Extraction Method Based On Typical Alteration Zones In Southern Peru Porphyry Copper ASTER Data

At present, many mining copper deposits on the verge of exhaustion, but the social development leads to the increasing demand for copper, therefore need to increase exploration efforts.The traditional geological prospecting takes a lot of time and manpower, and remote sensing alteration information extraction technology laid the foundation for the favorable geological ore delineation. Porphyry copper belt in southern Peru is an important copper metallogenic belt. The main copper type is porphyry copper, and mineralization Tertiary era. Study area with typical porphyry copper alteration zones is located in south of16°S Peru,which is rich lithology, surface leaching strong and good mineralization conditions.The typical porphyry copper features, from the inside to the outside as potassic, phyllic, argillic, propylitic rock and so on, which extended ring outward. Because of little effectiion on the extraction of potassium, this articles mainly extract the information of hydroxysteroid alteration, propylitic and iron staining based on existing geological data for the study area. As the six bands of ASTER SWIR improved its ability to identify the certain minerals, ASTER can distinguish the absorption spectrum, such as located near2.2μm hydroxysteroid alteration (mainly minerals are kaolinite, montmorillonite, sericite, illite, alunite, etc.) and the absorption spectrum of information located near2.3μm propylitization alteration (The main minerals are dolomite, calcite, chlorite, epidote, etc.).According to the above alteration minerals spectral characteristics, the article uses principal component analysis, ratio analysis and ratio-principal component analysis to extract information on the above alteration. Before alteration information extraction, the first step is doing a series of ASTER data preprocessing. Study area is located in a typical porphyry copper alteration zones within three provinces in southern Peru. Since ASTER data shortwave infrared bands has crosstalk phenomenon, so choosing the Crosstalk3.0to remove them. Using ASTER images do radio me tric calibration and atmospheric correction, we remove the border because ASTER data different bands has different size range. Finally, accourdingNDVI, B9/B1, B3high value cutting and B1low value removal methods, removing vegetation, water, flight area and background on study area.According to the spectral characteristics of the above alteration minerals, alteration information extraction choosing PCA1,4,6,7band combination to get hydro xystero id alteration information extraction, using band combination of PCA1,3,4,8to get propylitic alteration, choosing PCA1,2,3,4band combination to extract iron stained information.Ratio analysis method using B4/B6, B8/B4, B2/B1method to get hydro xystero id, propylitic and iron stained alteration of information extraction. And the ratio-principal component analysis method using B2/B1,B4/B6,B8/B4band combination to extract the alteration imformatioaASTER data also can identify silicification degree according to the spectral emissivity and ratio analysis in hermal infrared bands, that because the relationship between SiO2content and silicification degree. The degree of silicification and distribution characteristics of mining area is determined by the according to the calculatation of the percentage of the number of SiO2, and then compare with the existing geological data, the result is fit the data.Finally, compared the mehtods of principal component analysis, ratio, ratio-principal component analysis with the principal component analysis method of Landsat8, Geological information, Geological maps and the linear structure, finding that in this study area the principal component analysis method is best. According to the principal component analysis method of post processing, removing the false extracted alteration information. And according to "Mean+n times standard deviation (n take1.5,2,2.5)" method in the study area give the alteration information extraction results three graded display, that lay the foundation for the delineation of favorable mineralization.