Integration of Landsat imagery interpretation and geomagentic data on verification of deep‐seated transverse fault lineaments in SE Zagros,Iran

In this paper, Landsat images are used in the mapping of transverse fault lineaments in Zagros, Iran, and the origin of the fault lineaments as the result of basement reactivation faults is examined using geomagnetic maps. The area under investigation is located in the SE part of the Zagros Fold Belt (ZFB) and was affected by influence of concealed faults, or fault lineaments, during the late Alpine Zagros orogeny. Image interpretation of geological structures such as curvilinear geometry of fold hinges, en echelon pattern of surficial lineaments and younger folds, and breached salt plugs, has been used to map the fault lineaments. Two sets of strike‐lateral transverse fault lineaments have been detected. The first set, NW‐trending, was identified by right lateral curved geometry of the main fold hinges, generation of younger folds, and en echelon pattern of surficial lineaments. The second set, NE‐trending, was verified based on left lateral displacement of the structures and alignment of salt plugs pierced anticline hinges. The placement of Upper Proterozoic salt plugs on the surface along the fault lineaments, together with their correlation with the magnetic‐driven lineaments, implies that the fault lineaments have a basement origin. The trend of these fault lineaments can be correlated with the trend of basement faults in the northern margin of the Arabian plate. The key result of this study is that the fault lineaments identified by integration of remotely sensed data and geomagnetic maps are generated as first order wrench faults by reactivation of the N–S‐trending basement faults. The thick Hormoz Salt formations overlaying the basement do not allow the fault lineaments to emerge at the surface. Therefore, they can be mapped through regional remote sensing and their basement origin can only be recognized by their correlation with magnetic faults. It is also concluded that satellite imagery can greatly contribute to the structural mapping of the ZFB and is therefore a valuable aid for oil and gas exploration in analogous tectonic environments.     

Extraction of linear and anomalous features using ERS SAR data over Singhbhum Shear Zone,Jharkhand using fast Fourier transform

Digital filtering of ERS‐2 SAR data using the fast Fourier transform (FFT) has been attempted over Singhbhum shear zone (SSZ) and its surroundings for extraction of linear and anomalous patterns. The results show that numerous lineaments as well as drainage patterns could be identified and demarcated by FFT digital filtering method. Major as well as several minor drainage patterns are easily detectable from the filtered image, which are structurally controlled and not observed in the original map. Comparison of the present interpretation of the study area to existing geological map/earlier interpretation has been done effectively. This technique was found to be more effective in identifying the lineaments using ERS SAR data compared with using Landsat imagery over the study area. The present study reveals that maximum lineaments occurring in the north of SSZ are NNE, NNW and NW trending, while maximum lineaments occurring in the south of SSZ are NE, ENE, WNW, and NW trending. The demarcated geological structures may have a great significance to locate the hidden ore/mineral occurrences. The existences of various mines, such as Baharagora, Mosaboni, Surda, Narwa, Bhatin, Jadugoda, Rakha, and Tatanagar along the shear zone, correlate well with the interpreted results.     

The significance of lineaments mapped from remotely sensed images of the 1:250 000 Lau Sheet in the Benue trough of Nigeria

A lineament map of the 1:250000 Lau Sheet in the Benue trough of Nigeria is presented that is derived from LANDSAT and radar images. The two general trends of the lineaments correspond to the structural trend of the Nigerian basement rocks. New lineaments which are probably faults were delineated and recorded along with new circular features, There is a high probability of finding minerals of economic value in the study area, based on the lineament patterns and the tectonic history.     

Determination of palaeotectonic and neotectonic features around the Menderes Massif and the Gediz Graben (western Turkey) using Landsat TM image

Western Turkey contains both spectacular palaeotectonic and neotectonic features of the Anatolian block. The first of these features is the Menderes Massif, a huge metamorphic terrain comprising various lithologies; the second is the Gediz Graben, one of the most well‐known extensional features that formed during the neotectonic period of Turkey's complex geological history. In the study area, approximately E–W‐trending Neogene grabens, such as the Gediz, obliquely subdivide palaeotectonic massifs (such as the NE–SW‐oriented Menderes Massif) and mélange rocks. The terms Menderes Massif and Gediz Graben indicate different products of different tectonic regimes.

In this study, lithological components of the region were determined using a Landsat Thematic Mapper (TM) image. Band‐ratioing and principal component analysis (PCA) were chosen for lithological discrimination of the outcropping geological units. After processing, PCA gave the best results in terms of lithological differentiation. Furthermore, certain band‐ratio colour composites (5/7, 5/4, 4/1) are sensitive to lithological differences in RGB (red, green and blue) space and thus provide a general understanding of the distribution of rock‐forming minerals, such as known hydroxyl‐bearing and ferric iron minerals, as well as the vegetative characteristics of the region. However, a structural‐analysis study, including visual inspection and edge‐enhancement techniques, played a complementary role in the geological analysis of the region. Outcrops of the Menderes Massif metamorphic rocks, mélange rocks and Neogene cover associated with the Gediz Graben are favourable for remote sensing studies in so far as they allow ease of interpretation and geological evaluation by researchers. One of the most notable results derived from this study was the discrimination of younger neotectonic, fluviatile occurrences from the palaeotectonic Menderes Massif metamorphic rocks and Izmir–Ankara Suture Zone mélange rocks. Additionally, boundaries of the active Gediz Graben have been delineated.     

Neotectonic study of Ganga and Yamuna tear faults,NW Himalaya,using remote sensing and GIS

The Ganga and Yamuna rivers emerge from the Himalayas along two major faults known as the Ganga and Yamuna Tear Faults respectively. The two major strike-slip faults transverse to the Siwalik range are clearly seen in satellite imagery of the Dehradun area. Earthquake records, landslide and recent changes in geomorphological features indicate that the area between the Main Boundary Thrust and the Main Frontal Thrust is tectonically active. An effort has been made to study the tectonic evolution and neotectonism of the Ganga and Yamuna tear faults. Spectral and spatial enhancement techniques have been employed to the digital data of IRS-1B LISS-I to delineate the lineaments and major faults of the area. Based on Mohr's theory, failure criteria and statistical analysis of remotely sensed lineament data, horizontal compressive stress values (S_Hmax) have been estimated at various sites of the study area. These data are found to be consistent with the published S_Hmax orientation determined from earthquake focal mechanism solutions. Active faults and lineaments have been extracted from the remotely sensed lineament data. Past earthquake data and depth to basement contour data have been used in an integrated approach with available Geographic Information System (GIS) techniques to reconstruct a present-day regional geodynamic model. Attempts have been made to investigate the genesis of Ganga and Yamuna Tear Faults and possible causes of recent tectonic activities of the area with the help of the proposed geodynamic model.     

Automated alluvial fan discrimination,Quaternary fault identification,and the distribution of tectonically reactivated crust in the Gobi Altai region,southern Mongolia

In this study, we demonstrate the utility of SRTM topographic data as a tool for mapping alluvial fans and documenting the distribution of tectonically reactivated crust in the Gobi Altai region of southern Mongolia. The topographic data clearly reveal three diagnostic indicators of crustal reactivation: visible fault scarps, sharply defined faulted mountain fronts, and alluvial fan complexes adjacent to steep mountain fronts. These three variables are combined to produce a new surface tectonic activity map of the region. By selecting terrain with slope thresholds between 1 and 8° and then applying a topographic roughness filter, alluvial fan complexes are automatically discriminated and mapped throughout the region for the first time. This allows clear identification of Quaternary uplifted regions (and associated thrust faults) and the distribution of clastic basins which have experienced a two‐stage history: Mesozoic rifting and Late Cenozoic alluvial sedimentation. By analysing mountain front sinuosity and alluvial fan topographic roughness, the tectonic activity of individual mountain fronts is quantitatively compared and ranked. Most ranges are upthrust fault blocks with outward directed thrusts and bajadas bounding their N‐NE and S‐SW fronts. The spatial distribution of youthful mountain ranges, flanking fan complexes, and Quaternary thrust and strike‐slip faults is consistent with ongoing sinistral transpressional crustal reactivation throughout the region.     

Evolution of Kosi river fan,India: structural implications and geomorphic significance

Abstract

The Kosi river fan located in the northern part of India is one of the largest alluvial cones built by any river in the world. This 180 km long and 1501cm wide alluvial cone shows evidence of lateral shift exceeding 140 km during the past 250 years. The Kosi alluvial cone and its adjoining area has been studied in detail by remote sensing techniques. The data have been integrated with the available geological and geophysical information to decipher the causes responsible for the lateral shift of such a high magnitude fan.

The satellite image better defines the old palaeo-channels of the Kosi river and its confluence with the Mahananda river north of Lava prior to 1731. The dominant structural control, in shifting the river towards the west from one fault zone to another, is also discernible. Integrated study reveals the occurrence of dominant NNW-SSE and NNE-SSW trending faults/lineaments colinear with the pre-existing basement weak zones and their reactivation to date. The recent Himalayan relief, the thrusting of Siwaliks over the Gangetic alluvium, the development of inclined Holocene terrace in the piedmont zone and ocurrence of recent earthquakes amply demonstrates the continued neotectonic movements in the recent past. The structure contour map at the basement and Neogene-Quaternary level suggests a regional tilt from east to west along the Malda-Kishanganj fault, which got accentuated in the recent past due to reactivation along the faults/lineaments resulting in westward migration of the river.

Thus neotectonic movements result in rapid uplift in the catchment area and a gradual regional westward tilt responsible for building up this gigantic alluvial cone.     

3D model of a sector of the South Scotia Ridge (Antarctica)

A three-dimensional geological model was built to show and analyse a northern sector of the Scotia–Antarctica transform plate boundary.The South Scotia Ridge is a 400 km long submerged continental structural high representing the eastern continuation of the Antarctic Peninsula. South Scotia Ridge runs approximately in the E–W direction, separating Scotia Sea Plate from Antarctica Plates. Structures, due to the transform plate margin, are considered to be concentrated inside this continental high. The three-dimensional model, built using seismic profiles and a digital elevation model, is a powerful tool to visualize and help to understand deep geological structures. Maps and profiles, on the contrary, only give a two-dimensional view, and do not show the structure of the continental–oceanic boundary at depth.The model shows that the deformation style of the continental–oceanic boundary, and of the oceanic crust nearby, is related to the left-lateral movement of the main transform fault system. Furthermore, it seems to be connected to the orientation and geometry of the South Scotia Ridge with respect to the homogeneous deformation regime, which affects the entire Scotia Plate. Moving from west to east, the NW-dipping main fault surface becomes almost vertical with a sinistral strike–slip movement in the central sector. To the east, a south-dipping plane decreases its inclination and changes orientation (from E–W to ESE–WNW): here shortening features are visible.The three-dimensional geological model presents a western and central province wherein the continental–oceanic boundary involves the fragmented continental blocks, the continental slope, the oceanic basement and sediments. The sedimentary cover and the oceanic basement are not deformed in the eastern province.     

Significance of lineament patterns in rock unit classification and designation: a pilot study on the Gharib‐Dara area,northern Eastern Desert,Egypt

Satellite images and aerial photos are among continuous sources of data for mapping lineaments which frequently reflect surfaces of discontinuity in the rocks. The analysis of lineaments not only provides a method for detecting past tectonic trends but also helps in the exploration of minerals, oil and ground water and the seismic risk assessment for nuclear sites and repository studies as well.

In the present study, lineaments have been extracted from the digital satellite scene (Landsat 7, ETM⁺ data) for the Gebel Gharib‐Dara area using GeoAnalyst PCI EASI/PACE software. In a small test area, the lineaments that were digitally extracted for different settings of the GeoAnalyst parameters were compared with the visually interpreted lineaments for optimal settings of the parameters for lineament extraction.

The visual interpretation of the present false colour composite map (FCC) led to tentatively classify the rocks into 24 units to study the spatial distribution of the extracted lineaments. Lineament patterns in the form of lineament azimuth profiles (LAPs) are prepared and they are very characteristic for each unit. The NE lineament trend predominates over all the rock units while the NW trend characterizes those units located towards the Gulf of Suez. LAPs show that the younger granitic rock units of Gebel Gharib, Gebel Abu Khashaba and Gebel Dara (having relatively high radioactivity) are characterized by short amplitude of NW trends relative to the NE trends.

Correlating lineament density maps (LDM) with aeroradiometry total count contour maps and other ground radiometric maps show that rock units with high radioactivity are also characterized by high lineament density and lineament intersection density. Using the same reasoning, new possible uranium targets have been located.

The present study also shows that the younger granitoid is the only rock unit which has been classified into four sub‐lithologic units—G1, G2, G3 and G4—and they probably have a compositional variation that needs further field checking.     

Effectiveness of SRTM and ALOS-PALSAR data for identifying morphostructural lineaments in northeastern Brazil

This work provides a comparison between ALOS (Advanced Land Observing Satellite) PALSAR (Phased Array type L-band Synthetic Aperture Radar) and DEM (Digital Elevation Model) SRTM (Shuttle Radar Topography Mission) data aiming to evaluate their efficiency to detect morphostructural lineaments. An area in Northeastern Brazil was selected to perform this investigation because of its unambiguous evidence of tectonic fault activity from the Precambrian to the Quaternary. DEM enhanced by shading schemes and palettes was integrated with images representative of morphometric variables as aspect and horizontal curvature in order to enable the recognition of linear features. Images derived from HIS transformation and arithmetic operations of fine beam dual (HH+HV) polarization PALSAR images were processed to provide RGB compositions. Comparisons among lineament maps based on these two remote-sensing products attest to the highest efficacy of SRTM data in detecting geologically meaningful lineaments in the study area. These indicate a main E–W trend and secondary, NE–SW and NW–SE trends, which conform to dominant directions of tectonic fault zones previously mapped in northeastern Brazil. Geomorphological and geological field investigations carried out in the course of the current research further contributed to showing the best performance of this product for unravelling details of three expressive tectonic structures in the study area. This study shows that lineament attenuation in PALSAR images augments proportionally with increased land use. Other important interferences that either rule out or significantly attenuate linear structures are imposed by natural characteristics of the L-band PALSAR sensor, including layover and high-look azimuth in equatorial latitude. The latter might have particularly attenuated detection of lineaments parallel to illumination azimuth. Taking into account these interferences in PALSAR images, integration of DEM-SRTM data used herein offers a much more robust tool to help carry out morphostructural studies in terrains displaying characteristics similar to the ones in the study area.     

Classifying depth‐layered geological structures on Landsat TM images by gravity data: a case study of the western slope of Songliao Basin,northeast China

Geological structures on remotely sensed images, Landsat Thematic Mapper (TM) images in this case, can be classified by quantitative depth information on the basis of the comparison of results from Landsat TM images and geophysical data. Although the lineaments with different depths can be visually interpreted together on Landsat TM images, the depth information and geological significance of these lineaments are however hard to obtain solely from the Landsat TM images of a study area under a thick cover, and it is of much importance for hydrocarbon exploration in the Western Slope Belt of Songliao Basin, northeast China. During the present study, the 3‐dimensional field source information, including location and depth information, is derived from 3‐dimensional Euler deconvolution of gravity data in particular. As an example, it may be quantitatively classified into four groups of depth range: <100?m, 100–500?m, 500–1000?m, >1000?m. It is then superimposed onto the lineaments map from Landsat TM images using a geographical information system (GIS). With a comprehensive analysis of the superimposed maps, we obtain validation and quantitative depth information of the geological structures delineated on the Landsat TM images. Four depth‐layered maps of geological structures with different depths are presented here. It is concluded that the number of structures with depth greater than 1000?m on the Landsat TM images is fewer than those at the other three depth ranges. The detection of geological structures on Landsat TM images attributed to depth information derived from the geophysical data may also be possible by this approach.     

Is the Amik Basin (SE Turkey) a triple-junction area? Analyses of SPOT XS imagery and seismicity

In the eastern Mediterranean, plate motions occur between the Arabia/Anatolia, Africa/Arabia and Anatolia/Africa boundaries along the Amanos Fault, the Dead Sea Fault and the Cyprus Arc, and the extension of the latter on land. Detailed enhancement and classification procedures applied to SPOT XS imagery of the Hatay region, and centred on the Quaternary Amik Basin, have revealed a prominent NE–SW-trending tectonic lineament. Recent seismicity suggests that this NE–SW-trending lineament dies out in the Quaternary Amik Basin in the east and continues to the Cyprus Arc to the south-west. Structural lineament extensions derived from SPOT XS imagery using linear edge enhancement and unsupervised classification methods and the distribution of seismicity in the Hatay region show that this region has been affected by the East Anatolian Fault Zone, the Dead Sea Fault Zone and the Cyprus–Antakya Transform fault. These fault associations accommodate northerly movement of the African and Arabian plates toward the Eurasian plate. The Amik Basin appears to have been formed by interaction among the Amanos Fault interpreted here as a continuation of the East Anatolian Fault the left-lateral Dead Sea Fault, and the left-lateral Cyprus–Antakya transform fault. Active faults belonging to the aforementioned structural zones meet one another to form a triple junction at the Amik Basin near Antakya.     

基于遥感影像的线性构造自动提取

断裂带、断层等地质构造属于地质薄弱区,由于侵蚀等作用会形成线状地貌,表现出线性构造(lineament),可以通过遥感影像上的色调变化进行解译,进而了解断裂的空间展布,推测矿产资源的地下分布、判断地质稳定性。利用线段追踪法(Segment Tracing Algorithm,STA),首先以某一遥感像素为中心分若干个方向在给定大小的搜索窗口内搜索像素值的连续性,然后对连续性好的像素应用地质统计学按一定的阈值判定其是否为线素,再根据像素值在该方向上的变化进行脊谷判定,进而按照一定距离和角度标准把判别为山谷的像素连接成线性构造,最后将重复的线素删除,从而实现遥感影像的线性构造识别。从该方法在个旧锡矿遥感影像(DEM)的应用来看,STA识别的线性构造和实测断裂(层)的走向能较好的吻合,与实测断裂(层)之间的对应关系较好,但在线素连接上需要给定人为设置的参数,还需要进一步改进算法。     

Radar and infrared remote sensing of geothermal features at Pilgrim Springs,Alaska

Radar and thermal data collected by a high-altitude aircraft were used to study thermal anomalies and structural elements of the Pilgrim Springs, Alaska area. The radar data included like- and cross-polarized imagery acquired from perpendicular flight paths. The like-polarized imagery was most effective in delineating significant linears. A large number of linears were detected from the imagery. Many of these linears represent fractures and/or faults (lineaments); some of which may possibly provide conduits for the emergence of hot water at the springs. The lineaments have a wide range in orientation, but significant concentrations are parallel to the trends of the Kigluaik and Kuzitrin faults. Radiometer data and imagery from a thermal scanner were used to study radiant surface temperatures which ranged from 3°–17°C. Thermal anomalies associated with geothermal heat sources were detected on the evening imagery, utilizing density-slicing techniques. A radiant temperature difference of 2°C between surface features was required, before a recognizable signature could be detected. Areas of hot ground were detected in site-specific study, but gentle lateral gradients were not.     

Landsat TM analysis of fracture patterns: a case study from the Coastal Cordillera of northern Chile

Cretaceous rocks on the continental margin of northern Chile record a complex geodynamic evolution. Cycles of transtensional and transpressional deformation and of extrusive and intrusive magmatism are linked to the development of crustal-scale lineaments. The Landsat Thematic Mapper is used here as a tool to define these structural features. Geocorrected data were digitally enhanced and lineaments plotted directly from a hard copy image, thereby excluding artificial or non-geological features that might degrade the subsequent structural analysis. The lineaments were then digitized and analysed using a Weighted Moving Average (WMA) technique to suppress noise and to enhance azimuthal variation. Statistical analysis of the data reveals three lineament populations. The first is a set of NNE-trending lineaments that belong to the margin-parallel, sinistral Atacama Fault System. The second is a series of NW-trending lineaments with a similar orientation to large-scale structures identified across the South American continental plate. The third is a widely spaced set of NE-trending lineaments. The key result of this study is that lineaments identified from remotely sensed data may have orientation patterns that differ considerably from those identified by traditional geological mapping and that full structural analysis of structurally complex crustal regions will likely be incomplete without a comprehensive analysis of remotely sensed data. Although the NW-trending structures are numerically dominant on the Landsat TM image, they are seldom recorded at map scale and are under-represented on published geological maps. Of the 275 faults marked on the published geological map sheets, 89 are N to NNE-trending and only 88 are NW-trending. By contrast, of 841 lineaments identified from the satellite image, 455 are NW-trending and 178 are N- to NNE-trending. The lack of prior recognition of the NW-trending structures means that their importance has been underestimated in reconstructions of the geodynamic evolution of the region. In addition, as major ore deposits in the region are frequently located at intersections between two fracture systems, the recognition here of the NW-trending set of structures should illuminate future mineral exploration programmes.     

MAIS imaging spectrometer data analysis for Ni-Cu prospecting in ultramafic rocks of the Jinchuan group,China

The Jinchuan intrusion, situated in the Gansu province of China some 30 km NE of Yongcang city is an ultramafic dyke-like body emplaced in the Longshoushan uplifted terrain on the southwest margin of the Sino-Korea platform. The intrusion is 6 km long, 35 m wide and hosts a major Ni-Cu sulfide deposit. The main stratigraphic units include the highly metamorphosed Lower Proterozoic Longshoushan group and the less extensively metamorphosed Dongzigou and Hanmushan groups of Middle and Upper Proterozoic age. The Longshoushan group consists of serpentine marble, schist, gneiss and plagioclase amphibolite. The Dongzigou group comprises schists and granitic rocks. The Hanmushan group basically is represented by a large variety of volcanics. Small mafic-ultramafic intrusions are located along faults in the Jinchuan terrain. These ultramafic rock bodies show a concentric zoning with a core of dunites and olivine pyroxenites forming the margins of the bodies. Hydrothermal alteration (mainly serpentinization) has affected the rocks of the ultramafic bodies to a variable extent; the dunites are extensively altered whereas the pyroxene rich units are relatively fresh. Field spectroscopy is used to spectrally characterize the major rock units. Imaging spectrometer data was flown during the end of July until beginning of August of 1993 with a Chinese imaging spectrometer instrument called MAIS: the Modular Airborne Imaging Spectrometer. Feature characterization permits lithologic mapping from MAIS data. This aids in mineral potential mapping in the Jinchuan region and permits the identification of areas of possible Ni-Cu deposits.     

Computer vision-based framework for extracting tectonic lineaments from optical remote sensing data

ABSTRACT

The extraction of tectonic lineaments from digital satellite data is a fundamental application in remote sensing. The location of tectonic lineaments such as faults and dykes are of interest for a range of applications, particularly because of their association with hydrothermal mineralization. Although a wide range of applications have utilized computer vision techniques, a standard workflow for application of these techniques to tectonic lineament extraction is lacking. We present a framework for extracting tectonic lineaments using computer vision techniques. The proposed framework is a combination of edge detection and line extraction algorithms for extracting tectonic lineaments using optical remote sensing data. It features ancillary computer vision techniques for reducing data dimensionality, removing noise and enhancing the expression of lineaments. The efficiency of two convolutional filters are compared in terms of enhancing the lineaments. We test the proposed framework on Landsat 8 data of a mineral-rich portion of the Gascoyne Province in Western Australia. To validate the results, the extracted lineaments are compared to geologically mapped structures by the Geological Survey of Western Australia (GSWA). The results show that the best correlation between our extracted tectonic lineaments and the GSWA tectonic lineament map is achieved by applying a minimum noise fraction transformation and a Laplacian filter. Application of a directional filter shows a strong correlation with known sites of hydrothermal mineralization. Hence, our method using either filter can be used for mineral prospectivity mapping in other regions where faults are exposed and observable in optical remote sensing data.     

Fault tectonics of the Shillong plateau and adjoining regions,north-east India using remote sensing data

The Shillong plateau in north-east India shows innumerable fracture lineaments on satellite images. In fact the whole plateau is criss-crossed by fractures. The plateau has been subjected to extensive compressional forces mainly in N-S and E-W directions resulting from the collision of the Indian plate with the Tibetan and Burmese plates, respectively. This type of plate tectonism has been responsible for the formation of many significant faults, folds and other tectonic features in the Shillong plateau and adjoining regions. The well known E-W trending Dauki fault, N-S trending faults, NE-SW trending shear zone and other prominent lineaments and their associated structural features could be studied on the basis of remote sensing techniques. Folding in soft sediments along the Dauki fault reveals the compression direction. Directional compressional tectonism has been expressed through lateral movements along the NE-SW trending shear zone and N-S trending faults and folds in the area just south of the Hatlong thrust. It has been observed from the studies that the Dauki fault zone and the areas in Bangladesh show various tectonic features, which are mostly controlled by vertical movements. Seismicity of the Shillong plateau is quite scattered all over the area. The occurrence of several deep earthquakes (> 1OOkm) indicate deep tectonic activities in the upper mantle. Earthquakes have been found to occur near some faults and this is probably an indication of recent activities along these faults.     

Application of remote sensing and GIS for the demarcation of groundwater potential zones of a river basin in Kerala,southwest coast of India

An integrated hydrogeological investigation has been made to delineate the groundwater‐potential zones of the Muvattupuzha river basin, Kerala, along the southwest coast of India. The basin is characterized by charnockites and gneisses of Archean age covering more than 80% of the area and the remaining by Pleistocene laterites and Miocene formation. The basin receives high rainfall, measuring 3100 mm/year. However, acute water shortage occurs during the premonsoon season and hence, a number of dug wells are made to tap the groundwater. Seasonal rainfall during NE and SW monsoons is the major source of groundwater recharge. Further, hydrogeomorphology, geology, fracture systems and the slope of the terrain also play a significant role on the movement and behaviour of the groundwater of this basin. The integration of conventional and remote sensing data has been made through geographic information system (GIS) and it is found that about 50% of the area can be identified as very good or good potential zones, whereas the remaining area falls under moderate and poor categories. Most of the Muvattupuzha sub‐basin and the western part of the Kothamangalam and Kaliyar sub‐basins are classified as good groundwater‐potential zones, although the eastern upstream part of the basin has poor groundwater potential.     

3D modeling of uranium-bearing solution-collapse breccias in Proterozoic sandstones (Athabasca Basin,Canada)—Metallogenic interpretations

Unconformity-related uranium deposits are the highest grade, large tonnage uranium resources in the world. In the Athabasca Basin (northern Saskatchewan, Canada), which is the premier host for unconformity-type deposits, the ore deposits are frequently hosted and surrounded by breccias in sandstone. The significance of these breccias and their relation to mineralization are of major importance for the genesis of these high-grade deposits. Therefore, a modeling study, integrating results from structural geology and petrology, was performed with the gOcad 3D modeling software, in order to decipher geometrical and geological relationships between breccias, faults and mineralization zones. Mineralized bodies and the sudoite–dravite breccia bodies display strong spatial correlations. They appear to be controlled by reverse shear zones cross-cutting the unconformity and containing graphite in the basement. Geochemical computations evidenced that volumetric water–rock ratios up to 10,000 could be obtained in these breccia bodies for volume losses of up to 90%. Assuming reasonable values for quartz saturation, hydraulic conductivity and connected porosity, the minimal fluid volume and the time duration necessary to generate the sudoite–dravite breccia bodies were estimated at ca. 2 km³ and ca. 1 Myr, respectively. The comparison of these results with literature data suggests that the formation of sudoite–dravite breccia and mineralization could have been coeval. It may be proposed that within the space created by the quartz dissolution in the breccia body, a mixing between basement and basinal fluids could have induced U deposition and allowed the development of high-grade mineralization. The first-order uranium solubility that this coeval formation would imply is consistent with literature data, which suggests that this conceptual model is reasonable.