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A strange antiferromagnetic phase has controlled the magnetic and paleomagnetic properties of the Fe-Ti inversion spinel bearing rocks on the whole Earth globe

, 83-102. Orlický O., 1988: The determination of Curie temperatures and magnetic phase state of the Fe and Fe-Ti minerals on the base of the change of their magnetic susceptibility with the temperature. Mineralia Slovaka, 20, 519-536 (in Slovak). Orlický O., Fitykas M., Beˇnka J., Lipka J., Mihalíková A., Toman B., 1988: Magnetic and mineralogical investigation of remanent magnetization carriers in selected andesites and olivine basanites from Greece. Geologica Carpathica, 39, 4, 489-504 Orlický O., 1990: Detection of magnetic carriers

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

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.

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A New Original Conception in Rock Magnetism, Paleomagnetism and Geomagnetism: An Origin of the Reversed Magnetization of Rocks on Earth

Abstract

So far the field-reversal theory has been accepted to account for the reversed remanent magnetization (RM) of rocks on the Earth. Orlickỳ (2014) revealed a frequent occurrence of the antiferromagnetic (AFM) Fe-Ti oxides in the rocks. Now I have renamed these minerals as the Fe-Ti ferrimagnetic-antiferromagnetic chemical phases (Fe- Ti FriM-AFM ChPs). They may have either cubic spinel, or tetragonal spinel symmetry, respectively. They behave as the Fe-Ti polycrystalline materials. These Fe-Ti FriMAFM ChPs are the two sublattice A and B ChPs, with some specific magnetic behaviour. The titanomagnetite (Ti-Mt, Curie temperature, TC = 230 oC; FriM alignment) and the titanomaghemite (Ti-Mgh, Néel temperature, TN = 450 oC; AFM alignment) containing rocks have been identified as the representants of the the Fe-Ti FriM-AFM cubic spinel ChPs. The interactions with the magnetizing field, with the Weis molecular fields (Weiss-Heisenberg forces) have generated the reversally oriented internal field. The reversally oriented spontaneous magnetization has arosen in the rock. This internal field has been identified as the most important phenomenon leading to the production of the reversally oriented magnetization in the Fe-Ti FriM-AFM ChPs containing rocks. The equations expressing the magnetic behaviour of the magnetic susceptibility (κ) of rocks versus temperature have been derived. The Fe-Ti FriM-AFM cubic spinel can undergone the transition in favour of the Fe-Ti FriM-AFM tetragonal spinel in the rocks, due to a change of the thermodynamic conditions in nature. The reversed RM has supposed been inparted from the Fe-Ti FriM-AFM cubic spinel during this alteration-transition processess. Such tetragonal spinel is more stable and it is able to survive in the rocks in nature. The results of laboratory magnetization of the selected groupings of rocks have been presented below. The basic laboratory methods for the detection of the magnetic behaviour of the Fe-Ti FriM-AFM ChPs containing rocks are described as well. The presented results have shown that we do not need to apply the field reversal theory, because I have revealed the realistic mechanism which is able to generate the reversed RM of rocks under a presence of the normal geomagnetic field.

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High resolution airborne radiometric and magnetic studies of ilesha and its environs, southwestern Nigeria

wavenumber methods, Society of Exploration Geophysics Annual General Meeting, Calgary, Alberta, Expanded Abstracts. [44] Olowofela, J.A., Badmus, B.S., Ganiyu, S.A., Olurin, O.T., Babatunde, P. (2011): Source location and depth estimation from digitised aeromagnetic data acquired from the basement complex formation. Earth Science India , 4, pp. 136–142. [45] Geosoft INC. (2010). Geosoft INC. 85 Richmond Street, 8 th Floor, Toronto, Ontario, Canada. [46] Frantisek, H., Jiri, P., Jazek, J. Chadina, M. (2009): Out – of-Phase Magnetic Susceptibility of

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Geophysical investigation of banded iron ore mineralization at Ero, North – Central Nigeria

Abstract

The banded iron ore mineralization at Ero was investigated using aeromagnetic, resistivity and induced polarization (IP) methods with the aim of characterizing the deposit. Analysis of the aeromagnetic data involved the application of reduced-to-equator transformation, derivative filters, analytic signal and source parameter imaging techniques. Computer modelling of some of the identified anomalies was undertaken. The electrical resistivity and IP methods helped in discriminating between the iron ore and the host rock. The results showed that the banded iron formations (BIFs) were characterized by spherical analytic signal anomalies ranging from 0.035 nT/m to 0.06 nT/m within the granite gneiss and magnetic susceptibility of 0.007-0.014 SI. The iron ore had low chargeability (0.1-5.0 msec) and resistivity (1.5 × 102 to 2.5 × 103 Ωm). Structural features trending in the NE-SW, E-W, and NW-SE were identified, suggesting that the area had undergone many episodes of tectonic events. Depth to the BIF varied from the surface up to about 200 m. The chargeability response of the iron bodies suggested an average grade of 20%-40%, making the prospect for economic exploitation attractive.

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Reconstruction and appraisal of Akunu–Akoko area iron ore deposits using geological and magnetic approaches

Abstract

Geological mapping and magnetic methods were applied for the exploration of iron ore deposits in the Akunu–Akoko area of Southwestern Nigeria for the purpose of evaluating their geological characteristics and resource potentials. A proton magnetometer measures the vertical, horizontal and total magnetic intensities in gammas. The subsurface geology was interpreted qualitatively and quantitatively. The downward continuations and second vertical derivatives, the small-sized mineralised bodies and shallow features in the study area were mapped. The faults are trending in the following directions: NE–SW, NW–SE, N–S and E–W groups, while the iron ore mineralisation is structurally controlled by two major groups of fault trends, namely, the NE–SW and NW–SE; the N–S and E–W groups are mere occurrences that do not contribute to the structural control of the iron ore mineralisation in Akunu.

The upward continuation has a linear feature similar to the principal orientation of the regional faults, while Locations 2 and 3 have relatively high magnetic susceptibility zones; suspected to be iron ore deposits. The depths to the magnetic sources ranged from 25 m to about 250 m.

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