On The Repeatability And Optimization Of Remote Sensing Mineralized Alterations About The Porphyry Copper Deposits

Since Rowan discriminated the limonite alteration zone with Landsat image in the1970s, application of remote sensing mineralized alteration extraction has gained the rapid development. At present, remote sensing technology runs through the whole process of geological survey. As an important development direction, extraction and application of remote sensing mineralized alterations play important roles in the field of geological survey. With the rapid advancement of remote sensing technology at home and abroad, they can offer remote sensing data of different spatial resolution and spectral resolution and greatly enrich the information of geological survey. At the same time, the under-researched theoretical basis and application foundation have hindered the further development of remote sensing technology in depth and breadth.Based on the physical mechanisms of remote sensing and spectral features of altered minerals, remote sensing mineralized alterations, extracted from remote sensing data, refer to the remote sensing information related to wall rock alteration for mineral exploration. It has advantages of rapidness, efficiency and cost-effectiveness to make use of the remote sensing technology to extract the wall rock alterations of the porphyry copper deposits; however, because the mineralized alteration extraction from remote sensing data are influenced by many factors including the altered mineral combination, surface environment, remote sensing data source, extraction method, and expression method, the "repeatability" condition and "repeatability" mechanism of remote sensing mineralized alterations become the key factors of the application of remote sensing alterations.Taking typical porphyry copper deposits of wall rock of Tibet as example, this dissertation aims to explore the repeatability mechanism for remote sensing mineralized alterations with different extraction scales, quantitative expression methods and different data source based on a comprehensive summary of zoning rules of wall-rock alteration of porphyry copper deposit and spectrum responses of altered materials(combinations); it primarily establishes the evaluation criteria about screening, classification, and application principles.The main research results are listed as follows:1. As for the uncertain factors in the extraction and application of remote sensing mineralized alterations, this study puts forward the repeatability concept of remote sensing mineralized alterations. 2. It establishes the scale effect concept in the extraction of remote sensing mineralized alterations and evaluates the scale effect with parameters of anomaly threshold, anomaly plaque, anomaly density, principal component entropy, and anomaly entropy. Experimental results based on Duolong porphyry copper remote sensing anomaly of PCA (principal component analysis) show:scale effect has a significant influence on remote sensing mineralized alterations; the optimal extraction scale of ferric alteration is about5times of the typical deposit extent; and the results of hydroxy alteration will change the anomaly classes when the extraction scale exceeds120times of deposit extent.3. Experimental results based on Qulong porphyry copper remote sensing anomaly of PCA (principal component analysis) show that the fractal method is an optimal quantitative expression method because of its precise calculation and high stability through the comparative analysis of quantitive expression methods.4. It presents the concept of data repeatability in extraction of remote sensing mineralized alterations. Experiments of Yulong, Qulong and Duolong porphyry copper deposits show that remote sensing data have some certain influence on the repeatability in extraction of remote sensing mineralized alterations. In the unobvious differences of time phases, the results from the same sensor of remote sensing mineralized alterations have some degrees of comparability.5. From the aspects of mineralized geological condition, genetic mineralogy and fabric of remote sensing mineralized alterations, it initiates to establish optimal conditions of remote sensing mineralized alterations of porphyry copper deposit and promotes and defines the fabric analysis concept of remote sensing mineralized alteration; and then, on a basis of the theoretical model of hydrothermal alteration zone of porphyry copper deposit, it analyzes the optimal conditions of fabric analysis of remote sensing mineralized alterations.