Statistical enhancement of airborne gamma-ray uranium anomalies: Minimizing the lithological background contribution in mineral exploration

• Published in: Journal of geochemical exploration Vol. 198; pp. 100 - 113
• Main Authors: Pires, Augusto Cesar Bittencourt, Carmelo, Adriana Chatack, Martins-Ferreira, Marco Antonio Caçador
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.03.2019
• Subjects: Gamma-ray spectrometry; Lithological background; Multiple regression; Uranium prospection; Gamma-ray spectrometry; Uranium prospection; Lithological background; Multiple regression
• ISSN: 0375-6742; 1879-1689
• DOI: 10.1016/j.gexplo.2018.12.014

A methodological proposal is presented for uranium prospection using multiple regression of aerogeophysical data (gamma-spectrometry and magnetometry) via a case study in a large and geologically complex area in central Brazil, where known uranium deposits occur. The model seeks to identify and minimize the background variability in uranium concentration for the different lithotypes present in the study area. The multiple regression model is obtained based on the thorium channel data, the eTh/K, eU/K ratios and the magnetic field analytical signal amplitude. Areas with high uranium concentration, in various lithotypes, are highlighted by the subtraction of the regression model obtained from the uranium values measured during the aerial survey. The study area covers part of the southeastern region of the Goiás state, including the Catalão I Complex, which hosts a phosphate mine and includes well-known uranium anomalies as well as rare earth elements associated with the phosphate deposits. The proposed method reveals the presence of anomalous areas as a function of the independent variables, represented by the geophysical properties and the different lithotypes that constitute the geological environment. Besides areas with high uranium contents associated with the Catalão I Complex, new anomalous areas associated with other types of geological environments could be identified. The targets found by the application of the proposed method, were checked in the field via geochemical analysis of rock samples in addition to in situ measurements with a portable gamma-spectrometer. Field measurements showed that, in all cases analyzed, uranium contents presented values above the average concentration of this radioelement in the earth's crust. Geochemical analyzes results from the collected samples confirmed our results by revealing uranium levels ranging from 3.5 to 15.9 ppm. The presented method was successful in identifying specific sites of high uranium concentration via aerogeophysical data, previously concealed by the geological background. •Regression model minimizes background variability in U concentration.•High uranium concentration areas are highlighted by the method.•Previously unknown anomalous uranium targets were identified.