Search

A gamma spectrometric analysis of rock samples collected from the Precambrian Oban Massif, southeastern Nigeria, was performed to determine some primordial radioelements’ activity concentrations: U-238, Th-232, and K-40, and their associated radiological hazards. The mean activity of the primordial radionuclides was determined to be 1073.06 ± 0.65, 160.74 ± 1.32, and 250.76 ± 0.91 Bq·kg−1 for 40K, 238U, and 232Th, respectively, showing that they are inhomogeneously distributed, with activity changing with the rock type and location. The activity concentrations are highest in biotite garnet schist, quartz diorite, and biotite gneiss rock domains. The mean values of the radiological hazards are 0.08 Bq·kg−1 (alpha index), 2.15 Bq·kg−1(gamma index), 2.06 Bq·kg−1(internal) and 1.63 Bq·kg−1 (external4.30 Bq·kg−1(representative level index6), 602.23 Bq·kg−1, (radium equivalent), 780 nGy·h−1 (total absorbed dose rate), 270.91 nGy·h−1 (indoor), 509.78 nGy·h−1 (outdoor), 624.99, 1329.07 and 1954.06 mSv·yr−1 (outdoor, indoor and total annual effective dose equivalent, respectively), 6448.40 (cumulative excess lifetime cancer risk) and 248.94–3761.47 Bq·kg−1 (annual gonadal dose equivalent). These results are higher than their various permissible limits (except at Ako Community) and suggest that rocks in the area may be unsuitable for constructing dwelling places. It is strongly advised that basic safety standards and precautionary measures recommended by the European Commission should be strictly adhered to while dealing with these rocks.

In this study, the potential and efficacy of adapting the bioinspired Manta ray foraging optimization algorithm (MRFO) as a tool for estimating model parameters of two-dimensional gravity profile anomalies is presented. The process of implementing the MRFO algorithm for accurate estimation of shape/depth defining parameters over geometric geologic structures was assessed. The experimental data comprised synthetically generated gravity anomalies that were later corrupted with white Gaussian noise at levels of 5, 10, and 15%, and then, case examples were taken from mining sites across different parts of the world. The algorithm was found to be fast, stable, and consistent in its search for the global best solution to each of the geophysical inverse problems. Its performance was excellent when confronted with constrained multi-parameter non-linear inversion problems and exhibited admirable stability even in the presence of noise. The consistency of the estimated results, when compared to actual values, affirmed the reliability of the procedure. It is, therefore, a stable and efficient tool for performing geophysical data inversion and is recommended for use in inverting geophysical data with higher complexities like seismic reflection, self-potential and magnetic data, which require many corrections to be performed before reliable geological interpretations can be made.

Aeromagnetic data from the Ogoja region, Southeast Nigeria, were enhanced using high-precision methods including the tilt angle of total horizontal gradient (TAHG), the softsign function (SF), and the improved logistic function (IL) with the aim of creating a new structural map. This new map can help improve the understanding of the trend, spatial distribution, and pattern of the lineaments. The TAHG, SF, and IL methods generated geologic structures with correlating trends, distributions, and patterns. However, the SF and IL techniques mapped the borders of geologic structures more precisely. The lineaments extracted from the SF and IL maps were reduced to equator (RTE) magnetic data, and a GIS was used to create structural maps with NE–SW, NW–SE, NNE–SSW, and NNW–SSE orientations. Furthermore, the depths (0–2100 m) of these geologic structures were estimated using the tilt depth technique (TDT). The high lineament density and thin sedimentation observed in the study area were triggered by the widespread Santonian igneous intrusions associated with the Abakaliki Anticlinorium. The techniques applied in our study can be employed in areas with the same conditions around the world for the precise delineation of geologic structures from magnetic and gravity data.

The high rate of depletion of mineral resources in different parts of the World has prompted researchers to intensify their search for new deposits. These searches are usually conducted using different geophysical tools and algorithms. The potential and efficacy of adapting the bioinspired Manta rays foraging optimization algorithm (MRFO) as a tool for estimating model parameters of a two-dimensional dyke-like magnetic profile anomalies are investigated. The process of implementing the MRFO algorithm in accurate estimation of four distinctive model parameters- amplitude coefficient, inclination, halfwidth and depth of burial from the surface, of an infinitely dipping dyke was presented. The experimental data comprise synthetically generated magnetic anomalies that were later corrupted with noise at levels of 5, 10, 15 and 20%, and finally, case examples from two mining sites in Peru and China. The algorithm was fast, stable and consistent in its search for the global best solution to each of the geophysical inverse problems , which all terminated before the 1000 iterations fixed for it to do so. Its performance was excellent even in the presence of random noise with varying levels. Thus, the MRFO procedure is accurate and reliable procedure for solving geophysical inverse problems and is recommended for use in modelling other geophysical problems like vertical electrical sounding , gravity, self-potential and magnetotelluric data.