scholarly journals Magnetic and Very Low Frequency Electromagnetic (VLF-EM) investigations for gold exploration around Ihale in Bunnu-Kabba Area of Kogi, north-central Nigeria

2018 ◽  
Vol 48 (3) ◽  
pp. 191-205
Author(s):  
Olawale Olakunle Osinowo ◽  
Michael Oluseyi Falufosi
Keyword(s):  
Current Density ◽  
Low Frequency ◽  
Magnetic Anomalies ◽  
Magnetic Data ◽  
Pegmatite Vein ◽  
Geophysical Investigation ◽  
North Central ◽  
Very Low Frequency ◽  
Reference Profile ◽  
Ground Magnetic

Abstract This study integrates ground magnetic and Very Low Frequency Electromagnetic (VLF-EM) methods of geophysical investigation to probe the subsurface in terms of rock magnetic susceptibility and ground conductivity for the purpose of identifying mineralized pegmatite veins that could serve as host for gold and associated metallic deposits. Twenty five (25) carefully planned ground magnetic and VLF-EM profiles, each, were occupied east and west of a reference profile which was purposively established on an identified mineralized pegmatite vein around Ihale in Bunnu-Kabba area of Kogi, north-central Nigeria. The acquired ground magnetic data were filtered and Reduced To Pole at Low Latitude (RTPLL) to remove regional field effect, cultural noise as well as focus the peaks of magnetic anomalies over corresponding sources. The measured raw real and raw imaginary components of the EM fields were subjected to Fraser and Karous Hjelt filtering to remove harmonic noise, focus and make anomaly amplitudes relate directly to the causative conductor as well as generate current density employed to characterise the subsurface. Seven (7) zones of relatively high VLF-EM derived current density with matching high residual positive magnetic anomalies present closely correlate-able signatures with subsurface response obtained around the reference profile established where local mining activities indicate evidence of gold and associated metallic mineralization of the pegmatite vein. The delineated zones constitute targets for gold and associated base metal prospects which could be further developed for economic benefit of the community.

scholarly journals A model for estimating the relation between the Hall to Pedersen conductance ratio and ground magnetic data derived from CHAMP satellite statistics

2007 ◽  
Vol 25 (3) ◽  
pp. 721-736 ◽  
Author(s):  
L. Juusola ◽  
O. Amm ◽  
K. Kauristie ◽  
A. Viljanen
Keyword(s):  
Current Density ◽  
Geomagnetic Latitude ◽  
Magnetic Data ◽  
Equivalent Current ◽  
Champ Satellite ◽  
Long Time ◽  
Conductance Ratio ◽  
Ground Magnetic ◽  
Eiscat Radar ◽  
Magnetic Satellite

Abstract. The goal of this study is to find a way to statistically estimate the Hall to Pedersen conductance ratio α from ground magnetic data. We use vector magnetic data from the CHAMP satellite to derive this relation. α is attained from magnetic satellite data using the 1-D Spherical Elementary Current Systems (SECS). The ionospheric equivalent current density can either be computed from ground or satellite magnetic data. Under the required 1-D assumption, these two approaches are shown to be equal, which leads to the advantage that the statistics are not restricted to areas covered by ground data. Unlike other methods, using magnetic satellite measurements to determine α ensures reliable data over long time sequences. The statistical study, comprising over 6000 passes between 55° and 76.5° northern geomagnetic latitude during 2001 and 2002, is carried out employing data from the CHAMP satellite. The data are binned according to activity and season. In agreement with earlier studies, values between 1 and 3 are typically found for α. Good compatibility is found, when α attained from CHAMP data is compared with EISCAT radar measurements. The results make it possible to estimate α from the east-west equivalent current density Jφ; [A/km]: α=2.07/(36.54/|Jφ|+1) for Jφ<0 (westward) and α=1.73/(14.79/|Jφ+1) for Jφ0 (eastward). Using the same data, statistics of ionospheric and field-aligned current densities as a function of geomagnetic latitude and MLT are included. These are binned with respect to activity, season and IMF BZ and BY. For the first time, all three current density components are simultaneously studied this way on a comparable spatial scale. With increasing activity, the enhancement and the equatorward expansion of the electrojets and the R1 and R2 currents is observed, and in the nightside, possible indications of a Cowling channel appear. During southward IMF BZ, the electrojets and the R1 and R2 currents are stronger and clearer than during northward BZ. IMF BY affects the orientation of the pattern.

Geophysical investigation of the Beinn an Dubhaich Granite, Skye

1996 ◽  
Vol 133 (2) ◽  
pp. 171-176 ◽  
Author(s):  
N. R. Goulty ◽  
C. E. Darton ◽  
A. E. Dent ◽  
K. R. Richardson
Keyword(s):  
Magnetic Anomalies ◽  
Significant Finding ◽  
Geophysical Investigation ◽  
Previous Suggestion ◽  
Clear Cut ◽  
The Third ◽  
Minimum Depth ◽  
Valid Evidence ◽  
Granite Outcrop ◽  
Ground Magnetic

AbstractThere has been a long-standing controversy concerning the form of the Beinn an Dubhaich Granite, which intrudes Cambro-Ordovician limestones and contains enclosures of limestone at outcrop. We have undertaken a three-part geophysical investigation with the aim of resolving some issues raised by previous workers. Our most significant finding results from the measurement of a gravity profile across Beinn an Dubhaich. It reveals a negative anomaly of more than 2 mGal over the granite outcrop. Our preferred model to fit this anomaly is a steep-sided granite stock extending down to about 1 km depth, which implies that the limestone enclosures are roof pendants. In a supplementary study, we measured magnetic profiles across dykes in some of the limestone enclosures in order to determine the depth to the contact with the underlying granite. However, in the most clear-cut cases we could only determine a minimum depth of 20 m, and were unable to constrain the maximum depth. In hindsight, we suggest that microgravity surveying would be a better method for determining the thicknesses of the limestone roof pendants. In the third part of the investigation, we measured a tight grid of magnetic profiles to the northeast of the granite outcrop to test a previous suggestion that dyke-like lobes of granite intrude pre-existing fractures in the overlying limestones. We located several large magnetic anomalies associated with outcropping doleritic dykes and concluded that these had not been correctly identified in the earlier work. Consequently, the ground magnetic profiles acquired to date provide no valid evidence to support the idea of an interfingering contact between the limestones and the underlying granite.

scholarly journals Assessing the Potential Earthquake Precursory Information in ULF Magnetic Data Recorded in Kanto, Japan during 2000–2010: Distance and Magnitude Dependences

Entropy ◽  
2020 ◽  
Vol 22 (8) ◽  
pp. 859 ◽  
Author(s):  
Peng Han ◽  
Jiancang Zhuang ◽  
Katsumi Hattori ◽  
Chieh-Hung Chen ◽  
Febty Febriani ◽  
...  
Keyword(s):  
Low Frequency ◽  
Magnetic Anomalies ◽  
Prediction Performance ◽  
Magnetic Data ◽  
Optimal Prediction ◽  
Forecasting Performance ◽  
Earthquake Predictions ◽  
Precursory Information ◽  
Better Than ◽  
Magnetic Station

In order to clarify ultra-low-frequency (ULF) seismomagnetic phenomena, a sensitive geomagnetic network was installed in Kanto, Japan since 2000. In previous studies, we have verified the correlation between ULF magnetic anomalies and local sizeable earthquakes. In this study, we use Molchan’s error diagram to evaluate the potential earthquake precursory information in the magnetic data recorded in Kanto, Japan during 2000–2010. We introduce the probability gain (PG′) and the probability difference (D′) to quantify the forecasting performance and to explore the optimal prediction parameters for a given ULF magnetic station. The results show that the earthquake predictions based on magnetic anomalies are significantly better than random guesses, indicating the magnetic data contain potential useful precursory information. Further investigations suggest that the prediction performance depends on the choices of the distance (R) and size of the target earthquake events (Es). Optimal R and Es are about (100 km, 108.75) and (180 km, 108.75) for Seikoshi (SKS) station in Izu and Kiyosumi (KYS) station in Boso, respectively.

Natural‐field and very low‐frequency tipper profile interpretation of contacts

Geophysics ◽  
1987 ◽  
Vol 52 (12) ◽  
pp. 1697-1707 ◽  
Author(s):  
Victor F. Labson ◽  
Alex Becker
Keyword(s):  
Numerical Models ◽  
Low Frequency ◽  
Washington State ◽  
Trial And Error ◽  
North Central ◽  
Natural Field ◽  
Very Low Frequency ◽  
Basement Faults ◽  
Vertical Contact ◽  
Metasedimentary Sequence

Anomalous vertical magnetic field (tipper) profiles acquired using natural or very low‐frequency (VLF) radio transmitter sources can be interpreted simply and rapidly for a number of geologic settings. The relations between computed numerical models, and outcropping dipping and buried vertical contacts are presented here in a series of interpretation charts. Use of the tipper phase in the analysis minimizes the effect of transmitter azimuth in the VLF case. Two examples illustrate the application to field data. An audiofrequency natural‐field tipper profile over a conductive bed in a north‐central Washington State metasedimentary sequence demonstrates the interpretation procedure for a dipping contact. VLF profiles over covered basement faults in Ontario demonstrate the application for a buried vertical contact. In both cases the quick results are in agreement with the much more laborious trial‐and‐error matching to two‐dimensional models.

scholarly journals Mineral Prospect Identification Using Inducedpolarization And Very Low Frequency-EM Methods At Sangon, Kalirejo Village, Kokap Sub-District, Kulonprogo Regency, Special Region Of Yogyakarta, Indonesia

2020 ◽  
Vol 22 (3) ◽  
pp. 1
Author(s):  
Adera Nurul ◽  
Arga Kunang ◽  
Arief Khoiruddin ◽  
Arif Fikri ◽  
Benedicta Nathania ◽  
...  
Keyword(s):  
Electric Current ◽  
Current Density ◽  
Low Frequency ◽  
Induced Polarization ◽  
Electric Current Density ◽  
High Resistivity ◽  
Alteration Zone ◽  
Frequency Method ◽  
Very Low Frequency ◽  
Low Sulfidation

A research of induced polarization and very low frequency method was carried out at Sangon Village, Kulonprogo to identify mineralization zone. The result of these methods were able to be used to support each other. Mineralization zone is shown by high resistivity and high hargeability area of induced polarization method, and is also shown by high electric current density area of very low frequency method. Interpretation of resistivity and chargeability model shows that mineralization zone is mostly located at the depth below 10 m from surface. On the other hand, interpretation of electric current density models at depth 10 m and 20 m show that mineralization zone is not well distributed respect to alteration zone, which is the character of low sulfidation epithermal type, mostly at north-south direction.

scholarly journals Low frequency modulation of transionospheric radio wave amplitude at low-latitudes: possible role of field line oscillations

2002 ◽  
Vol 20 (1) ◽  
pp. 69-80 ◽  
Author(s):  
A. K. Sinha ◽  
B. M. Pathan ◽  
R. Rajaram ◽  
D. R. K. Rao
Keyword(s):  
Radio Wave ◽  
Field Line ◽  
Local Field ◽  
Low Frequency ◽  
Magnetic Data ◽  
Main Body ◽  
Radio Waves ◽  
Ion Distributions ◽  
Low Latitudes ◽  
Ground Magnetic

Abstract. Ionospheric scintillations of radio waves at low-latitudes are associated with electron density irregularities. These irregularities are field-aligned and can provide excitation energy all along the field line to non-local field-aligned oscillations, such as the local field line oscillations. Eigen-periods of toroidal field line oscillations at low-latitudes, computed by using the dipole magnetic field and ion distributions obtained from the International Reference Ionosphere (IRI) for typical nighttime conditions, fall in the range of 20–25 s. When subjected to spectral analysis, signal strength of the radio waves recorded on the 250 MHz beacon at Pondicherry (4.5° N dip), Mumbai (13.4° N dip) and Ujjain (18.6° N dip) exhibit periodicities in the same range. For the single event for which simultaneous ground magnetic data were available, the geomagnetic field also oscillated at the same periodicity. The systematic presence of a significant peak in the 20–25 s range during periods of strong radio wave scintillations, and its absence otherwise suggests the possibility that field line oscillations are endogenously excited by the irregularities, and the oscillations associated with the excited field line generate the modulation characteristics of the radio waves received on the ground. The frequency of modulation is found to be much lower than the characteristic frequencies that define the main body of scintillations, and they probably correspond to scales that are much larger than the typical Fresnel scale. It is possible that the refractive mechanism associated with larger scale long-lived irregularities could be responsible for the observed phenomenon. Results of a preliminary numerical experiment that uses a sinusoidal phase irregularity in the ionosphere as a refracting media are presented. The results show that phase variations which are large enough to produce a focal plane close to the ground can reproduce features that are not inconsistent with our observations.Key words. Magnetospheric physics (magnetosphere – ionosphere interactions) Ionosphere (ionosphere – magnetoshere interactions; ionospheric irregularities)

Modeling and inversion of magnetic and VLF-EM data with an application to basement fractures: A case study from Raigarh, India

Geophysics ◽  
2007 ◽  
Vol 72 (5) ◽  
pp. B133-B140 ◽  
Author(s):  
V. Ramesh Babu ◽  
Subhash Ram ◽  
N. Sundararajan
Keyword(s):  
Spatial Distribution ◽  
Low Frequency ◽  
Analytical Signal ◽  
Magnetic Data ◽  
Fracture Zones ◽  
Very Low Frequency ◽  
Subsurface Resistivity ◽  
Spatial Locations ◽  
And Inversion

We present modeling of magnetic and very low frequency electromagnetic (VLF-EM) data to map the spatial distribution of basement fractures where uranium is reported in Sambalpur granitoids in the Raigarh district, Chhattisgarh, India. Radioactivity in the basement fractures is attributed to brannerite, [Formula: see text] complex, and uranium adsorbed on ferruginous matter. The amplitude of the 3D analytical signal of the observed magnetic data indicates the trend of fracture zones. Further, the application of Euler 3D deconvolution to magnetic data provides the spatial locations and depth of the source. Fraser-filtered VLF-EM data and current density pseudosections indicate the presence of shallow and deep conductive zones along the fractures. Modeling of VLF-EM data yields the subsurface resistivity distribution of the order of less than 100 ohm-m of the fractures. The interpreted results of both magnetic and VLF-EM data agree well with the geologic section obtained from drilling.

scholarly journals Geophysical prospecting for iron ore deposit around Tajimi village, Lokoja, North–Central Nigeria

2016 ◽  
Vol 63 (3) ◽  
pp. 151-160 ◽  
Author(s):  
Oyelowo Bayowa ◽  
Gbenga Ogungbesan ◽  
Razak Majolagbe ◽  
Simeon Oyeleke
Keyword(s):  
Iron Ore ◽  
Ore Deposits ◽  
Magnetic Data ◽  
Ore Deposit ◽  
North Central ◽  
Sudden Drop ◽  
Electrical Resistivity Survey ◽  
Subsurface Layers ◽  
Ground Magnetic ◽  
Iron Ore Deposit

Abstract Ground magnetic and electrical resistivity survey were undertaken to investigate the occurrence and geometry of iron ore deposit around Tajimi village, Lokoja, North-Central Nigeria. The generated residual map of the ground-magnetic data acquired at 250 stations along 15 traverses revealed numerous prominent anomalies, mostly trending in the N-S direction. The radial power spectrum revealed the depth to magnetic sources between 6 m to 20 m. The interpreted VES data characterized the area into three subsurface layers: top soil, presumably iron ore layer and weathered/fresh basement. The result of vertical electrical sounding curves showed a sudden drop in resistivity (42-241 Ωm) over high magnetic response. The geo-electric section revealed that the study area is generally characterized with thin overburden (0.5-1.7 m) and the thickness of the second layer (presumed to be the iron ore layer) ranged between 6.2-25.1 m. The study concluded that areas of high magnetic intensity showed a sudden drop in resistivity value for the VES points, which give an indication of the presence of an electrically conductive structure presumed to be iron ore deposits.

scholarly journals Effect of Magnetic Anomalies on Very Low Frequency Discrete Emissions

1963 ◽  
Vol 16 (4) ◽  
pp. 588
Author(s):  
RL Dowden
Keyword(s):  
Field Line ◽  
Geomagnetic Field ◽  
Low Frequency ◽  
Magnetic Anomalies ◽  
Emission Frequency ◽  
Geomagnetic Field Line ◽  
Very Low Frequency ◽  
Cyclotron Radiation

The author has suggested (Dowden 1962) that. the spectrogram (frequency v. time) shapes of V.L.F. discrete emissions can be explained as Doppler-shifted cyclotron radiation from electrons spiralling along a geomagnetic field line away from the observer. The emission frequency is given by Eidman (1958),

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