A Study On Methods Used To Quantitatively Extract Mineralized Alteration Information From ETM Data

The extraction of mineralization information based on mutilspectral data has been hotand difficult for years. Although there are a lot of techniques summarized both qualitativelyand quantitatively, there is no complete method aiming at the target areas short of basicgeologic data. How to delineate an alterated zone directly through mutilspectral data to directgeologic prospecting is an important issue to be solved. The application of vegetation indexesto agriculture and forestry is proved to be very effective;therefore there may exist the samekind of mineralized alteration factors which can be used to delineate an alterated zone directly.If this issue can be solved, it is certain to result in a breakthrough in mutilspectral data'sapplication to mineral prospecting. Meanwhile, human's visual habits require a more vivid3D positive landform images rather than the traditional remote sensing images and alterationinformation, which is also a very important issue. The research of this paper centers aroundthe above issues.In this paper ETM data of the sparsely covered east Tianshan Mountains and Altai areain Xinjiang as well as Silver Mountains in Chile were chosen to extract mineralized alterationinformation based on a method from the known to the unknown and from theoretical analysisto practical experiment;as a result the following was achieved.(1) Concepts of ferrous mineralization factor, argillation factor, and comprehensivealteration factor were invented through the research on the mechanism of alterated minerals,rock spectral characteristics, and alteration information extraction.IFE=ETM3/1;IOH=ETM5/7;I 综合=ETM(5+3)/(7+1)(2) According to RS data statistical analysis, a formula to calculate the lower rangevalue of alteration anomaly based on mean, bias, and standard deviation were summarized,which solved the issue of quantitatively extracting alteration information by using RS datain an area without existing geologic data.(3) RS alteration information is an integration of different alterated minerals (rocks);therefore both the magnitude of alterated factors and the collective features of differentalterated minerals should be taken into consideration for alteration classification. In thispaper through the study on classification and categorization of alteration (anomaly), it'sconsidered that the dynamic clustering method and the optimal partitioning method are themost ideal ones.(4) Due to the existence of such non-mineralized anomalies as "desert varnish", "ferricoxide films" on rock surface, normally deposited clay, and vegetation, screening is requiredfor RS alteration anomalies. In this paper three screening methods are put forward, whichare the comprehensive interpretation method, the multiple-information analysis method,and the filed verification method.(5) Based on thorough analysis of RS imaging mechanism and human's visual habits,in this paper a positive landform representation method was invented, which has beenpatented.