GISdevelopment.net ---> AARS ---> ACRS 1992 ---> Geology Interpretation of Remote Sensing information related to uranium mineralization in quaternary covering azrea Huang Xianfang, Luo Fusheng, Tian Hua Zhang Shuiming, Feng Jie Beijing Research Institute of Uranium Geology Lin Shuangxing Zhang Haifeng 216 Geologic Team, North-West Geology Bureau Abstract Up to now, interpretation of Remote Sending information in Quaternary covering area is still a tough problem to a solved in Remote Sensing geology. This paper is aimed at discussing how to utilize satellite image processing method combining with multiple information interpretation to extract useful geological information covered by heavy quaternary sediment. By means of comprehensive interpretation of image signature, “prospective successfully differentiate the image features between the covering strata and the buried terranes and ascertain ore-controlling factors. Taking the Yili basin for example, the faults (including the buried faults) which control formation and development of the basic have been interpreted, the productive uranium formations which dominate uranium distribution have been delineated, the uplift and subsidence which are related to sedimentary environment have been discriminated, the stable area and active block which are connected with uranium concentration and preservation have been discerned. The results have proven to be useful not only in revealing the distribution regularities but also in guiding further uranium reconnaissance and exploration in the covering area. Introduction The Yili basin is a productive uranium basin covered with Quaternary sediments. It is known that satellite image is comprehensive expression of spectral features of geological bodies on the surface. So good results can be obtained when Remote Sensing technique is utilized in outcrop area. How about in Quaternary covering area? Is it possible for us to employ Remote Sensing technique in the covering area? “certainly”, the answer is affirmative based on the practice in the Yili basin. The practice ahs indicated that Remote Sensing technique not only can be used to interpret fault and lithology but also to ore-controlling factors in the covering area. Methods and Procedures The purposes of image interpretation is to ascertain the image signatures which are related to the uranium mineralization, establish deposit image model and apply the deposit image model to optimize prospect targets. Usually, it is easy to get comprehensive image features of ore-controlling factors in the outcrop area. While in Quaternary covering area, the things are different. In order to get useful information, on the one hand we have to master ore-controlling factors, on the other hand we must understand the image characteristics of the overburden. Sure we should try our best to do image processing and get ideal images with which the geological bodies in the depth can be identified. The methods and procedures are as follows : 1. Image Processing Image processing is a very important step in Remote Sensing geology. In order to get better interpretation results, the prerequisite is to prepare good quality image. Since the study area is covered with Quaternary sediment, when doing image processing, we not only want to enhance the covering strata information but also extract the concealed geological terrain information and require all the image signatures can be compared with each other. So we not only pay attention to sub scene image processing but also emphasize on mosaic image processing. As the study area consists of four Landsat scenes which are acquired in different time, we must do digital color mosaic so that he image features in study area can be compared with each other. The result has shown that the digital color mosaic image we have processed is much better than those made by artificial (Figure 1). Figure 1. Digital Color Mosaic Image in Yili Basin 2. Image Feature Analysis of the Covering Area Image features mean the image elements such as tone and color, size, shape, lamination, texture and pattern. In the outcrop area, as different terranes have different spectral properties, different spectral properties , different geological bodies are easy to be discriminated based on the image interpretation. In the covering district, as concealed geological terrain features such as geomorphic features, drainage patterns are inevitably reflected in the covering area, the image characteristics are comprehensive reflection of the covering strata spectral features as well as buried geological body features. It is very important for us to differentiate the image features between covering strata (including Quaternary and vegetation ) and buried terranes and fully explore image signatures which are connected with the buries terranes. In this way, we can penetrate the covering strata, identify the true features of buried geological bodies. 3. Ore – controlling Factor Analysis Uranium mineralization type in the study area is sandstone type uranium deposit controlled by interstratified oxidation zone. The ore-controlling factors are as follows : Uranium mineralization is controlled by sandstone strata, confined in favorable productive uranium formation. Uranium mineralization is controlled by uplift and subsidence, located in relative subsidence district. Uranium mineralization is controlled by tectonic environment, occurred in relative stable block. Uranium mineralization is controlled by faults. On the one hand, faults controlled the formation, development and rework of the basic, on the other hand, the mineralization is controlled by intersection between faults and favorable between and favorable strata forming double roll-type and stack uranium ore-bodies. 4. Image Features and Interpretations of ore-controlling Factors. As mentioned before, the study area is Quaternary covering district. It is impossible or recognize the buried geological bodies only based on the covering strata image signatures. We should fully employ geomorphic information, drainage pattern information and prospective information so that the ore-controlling factors can be revealed. Image Features can interpretations of Productive Uranium Formation Productive uranium formation in the study area is distributed between volcanic rock basement and upper coal-seam. Because the image features between the productive uranium formation and volcanic rock are quire different, it is very easy to discern the boundary between them in the image. Since both productive uranium formation and upper coal-seam are covered with Quaternary sediments, it is difficult to delineate the boundary between them. Based on the comprehensive analysis and interpretation, a very special image pattern – “Inverted fan-shaped image pattern” is found. The inverted fan-shaped image patterns are developed in covering strata and are comprised of centripetal drainages, but the direction of convergence and divergence is in opposition to alluvial fan (Figure 2). In order not to confuse with the alluvial fan, we name it “inverted fan-shaped image pattern”. Figure 2 Alluvia Fan Image Feature (A) and Inverted Fan-shaped Image Feature (B). The Former is Quaternary Image Feature, Showing the Quaternary Geomorphic Feature, The Latter Is Image Feature of Geological Body Beneath the Overburden Reflecting Geological Terrain Attribute in the Depth. The meaning of alluvial fan and inverted fan-shaped image pattern is different. The alluvial fan is reflection of Quaternary geomorphic feature, while the inverted fan-shaped image pattern is indication of buries geological body attribute. According to the special image pattern, the top boundary of productive uranium formations is interpreted and spatial distribution of formations is determined. Image Features and Interpretations of Uplift and Subsidence Uplift and subsidence are interpreted in the light of the drainage pattern developed in Quaternary. On the whole, the drainage direction taken the north-south orientation and rivers flow from north to south in the north margin of the basin. In the uplift area, when drainages encounter the uplift, they are forced to deflect toward east or west respectively due to the obstruct from the uplift, forming arcuate drainage around the uplift, expressing as circular feature in the image. While in the subsidence, a series of centripetal drainages are developed and a group of alluvial fans are developed at end of the centripetal drainages, exhibiting semi-arcuate skirt-shaped image feature in the image. Image Features and Interpretations of Relative stable and Active Area. In the digital colour mosaic image, the image features of stable district are expressed as even gray-white colour, simple and monotonus texture. While in active area, the tone and colour are varied. Lamination and texture are more complex, expressing as complex-speckle colour image. By means of the image features, relative stable and active areas are delineated in the basin. Image Features and interpretations of faults Image features of faults are very clear, displaying obvious linear feature and sometimes it is the boundary between different geomorphic landscape. In the Quaternary covering area, the concealed faults are expressed as linear dark colour halo because of high content of water in the fault. The field check has indicated that the springs are distributed along the fault. As the dark colour halo-zones are very conspicuous in the gray-white background. It is very easy to interpret the concealed faults from the image. In the light of interpreted faults, the structure framework was established. The structure type which controlled the formation, development and rework of the basic has been put forward. The basin is controlled by ramp structure which consists of imbricate structures. Furthermore a new clue for looking for stack, tabular and double roll-type uranium mineralization are also provided based on the concealed fault interpretation. Summary Above mentioned indicated that the Remote Sensing technique can be used in Quaternary covering area. According to the practice in Yili basin, we have mastered how to interpret Remote Sensing information related to uranium mineralization in Quaternary district and discriminate the image features between the covering strata and buries geological terranes. By means of inverted fan-shaped image pattern, the concealed productive uranium formation has been deciphered; In the light of comprehensive analysis of varied image information, uplift and subsidence, relative stable and active block, concealed faults have been determined. As a result, the uranium concentration and distribution regularities have been ascertained and the favorable targets have been selected according to the image interpretation and the criteria. It is of significance not only in guiding uranium reconnaissance and prospecting but also in opening the way for applying Remote Sensing geology technique into the covering area. References Floyd F. Sabin, JR. 1987, Remote Sensing Principles and Interpretation. Cui Zhenkui, Huang Xianfang and others, 1990, Deposit Image Model and Optimization of Prospect Targets, Proceedings of the 11th Asian Conference on Remote Sensing.