Thorium minerals of Morro do Ferro, Pocos de Caldas, state of Minas Gerais, Brazil

The thorium and R.E. minerals of Morro do Ferro are classified into three types: 1) primary minerals not resistant to weathering as thorium rich R.E. silicates or allanite, gelzircon, thorogummite and thorium bearing fluorite, and the resistant minerals such as monazite, cheralite, microlite, huttanite and zircon, all being relatively rich in thorium; 2) secondary minerals , the most important being thorbastnae-site; 3) thorium and R.E. oxides or hydroxides produced by composition of primary and secondary minerals which are mostly absorbed on clay components of soil. This state is responsible for most of the mobilization of thorium in soluble or particulate forms. (Author)