In previous studies,in terms of extraction methods of mineralization remote sensing alteration information,the interference information such as vegetation,shadow,cloud and snow,water,etc.were usually removed by masking in early data processing,resulting in the failure of a large number of original data to participate in the calculation,which affected the extraction integrity and accuracy of mineralization remote sensing alteration information.In terms of extraction data of mineralization remote sensing alteration information,high-resolution remote sensing data such as worldview-3 and aerial remote sensing are expensive,and low-resolution remote sensing data such as TM and ASTER have relatively low accuracy in the extraction of mineralization remote sensing alteration information.There are still defects in the wide range and high precision application.In addition,the in-depth analysis of mineralization remote sensing alteration information is still insufficient,and it remains to be explored whether it has indicative significance to the metallogenic structure.Combined with the distribution characteristics of extracted mineralization remote sensing alteration information and metallogenic structure,we can understand the mining area more thoroughly and guide the prospecting exploration more effectively.In view of this,this study takes the Pulang porphyry copper deposit in Yunnan province as the research area.It has typical alteration zoning characteristic of potassic-sillicification zone – sericitization zone – propylization zone outwards from centre,and propylization zone is the sign of near ore,potassic-sillicification zone and sericitization zone are important symbol of high grade porphyry copper ore prospecting.In this study,the energy spectrum-area(S-A)method based on the multi-fractal theory was innovatively introduced,and the principal component analysis(PCA)was combined to construct the weak mineralization remote sensing alteration information extraction method of "PCA+ S-A".The optimized "PCA+ S-A" and the traditional "mask + PCA " were used to carry out the experimental comparative study on the extraction of mineralization remote sensing alteration information.ASTER and sentinel-2A data,which are freely available and complementary,are used to achieve the unification of surface reflectance through spectrum matching.Then,ASTER+ sentinel-2A fusion data with the optimal fusion effect is obtained through fusion comparison experiments using different fusion methods.A comparative study on extraction of mineralization remote sensing alteration information based on ASTER data,worldview-3 data and ASTER + sentinel-2A fusion data was conducted by using the optimized "PCA+ S-A" method,and the feasibility extraction of mineralization remote sensing alteration information based on ASTER + sentinel-2A fusion data was evaluated.Through in-depth analysis of the mineralization remote sensing alteration information in Pulang porphyry copper deposit,the significance of its metallogenic structure was explored,the new understanding of the metallogenic structure and the spatial distribution of mineralization alteration in Pulang porphyry copper deposit was put forward,and the favorable ore-prospecting potential areas were further delineated.This study not only provides scientific basis for prospecting and exploration of Pulang porphyry copper deposits,but also provides reference and demonstration for prospecting and exploration in similar areas.The main research achievements are as follows:(1)The spectrum-area(S-A)method based on multi-fractal theory was introduced to construct the mineralization remote sensing weak alteration information extraction method of "PCA + S-A" under complex geological background.This method can overcome the deficiency of removing all the interference information such as vegetation,water,shadow,cloud and snow from the complex geological background area and causing the loss of weak mineralization alteration information.Experimental comparison shows that the accuracy of "PCA + S-A" method is 11.72% higher than that of "mask + PCA" method,which shows that "PCA + S-A" method can effectively extract the weak mineralization remote sensing alteration information.(2)ASTER and Sentinel-2A data are used to achieve the unification of surface reflectance through spectrum matching.On this basis,three fusion methods,PCA,Gram-Schmidt(GS)and High-Pass Filtering(HPF),were used to perform data fusion comparison experiments,and the results show that the HPF fusion method has the best effect.The high-resolution bands of Sentinel-2A was used to fusion with low-resolution bands of Sentinel-2A and visible to short-wave infrared wavelengths bands of ASTER to build the ASTER + Sentinel-2A fusion data set based on HPF fusion method.Compared with the original data,this data set not only has significantly improved spatial resolution,but also has better spectral fidelity.The data fusion method can provide reference for the comprehensive application of multi-source satellite data.(3)Based on ASTER data,WorldView-3 data and ASTER + Sentinel-2A fusion data,the "PCA+ S-A" method was adopted to carry out a comparison experiment on extraction of mineralization remote sensing alteration information in Pulang porphyry copper deposit.The results show that the extraction accuracy based on ASTER+ sentinel-2A fusion data is more accurate than that of ASTER data,in addition,although the extraction accuracy based on ASTER+ sentinel-2A fusion data is slightly lower than that of worldview-3 data,there is no disadvantage that worldview-3 data is difficult to be widely used due to its high price because ASTER and sentinel-2a data are available for free.Therefore,ASTER+ sentinel-2A fusion data can be used as a new data source to extract mineralizationd remote sensing alteration information which can be widely used for free and high accuracy.(4)In-depth analysis of the extracted remote sensing alteration information with WorldView-3 data and the "PCA+ S-A " method,A new understanding of the metallogenic structure and the spatial distribution of mineralization remote sensing alteration in the Pulang porphyry copper deposit was presented and well verified in the field: ?In the northeASTERn part of Pulang porphyry copper deposit,there is a metallogenic structure with NE distribution,which is supposed to be a normal fault;?The alteration zoning of Pulang porphyry copper deposit is reclassified,in addition to the original alteration zoning center on the west side of the newly discovered fault,there is also an alteration zoning center on the east side of the fault,which has typical alteration zoning characteristic of potassic-sillicification zone – sericitization zone – propylization zone outwards from centre;?In the eASTERn part of Pulang porphyry copper deposit,there is a great potential for ore exploration at the junction of the newly defined potassium-silicification zone and sericitization zone. |
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