scholarly journals Structural features derived from a Multiscale Analysis and 2.75D Modelling of Aeromagnetic Data over the Pitoa-Figuil Area (Northern Cameroon)

2020 ◽  
Author(s):  
Voltaire Souga Kassia ◽  
Theophile Ndougsa-Mbarga ◽  
Arsène Meying ◽  
Jean Daniel Ngoh ◽  
Steve Ngoa Embeng
Keyword(s):  
Multiscale Analysis ◽  
Structural Features ◽  
Magnetic Data ◽  
Horizontal Gradient ◽  
Aeromagnetic Data ◽  
Near Surface ◽  
Subsurface Structures ◽  
Northern Cameroon ◽  
Processing Techniques ◽  
Geological Formations

Abstract. In the Pitoa-Figuil area (Northern Cameroon), an interpretation of aeromagnetic data was conducted. The aim of this investigation was first to emphasize lineaments hidden under geological formations and secondly to propose two 2.75D models of the subsurface structures. Different magnetic data processing techniques were used, notably horizontal gradient magnitude, analytic signal, and Euler deconvolution. These techniques in combination with the 2.75D modelling to the aeromagnetic anomaly reduced to the equator permit to understand the stratification of the deep and near surface structures, which are sources of the observed anomalies. We managed to put in evidence and characterize 18 faults and some intrusive bodies. According to Euler's solutions, anomaly sources go up to a depth of 5.3 km.

Three-dimensional distribution of igneous rocks near the Pebble porphyry Cu-Au-Mo deposit in southwestern Alaska: Constraints from regional-scale aeromagnetic data

Geophysics ◽  
2014 ◽  
Vol 79 (2) ◽  
pp. B63-B79 ◽  
Author(s):  
Eric D. Anderson ◽  
Wei Zhou ◽  
Yaoguo Li ◽  
Murray W. Hitzman ◽  
Thomas Monecke ◽  
...  
Keyword(s):  
Porphyry Copper ◽  
Regional Scale ◽  
Copper Deposit ◽  
Magnetic Data ◽  
Horizontal Gradient ◽  
Aeromagnetic Data ◽  
Near Surface ◽  
Magnetic Inversion ◽  
Tilt Derivative ◽  
Southwestern Alaska

Aeromagnetic data helped us to understand the 3D distribution of plutonic rocks near the Pebble porphyry copper deposit in southwestern Alaska, USA. Magnetic susceptibility measurements showed that rocks in the Pebble district are more magnetic than rocks of comparable compositions in the Pike Creek–Stuyahok Hills volcano-plutonic complex. The reduced-to-pole transformation of the aeromagnetic data demonstrated that the older rocks in the Pebble district produce strong magnetic anomaly highs. The tilt derivative transformation highlighted northeast-trending lineaments attributed to Tertiary volcanic rocks. Multiscale edge detection delineated near-surface magnetic sources that are mostly outward dipping and coalesce at depth in the Pebble district. The total horizontal gradient of the 10-km upward-continued magnetic data showed an oval, deep magnetic contact along which porphyry deposits occur. Forward and inverse magnetic modeling showed that the magnetic rocks in the Pebble district extend to depths greater than 9 km. Magnetic inversion was constrained by a near-surface, 3D geologic model that is attributed with measured magnetic susceptibilities from various rock types in the region. The inversion results indicated that several near-surface magnetic sources with moderate susceptibilities converge with depth into magnetic bodies with higher susceptibilities. This deep magnetic source appeared to rise toward the surface in several areas. An isosurface value of 0.02 SI was used to depict the magnetic contact between outcropping granodiorite and nonmagnetic sedimentary host rocks. The contact was shown to be outward dipping. At depths around 5 km, nearly the entire model exceeded the isosurface value indicating the limits of nonmagnetic host material. The inversion results showed the presence of a relatively deep, northeast-trending magnetic low that parallels lineaments mapped by the tilt derivative. This deep low represents a strand of the Lake Clark fault.

The role of airborne geophysics for detecting hydrocarbon microseepages and related structural features: The case of Remanso do Fogo, Brazil

Geophysics ◽  
2012 ◽  
Vol 77 (2) ◽  
pp. B35-B41 ◽  
Author(s):  
Julia B. Curto ◽  
Augusto C.B. Pires ◽  
Adalene M. Silva ◽  
Álvaro P. Crósta
Keyword(s):  
Gamma Ray ◽  
Sedimentary Cover ◽  
Structural Features ◽  
Magnetic Data ◽  
Gamma Ray Spectrometry ◽  
Horizontal Gradient ◽  
Near Surface ◽  
Residual Values ◽  
Basement Structures ◽  
New Occurrences

The first direct indication of hydrocarbon occurrence in Remanso do Fogo area (Minas Gerais State, Brazil) was the existence of microseepages. However, Quaternary sedimentary cover in the area made the identification of new occurrences and associated controlling structures quite difficult. This study investigated the spatial distribution of hydrocarbon related gases in shallower to intrasedimentary depths in Remanso do Fogo area, using airborne gamma-ray spectrometry and magnetic data. The geophysical data were processed using techniques designed to suppress the influence of regional geological signatures. Known and possible new occurrences of microseepages were detected by mapping low residual potassium values and high uranium residual values in relation to potassium, termed as DRAD values, which resulted from the subtraction of potassium from uranium residual values, using a Thorium (Th)-normalizing approach. The validation of these occurrences was done based on existing gas geochemistry data in the soil. For the magnetic data, the amplitude of the analytic signal, combined with the total horizontal gradient of the subtraction between the 1200- and 400-meter upward continuations, enhanced the northwest–southeast and east–west magnetic lineaments, which are partially related to the microseepages and the drainage of the area. The distinction of near-surface and deep signatures also allowed the general identification of intrasedimentary and basement structures, which are potentially controlling the occurrences of seepages in the area.

scholarly journals Subsurface structures of a quick-clay sliding prone area revealed using land-river reflection seismic data and hydrogeological modelling

2019 ◽  
Author(s):  
Silvia Salas-Romero ◽  
Alireza Malehmir ◽  
Ian Snowball ◽  
Benoît Dessirier
Keyword(s):  
Large Scale ◽  
Geophysical Methods ◽  
Coarse Grained ◽  
Magnetic Data ◽  
Near Surface ◽  
Side Scan Sonar ◽  
Reflection Seismic ◽  
Subsurface Structures ◽  
Geotechnical Investigations ◽  
Quick Clay

Abstract. Quick-clay landslides are common geohazards in Nordic countries and Canada. The presence of potential quick clays is confirmed using geotechnical investigations, but near-surface geophysical methods, such as seismic and resistivity surveys, can also help identifying coarse-grained materials associated to the development of quick clays. We present the results of reflection seismic investigations on land and in part of the Göta River in Sweden, along which many quick-clay landslide scars exist. This is the first time that such a large-scale reflection seismic investigation has been carried out to study the subsurface structures associated with quick-clay landslides. The results also show a reasonable correlation with the radio magnetotelluric and traveltime tomography models. The morphology of the river bottom and riverbanks, as e.g. subaquatic landslide deposits, is shown by side-scan sonar and bathymetric data. Undulating bedrock, covered by subhorizontal sedimentary glacial and postglacial deposits is clearly revealed. An extensive coarse-grained layer exists in the sedimentary sequence and is interpreted and modelled in a regional context. Individual fractures and fracture zones are identified within bedrock and sediments. Hydrological modelling of the coarse-grained layer confirms its potential for transporting fresh water infiltrated in fractures and nearby outcrops. The groundwater flow in the coarse-grained layer promotes leaching of marine salts from the overlying clays by slow infiltration and/or diffusion, which helps in the formation of potential quick clays. Magnetic data show coarse-grained materials at the landslide scar located in the study area, which may have acted as a sliding surface together with quick clays.

scholarly journals Reconnaissance geochemical and geophysical exploration for gold at Iri gold field, north central Nigeria

2020 ◽  
Vol 18 (2) ◽  
pp. 19-31
Author(s):  
Ahmed Sidi Aliyu ◽  
Nuhu Musa Waziri ◽  
Hadiza Liman Mohammad ◽  
Mohammed Abubakar Mohammed ◽  
Apeh Aromeh Gideon
Keyword(s):  
Gold Mineralization ◽  
Structural Features ◽  
Parent Material ◽  
Geological Mapping ◽  
Magnetic Data ◽  
Geochemical Data ◽  
Aeromagnetic Data ◽  
Geophysical Exploration ◽  
Rock Types ◽  
Soils And Sediments

Reconnaissance geochemical and geophysical exploration for gold was carried out at IRI Gold field. Geological mapping was conducted and rocks, soils and sediments samples were collected. The outcome revealed rocks of the basement complex of Nigeria made up of mainly, Migmatite Gneiss, Older Granite and the Schist. The major lithology in the area is silicified sheared rocks and large quartz vein. Isolated occurrence of undifferentiated schist was found as parent material on which quartzite intruded possibly during a major geological activity. Shattering of the rocks left boulders and rubbles of quartzite all around two major ridges within the study area. The rocks have shown weak geochemical anomaly except in two locations were positive anomalies were observed and identified as target for further exploration. Gold veins are prominent in the area suggesting potential gold mineralization. Interpretation of the aeromagnetic data give the orientations of the structural features, the major structural trend in the area is NE-SW. The lineaments extracted from the magnetic data range in length from 46.43m to about 1251.66m. Most of the lineaments extracted from the area are subsurface within the quartz-mica and migmatites while some of them have surface expressions even though not clearly defined. These magnetic lineaments could be the contacts between two rock types of contrasting magnetic   susceptibility   or   edges   of   structures   that   could   be faults or intrusive bodies. Interpreted satellite data show several subsurface structures which could be hosts to gold mineralization in the area. Results of the geochemical analysis of rocks, soils and sediments were super imposed on the interpreted aeromagnetic data and similar geochemical and geophysical signatures were established.   Index Terms: Gold mineralization, aeromagnetic data, geochemical data, schist belt, Nigeria

scholarly journals Exploiting Aeromagnetic and Gravity Data Interpretation to Delineate Massif Deposits of Rehamna Area (Western Meseta-Morocco)

2021 ◽  
Vol 54 (2C) ◽  
pp. 13-28
Author(s):  
Kawtar Benyas
Keyword(s):  
Gravity Data ◽  
Precious Metals ◽  
Data Interpretation ◽  
Structural Features ◽  
Magnetic Data ◽  
Gravity Gradient ◽  
Horizontal Gradient ◽  
Geological Structures ◽  
Magnetic Signatures ◽  
First Vertical Derivative

The analysis of the magnetic signatures and gravity gradient values of the Rehamna Massif south of the Moroccan Western Meseta by using Geosoft Oasis Montaj 7.0.1 software, allowed us to detect several useful anomalies to be exploited and which are related to magmatic bodies and structural features within the study area. These data were analyzed by applying several techniques, including the horizontal gradient filters combined with the first vertical derivative. Subsurface structures; such as geological boundaries, faults, dykes and folds, were visualized as lineaments on geophysical maps, then results were compared with structural features provided by previous studies in the region. Thus, the Rehamna Massif structural map shows sets of linear features which may represent faults or boundaries of geological structures, which can be either faults or boundaries of geological structures, and they are mostly oriented in the directions: N-S, NNE-SSW, NE-SW, E-W with the predominance of the NNE-SSW to NE-SW directions. In addition, the super position of the minerals bearing beds or formations were distinguished from gravity and magnetic data processing results. Some of the recognized anomalies are related to the existence of precious metals which belong to the granitic bodies within the study area.

Practical considerations in the use of edge detectors for geologic mapping using magnetic data

Geophysics ◽  
2017 ◽  
Vol 82 (3) ◽  
pp. J1-J8 ◽  
Author(s):  
Mark Pilkington ◽  
Victoria Tschirhart
Keyword(s):  
Magnetic Field ◽  
Detection Methods ◽  
Magnetic Data ◽  
Horizontal Gradient ◽  
Recent Effort ◽  
Aeromagnetic Data ◽  
Geologic Mapping ◽  
Magnetization Direction ◽  
Model Studies ◽  
Edge Detectors

Locating the edges of magnetized sources provides a fundamental tool in the geologic interpretation of magnetic field data. Much recent effort has been expended on developing improvements to existing edge-detection methods, resulting in purported increases in accuracy and continuity along edges, reduction of noise effects, and limiting the influences of variable depth to source, magnetization direction, and source dip. These endeavors are valuable and provide interpreters with a wider range of tools to carry out geologic interpretations of aeromagnetic data. Nevertheless, survey parameters such as flight height and line spacing impose limits on the quality of edge locations that can be achieved. Using model studies, we quantify the effects that source size, depth, and interference between sources have on calculated edge locations. Based on the known behavior of established edge detectors, we found that many of the newer approaches offer limited advantages over older methods. Consequently, we studied an example of field mapping of geologic contacts in the Canadian Shield, supported by aeromagnetic data, using calculation of a standard edge detector: the horizontal gradient magnitude of the total magnetic field or TF-hgm. Calculated edge locations estimated from this method appear sufficiently accurate and continuous to provide a solid basis on which the mapping campaign was based and executed successfully.

Linear feature analysis for aeromagnetic data

Geophysics ◽  
2006 ◽  
Vol 71 (6) ◽  
pp. L61-L67 ◽  
Author(s):  
R. O. Hansen ◽  
Eduard deRidder
Keyword(s):  
New York ◽  
Principal Curvature ◽  
New York State ◽  
Synthetic Data ◽  
Depth Estimation ◽  
Structural Features ◽  
Horizontal Gradient ◽  
Aeromagnetic Data ◽  
Linear Feature ◽  
Total Gradient

This paper presents a new approach to detecting and two approaches to displaying lineaments associated with high-angle magnetic contacts, based on analysis of the curvature of the total horizontal gradient of the total magnetic field reduced to the pole. The first display is a contour or color plot of minus the principal curvature of largest absolute value. The second is a point plot of the local maxima of minus the largest principal curvature in regions where this curvature is negative. The paper also develops a depth-estimation technique for magnetic contacts based on the ratio of the curvature of the total gradient to the total gradient itself. Tests on synthetic data yield excellent results in detecting and delineating magnetic contact edges, and reasonable performance in producing depth estimates for the magnetic contacts. Results obtained using aeromagnetic data from the Finger Lakes region of New York State show good correlation with known structural features.

INTEGRATING SEISMIC, GRAVITY AND AEROMAGNETIC DATA IN THE STRUCTURAL INTERPRETATION OF THE MERLINLEIGH SUB-BASIN, WESTERN AUSTRALIA

1997 ◽  
Vol 37 (1) ◽  
pp. 205
Author(s):  
A. J. Mory ◽  
R. P. lasky
Keyword(s):  
Potential Field ◽  
Gravity Data ◽  
Low Cost ◽  
Late Carboniferous ◽  
Petroleum Exploration ◽  
Magnetic Data ◽  
Limited Information ◽  
Aeromagnetic Data ◽  
Near Surface ◽  
Potential Field Data

The southern Merlinleigh Sub-basin is a frontier area for petroleum exploration within the onshore Southern Carnarvon Basin, with limited seismic coverage and only two deep exploration wells. High resolution aeromag- netic and semi-detailed gravity data acquired in 1995 provide relatively low cost structural inf ormation"comple- mentary to the regional seismic coverage.Two-dimensional seismic data can be mapped with confidence if the lines are closely spaced. By identifying lineaments on potential-field images, orientations for structures within the sedimentary succession, and at basement or intra-basement levels, can assist in the interpretation of faults and structures in areas of limited seismic coverage, and to extrapolate them outside areas of seismic control. Consequently, by integrating seismic and potential-field data, a more rigorous interpretation of the structural geometry can be achieved and thereby assists in reconstructing the evolution of a sedimentary basin.The aeromagnetic data provided only limited information about the structure of the Merlinleigh Sub-basin because magnetic anomalies appear to be dominated either by near-surface or deep intra-basement sources. In contrast, the gravity data provide a more reliable definition of the structure at basement level and, to a lesser extent, within the sedimentary sequence.Seismic, gravity and magnetic data show that the region is a large north-trending Late Carboniferous to Permian depocentre and can be sub-divided into two main troughs east of the Wandagee and Kennedy Range Faults. These are en-echelon fault systems with syn- depositional growth during the main period of rifting in the Late Carboniferous to Early Permian.

scholarly journals Evidence of Major Structural Features over the Pan-African Domain in the Bertoua-Mbangue Area (East Cameroon) from a Multiscale Approach of Modeling and Interpretation of Aeromagnetic Data

2019 ◽  
Vol 2019 ◽  
pp. 1-12
Author(s):  
Owono Amougou Olivier Ulrich Igor ◽  
Ndougsa Mbarga Theophile ◽  
Meying Arsène ◽  
Assembe Stephane Patrick ◽  
Ngoh Jean Daniel ◽  
...  
Keyword(s):  
High Amplitude ◽  
Structural Features ◽  
Short Wave ◽  
The Other ◽  
Horizontal Gradient ◽  
Multiscale Approach ◽  
Magnetic Intensity ◽  
Aeromagnetic Data ◽  
Pan African ◽  
Basement Structures

The aim of this study is to investigate crustal structures from East Cameroon, using aeromagnetic data. The modeling of aeromagnetic data is conducted using the Oasis Montaj 8.0 software. The total magnetic intensity map reduced to the equator (RTE-TMI) shows important anomalies features, namely, the Northern East magnetic anomalies of high amplitude, the Southwest where very low values of the magnetic intensity were observed, and a corridor with negative values relatively high, separating the anomalies. The horizontal gradient map shows on the one hand brittle and folded structures carried out in the area of study and on the other hand various rectilinear, narrow, and short-wave anomalies that can be classified as a family of little faults. The maxima observed on the RTE-TMI maps are correlated to intrabasement contacts; and the map derived from Euler’s solutions permitted to evaluate the depth of the geological accidents observed from the other filters. This map also reveals new faults with a depth greater than 5000 m. The lineaments identified in the Southwestern part could be linked to the Pan-African orogeny and seem to correspond to deep-seated basement structures, which are referred to the tectonic boundary between Congo Craton and the Pan-African orogeny belt. A 23/4-D modeling confirmed the observations derived from the RTE-TMI and HGM maps analyses. It shows intrusive bodies composed of gneiss and porphyroid granite and some domes with their roof situated at various depths not exceeding 1800 m from the surface. The structural map of the study area shows the trending of the structural features observed, namely, NE-SW, NW-SE, ENE-WSW, and WNW-ESE, respectively, while the E-W and N-S are secondary orientation of the observed tectonic evidence. Moreover, circular anomalies observed over the area are assimilated to intrusions of high magnetic materials or to granitic domes.

scholarly journals Major tectonic structures in northeastern Greece deduced from geophysical and seismological data

2018 ◽  
Vol 40 (3) ◽  
pp. 1279
Author(s):  
A. Stampolidis ◽  
G. Tsokas ◽  
A. Kiratzi ◽  
S. Pavlides
Keyword(s):  
Noise Suppression ◽  
Active Tectonics ◽  
Gravity Anomalies ◽  
Structural Features ◽  
Magnetic Data ◽  
Physical Parameters ◽  
Tectonic Structures ◽  
Buried Structures ◽  
Near Surface ◽  
Gravity And Magnetic

We apply lineaments analysis on the gravity and magnetic data of NE Greece, and combine seismological and geophysical data in order to delineate the major structural features. These methods are frequently used for extracting the dimensional and physical parameters of the buried structures that stimulate gravity and magnetic fields. These estimates concern the location, local depth, strike, dip and physical quantity contrast, of potential field contacts. We used results from previous studies in order to correct the Bouguer data for the gravity effect of the crust. The isostatic residual gravity anomalies, produced from the subtraction of the effect of the crust, are related to near-surface features. Noise suppression was achieved by slightly upward continuing the data by one cell size. Geologic significance of detected lineaments is confirmed by comparisons with the known geology, active tectonics and seismicity as well as with topographic lineaments

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