Tilt Angle Derivative Research Articles

Integration of airborne geophysical data for the characterization of the geothermal system in Valle del Cura, high central Andes

The Valle del Cura region, located in the High Central Andes, over the Pampean flat-slab segment, exhibits several geothermal manifestations suggesting structural rather than magmatic controls. However, the structural and favorable conditions of this geothermal system have not been studied in detail yet. By integrating high-resolution airborne geophysical data with existing geological information using GIS tools, we can better characterize the structural controls of the thermal areas. The application of the upward continuation filter and tilt-angle derivative to the reduced to pole magnetic anomaly map allowed us to delineate structural lineaments that correlate well with known faults in the area. Euler deconvolution successfully identified local structures controlling the subsurface water upwelling and provided reliable depth estimations. Results indicate that the Despoblados area is characterized by NW-oriented deep structural controls reaching depths of up to 5 km. In contrast, the Bañitos-Gollete and the northern thermal areas are controlled by the intersection of N-S with E-W shallow structures at less than 3 km deep. Aeroradiometric data provided additional information for the characterization of several lithological units based on the dominance of radioelements (K, Th and U) in near-surface rocks by using individual and ternary maps. In addition, estimations of radiogenic heat production were crucial for assessing the potential energy of geothermal resources in the region. In particular, higher average values were obtained for igneous and metamorphic basement which may contribute to the geothermal gradient and temperature distribution at depth. Further studies, including new geophysical data acquisition and field verification, are still needed to fully describe the regional and local structures involved in these geothermal areas.

Insights into Afikpo Synclinorium structures: Subsurface analysis and intrusion outlining from airborne magnetic data

The airborne magnetic data over Afikpo Synclinorium were used to highlight subsurface structures and establish the orientations of tectonic features and their influence on the hydrocarbon play of the area. The characteristic trends of the lineaments were achieved through the center for exploration targeting of grid data analysis. The results of the TMI, residual magnetic field, first vertical, horizontal derivative, Analytic signal, and Tilt angle derivative classified the area into regions of high magnetic intensity observed around the northeastern, southwestern, and central portions of the study area. These areas characterized by anomalous signatures of short magnetic wavelengths delineate shallow magnetic sources. Conversely, regions with medium to low magnetic intensities are characterized by long magnetic wavelengths which indicates deep-seated magnetic source(s) and prospect for hydrocarbon (if other play concepts are emplace); due the thick sediment cover at the southern portion of the area (around, southern part of Nguzu, Ohafia, Biakpan, Abriba and Bende areas). The sediment thickness decreases towards north, west, North-east and north-west (dominated by Benue Trough deposit). Depth to the anomaly sources is of two categories, namely, shallow <1.0 km (dominated by NE trending structures) and deep ≥2.5 km. Ground-truthing confirmed the anomalous zone of high magnetic sources in the northeastern and central regions as Tertiary related tectonic-magmatic intrusion. The most prominent intrusion cuts across Amangwu Edda in Afikpo South through Amaeta-Oziza to Cross River State in a fissure form. This intrusion occurrence conformed to the high magnetic signature identified as a dolerite sill within the Afikpo Sub-basin. It stretches over 16 km in length with an average width of about 1.2 km, having its widest part in the northern parts of Mata Hospital Afikpo. The subsurface topographic model indicated that no fewer than 50% of the study area is characterized by sporadically distributed intrusive rocks. The result revealed several structural lineaments with high lineament density at the northcentral corner of the area trending NE-SW with fault lines (slip fault) perpendicular to it, offsetting the Akpoha, Ibii, Amasiri. and Ozara-ukwu ridges. The major drainage systems across the area followed major structural trends perpendicular to the identified major lineaments, passing through the major regional structural displacement pattern of the Basin. The emplacement of these intrusions might have impacted the hydrocarbon potential of the basin.

Mapping of geological structures and sediment thickness from analysis of aeromagnetic data over the Obudu Basement Complex of Nigeria

Abstract In this study, geologic structures, as well as attendant orientations and sediment thickness, in the Nigerian Obudu Complex were delineated using the Centre for Exploration Targeting (CET), and depth determination methods such as source parameter imaging (SPI) and standard Euler deconvolution (SED). The CET, SPI, and SED procedures were applied on the total magnetic intensity data. Also, the enhanced TMI data using analytic signal, first-vertical derivative, total-horizontal derivative, and tilt-angle derivative filters were further subjected to CET operation, with the aim of mapping both subtle and prominent lineaments. In general, mapped geologic structures trends in the NE–SW, NNE–SSW, E–W, and N–S directions. Overall, the dominant geologic structural orientations of NE–SW and NNE–SSW reflect the regional strike orientation. The regional striking of the lineation, which is caused by the Pan-African orogeny and subsequent post-orogenic processes, has an impact on these orientations. The N–S and E–W structural deviations from the main NE–SW and NNE–SSW trends are initiated by the YGS of the post-orogenic events. Overall, these complex geologic structures are probable sites for metallogenic minerals.

Identification of potential mineral exploration targets from the interpretation of aeromagnetic data covering the Sirwa region (Central Anti-Atlas, Morocco)

Situated at the junction between the Moroccan High Atlas and the Anti-Atlas, the Sirwa Massif has always been a perfect target for mining exploration for its unique geological characteristics that provide an economically valuable concentrations of metals. It corresponds to a crustal uplift at an elevation above 2000 m that were slightly folded and lifted during the Hercynian and Alpine orogeny. The structural settings of this area are very complicated due to the acute shortage of surface and subsurface structural data. The aeromagnetic data represents a powerful tool for the identification and the delineation of the poorly exposed faults, that could promote the development of new ore deposits.The processing of the residual magnetic map was carried out to locate anomalies, define the trends and boundaries of the buried structures and identify the magnetic contacts that might represent faults, fractures or lithologic boundaries. This is done by the reduction to the north pole (RTP) filter and several edge detectors processes (i.e., total horizontal derivative, the tilt angle derivative and the 3D-Euler deconvolution). The orientations of lineaments extracted from the total horizontal derivative and Tilt derivative maps predominantly suggest NE-SW to ENE-WSW trending structures, in agreement with the post-Pan-African rifting event. However, we have identified a few NW-SE and NNW-SSE trending lineaments probably related to the recent Variscan movements. The 3D Euler deconvolution (ED) suggests a depth solution that ranges from 600 m to 3400 m. The deepest lineaments have an ENE-WSW direction, and the shallowest with a depth of about 600 m, shows a NE-SW/NW-SE direction. These results reveal new tectonic features that can be useful for future mine exploration

Imaging Islamic architecture in the multileveled archaeological settlement of Tell Dibgou, Northeast Nile Delta, Egypt

Abstract Tell Dibgou, northeastern Nile Delta (Egypt), is a typical type of complex archaeological site that contains ruins from different chronological periods (Pharaonic, Byzantine, Greece-Roman and Islamic), as evidenced by the findings of pottery kilns, pottery shards, fired brick and colored glass. This study aims to image the topmost archaeological layer of Islamic architecture using electrical resistivity tomography and land-based magnetic surveys. Two nearby areas in the northern part of Tell Dibgou were investigated; the first was surveyed using resistivity tomography and magnetics, and the second used total-field and vertical magnetic gradients. Several electrode arrays (dipole–dipole, Wenner Beta, Wenner Schlumberger and pole–dipole) were tested to select the one that provides better resolution. Two inversion schemes were applied where the smoothness-constrained inversion smeared and blurred the archaeological boundaries, and the robust inversion produced models with well-defined and sharp edges. The vertical extent of the topmost archaeological layer of Islamic settlers was imaged using the electrical resistivity tomography; however, the presence of slag debris, collapsed bricks, and pottery shards at shallow depths complicated the discrimination of the closest walls. The interpretation of magnetic data (total and vertical gradients) in terms of depth and geometry was executed using semi-automated techniques such as three-dimensional, Euler deconvolution and tilt angle derivative. The geometry of archaeological targets is interpreted to be closed rooms, water tanks and corridors constructed from fired brick walls filled with clay sediments. The depths yielded from both techniques are comparable and range from &amp;gt;1 m to up to 2 m.

Mineral exploration of Iwo-Apomu Southwestern Nigeria using aeromagnetic and remote sensing

The tectonic framework, lithostructural and mineralised zones of Iwo-Apomu region of Precambrian Basement Complex rocks were investigated using integrated aeromagnetic and satellite remote datasets. Fast Fourier Transforms (FFT) performed on aeromagnetic data were: Butterworth Filter (BF), Reduction to Magnetic Equator (RTE), Regional field, Residual field, Tilt-Angle Derivative (TDR), First and Second Vertical Derivative (FVD and SVD), Tilt angle and Total horizontal derivative (TDR and TDHR), and Total Gradient Amplitude (TGA); which range from −31.97 – 123.24, −27.12 – 131.75, 1.52 – 117.90, −58.55 – 50.42, −1.35 – 1.36, −0.0712 – 0.0643, 0.0004 – 0.0102, 0.005 – 0.261 respectively. Continuations and Radially Average Power Spectrum; revealed the variations of the deep-seated basement rocks, the structures and the mineralised anomalous bodies with depth. The upward continuation maps also show that the regional trends of the mapped lithologies and lineaments/faults in the area are generally in NW-SE, E-W, and NW-SE directions. These filters defined the lithostructures, lithological boundaries, geological structures, contacts, faults, folds and mineral deposit. The results of satellite data on Principal Component Analysis (PCA), False Colour Composite (FCC) images and Band Ratio (BR) discriminated the different rock types, lithostructural boundaries and alteration zones that hosted the mineralized ore bodies which trend in NE–SW and minor NW–SE and E–W directions. The combined techniques generated showing the probable positions and trend of suspected fault/fracture, mineral deposit as well as other basement structures.

Interpretation of gravity data of Hadejia and its environs using tilt angle derivative method

Tilt angle derivative method was applied to satellite gravity data of Hadejia and surrounding for subsurface delineation. The study area falls in the contact region between Chad sedimentary formation and the crystalline basement complex in the Northeastern Jigawa state and Northwestern Yobe state of Nigeria which lies between latitude 80N - 140N and longitude 110E -130E. Satellite gravity data of the area was obtained from Bureau Gravimetrique International (BGI). The Bouguer correction was already applied on the data and the Bouguer graph was plotted using surfer software. Low gravity anomalies are detected in the dominant part of the map with its minimum value appearing in the south-eastern and north-eastern part of the map. The low anomalies are probably due to existence of thick sedimentary sections in these parts of the study area. Edges and Depth of the source of anomaly were also derived from the tilt angle. The tilt angle ranges between -3.5 degrees to 3.5 degrees with edges(boundary) at zero. This describes the edges/boundaries between the two formations. The method also revealed that the area has a depth ranging between 2km to 18km. The sedimentary areas were identified and isolated. Those areas with low anomaly and high depths are sufficient for hydrocarbon accumulation.

The Use of Edge Enhancement Methods and Euler Deconvolution to Estimate an Ore Deposit Depth from Gravity Data

The Hercynian massif of the central Jebilet (Morocco) is characterized by the outcrop of many gossans with great economic importance. This work focuses on interpreting gravity data of Benslimane gossan, located about thirty kilometres to the North-West of Marrakech. The residual gravity map of the study area highlights several anomalies which coincide with the mining and geologi-cal contexts. Applying edge detection methods, for example, tilt angle derivative (TDR), the total horizontal derivative of the tilt angle derivative (HDR_TDR) and the 3D Euler deconvolution, allowed us to estimate the depth of the Benslimane deposit. As a result, the average depth of the ore deposit was estimated to exceed 200 m. The results are promising, and the processing methods must be applied to the other gossan in the Jebilet massif for further exploration studies.

Structural and lithological interpretation of aero-geophysical data in parts of the Lower Benue Trough and Obudu Plateau, southeast Nigeria

High resolution airborne magnetic and radiometric data were used to map probable sites for polymetallic-magmatic hydrothermal deposits in the study area. The first and second vertical derivatives, horizontal gradient, analytic signal and tilt angle derivative were used to enhance magnetic data in order to determine the location of short wavelength anomalies, magnetic sources and geologic boundaries. Also, to understand and detect radiometric anomalies controlling mineralization in host rocks, enhancement operations involving potassium (K), equivalent thorium (Th), equivalent uranium (U) concentrations and ternary imageries were carried out. All these operations enabled the delineation of responses associated with mineralization, lithology and geologic structures. Generally, lineaments trend in the NE-SW, NNE-SSW, NW-SE and E-W directions, and serve as potential pathway for hydrothermal fluid migration and mineralization. Radiometric anomalies from spectrometric imageries are caused by felsic minerals, hydrothermal rock alterations, widespread shales, residual clay, oxides and accessory minerals that constitute regolith of the area. The coincident high magnetic and potassium intensities sites in Anambra Bain (AB), Abakaliki Anticlinorium (AA), Ikom-Mamfe Rift (IMR) and Obudu Plateau (OP) are probable sites for polymetallic-magmatic hydrothermal deposits. Generally, the joint magnetic and radiometric results were able to establish link between lithology, geologic structures and hydrothermal alteration patterns.

Structural trends and basement depths across Nigeria from analysis of aeromagnetic data

This study analyses Aeromagnetic Survey Data to delineate magnetic lineaments associated with fault system trends across Nigeria. A High-Pass filter is used to separate the Total Magnetic Intensity's regional and residual components. A filter like Total Horizontal Gradient, Grid Analysis and Tilt Angle derivative are used to enhance the structural trends and fault systems that predominantly trend Northeast-Southwest and East-West. Some of the magnetic signatures on the southern and northeastern Nigeria follow the rift system trend that connects the South Atlantic and inland West Africa. The Euler deconvolution depth estimate of faults range between 1840 and 6321 m (meters) across the region. The Werner deconvolution and two-dimensional forward modelling are used to infer sedimentary thicknesses beneath ten profiles (each profile traverses a major river basin in the country). The estimated depths to basement range between 1500 and 7500 m beneath the Cross-River Basin (in the south) and the Gongola Basin (in the northeast). The Hadejia River Basin in northeast Nigeria is characterised by distinct magnetic anomaly lows and a shallow depth to the basement. Further investigation of this basin is recommended.

An investigation on the structures and the basement depth estimation in the western Anatolia, Turkey using aeromagnetic data

This paper provides an investigation on describing the location of the boundaries and the vertical-horizontal dimensions of the causative bodies for Western Anatolia, Turkey. The selected study area has a crucial importance due to its location defined as one of the most rapid extensive regions in the world. Hence, it is essential to explore its structural properties and estimate the basement depth. To this end, several techniques such as tilt angle derivative, total horizontal of tilt, analytic signal are applied to aeromagnetic data of the study area. Firstly, the tilt angle derivative map is obtained from the arctangent of the ratio of vertical derivative to total horizontal derivative of the magnetic field. The map clearly shows the boundaries of the magnetic sources and they generally run along southwest-northeast directions due to the extensional regime. Moreover, using the half distance method on this map, depth of upper Turgutlu granitoid (TG) is calculated to be 4.5 km and 3.2 km for west and east, respectively. With those results, it is determined the locations of hot springs which are characterized by the low values in the tilt angle derivative map. Secondly, analytical signal method is employed to compute the basement depth. It is observed that the basement depth varies 1.4 km to 8.7 km beneath sea level. All the results and observations provide valuable insights about the region. They have a promising potential for 3D geophysical modeling of the study area as well.

Structural and hydrothermal alteration mapping related to orogenic gold mineralization in part of Kushaka schist belt, North-central Nigeria, using airborne magnetic and gamma-ray spectrometry data

This paper presents an interpretation of airborne magnetic and gamma-ray spectrometry data over a part of the Kushaka schist belt of Nigeria with a view to assess the sub-surface structural framework and hydrothermal alteration haloes that are related to orogenic gold mineralization in the study area. The geophysical analyses performed to improve the quality of the aeromagnetic data for better understanding of the subsurface geology were reduction to the equator, upward continuation, total horizontal derivative, analytical signal, source edge detection, tilt-angle derivative of total horizontal derivative. The analyses performed on the airborne gamma-ray spectrometry data were made on K/eTh, F parameter and deviation of ideal K values (Kd). Deep-seated, brittle–ductile shear/fracture zones with characteristic depth of 428.0–607.6 m and area extent of 15.5 km by 6.5 km that were delineated in the area coincide with beehive of artisanal miners exploiting gold deposits. In this study, subsurface geologic structures, specifically dykes/faults, that trend in the ENE–WSW direction constitute a first-order control on orogenic gold mineralization in the study area. The hydrothermally altered zones mapped in the area indicated they are structurally controlled and closely associated with orogenic gold mineralization. Apart from geologic structural evidences that are controlling orogenic gold mineralization, this study has indicated that hydrothermal alteration mapping is equally important for a promising orogenic gold mineralization mapping.

Source edge detection (SED) of aeromagnetic data: synthetic examples and a case study from Haimur area, south Eastern Desert, Egypt

Delineating the horizontal boundaries of magnetic sources presents a significant tool for understanding geologic structures. Many of enhancements for recognizing the boundaries of magnetic sources have been introduced. These enhancements are generally proposed based on the gradients of the magnetic field (horizontal and vertical). In this paper, the horizontal gradient magnitude (HGM), tilt derivative (TD), and horizontal tilt angle derivative (HTAD) filters were utilized to synthetic magnetic data. These filters are further applied to real aeromagnetic data of Haimur area, south Eastern Desert (ED) of Egypt data for source edge detection (SED) of the residual and regional geologic features. The adequacy of the HTAD filter is indicated using synthetic models and real data. Compared with the conventional HGM and TD methods, the SED-HTAD filter provided more detailed imaging for buried models and represented the residual and regional sources of Haimur area more clearly than HGM and TD filters.

INTEGRATION OF MAGNETIC RESIDUALS, DERIVATIVES AND LOCATED EULER DECONVOLUTION FOR STRUCTURAL AND GEOLOGIC MAPPING OF PARTS OF THE PRECAMBRIAN GNEISSES OF AGO-IWOYE, SOUTHWESTERN NIGERIA

Ground based magnetic survey conducted between longitude 06O 55I 51IIN – 06O 55I 54IIN and latitude 03O 52I 06IIE – 03O 52I 4.8IIE (Olabisi Onabanjo University) remarkably revealed a consistent subsurface NW - SE structural azimuth of localized discontinuities within the shallowly buried heterogeneous basement rocks, which at exposed locations are composed of strongly foliated granite gneiss and migmatite-gneiss with veins and veinlets principally orientated in NNW – SSE direction. Magnetic survey of the area was preceded by site inspection to avoid metallic objects interferences. Field procedure in the area involved Cartesian gridding, base station establishment, data acquisition at gridded points, and repeated bihourly diurnal checks at the base station. At the processing stage, diurnal variation effect was aptly removed before subjection to Kriging (gridding). The gridded data was then prepared as input for Forward Fourier Filter Transform (FFT), which upon definition and implementation enabled Butterworth filtering of isolated ringing effects, reduction to the equator (RTE) for geomagnetic correction, and the use of Gaussian and Upward Continuation filtering for regional magnetic intensity trend determination. Removal of the regional magnetic intensity (RMI) from the total magnetic intensity (TMI) resulted in the derivation of the residual anomaly. Enhancement filters adopted for better resolution of the residual magnetic gradient include analytical signal (AS), tilt-angle derivative (TDR), vertical derivative deconvolution (VDD), and the first vertical derivatives (FVD). TMI and RMI values range between 32925nT – 33050nT and 32935nT – 333050nT respectively, while the residual gradient ranges between 15nT/m and 10nT/m; AS ranges between 0.28nT/m and 4.1nT/m; and TDR ranges from -1.4nT/m to 1.4nT/m. Source depth calculation estimated from power spectrum analysis and Euler deconvolution ranges between 1m and 15m. Composite overlay of magnetic maps revealed jointed and faulted zones within the area; exhibiting a NW-SE principal azimuth of Liberian orogenic impress, which are in consistence with the foliation direction of the jagged foliated bedrock with an estimated maximum overburden of about 15m. The structural significance of this area as a prospective hydro-geological centre, and as an undesirable spot for high-rise building has been accurately evaluated from research findings. Application of integrated geophysical approach, complemented by detailed geological studies may furnish greater information about the subsurface structural architecture. Keywords: Gneisses; Ground Magnetic Surveying; RTE; Structural discontinuities; TDR. DOI 10.35180/gse-2020-0027

Aeromagnetic Mapping of Iwo Region of Southwestern Nigeria for Lithostructural Delineation

Abstract The IGRF filtered Aeromagnetic data over Iwo, southwestern part of Nigeria within the basement complex was subjected to reduction to magnetic equator filtering, residual filtering, upward and downward continuation filtering, automatic gain control filtering, tilt angle derivative, second vertical derivative, analytical signal and Euler deconvolution. This reveals the geologic information such as structural trend. Based on the result of the total magnetic intensity map, reduction to equator map, analytical signal map and residual magnetic intensity map, it can be concluded that; The rocks in the study area have a trend of approximately northeast-southwest direction as seen on the upward continuation map. Most of the delineated lineaments found within the study area strike mostly in NNE-SSW, NE-SW and NW-SE with minor trend of E-W and ENE-WSW direction. Structural lineament orientation suggested that they were products of Pan-African orogeny (NE-SW, NW-SE and NNE-SSW trends) and pre-Pan-African orogeny (NNW-SSE and E-W trend). The interpretation of the aeromagnetic dataset gave an insight into the regional geology and structural trends of the area.

Interpretation of high resolution aeromagnetic data for structures study and exploration of polymetallic deposits in Kalatage area, eastern Tianshan (NW China)

A high resolution aeromagnetic survey of Kalatage area was carried out, aimed at providing detailed geological structures information and guiding for further mineral prospecting. The recently acquired data was processed and interpreted to better understand the mode of occurrence of the Cu-Au polymetallic deposits and associated structural features. Several analysis techniques, such as reduction to the pole, spectral analysis, low-pass filtering, were applied to process the aeromagnetic data to understand the distribution of magnetic sources. The depth of magnetic sources was estimated by spectral analysis, and the shallower and deeper sources anomalies were analyzed. The Euler deconvolution, total horizontal derivative, tilt angle derivative and theta map were used to study lineament structures. The new structural scheme was established by comparison of above derivative results and geological data of the Kalatage area. The results show that the study area is affected by sets of NWW-SEE/NW-SE, NNE-SSW/NE-SW and nearly E-W directions faults structures; various probable magmatic rocks may be the results of the ascent and intrusion of magma along these regional fractures in the process of large-scale and deep tectonic-magmatic activities. The polymetallic ore deposits are mainly distributed within the eastern portion of the study area and are confined probably along structure lineament suggesting that it is structurally controlled. Furthermore, the favorable area for mineralization was proposed. These analyses help the recognition of structure features of differing magnetizations, interpretation of tectonic evolution, which could have important reference for further mineral prospecting.

Interpretation of gravity anomaly to delineate thrust faults locations at the northeastern part of India and its adjacent areas using source edge detection technique, tilt derivative and Cos(θ) analysis

The Northeast India and its adjacent areas converge among the three different plates, viz. Eurasia, India and Sunda plates. The tectonic interaction of Northeast India and underlying dynamics of the Himalayas as well as the Indo-Burma Ranges might cause the Assam Syntaxis. The area of study is located between latitude 23°–28°N and longitude 88°–96°E and situated in one of the most seismically active tectonic provinces in the world with seismic zone-V. This area had demonstrated several thrust faults activities and tectonic evident accomplishments during the recent past. The complicated geotectonic setups inspirits various smaller magnitude earthquakes, and the current seismicity shows seismic activities are still enduring in the Shillong Plateau, Arakan-Yoma fold belt, Bengal Basin, Naga Hills, Mikir Hills, Upper–Lower Brahmaputra Valley and Mismi Hills of Himalayan foothills. It is imperative to obtain wide-ranging learning tectonic configuration, thrust faults delineation for improved geoscientific study. Parts of the areas are extremely unreachable, and very limited thrust faults were marked by studying GIS map received from the various agencies and field geological study. During the past studies, most of the prominent lineaments/thrusts are marked; however, many active and hidden thrust faults are still unidentified. Seismic data can provide better information about the thrust faults locations, but due to small number of seismic data, the information is not adequate. In this paper, attempt has been made to study and reinterpret the available ground gravity data of northeastern parts of India for understanding thrust fault locations using various applications of gravity derivatives like analytical signal, horizontal gravity gradient, tilt derivative, horizontal tilt angle derivative and Cos(θ) analysis. Source edge detection technique has also been premeditated to categorize thrust fault locations. It is understandable that the low gravity is observed at Assam Valley which contributed sediment accumulations and higher gravity anomaly observed at Shillong Plateau and Bengal Basin containing denser formations. Bouguer gravity data is used after isostatic correction assuming Airy’s isostasy root depth model and first-order trend removal using least square technique. The derived thrust fault locations from the present study are superimposed with the existing thrust-fault locations for correlation. Some additional thrust faults are narrated which are not previously mapped. It is also suggested that Brahmaputra Thrust, Dauki Fault, Naga Thrust, Disang Thrust and Kopili Fault have key responsibility for high seismicity and tectonic movement causing upliftment and depression that encouraged some anticlockwise rotation in the area.

An aeromagnetic investigation of the Dapai deposit in Fujian Province, South China: Structural and mining implications

The Dapai region is considered as one of the largest polymetallic reserves in Fujian Province, South China. As exploration advances, so does the demand for prospecting the deeper concealed deposits in this place. However, in the past few years, due to the rugged surface topography and dense vegetation, few high-precision and large-scale ground surveys have been carried out in this area. Therefore, the understanding of the overall structure and non-exposed deposits remains insufficient to meet the challenges involved in deeper ore prospecting. In the present study, we applied a cost-effective and high-precision aeromagnetic survey to investigate the structural trends prevailing in the study area and delimit the areas with potential for finding deposits. To achieve the aforementioned goals, the tilt angle derivative was conducted on the pre-processed magnetic anomalies to highlight any deeply seated structural features, based on which reliability of the geologically-inferred faults was analyzed, and seven major faults and 22 minor faults were identified for the first time. Most of these deduced faults show an NS trend in the center part and an NW/NE trend in other parts of the study area. In addition, 3D generalized physical property inversion of the obtained residual magnetic anomalies was implemented to delineate the potential ore bodies, based on which an integrated prospecting target map was established. Our inversion results indicate that there are several isolated magnetic sources in the subsurface extending from a depth of a few hundred meters to no more than 3 km. This presented study not only leads to a deeper understanding of the Dapai deposit, but also provides references for studying other similar deposits where large-scale ground studies are hard to be executed.

Integrating magnetic and stratigraphic data to delineate the subsurface features in and around new Galala City, Northern Galala Plateau, Egypt

ABSTRACTThe Egyptian Government is developing a new city, Galala, above the Northern Galala Plateau, western side of Gulf of Suez between Ain Sukhna and Zafarana. The aim of the study is integrating magnetic and stratigraphic data to delineate the subsurface features beneath the New Galala City, in order to avoid the possible geological hazards. The stratigraphic succession in the study area consists of Precambrian basement complex overlain unconformably by Phanerozoic sequence. The Phanerozoic sequence composed mainly of siliciclastic-dominated rocks superimposed by carbonate-dominated rocks. The carbonate-dominated rocks cover most surface area, whilst the siliciclastic-dominated rocks exposed along eastern and southern foot slope of the Northern Galala Plateau. The observed palaeo-karst surfaces, fissures, caves, sink-holes and fault zones within carbonate rocks may cause some geological hazards in the study area. The total intensity aeromagnetic map was subjected to un-prescribed structural index 3D-Euler Deconvolution (ED), the tilt angle derivative (TDR) and the power spectrum in order to estimate both trends and source depths. The source depths range from 500 m to 4000 m, which result from the Precambrian basement complex. However, the trends of encountered structural elements are mainly NE–SW, NW–SE, NNW–SSE and E–W directions.

3D Modeling and Tectonic Interpretation of the Erzincan Basin (Turkey) using Potential Field Data

Erzincan Basin was investigated using gravity data within the scope of this study. It is also aimed to reveal the discontinuities in the work area as well as the buried discontinuities. Boundary determination filters and analysis of the structure of the data and its connection are revealed and clear information is obtained. Gravity anomalies were applied with an upward continuation method for 0.25, 0.50, 0.75 and 1 km levels. Total Horizontal Derivative (THD) filter, Analytical Signal (AS) filter, Tilt Angle Derivative (Tilt) filter, Total Horizontal Derivative (THDR) filter, Theta Angle Derivative (Cos ɵ) filter, Hyperbolic Tilt Angle Derivative (HTAD) were applied to upward continued data. The discontinuities in the region and the boundaries of the geological structure were revealed. Tilt and Theta Angle derivatives yield the best results from the applied derivative based filters. The obtained data were compared with the existing surface geology and the compatibility between the formations was checked. New discontinuities were found in addition to the discontinuities determined from surface observations in the light of the obtained results. Erzincan Basin was modeled in three dimensions using gravity data of the study area. As a result of modeling, Erzincan Basin has been determined to have an average thickness of 7 km.Total Horizontal Derivative (THD) filter, Analytical Signal (AS) filter, Tilt Angle Derivative (TAd) filter, Total Horizontal Derivative (THDR) filter, Teta Angle Derivative (Cos ɵ) filter, Hyperbolic Tilt Angle Derivative (HTAD) were applied to upward continued data. The discontinuities in the region and the boundaries of the geological structure were revealed. Tilt and Theta angle derivatives yield the best results from the applied derivative based filters. The obtained data were compared with the existing surface geology and the compatibility between the formations was checked. New discontinuities were found in addition to the discontinuities determined from surface observations in the light of the obtained results. Erzincan basin is modeled in three dimensions using gravity data of the study area. As a result of modeling, Erzincan Basin has been determined to have an average thickness of 7 km.