The use of Geoelectrical Methods for Delineation of Lead-Zinc Mineralization: A Case Study of Eziama Village, Abia State, South- East, Nigeria

2D Electrical Resistivity (ER) and Instantaneous Potential (IP) geophysical techniques were used at Eziama village in Abia state of Nigeria to investigate possible Pb-Zn mineralization. The dipole-dipole electrode configuration was employed for data acquisition and Earth Imager software was used for inversion of the acquired data. The analysis of the result of the study showed the presence of the Pb-Zn ore along traverses 1, 2 and 3 while traverses 4 and 5 appear barren. Along traverse 1, the mineralized zone falls within the fractured basement and is characterized by low resistivity (about 316 – 5623 ohm-m) and high chargeability (33.2 – 128 ns) at lateral distance of 73 – 103 m. On traverse two, the ore body was identified at lateral distance of about -18 to 53 m as delineated on the IP structure with resistivity and chargeability of the anomalous zone ranging from 4.6 – 677 ohm-m and 41.8 – 142 ns respectively at depth of about 21.4 m while on traverse three, two ore bodies labeled a, a’ and b, b’ on the ER and IP cross-sections were delineated at lateral distance of about -130 to -93 m and 78 to 98 m respectively with depth to the top of the suspected ore bodies ranging from about 7.1 m for body ‘a’ and about 14.3 m for ‘a’. Traverses four and five however showed no prospect for Pb-Zn mineralization. The result of this investigation has once again demonstrated the usefulness of combined electrical resistivity and induced polarization techniques in solid mineral exploration.

Signs of anomalous behavior of the ionosphere in 2003–2014 at F1-layer heights over Irkutsk

We have detected an anomalous electron density Ne increase in winter months in Irkutsk in some years of the period 2003–2014. This effect was manifested when we compared the experimental values obtained by the Irkutsk ionosonde with model calculations at F1-layer heights (120–200 km). Two anomalous time zones have been found. The first was observed in the period 2003–2006 near solar minimum. In this zone, 2003 is the year of maximum manifestation of the winter Ne increase over the entire research period. The second anomalous zone — 2012, 2013, 2014 — was detected during solar maximum. We have explored possible causes of the Ne change in winter at the F1-layer heights in all the years under study. We have found that the main factor causing the winter increase in Ne is significant geomagnetic disturbances in the above time periods.

Signs of anomalous behavior of the ionosphere in 2003–2014 at F1-layer heights over Irkutsk

We have detected an anomalous electron density Ne increase in winter months in Irkutsk in some years of the period 2003–2014. This effect was manifested when we compared the experimental values obtained by the Irkutsk ionosonde with model calculations at F1-layer heights (120–200 km). Two anomalous time zones have been found. The first was observed in the period 2003–2006 near solar minimum. In this zone, 2003 is the year of maximum manifestation of the winter Ne increase over the entire research period. The second anomalous zone — 2012, 2013, 2014 — was detected during solar maximum. We have explored possible causes of the Ne change in winter at the F1-layer heights in all the years under study. We have found that the main factor causing the winter increase in Ne is significant geomagnetic disturbances in the above time periods.

Regional soil geochemistry for Sb and Hg in Guadalmez and Almadén synclines, South-Central Spain

<p>The geochemical similarities between Hg and Sb (along with W and As), have produced ore deposits in which both elements are present. In the present work we investigate the relationships between the Sb deposits of the Guadalmez synclinal and the Hg deposits of the Almadén synclinal, separated only 8 kilometres. To accomplish this porpoise a regular sampling grid was used, locating samples in each square (4 km2) according to lithologic criteria. In total, 116 soil samples have been taken at two depths using an Ejkelkamp sampler. The samples have been taken in an area of around 100 m2 around the set point at different depths, sample A at 2-15 cm and sample B at 15-30 cm. Each sample represents a composite sample of 3 subsamples taken at different but close locations, randomly chosen. The preparation of the samples has included drying at room temperature to avoid Hg losses, as well as its disaggregation and homogenization, prior to obtaining an aliquot of 100 grams that was ground in agate mortar until obtaining a grain size of less than 100 microns. The geochemical characterization of the samples included the analysis by energy dispersion X-ray fluorescence (EDXRF) to obtain the concentrations of major and trace elements. Total Hg data has obtained by means of Atomic Absorption Spectrometry using a Lumex equipment with a pyrolysis attachment. The distribution of Sb and Hg contents in the two synclines studied has not shown appreciable similarities. The highest concentrations of Sb have been found in the Guadalmez syncline, where the known mines of La Balanzona and Accesos are located. A particularly anomalous zone has been located in the southeaster zone of the Guadalmez synclinal, in the Ordovician age materials. Elevated Sb contents have also been found in the Almadén syncline, especially in the western zone without an observable predominance by lithology using a 4 km² grid size that could be less sensitive to scarces lithologies (e.g dykes). The Hg distribution, on the other hand, offers its maximum contents, as expected, in the Almadén syncline, particularly at the southeast part. Some anomalous Hg values have been found in Devonian materials of Guadalmez syncline. Concentrations of Cr and Ni are clearly related with the volcanic rocks of Almadén syncline, as well as with the presence of diabase intrusions in the Guadalmez syncline. Considering the age, a higher variability is observed in Hg contents than in Sb, especially in Devonian materials. Sb contents show little variability in general, but this is appreciable in the Ordovician materials of the Gualdamez syncline.</p><p>This work was funded by the ANR (ANR-19-MIN2-0002-01), the AEI (MICIU/AEI/REF.: PCI2019-103779) and author’s institutions in the framework of the ERA-MIN2 AUREOLE project, as well as by Project SBPLY/17/180501/000273, Consejería de Educación, Regional Government of Castilla-La Mancha, Spain.</p>

Detection of zones of soil contamination with contrast-in-resistivity ecotoxicants by profiling

A method for detecting zones of soil contamination with contrast-in-resistivity ecotoxicants, as well as geophysical methods for monitoring soil decontamination processes, are discussed in the article. A zone of soil contamination was designed and simulated using electrical prospecting methods - sounding and profiling. The direct and inverse problem of electrical prospecting of a contaminated zone in the form of a sphere inside a homogeneous soil body was solved in this work, while the main design dependencies were determined, which most accurately describe the data obtained experimentally. The proposed algorithm, based on adaptive step size random search, allows to quickly determine the depth and the effective radius of a zone of contamination with contrast-in-resistivity ecotoxicants, based on the results of profiling, and to estimate the degree of pollution by the ratio of the resistivity of the anomalous zone to that of the host medium.

REFLECTION OF MAGMATISM AND TECTONICS IN THE GEOPHYSICAL FIELDS OF THE SOUTHWESTERN PRIMORYE

The results of a comprehensive interpretation of geophysical fields (magnetic, gravity and radioactivity) of the South-Western Primorye (Khasansky district) are presented. The authors give schemes reflecting the relationship of geophysical fields with various surface and deep geological structures, and discontinuous disturbances of various orders. The deep boundaries of the local granitoids massifs of the Jurassic age emerging on the surface are determined. The distribution areas of Cenozoic magmatism are outlined. The anomalous zone of increased values of the radioactive field, associated with the introduction of magmatic bodies with a high content of potassium, was identified. An assumption is made about the existence of a long-lived fluid-permeable zone that controls magmatic processes in the region.

Fast 2D full-waveform modeling and inversion using the Schur complement approach

In most full-waveform inversion (FWI) problems, sufficient prior information is available to constrain the velocity of certain parts of the model, e.g., the water column or, in some cases, near-surface velocities. We take advantage of this situation and develop a fast Schur-complement-based forward modeling and inversion approach by partitioning the velocity model into two parts. The first part consists of the constrained zone that does not change during the inversion, whereas the second part is the anomalous zone to be updated during the inversion. For this decomposition, we partially factorize the governing system of linear equations by computing a Schur complement for the anomalous zone. The Schur complement system is then solved to compute the fields in the anomalous zone, which are then back substituted to compute the fields in the constrained region. For each successive modeling steps with new anomalous zone velocities, the corresponding Schur complement is easily computed using simple algebra. Because the anomalous part of the model is comparatively smaller than the whole model, considerable computational savings can be achieved using our Schur approach. Additionally, we showed that the Schur complement method maintains the accuracy of standard frequency-domain finite difference formulations, but this comes at a slightly higher peak memory requirement. Our FWI workflow shows reduced runtime by 15%–57% depending upon the depth of the water column without losing any accuracy compared to the standard method.

Seismicity Pattern Changes Prior to the 2008 Ms7.3 Yutian Earthquake

Seismicity pattern changes that are associated with strong earthquakes are an interesting topic with potential applications for natural hazard mitigation. As a retrospective case study of the Ms7.3 Yutian earthquake, which was an inland normal faulting event that occurred on 21 March 2008, the Region-Time-Length (RTL) method is applied to the seismological data of the China Earthquake Administration (CEA) to analyze the features of the seismicity pattern changes before the Yutian earthquake. The temporal variations of the RTL parameters of the earthquake epicenter showed that a quiescence anomaly of seismicity appeared in 2005. The Yutian main shock did not occur immediately after the local seismicity recovered to the background level, but with a time delay of about two years. The spatial variations of seismic quiescence indicated that an anomalous zone of seismic quiescence appeared near the Yutian epicentral region in 2005. This result is consistent with that obtained from the temporal changes of seismicity. The above spatio-temporal seismicity changes prior to the inland normal faulting Yutian earthquake showed similar features to those reported for some past strong earthquakes with inland strike faulting or thrust faulting. This study may provide useful information for understanding the seismogenic evolution of strong earthquakes.

ON SEISMIC TOMOGRAPHY ALGORITHM TO PREDICT DISCONTINUITIES IN COAL SEAMS

The article describes the algorithm for seismic imaging data processing that enables detecting and evaluating geological anomalies based on the system of specific criteria. Employing the algorithm we can complete the process of profile record, amplitude and velocity spectra computation, filtering and imaging of T-X curves. Subsequently computation and statistical processing of kinematic and dynamic parameters are made in the selected velocity windows. The main procedures for the algorithm include tomographic recovery of wavefield parameters in the plane of extraction panel, detection and interpretation of anomalous zones based on the prediction criteria to determine type of the discontinuity. There is a good reason that tomography in the plane of extraction panel shall be made in velocity windows of the dedicated wavetrains step by step for the main informative parameters. Analysis of the velocity distribution for the amplitude module maximum provides high accuracy when it comes to detect anomalous zones. This parameter is marked by relative independence on chance factors. Analysis of typical wavetrain frequency shift is determining factor indicative not only of the discontinuity but also of its type. Recording of wavetrain amplitude distribution is characterized by high accuracy in terms of anomalous zone detection. However, recording is complicated by dependence on a host of chance factors. The other parameters have much lesser quality and can be used as auxiliary. The algorithm is implemented into software capable to computerize most time-consuming operations. Use of this algorithm is illustrated as a case study for the results of data analysis and interpretation for seismic exploration at 37К10-В longwall panel section in Kuzembaev Mine (Kazakhstan).