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Geology
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Tectonic fabric mapping of the Sungei Jelai area, Pahang, Malaysia by Remote Sensing and digital processing techniques
Lai Kok Hoohu
Geological Survey of Malayisa
Abstract
A tectonic fabric map of the Sungai Jelai area, a heavily vegetated area was produced by interpretation of digitally enhanced landsat MSS images. The image: were found to be affected by aspect ratio distortion which was rectified by registering the at infected images to digitized map data. A large amount of structural geology information., including previously unmapped lineaments and circular features were revealed by complementary sets of directional edge and contrast enhancements of Landsat 4 MSS band 4 (infrared) images. The structural information derived from the images was integrated with overlays of digitised geological map data which included mineral occurrences and geochemical anomalies to produce an 'image map' and a hard copy obtained by computer-aided mapping. The integrated data revealed that some in the study area. In this respect, N-S NNW-SSI, and NNE-SSW trending linears and some circular features were the most significant.
Introduction
Major linear features have long been used as guides to the regional search for one deposits. Some lineaments represent zones of weakness through which mineralizing fluids may he directed and as such represent lines which mineral deposits are likely to occur. However, the mapping of lineaments (tectonic fabric) by application of remote sensing in an equatorial contry like Malaysia has many problems. Notwithstanding cloud and naze problems, vegetation cover imposes serious constraints on interpretation of remotely sensed imagery. Traditional image interpretation is limited by the eye's sensitivity to subtle changes of hue, texture and tone of vegetation cover. Mortunately, image enhancement by digital processing can be used to emphasize such subtle features, making the interpretator's task easier. Details which were previously imperceptible may be revealed. Purthermore, the information so derived can be integrated with other geological data for currelation or spatial analysis.
The Study Area
The Sungei Jelai area covers about 3000 sq. km in the northwestern part of the state of pahang in central Peninsular Malaysia. This area is mostly vegetated with primary and secondary forests, with parts alienated for agriculture. The main cultivation is oil palm planation and the rest are small holdings of rubber trees and fruit orchards.
The western part of the area is underlain by a narrow belt of Lower Palaeozoic rocks which form a narrow mountain range. The rocks consist mainly of sandstone and conglomerate. Immediately east of these rocks is a broad belt of low undulating to hilly terrain which is underlain by Carboniferous to Permian rocks consisting of three distinct facies; an argillaceous, a calcareous and volcanic facies. These Permo-Carboniferous rocks are intruded by several small igneous bodies of late Triassic age. They are mainly granitites, except for one body, which is composed of syenite and related rocks.
Within the study area there is significant mineralization of gold and base metals. The muneralization is reported to be structurally-controlled )Lee, et al, 1986) and deposits occur mainly as fissure-fillings.
Data sources and digital processing
The data used in this study consist of (1) three 1:63, 360 scale geological maps (richardson, 1950 and Procter, 1972) in a N-S sequence with Lopographic and drainage Features, (2) and digital LANDSAT MSS CCT, picture center 127/57, acquired on 28 June 1985, (3) a regional recognissance geochemical anomalies map (lee, et al, 1982) and (3) a file on mineral occurrences from the Geological Survey of Malaysia's Archive.
Image rectification
The area under study covered to full resolution 512x512 pixels subscene but the images were severely distorted by aspect ratio distortion, a common occurrence in LANDSAT MSS (Richards, 1986). Rectification of the images were performed by image to image registration. Briefly, the operation consisted of digitizing the three geological maps, which are 15x15 mins. square on the Malayan Rectified Skew Orthomorphic projection as a single base amp including a set of control points which were positively identified of both the maps and images.
A raw image 2048x1536 pixels covering an area in excess of that covered by the map was then warped or titled into the map to produce three full resolution sub scenes registered to the base map at a scale of 54x54 m per m per pixel. This procedure,, described in detail by Lai ( 1988), was a pixel to pixel operation. Degradation of images data was kept to a minimum for sufficient fidelity to be retained for further analysis and interpretation. Furthermore other spatial data such as geochemical anomalies, known lithology and mineral occurrences can be readily registered together, thereby creating simple Geographic information System (GIS) database.
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