Integration of in situ measurement of radiometric signatures and aeroradiometric data in geologic mapping of parts of so
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ORIGINAL PAPER
Integration of in situ measurement of radiometric signatures and aeroradiometric data in geologic mapping of parts of southern Benue Trough and Anambra Basin Martina Onyinye Eze 1
&
L. I. Mamah 2 & A. I. Oha 2
Received: 30 April 2018 / Accepted: 17 January 2019 # Saudi Society for Geosciences 2019
Abstract Based on the color differences due to radioelement variations of the formations/rocks within the study area, five lithologic units were delineated using the ternary image technique. The units are named classes 1, 2, 3, 4, and 5. The radiometric signature of some of the outstanding anomalies interpreted using Airborne radiometric data in parts of the southern Benue Trough and Anambra Basin was measured at 15 locations in situ. Each value in this report represents an average of multiple readings in the field. The igneous rocks are in the form of cobbles, boulders, diorite, and granodiorite that follow the normal trend for radioelement content that is increased in radioelement content with increasing silica (sio2) content; the biotite-rich granitic rock in the area has a higher radioelement content than other igneous rocks. The granitic rocks at location 10 and 11 and shale at location 14 have the highest radioelements content. The felsic rocks (biotite granite and coarse porphyritic granite) at locations 10 and 11 have higher potassium percentage (1.5% and 3.7%), this is because of the presence of potassium in primary rock forming minerals such as K-feldspars in the rock. There is no trace of potassium mineral concentration on pyroclastic rocks in the area. Abakaliki consolidated shale contains an average value of 2.40% K, 4.80 ppm uranium, and 20.1 ppm thorium. The metamorphic rocks from the area (gneissic rocks) recorded low radioelement values, and this suggests that metamorphism affected the radioelement content. Keywords Radiometric . In situ . Gamma-ray . Benue Trough
Introduction The use of gamma ray spectrometry as a tool for geological mapping has been in use several decades ago and continues to develop (IAEA 2003). Aerial gamma ray surveys involve the measurement of natural radiation from the radioelements potassium (K), uranium (U), and thorium (Th) in rocks and minerals (Killeen et al. 2015). Uranium and thorium are measured
* Martina Onyinye Eze [email protected] L. I. Mamah [email protected] A. I. Oha [email protected] 1
University of Agriculture Umudike, Umuahia, Abia State, Nigeria
2
University of Nigeria, Nsukka, Enugu State, Nigeria
indirectly from their radioactive decay products; thus, the values are referred to as equivalent uranium and thorium, designated eU and eTh. The gamma radiation measured comes from a shallow surface layer of no more than about 30 cm in rock (Jones and Schcib 2007). Airborne radiometric surveys use rotary wing (helicopter) aircraft that must fly on reylar grid lines recording the radioelements on a ship chart recordings or magnetic tape (Malcolm 1981; Dobrin and Savit 1988). The readings are used to produce radiometric maps on which th
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