Analysis of the Czech magnetic anomaly data obtained by ground-based and airborne magnetic surveys

2020 ◽  
Author(s):  
Pavel Hejda ◽  
Dana Čápová ◽  
Eva Hudečková ◽  
Vladimír Kolejka
Keyword(s):  
Magnetic Anomaly ◽  
Magnetic Anomalies ◽  
Data File ◽  
Ore Deposits ◽  
Substantial Contribution ◽  
Magnetic Survey ◽  
Contour Maps ◽  
Anomaly Map ◽  
Ground Magnetic ◽  
Airborne Survey

<p>The modern epoch of ground magnetic surveying activity on the Czech territory was started by the Institute of Geophysics by setting up a fundamental network of the 1<sup>st</sup> order in 1957-58. It consists of 199 points and was reoccupied in 1976-78 and 1994-96. The anomaly maps were constructed by subtraction of the IGRF model.</p><p>Extensive aeromagnetic measurements have been performed from 1959 to 1972 by permalloy probe of Soviet provenience. The accuracy of the instrumentation was about (and often above) 10 nT. The second period of airborne survey started in 1976. Thanks to the deployment of proton precession magnetometer, the accuracy improved to ~ 2 nT. Since 2004 the measurements were carried out by caesium magnetometer. The data were digitized, known anthropogenic anomalies were cleared away and data were transformed to the regular grid with step 250 m. The final data file of magnetic anomalies ΔT, administered by the Czech Geological Survey, represents a substantial contribution to the exploration of ore deposits and to the structure geology in general.</p><p>In view of the fact that data file of magnetic anomalies was compiled from data acquired by heterogeneous methods in the course of more than 50 years, our recent study is aimed at looking into the homogeneity of the data by comparison them with ground-based magnetic survey. A simple comparison of the contour maps showed good similarity of the large regional anomalies. For more detailed analysis, the variation of ΔT in the neighbourhood of all points of the fundamental network was inspected and the basic statistic characteristics were computed. Summary results as well as several examples will be presented accordingly as the INSPIRE compliant services and eventually as the user-friendly web map application and made available on the CGS Portal http://mapy.geology.cz/ and on the updated web of the CzechGeo/EPOS consortium www.czechgeo.cz. Incorporating the map into the World Digital Magnetic Anomaly Map (WDMAM – IAGA) is also under consideration. This data will also be interesting for the EPOS.</p>

Ground magnetic survey for the investigation of magnetic minerals at Iboro Village, Abeokuta, south-western Nigeria

2021 ◽  
Vol 20 (2) ◽  
pp. 99-106
Author(s):  
O.I. Popoola ◽  
O.A. Adenuga ◽  
E.O. Joshua
Keyword(s):  
Magnetic Anomalies ◽  
Geological Structure ◽  
Magnetic Survey ◽  
Magnetic Minerals ◽  
Contour Maps ◽  
Ogun State ◽  
Geological Map ◽  
Regional Gradient ◽  
Ground Magnetic ◽  
Iron Ore Deposit

The geological map of the old western region of Nigeria indicates the presence of iron ore deposit at Iboro village Ogun state (7.9983o - 7.99933o N, 3.5790o - 3.5890o E). Hence a ground magnetic survey was carried out at a location at Iboro village so as to delineate the subsurface magnetic anomalies and to know whether the anomalies favour accumulation of magnetic minerals. The survey was carried out using high resolution proton precession magnetometer model G-856X. Eight traverses were run at 5m separations and earth magnetic intensity values were measured at 10m intervals along each traverse; the acquired data were corrected for drift. The residual anomalies obtained by removal of regional gradient from observed data using trend analysis were presented as profiles and maps. The treated data were qualitatively and quantitatively interpreted and the results gave values for the total ground magnetic anomalies that varied between a minimum and maximum peak values of about -33.0 and 30.6nT respectively. Depth to the basement rock was estimated using Peter’s half slope method which gave a maximum depth of about 13m. The contour maps and the total relative graphs present the subsurface picture of the geological structure that is assumed to harbour the metallic minerals through the action of the field towards the concentration of anomalies. It was suspected that the overburden was relatively thin in the study area and the minerals were at a shallow depth.

scholarly journals Acquisition procedures, processing methodologies and preliminary results of magnetic and ROV data collected during the TOMO-ETNA experiment

2016 ◽  
Vol 59 (4) ◽  
Author(s):  
Danilo Cavallaro ◽  
Luca Cocchi ◽  
Mauro Coltelli ◽  
Filippo Muccini ◽  
Cosmo Carmisciano ◽  
...  
Keyword(s):  
Magnetic Anomaly ◽  
Magnetic Anomalies ◽  
High Amplitude ◽  
Structural Features ◽  
Magnetic Survey ◽  
Remotely Operated Vehicle ◽  
Ne Sicily ◽  
Mt Etna ◽  
Source Study ◽  
Anomaly Map

<p>The TOMO-ETNA experiment was devised for the investigation of the continental and oceanic crust beneath Mt. Etna volcano and northeastern Sicily up to the Aeolian Islands, through an active source study. In this experiment, a large amount of geophysical data was collected both inland and in the Ionian and Tyrrhenian Seas for identifying the major geological and structural features offshore Mt. Etna and NE Sicily. One of the oceanographic cruises organized within the TOMO-ETNA experiment was carried out on the hydrographic vessel “Galatea” by Italian Navy. During the cruise a detailed magnetic survey and a set of ROV (remotely operated vehicle) dives were performed offshore Mt. Etna. The magnetic survey allowed the compilation of a preliminary magnetic map revealing a clear direct relationship between volcanic structures and high frequency magnetic anomalies. Significant positive magnetic anomalies were identified offshore the Timpa area and along the easternmost portion of the Riposto Ridge <span>and</span> correlated to a primitive volcanic edifice and to shallow volcanic bodies, respectively. On the whole, the magnetic anomaly map highlights a clear SW-NE decreasing trend, where high amplitude positive magnetic anomaly pattern of the SW sector passes, northeastwardly, to a main negative one. ROV dives permitted to directly explore the shallowest sectors of the Riposto Ridge and to collect several videos and seafloor samples, allowing us to identify some locally developed volcanic manifestations.</p>

REPORT OF THE SEG COMMITTEE FOR A NATIONAL MAGNETIC ANOMALY MAP

Geophysics ◽  
1976 ◽  
Vol 41 (5) ◽  
pp. 1055-1055
Keyword(s):  
Magnetic Field ◽  
Magnetic Anomaly ◽  
Developed Countries ◽  
Magnetic Survey ◽  
Accurate Representation ◽  
Anomalous Magnetic Field ◽  
Anomaly Map ◽  
The U.S ◽  
Airborne Magnetic ◽  
Airborne Magnetic Survey

Our country’s urgent need to find new sources for minerals and energy and its need to know more about the planet on which we live could be greatly assisted by preparation of a national magnetic anomaly map (NMAM)—a map which will provide an accurate representation of the earth’s anomalous magnetic field. It is startling to note that the U.S. is one of the few developed countries which has not commissioned a detailed airborne magnetic survey of the whole country, followed by production of a national magnetic anomaly map.

Influence of systematic error on the magnetic anomaly map in marine magnetic survey

2014 ◽  
Author(s):  
Gang Bian ◽  
Wei Xia ◽  
Shaohua Jin ◽  
Xinxuan Sun ◽  
Yang Cui ◽  
...  
Keyword(s):  
Systematic Error ◽  
Magnetic Anomaly ◽  
Magnetic Survey ◽  
Anomaly Map

Regional Magnetic Anomalies and Geology in Fennoscandia: A discussion

1972 ◽  
Vol 9 (3) ◽  
pp. 219-232 ◽  
Author(s):  
R. P. Riddihough
Keyword(s):  
Magnetic Anomaly ◽  
Magnetic Anomalies ◽  
Fracture Zones ◽  
West Central ◽  
Anomaly Map ◽  
The Baltic

A contoured magnetic anomaly map constructed from aeromagnetic profiles reflects the established tectonic patterns of the Fennoscandian region and permits speculations about such features as continental discontinuities colinear with oceanic fracture zones. An interpretation of the most outstanding magnetic anomaly of the region, in west-central Sweden, shows that its source is associated with a Precambrian anorogenic complex and has an unusually high magnetization. Magnetic similarities between the Baltic and Canadian shields are briefly discussed.

scholarly journals A Geophysical Survey with Magnetic Method for Interpretation of Iron Ore Deposits in the Eastern Nusawungu Coastal, Cilacap Regency, Central Java, Indonesia

2020 ◽  
Vol 5 (1) ◽  
pp. 47-55
Author(s):  
Muhammad Sehah ◽  
Sukmaji Anom Raharjo ◽  
Azmi Risyad
Keyword(s):  
Magnetic Anomaly ◽  
Iron Ore ◽  
Magnetic Anomalies ◽  
Research Area ◽  
Ore Deposits ◽  
Magnetic Method ◽  
Contour Map ◽  
Strength Data ◽  
Central Java ◽  
Iron Ore Deposits

Geophysical survey with magnetic method to interpret the iron ore deposits in the Eastern Nusawungu Coastal, Cilacap Regency, Central Java, Indonesia was carried out during six month, i.e. March –August 2017, covering the area in the geographical position of 109.3462° – 109.3718° E and 7.6958° – 7.7098° S. This survey has produced total magnetic field strength data at each measuring point in the research area. The magnetic field strength data which have been obtained, then be processed, corrected, and mapped so that the local magnetic anomaly contour map can be obtained. The local magnetic anomaly contour map shows the distribution of magnetic anomalous sources in the subsurface of research area. The 2D-modeling of magnetic anomalies data has been carried out along the AB trajectory extending on the local magnetic anomaly contour map from the position of A(109.3463°E and 7.7023°S) to B (109.3688°E and 7.7053°S), so that some subsurface anomalous objects is obtained. The modelling results of magnetic anomalies data show that the research area is estimated to have the potential of iron ore deposits. The subsurface rocks deposits containing iron ore are estimated to be located below the AB trajectory with a length about of 164.85 meters, a depth ranging of 1.709 – 31.909 meters, and a magnetic susceptibility value of 0.0122 cgs unit. These rocks are interpreted as sand deposits which coexists with silt and clay containing iron ore grains from the alluvium formation. Further, iron ore is also estimated to be present in the rocks deposits below the AB trajectory which have a depth of 24.405 – 49.809 meters and 3.989 – 11.111 meters, with the magnetic susceptibility values of 0.0093 and 0.0073 cgs units.

Kimberlites and exploration geophysics

Geophysics ◽  
1979 ◽  
Vol 44 (8) ◽  
pp. 1395-1416 ◽  
Author(s):  
James C. Macnae
Keyword(s):  
Magnetic Anomaly ◽  
Magnetic Anomalies ◽  
Magnetic Data ◽  
Magnetic Survey ◽  
Emplacement Mechanism ◽  
Geophysical Technique ◽  
Geologic Model ◽  
Main Factors ◽  
Original Size ◽  
Large Survey

This paper discusses geophysical prospecting techniques for kimberlite pipes, a major source of diamonds. A simple geologic model based on descriptions by Hawthorne (1975) and Nixon (1973) is given, and the varied geophysical responses obtained over kimberlite pipes are interpreted in terms of this model. The three main factors controlling these responses are the original size and inhomogeneity of the pipe, the depth of erosion, and the degree of weathering. Kimberlite pipes are roughly elliptical in surface exposure in most cases, with a “carrot shaped” extension at depth. The unweathered portion of the pipe generally contains a few percent magnetite, and this in most cases produces a clearly detectable magnetic anomaly. The presence of deep weathering may alter the magnetite in the top of the pipe to nonmagnetic oxides of iron, thus resulting in an increased depth to the magnetic source. If this depth is large, the magnetic response may not be large enough to detect the kimberlite in the presence of noise and the effect of other structures. In addition, if little erosion has taken place since emplacement, kimberlitic sediments known as epiclastic kimberlite will be present to considerable depths in the pipe, and this may also lead to the absence of a clear magnetic anomaly. In one large survey in South Africa, electromagnetic (EM) techniques have proven to be remarkably effective in detecting the presence of weathered clays or epiclastic kimberlite contained within the pipes. All pipes discovered during this survey had unmistakable EM signatures, while five out of eight had very small magnetic anomalies which would not likely have been selected as potential targets on the basis of magnetic data alone. These examples would indicate that in any area where deep weathering is expected, an EM survey is essential in combination with a magnetic survey if reconnaissance is to be based on airborne geophysical techniques. Due to the emplacement mechanism of kimberlite, considerable inhomogeneity within a pipe may be present, leading to significant variation in the response of any geophysical technique to one pipe, with resultant interpretation difficulties. Although this is not a limitation in the discovery of new pipes, it does make their geophysical delimitation difficult.

Intermediate‐scale magnetic anomalies of the Earth

Geophysics ◽  
1985 ◽  
Vol 50 (12) ◽  
pp. 2817-2830 ◽  
Author(s):  
J. Arkani‐Hamed ◽  
D. W. Strangway
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Magnetic Anomaly ◽  
Correlation Coefficients ◽  
Sedimentary Basins ◽  
Magnetic Anomalies ◽  
The Earth ◽  
Asymmetric Component ◽  
Anomaly Map ◽  
Well Correlation

Four separate magnetic anomaly maps of the earth are derived from magnetometer satellite data acquired at dawn and at dusk using two different altitude ranges. The magnetic anomalies on the two dawn maps (or dusk maps) are well correlated for spherical harmonics of degree less than 51, suggesting that the time varying external magnetic field and leveling noise have negligible effects on these harmonics. Dawn and dusk maps have an appreciable asymmetric component for harmonics of degree n ⩽ 5 and n = 15 and 17, arising from the quasi‐stable external magnetic field. Dawn‐dusk covariant harmonics of degree [Formula: see text] with signal‐to‐noise ratios greater than 1.5 correlate well. Correlation coefficients are higher than 0.75, implying that these harmonics can be repeatably derived. A global scalar magnetic anomaly map is derived based on these harmonics. The map is then converted to a magnetic susceptibility anomaly map by an inversion technique. The susceptibility anomalies delineate the ocean‐continent differences as well as the boundaries of tectonic provinces, modern uplifts, crustal rifts, and sedimentary basins.

New model alternatives for improving the representation of the core magnetic field of Antarctica

2006 ◽  
Vol 18 (1) ◽  
pp. 101-109 ◽  
Author(s):  
Luis R. Gaya-Piqué ◽  
Dhananjay Ravat ◽  
Angelo De Santis ◽  
J. Miquel Torta
Keyword(s):  
Magnetic Field ◽  
Magnetic Anomaly ◽  
Secular Variation ◽  
Reference Model ◽  
Accurate Determination ◽  
The Core ◽  
Continuous Models ◽  
Anomaly Map ◽  
Ground Magnetic ◽  
The Antarctic

Use of the International Geomagnetic Reference Field Model (IGRF) to construct magnetic anomaly maps can lead to problems with the accurate determination of magnetic anomalies that are readily apparent at the edges of local or regional magnetic surveys carried out at different epochs. The situation is severe in areas like Antarctica, where ionospheric activity is intense and only a few ground magnetic observatories exist. This makes it difficult to properly separate from ionospheric variations the secular variation of the core magnetic field. We examine two alternatives to the piecewise-continuous IGRF core magnetic field in Antarctica for the last 45 years: the present global Comprehensive Model (CM4) and the new version of the Antarctic Reference Model (ARM). Both these continuous models are better at representing the secular variation in Antarctica than the IGRF. Therefore, their use is recommended for defining the crustal magnetic field of Antarctica (e.g. the next generation of the Antarctic Digital Magnetic Anomaly Map).

Ground Magnetic Survey for The Investigation of Mineral Deposit at Itesi Village in Orile Ilugun, Odeda , South West Nigeria

2013 ◽  
Vol 2 (2) ◽  
pp. 110-117
Author(s):  
Sedara S. O ◽  
Joshua E. O ◽  
Popoola O.I
Keyword(s):  
Data Interpretation ◽  
Mineral Deposit ◽  
Magnetic Survey ◽  
Basement Rock ◽  
Contour Maps ◽  
Ogun State ◽  
Line Spacing ◽  
Positive Peak ◽  
Ground Magnetic ◽  
Peak Value

Advances in technique development and data interpretation have greatly improved our ability to visualize the subsurface. A Magnetic survey was carried out at a site in Itesi village, Ilugun, Odeda Local Government Area of Ogun State, Nigeria using a portable proton precession magnetometer (G-856 AX). A total of ten profiles were established in an E-W direction in the study area. The acquired magnetic field data were corrected for drift. Qualitative and quantitative interpretations were adopted to obtain negative peak value and the maximum positive peak value. The depth to top of basement rock was estimated using Peter’s Half slope. Likewise the depth to centre of basement rock was estimated using the Half width rule. The contour maps, 3-D surface map and the 1-grid vector map present the subsurface image. The whole survey area has a total length of 100 m at a line spacing of 10 m and a breadth of 45 m at 5 m spacing. The whole area was characterized by complete varying negative amplitudes from a very low peak value of about -9.9 nT and a maximum positive peak value of about 17.4 nT respectively. The closely spaced, linear sub-parallel orientations of contours from the South western part of the map suggest the possibility of faults or local fractured zones.

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