Gamma-ray spectrometry applied in the identification of potential acid mine drainage generation zones in waste rock pile with uranium ore and associated sulfides (Caldas, Brazil)

Abstract

Metal mining deeply modifies local environmental dynamics and produces large volumes of waste rock and residues, which is expected to be carefully disposed in order to prevent soil, water, and environment degradation. The Osamu Utsumi mine was a pioneer uranium ore exploitation site in Brazil, located in the State of Minas Gerais. The open pit and the high concentration of sulfide in waste rock piles are nowadays a dispendious concern to the Nuclear Industries of Brazil (INB, in Portuguese), due to sulfide oxidation and the resultant acid mine drainage (AMD). The objective of this research is to analyze the correlation between gamma-ray spectrometry data and the generation of AMD in a waste rock pile, locally known as BF-04. Potassium concentrations can be used to distinguish zones of rock depletion, lowest concentrations, and radioelement sedimentation. The radiometric data acquisition combined with previous studies indicates that high uranium and thorium concentrations are associated with high sulfide zones. The mineralized uranium ore includes sulfides that are rapidly destroyed by surface hydration conditions, responsible for generating acid mine drainage. In this sense, superficial zones in the waste rock pile with high levels of eU and eTh are areas exposed to oxidation and hydration of sulfides, and, therefore, their recognition and neutralization can contribute to decrease AMD generation in the study site and areas with similar characteristics. The gamma-ray spectrometry results can subsidize more effective and low-cost remediation techniques.