|
|
|
Geology/Disaster 2
|
An automatic technique and its effect by using Landsat TM data to extract hydrothermal alteration information in subtropical volcanic rock area
Application Results
Bamao is situated in subtropical climate zone with 70-80 per cent total cover in Eastern Zhejiang province. Upper Jurassic and Lower Cretaceous volcanic rocks are the predominant rock units exposed at the surface. T shi range is chosen as the study area because of the presence of extensive hydrothermal alternation, excellent mineralized conditions. Nine mineral occurrences have been discovered here, and all their orebodies occur insilicified quarts veins, which are enclosed by clay zones.
The Ladnsat-5 TM data selected for analysis were acquired on February 11, 1987. For distinguishing the intensity of clay alteration, an alteration zone-displaying image on which two grades of alteration are displayed is made successfully, and our field checking has shown that the displaying image has very good effects.
Fig.2. Displaying image of alteration zone, Red color--Strong alteration, Green color--Weak alteration
Fig.3. Schematic interpretation map
- All nine known mineralized alteration zones are displayed exactly, except Changzhao (A7) (with near 100% vegetation cover).
- Distribution shape of alteration zones are expressed very well. for example, Qianguanling (A4) is a strong alteration district with a wide range; the linear alteration zone trending SN in Houan (A5) corresponds to a silicified quarts vein that trend SN; and huanggongkeng (A9) is contributed by an epidotization zone trending NW etc.
- There are alteration zoning in some known mineral occurrences, it is displayed as the strong alteration zone surrounding by weak alteration. Such as Qianguanling, Houan, Xiaolontinshan (A1), Caopenghsna (A2) etc.
- We have checked seven previously unknown alteration zones revealed on the image, and find it all be displayed exactly. Such a Wangjianshan (B5), eastern Houan (B40 are strong sericitization; Bainu (B6) is a chloritization zone; and Xianjiancun (B2) corresponds to a silicified quarts vein. Especially, there is a crossed alterationzone displayed in Western Lanyan (B3), the one trending NNE corresponds to a silicified quarts vein, and another one trending NWW is controlled by a fault by which there is a strong sericitization zone.
- The distribution of alteration zones corresponds to known ore-controlling structures, volcanic apparatus. For example, Xiaolongtingshan, Caopengshan, Xishan (A3), Qianguanling lie in the Bamao volcanicn basin; furthermore, by the fault passed 1. Xinchang country seat; 2. Xinchang river; 3. Boundary of training area; 4. Changzhao reservoir; 5. Known mineral occurrence and its serial number; 6. Checked unknown alteration zoen and its srail numerb; 7. Inferred volcanic vent; 8. Inferred linear structure; 9. Inferred silicified quarts vein; 10. Inferred mineral potential district and its serial number
through Lanyan, Huanggongkeng, Liumenshan and Yanwo, a series of alteration zones are revealed. The alteration zone Wangjiangshan, Baibu, Huangputing is situated in a fault zone trending NE, and all the three zones lie in the edge of volcanic vents predicted here.
- Basing on the displaying image, we have delineated three strong alterationdistricts (C1, C2, C3) a regional tectonics just passed by it. Especially, the district C1 is displayed as very strong alteration area. Out field checking has shown it is mainly contributed by strong sericitization minerals, and silicified quarts vein also has been found there, perhaps it is a very valuable district for multimetal deposit exploration, and has been come into notice.
In general, this study is successful. It has important significance for large scale mineral prospecting, and can supply can effective method for alteration information extraction, geological structure feature analysis and integrated mineral prospecting in subtropical volcanic rock area in well vegetation.
References
- Ailicia.W.Seigrists: Optimum Spectral Bands for Rock Discrimination. Photogrammetric Engineering and Remote Sensing, Vol. XL. VI, No.9 1980, 1027.
- Segal.D.B: Use of Landsat Multispectral Data for Definition of Limonitic Exposure in Heavily Vegetated AREas. Economic Geology, 78, 711, 1983.
- F.A. Kruse: Munsell Color Analysis of Landsat Color-Ratio Composite Images of Limonite Areas of Southwest New Mexico. Proceedings of International Symposium on remote Sensing of Environment, 3rd Thematic Conference: "Remote Sensing for Exploration Geology", 1984, 761-763
- D.R. Gladwell, P. Lawrence, M.Ancziger: The Application of Rapid, Semi- Quantitative Clay Mineral Determination at the Cortez Gold Mine, Nevada. Proceedings of international symposium on Remote Sensing of Environment. Fourth thematic Conference: "remote Sensing for Exploration Geology", April 1-4, 1985, 403.
- Nevin L. miller and Hristopher D. Elvidge: The iron Absorption Index : A comparison of Ratio-Based and Basetine-Based Techniques for the Mapping of Iron Oxides. Proceedings o Inernational Symposium on Remote Sensing of Environment, Fourth Thematic Conference: "Remote Sensing for Exploration Geology", April 1-4, 1985, 405-415.
- Elvidge.C.D, and Lyon R.J.P: Estimation of the Vegetation Contribution of The 1.65mm/2.22mm Ratio in Airborne Thematic Mapper imagery of The Virginia Range, Nevada. International Journal of Remote Sensing, No. 6, 1985,75.
- S.J. Fraser and A.A. Green: A Software Defoliant for Geological Analysis of Band Ratios. International Journal of Remote Sensing, Vol. 8, No. 3, 1987, 525-532.
|
|
|
|
|
|
|
