Alteration Mineral Mapping Using Masking Technique and Fusion with Geochemical Data for Mineral Exploration: A Case Study in Areletuobie, Xinjiang (China)
The use of TM or ETM+ data in mineral exploration has been very successful in the identification of key minerals over arid and semi-arid terrains. The methods mainly contain the ratio imagery, the principal component analysis (PCA) or Crosta technique, the supervised classification and even the spectral enhancement. However, the above methods often fail to identify the hydrothermally altered targets. Main reasons are the similarities in relative intensities of vegetation and minerals, the ubiquitous soils and the disadvantages of the TM data and the techniques themselves. In this study, different approaches, including ratioing, principal component analysis involving Crosta technique and Principal Component Analysis using TM1 ～7 (without TM6) and the synthetic application of the two,are used to enhance the oxides and hydroxyl-bearing minerals in the Areletuobie district. The relevant images, for instance, hydroxyl layer from TM1, 4, 5 and 7, were classified by four thresholds, i.e.,＜μ+1.64σ, μ+1.64σ～μ+2σ,μ+2σ～μ+3σ and ＞μ+3σ. The last three groups were endued with special colors and overlapped with the false composite images as remote sensing anomalies. The images show that the vegetation and cloud but not the altered rocks were accentuated. The redundant vegetation and cloud may seriously interfere with the discrimination of the minerals with diagnostic features. As a result, masking technique was undertaken to eliminate the influence of the vegetation and cloud. Areas where vegetation or cloud was predominant where assigned a value of 0 to obtain an image where only pixels with a major component of outcrops were assigned a value of 1. This image was multiplied by the multi-spectral image and consequently only the areas that presented outcrops were left for further processing. Crosta technique and the principal component analysis using TM1～5 and 7 were taken to the new images to identify the diagnostic features of the hydroxyl-minerals, carbonate-minerals and the iron oxides. The relevant images were classified by the above mentioned four thresholds based on the band load tables and the last three groups were treated as remote sensing anomalies. In order to have a synthetic analysis of the remote sensing anomalies and geochemical data, a supervised classification was applied to the geochemical surveying datum of Au, Ag and Cu (at the scale of 1:200,000). Then methods of geometric mean and conditional differentiation based on maths were undertaken to have a data fusion with the raw remote sensing images. The remote sensing anomalies were used to overlie the false color composites after data fusion. Its well known that the mineralization may be controlled by the presence of structures. Therefore, another important work is to identify the main structures in the area and their relation with hydrothermally altered rocks. Principal component analysis using TM1 ～3 was done and directional filters,involving NW, NE, NS and EW, were applied to the first principal component as it contains the information of the geomorphology of the area. Most structures from the method and the geological map (at the scale of 1:200,000) coincide with the remote sensing and geochemical anomalies. The mineral exploration work was carried through by synthetic analyses of the remote sensing images, geochemical surveying data and structures. The occurrence of hydrothermal alteration, presence of main faults and geochemical anomalies have high correlation hence its worth having further detailed exploration programmes.
Lei Liu Bin Luo Jun Zhou Yanyan Xu
School of Tour and Geographical Science, Jilin Normal University, Siping 136000, China State Key Laboratory of Resources and Environment Information System, Chinese Academy of Science, Be School of Earth Sciences and Resources Management, Changan University, Xian 710054,China
国际会议
北京国际地理信息系统学术讨论会第七届会议（7th International Workshop Geographical Information System
北京
英文
329-335
2007-09-14（万方平台首次上网日期，不代表论文的发表时间）