GISdevelopment.net ---> AARS ---> ACRS 1990 ---> Poster Session Application of multi-source data synthetic analysis to Uranium exploration in Northern Hebei and Langshan area, inner Mongolia Wang Wenjian, Cao Hongjing, Gao Shuhui Airborne Survey and Remote Sensing center China National Nuclear Corporation ShijiaZhuang , China Abstract In this paper, the new discoveries and developments of multi-source data for synthetic geological interpretation are introduced to examine volcanic and sandstone types of uranium deposits in northern Hebei and Langshan area, Inner Mongolia. These multi-source data consist of space remote sensing information, airborne remote sensing and telemeter information and geological information, etc. The geological products obtained from synthetic interpretation and analysis present obvious effect in guiding uranium exploration. For examples, discovering of alternation zones in ore-controlling fault structures and gilding to look for mineral deposits; establishment of image models of volcano-tectonic type and relationship between these models and uranium mineralization; image model of stratabound sandstone type uranium deposit in the basin and are prospecting; synthetic interpretation correcting some misled judgements on fundamental geology, thus expanding the realm of ore prospecting and reducing the ore targets. All above- mentioned are dealt with in this paper. Our center has made a synthetic interpretation for remote sensing geology in northern Hebei and Langshan area which are located in the transitional zone between north China Platform and Inner Mongolia geosyncline in order to make attempt to achieve new progress in exploration for upper Jurassic volcanic type uranium diposit in northern Hebei and Cretaceous sandstone type uranium deposit in Langshan area, Inner Mongolia by synthetic analysis of multi-source data (space remote sensing images, color infrared aerial photographs, airborne side-looking radar images, aerial energy spectrum measurements, aeromagnetic survey, and routine geology, etc. ) In recent years, the practice have shown that the synthetic interpretation have got out standing achievements to guide uranium exploration in two regions above mentioned and the expected purpose has been attained. Several typical examples of synthetic interpretation will be introduced in the following parts. Discovery of alteration zones in ore-controlling fault structures By synthetic interpretation for space and serial remote sensing images the framework of fault structures has been established in northern Hebei. The strikes of these fault structures can be divided into EW, NS, NE, NNE and NW directions in which the EW and NS directional faults are the important discoveries. The EW and NS striking light-colored zones appeared in space remote sensing image, have been mutually proved by synthetic geological interpretation and identified by actual observation. Along the fualt structures, the slight negative landforms are displayed with about 2-3 km in width and are in parallel reappeared with 8-11 km at interval. The scattered material of broken and altered hydromicazed volcanic rock are widespread all over the low foothill, where vegetation is obviously sparse in contrast with the background. The light-colored zones appeared in TM visible light image, the bluish zones in TM 4,5,7 bands false-color composite image, the extremely bright-colored zones in TM (5/7 - 4/3) ratio image, the dark blue zones infrared false color image; and in aerial energy spectrum U, Th and K content images, the linear low field is in agreement with fault structures in position. The linear expanding gradient zones in aerial magnetic image coincide with fault structures for the most part. Aeromagnetic maps continued down to different depth show the faults are inclined to the north and extend to the north and extend to the depth more than 18 km. By synthetic analysis it is known that they are crust-cutting faults formed in accompany with inner Mongolia axis, having long and complex active history and controlling geological and mineral developing history from Lower Proterozoic era to Mesozoic-Cenozoic era. During Lower Proterozoic in the north margin of Inner Mongolia axis they restrict accretion of the platform, to set apart from Inner Mongolia geosyncline with a fault zone. The eruptive zones in volcanic rock extending in EW direction was controlled by late Jurassic epoch to be closed and opened for many times. From late Yanshanian period to Himalayan period, reactivation of EW and NS striking faults and stretching to cover volcanics caused fracturing and hydrothermal alternation in volcanic rock strata, to bring about multiple mineralization of polymetals, precious metals and metallic uranium, therefore, fault structures can be interpreted from images, and become regional structural indications for uranium and gold exploration. Now, lead, zinc, copper, gold and uranium deposits and occurrences discovered almost occur in alternation zones in EW and NS striking fault structures and their vicinity, so it is verified that distribution of end genetic metal minerals coincide with regional EW and NS striking fault structures. Prospecting for uranium and gold deposits arranging in the developed portion of EW and NS striking deep faults by following synthetic interpretation has received primary effect. One uranium prospect, two surface exposed points of uranium and two points of gold mineralization have been discovered. Among them, one gold mineralized structure zone with a length of over 3,000m and a mineralization range of 200m are considered to be promising areas to search for altered rock of gold deposit. The satellite image can clearly reflect altered structure zone, which has been mutually proved by synthetic interpretation and has been confirmed that it is an or-controlling structure. This obvious effect of ore prospecting by remote sensing is certainly is certainly a rare example. Establishment of volcanic appratus type of image model Upper Jurassic volcanic rocks are widely distributed in northern Hebei, in which numerous mineral deposits are located. By synthetic interpretation of remote sensing geology, it has been discovered that the known large type lead-zinc deposit occurs in central edifice at the intersection of EW and NS deep faults. A large type type of uranium-molybdenum deposit and several occurrences are related with volcanic apparatus compounded with deep faulting, and mineralization is present in sub volcanic rock body and contact zone controlled by volcanic apparatus. Therefore, they will cause great interest in remote sensing geological interpretation, if in the interpretation of volcanic apparatus, a great attention is paid to the difference between types, and their spatial and genetic relation with mineral deposits. A perfectly developed volcanic appratus is a volcanic appratus regularly consisting of multiple structural elements as a whole. Because of different modes of volcanism, Corresponding characteristic types of volcanic appratus are produced, providing marks for the interpretation of remote sensing image. Many circular patterns are interpretated by carefully contrasting and analysing and based on similarity of image structure feature, five types of image models of volcanic appratus have been established and determined by field verification. Image Model of Volcanic Domal Structure The patterns of volcanic activity never only are strongly explosive or effusive. If the upwelling strength of volcanic matter is no enough, then it may produce sub volcano or cryptovolcano which overlie the wall rock to form as modal. This is just the formation mechanism of volcanic modal structure. In general, the principal features of modal structure image behave as the multilayer ring structural imagery units. The center of dome is generally negative landform, and ring mountain bodies and ring valleys intermitting with multilayers are alternately around the center, some-times associated with radiated valleys. The slopes of the ring mountain bodies are long and gentle or short and steep for backing or facing to the center respectively, that is the reflection of landform of volcanic rock strata inclined from domal center outward. Image Model of the structure in the Subsidence volcanic Basin In the course of the formation of volcanic basin, the base of basin constantly and slowly descends, forcing volcano-sedimentary rock naturally to incline from the basin circumference to center. In image, this type of volcanic apparatus is very similar to volcanic dome. It can be distinguished in two aspects : First, the center ring is more large and open; second , the slopes of ring mountain bodies are short and steep or long and gentle for backing or facing to the center respectively. Image Model of Collapse Volcanic Apparatus Collapse volcanic apparatus is formed on the basis of subsidence volcanic basin. A great mass of material jets up from the magma tic chamber or lower basin. Because of nothing to supply the void and to support the overburden pressure timely, the slump occurs suddenly to bring about ring, radiated, linear faults and skirt-placated structure. Image patterns corresponding with these structure are rate shadow stripes of ring or radiated rifted valley, the collapse centers among valleys are surrounded by complex mountain group consist of volcanic rock strata. Image Model of subsidence-Collapse Volcanic Apparatus Subsidence-collapse volcanic apparatus is caused by alternation of volcanic subsidence and collapse, the most typical examples are the two Upper Jurassic volcanic basins at Baochang - Duolun. Image shows the ring image units consisted of trade and fine ring stripes, the ones are the reflection of ring collapse faults and the fine ones are the reflection of micro-landform of volcanic rock strata inclined to the basin center. The scale of this type of volcanic apparatus is very large, the diameter of which is up to several tens of kilometers, and the boundary covers over a single volcanic basin. Volcanic activity is frequent, having varied rhythmic and cyclic layering and the depositional center of the basin occurred several times of displacements. Image Models of Center - Volcanic Apparatus In this area, a great many of center -volcanic apparatus are developed, a typical example is the center-volcanic apparatus in Hebaoguo fissure. In image, single volcanic appratus appears as a rude shadow stripe structure, shapes of which are of single ring, complex ring or radiated ring, etc. But its landform features are funnel-shaped, horseshoe-shaped or multilayered ring fracture valley alternately surrounded with ring mountain body. It is seen from the relationship between mineral resources and the type of volcanic apparatus that most of mineralization is, no doubt, chiefly controlled by center and collapse volcanic apparatuses, and by volcanic dome and subsidence-cooapse volcanic apparatus, there are only two examples, but mineralization is possible only if there must be compounded with consequent activity of altered deep fault structure. Now, any former example of mineralization controlled by the structure in subsidence volcanic basin has not been discovered. Expanding ore prospecting field by modifying geological unit For many years practices to search for minerals have shown that uranium deposits are principally present in Upper Jurassic acidic volcanic rocks, and gold deposits in Archaean metamorphic rocks and igneous rocks at content Zone. The synthetic geological interpretation has corrected some mistakes in geological strata (bodies) and litho logical units, thus expanding ore prospecting field and clearly defining the geological strata (bodies and litho logical targets to search for minerals. In the initial stage of analyzing information, the sub volcanic rock bodies distributed over large areas on original geological map have been doubted. If the sub volcanic rock bodies in the original geological map were the intrusive rocks of the name, they would certainly be the plutonic intrusive rock fancies, but not the sub volcanic faces. So the conclusion would be that the deeply denuded volcanic rock strata are not good for prospecting potential. We have undertaken a synthetic interpretation with this important problem. From image shadow stripe structure, tone, U, Th, K contents and magnetic fields features, it can be seen that the primary sub volcanic rock bodies agree with homo-compositional volcanic lava of background and both are undistigusgh able. By the experience from interpreting similar geological environments, it is contrarily evidenced that among those intrusive rocks with same compositions but at different stages and phases and among those background volcanic lava, they can be distinguished, because of the difference of structure or apparatus in different circumstances. Conversely the products of common constituent in same circumstances are undistinguishable. Through prompting of synthetic interpretation, theoretical analysis on the occurrence and origin of rock bodies and field examination, it has been confirmed that the original Subquartz porphyry actually is the acid mortar lava, so the two problems in searching for minerals have been solved : It has been proved that the volcanic rock strata were denuded only superficially, so it is still good for prospecting potential; The acid mortar lava is the ideal objective stratum for uranium prospecting, since there is a relatively high abundance of uranium content; the former examples forming large ore field have been encountered in this of strata . In recent years many altered structure zones, with 1/10000 uranium content, have been discovered in this stratum, so the economic ore deposit is very hopefully to be looked for. The most part of the known uranium deposits, prospects and mineralized points concentrated in the three-lithologic segment (rhyotaxitic volcanic rock) of Upper Jurassic Zhangjiakou Formation and two-lithologic segment (trachyte) in the contact zone. These two segments are the favorable mineralized location combining stratum structure and lithology. Because the cover seriously influences correct delimitation of stratigraphic units, a considerable part of three lithologic segment has been mistaken as ore-litho logic segment. Based on magnetic field feature and actual examination to denysubtrachyte, the synthetic interpretation has corrected misconception for original stratigraphic units. The causes for misconception are that the fold and fault caused the replication of strata, and vague cover structure on the surface. Image model of strata bound standstone uranium deposit By synthetic interpretation of multi-source data dominated by satellite imagery and analysis on geological setting of occurring the sandstone uranium deposits in Langshan area, Inner Mongolia, some geological information closely related with uranium deposits have been extracted, a new recognition has been generalized that mineralization is controlled by the tonal anomaly, arcuate, ring and linear image model (four-in-one image model). The limitation of former study has been broken through and better result of ore prospecting is obtained. Image Tonal Anomaly of Uranium-bearing Basin and Ore-bearing Strata. The uranium-bearing basin exposes a grey white rhombic block body in the black-white image and light yellow or yellow-white in color image. its boundary mainly is of irregular saw. The four strata of image structure reflected by combination of shape, color and shadow stripe correspond with four stratigraphic units from Lower Cretaceous to Upper Cretaceous respectively. One of them K21 is the positions of orebearing strata, exposing light yellow-yellow green fine grained shadow stripe. But the thermal altered ring regions relating to mineralization are yellow brown mottled blocks. Occurrence of Uranium-bearing Basin Controlled by Arcuate Structure The occurrence of uranium-bearing basin is controlled by the arcuate structure system consisted of four tremendous arcuate faults prominent to the north. By the action of left lateral rotational structural stress field, a series of second-order rotational structures were developed in late Mesozoic era, bringing about a batch of fault blocks. The divergences between these fault blocks in elevation and subsidence formed interlaced distribution of uplift and depressions. This structural framework controls the distribution of provenance granite bodies and the occurrence of Mesozoic uranium-accumulating basin. Volcanic Ring Structure- a Condition of Thermal Reworking and Mineralization The ring structures of intermediate-basic volcanic activity are mainly developed in ore-bearing strata, with different sizes and forms. Wall rock hydrothermal alternations are sericitization and silicification which are shown as hydrothermal alternation haloes at post-volcanic stage. The uranium mineralization mainly clusters around the ring regions. it is proved by investigation that (A0 mineralization temperature of pitchblende is 126-256 C, the metallogenetic epoch is 12.7 Ma and 20.1 Ma, later than ore-bearing starta (110-120Ma), attributed to the product of Himalayan period (B) Hg, Sb, Bi, S, etc. trace elements are contained in the ores , indicating that hydrothermal solutions were involved in metallogenetic remobilzation at the post-volcanic stage resulting in uranium concentration into ores in the ore-bearing strata. Linear Structure Knot ia Positioning Element for Uranium Deposit Two periodic faults have developed in the ore bearing strata, one of them is the NW and NE direction torsional faults and NNE direction tensional-torsional fault relating with arcuate structure another is the NNE direction compressional-torsional fault in later period, restricting the undulation of the basin basement. The compound intersecting structural knots of NE 20, NE65 and NW 335 are the important positioning elements of uranium uranium deposits. Hence, the conclusion is that in this region the sandstone uranium deposit of reworking type, which is doubly controlled by lithofacies strata and structure as well as epigenetic hydrothermal reworking. Therefore, in the arcuate structuralsstem, the light blocks are applied to determine potential basins of mineralization, the light yellow-green zones to ore bearing strata, the ringstructral legions to potential e and the linear structural knot to mineralized target areas. As above, the "four-in-one" Image model can be used to guide for ore prospecting, the six potential basins have delineated. In one of the basins five deeply exposed target areas have been predicted. High-grade ore bodies have been found at depth, and industrial reserves have increased by times. At present there deposits and some hundred mineralized points are conformed, greatly raising the benefit of ore prospecting. Conclusion Synthetic interpretation is a direction of development in remote sensing geology. Single remote sensing means can only solve some aspects of geological problem, but by using the multichannel function of synthetic remote telemetering, could the success of our center in the guide for uranium and gold exploration is that in remote sensing geological interpretation we have adopted the space and aerial remote sensing methods, used MSS, TM sensor multi-band information sources, infrared pseudo-color, side-looking radar image as well as aerial energy spectrum survey of lithologic U, Th and K contents, aeromagnetic survey by different lithologic magnetic permeability etc. The synthetic geological interpretation in northern Hebei and Langshan area, Inner Mongolia have reached expected purpose obtained good effects. Several EW and NS directional altered structure zones are interpreted and examined, thus achieving more through understanding. They are confirmed to be ore-controlling structural zones of polymetals, precious metals and metallic uranium; identifying the existence of considerable volcanic appratuses and dividing their types, establishing corresponding image models, pointing out their spatial association with mineral resources; establishing image model of strata bound uranium deposit in the basin effectively guiding the exploration of sandstone uranium deposit in the basin; setting up fault structure framework of this coverage area, correcting some misconception to geological strats or bodies expanding the field for ore prospecting, clearly defining the prospecting targets; some deeply understanding metallogenetic geological conditions in working areas, presenting some potential areas and segments for uranium deposits have preliminarily effected ,and will produce a marked effect continually.