Remote Sensing Alteration Minerals(Groups) Mapping Based On Topographic Correction

Located between the Indian and Asia-Europe plates,with strong geological tectonic activities and magmatic rocks,Tibetan Plateau has an advantageous geological environment for the formation of porphyry copper deposits and epithermal hypothermal deposits.Due to the complex topography and undulating terrain,field geological exploration work is more difficult.With the maturity of satellite remote sensing information identification technology,the use of remote sensing in geological prospecting has become more and more mature.However,in regions with complex topography and fluctuating terrain,the spectral characteristics of the surface features are strongly influenced by the terrain,and changes of slope and aspect lead to“anisotropic reflection”phenomenon,which will affect the accuracy of remote sensing prospecting.In recent years,the topographic correction model based on Landsat data has developed rapidly and achieved good results.However,the 2 to 3bands set in SWIR of Landsat sensors is unable to effectively identify Al-OH minerals and Mg-OH minerals.The ASTER image data mounted on the Terra satellite has 6bands in the SWIR range,and contains a large amount of surface alteration minerals（groups）information,which has obvious advantages in terms of subdivided mineral types,divided alteration zones,and quantitative/semi-quantitative studies.In this paper,based on ASTER data,two typical porphyry copper deposits of Qulong and Chongjiang-Tinggong districts are used as study area,this research is conducted in three aspects.（1）Topographic correction of ASTER data.（2）Quantitative evaluation of topographic correction.（3）Based on topographic correction imagery,the alteration mineral（groups）information are extracted and the surface alteration zone are divided in the study area with MTMF method.Then combine with the copper geochemical anomalies,alteration information evaluation and ore prediction are carred out.The main research results are listed as follows:（1）Analyzed and evaluated the effect of topographic correction in the study area.The topographic effects is all mostly weakened with the seven topographic correction models.Compared with other models,the Teillet-regression model achieved the best results in the Qulong research area,and the most suitable model in the Chongjiang-Tinggong research area is the VECA model.With a strong overcorrection phenomenon,the Cosine model and the SCS model are not suitable for the topographic correction in the study area.（2）Based on the topographic corrected images,altered mineral（groups）information is extracted in the study area.There are four alteration group minerals of Qulong porphyry copper deposits with MTMF method:muscovite+kaolinite/Montmorillonite,kaolinite+illite+rectorite,chlorite+epidote+phlogopite and goethite+hematite+jarosite.Moreover,based on the MTMF method,the four surficial alteration group mineral zones of Chongjiang-Tinggong research area are muscovite+montmorillonite,kaolinite+illite,chlorite+epidote and goethite+jarosite.（3）Remote sensing surface alteration model is established in the study area.Mapping results show that the three alteration zones from the interior to the exterior are phyllic+argillic zone,argillic zone and propylitic zone,and the Fe³⁺group alteration minerals mainly overlop with phyllic zone and argillic zone.After topographic correction,two alteration zones with better spatial confinement and relationship were produced,which are largely consistent with the typical“monzonite”model of porphyry copper deposits,and has a good prospecting prospects.Using the corrected image based on VECA model,a remote sensing surface alteration zoning model was established in the study area of Chongjiang-Huantong.From the interior to the exterior are phyllic zone,argillic zone and propylitic zone,but the growth of propylitic zone is poor.The Fe³⁺group alteration minerals are distributed in the three-zone overlap and its outside.Five prospecting target areas have been delineated according to the metallogenic geological features of the known deposits in the study area,which can be used as key areas for field geological exploration.