Analyses of Alteration Mineral Mapping and Mineral Resources Prospecting Using TM or ETM Data

Several methods exist in the alteration mineral mapping using TM or ETM data.Those mainly comprise the ratio imagery,principal component analyses or Crosta technique and the supervised classification based on known altered mineral localities and spectral angle methods.Detailed analyses and lots of applications related to this study show certain problems in the methodology.Firstly,all of them are notably hampered by certain natural factors like vegetation,topography and soil cover.Secondly,mixture pixels and the related mixture reflectance can be readily caused by smaller altered mineral targets and larger remote sensing data pixels,in addition to the common presence of some high reflectance minerals like quartz and feldspar in the altered mineral belt,which may seriously influence normal occurrence of the so-called diagnostic spectral absorption that acts as the basis of all the alteration mineral mapping methods.Lastly,certain data processing-based methods using the reflectance of relevant "pure materials",such as the sub-pixel classifying,spectral mixture analysis and fuzzy classification,can solve the problem to some extent and even so they are confined to locating the surface altered mineral targets only.Therefore,it is important to employ multi-methods including geology,geophysical and geochemical exploration and remote sensing in mineral resources prospecting,and that will largely reduce a lopsided view resulted from a single method.