Gold Mineralization Information Processing On TM Images
He Guojin, Hu Deyong
(China Remote Sensing Satellite Ground Sttion, Beijing 100086)
Abstract
Geological structural and lithological characters, minieralization and alteration as well as biogeochemical anomalies are the three types of information features that have been normally considered in the procedure of minerogenetic prognosis using remotely sensed data. By now, the method for structure features extracting has been widely, successfully performed. It is of course more difficult to achieve mineralized (alternation) information along with bio-geochemical anomalies from satellite-based images.
As a type of field information, satellite-based remote sensing information is the result of all the objects on the surface interacting with electromagnetic wave. Thus, all the objects on the surface are information carriers in which geological anomalies are involved. This results in a weak presentation of geological anomalies in TM images. This kind of weak information is just the target that we usually operate on by image processing.
For the reasons above, we propose an ideal named "micro-different information processing." Its general views are as follows: Feature information reflecting the common characteristics of natural objects should be dispelled, and the variation information should be identified. For the variation information probably indicate geological anomalies. Thereby, according to these viewpoints, vegetation and soil are not again regarded as only disturbing coverage for mineralization information extraction.
On the basis of the ideal of "micro-difference information processing," Some tests have been done to obtain gold mineralization anomalies from TM images in more than ten areas of China, where the coverage is much different. The results have shown good indications of gold mineralized information or vegetation anomalies. This information is very clear in processed TM images, and has been proved to be highly accurate by fieldwork. Among them, several gold deposits have been discovered.
Introduction
Satellite remote sensing has provided us an effective method for geological mapping and mineral surveying. Geological structures and lithological characters, mineralization and alteration as well as bio-geochemical anomalies are the three types of information features that have normally considered in the procedure of gold minerogenetic prognosis using remotely sensed data. By lithological interpretation and structural analysis, geologists can get some supplementary information for gold exploration from satellite images. On geological studies using remote sensing technique, researchers have recognized various kinds of liner and circular phenomenon existed in the satellite images. This caused an extensive study on the relationship about minerogenetic geological background and the statistical information of liner-circular structures, and results in people's high attention to the ore-controlling function of these structures. Statistic shows that 909 of 1000 endogenic metal deposits in China are closely related to liner-circular structures, while gold deposits reach to a ratio of 99.22%. In the East of Shandong province, 39 among the 40 gold deposits are linked to various kinds of circular bodies (Xue Chongshen 1993). The high statistical density of geological structures has positive relation to gold anomalies. It is therefore possible to obtain some useful information for gold mineral exploration with spatial analysis of liner-circular structures and their mathematical frequency statistics.
As far as the mapping of mineralization (alteration) and bio-geochemical anomalies using satellite images is concerned, researchers have taken great effort to the studies since Rowan succeeded to map the gossan distribution using Landsat-MSS data in 1977, and have achieved much accomplishment. Some works have been successfully done to abstract the alteration information is different bare areas with TM5/TM7 and TM3/TM1 (rowan 1982, Abrams 1984, Chzves 1989 and Yuan Jihui 1990 etc.), While the combining way of bands' ratio and Principal Components Analysis has also been carried out to measure the alteration information in areas with dense vegetations coverage (Huntington 1988, zhao Yuanhong 1990, Chen Guanghuo 1990 and Ma Jianwen 1993 etc.). Then Lv Huiping made in inquiry into the methods of bio-visible - near infrared spectra (0.4-2.5 um) of TM data, the spectral reflectance of altered rock is far different from that of unaltered rock. The altered rock has a very high reflectance ratio in Band5 (1.55-1.75um) of TM, and an absorption band in band 7(2.08-2.35um). In addition, it is possible to bring about the ecological variation of the plants due to the high content (or loss) of some mineral elements in soil, and results in change of plant's spectral characteristics. All above is the theoretical basis that we are according to abstracting gold mineralization (alteration) information and bio-geochemical anomalies from satellite remotely sensed data. However, as a spectral information, it is the result of all the objects on the surface interacting with electromagnetic wave. Thus all the objects on the surface are information carriers in which geological anomalies are involved. Compared to the common information, the mineralization (alteration) is very weak in TM images. On the basis of the knowledge above and having performed trails on gold mineral exploration in more than ten areas of China, Prof. Hu Deyong raised an ideal named "Micro-difference information processing" with which gold mineralization information can be abstracted directly from TM images. Its application in remote sensing geology and image processing have conducted on obvious economical result and a long-term social result.
