Migration of radium from the thorium ore deposit of Morro do Ferro, Pocos de Caldas, Brazil

A large thorium ore deposit is located in Morro de Ferro, a hill in the Pocos de Caldas Plateau, Minas Gerais, Brazil, which contains an estimated 30 000 t of Th and 100 t of U in a highly weathered matrix exposed to erosion and leaching. 228Ra and 226Ra were analyzed in surface waters collected at various points in the drainage basin and in groundwaters from wells drilled through and around the ore body. The concentrations in groundwater demonstrated that radium is markedly leached by rainwater percolating through the ore body. In its transit underground, radium is removed from groundwater by sorption on soil particles and this natural process greatly reduces the radium discharged to the environment. In dry weather, the concentration of dissolved 228Ra in the main stream draining the Morro do Ferro is 7.0+-1.1 mBq litre-1 and in a control stream 1.6+-0.3 mBq litre-1. The estimated 228Ra mobilization rate by solubilization is of the order of 10-7 y-1. (author)