Gold Mountain (ASX:GMN) started diamond drilling at the Irajuba prospect within the Down Under project in Brazil, according to a Friday filing with the Australian bourse.

The program aims to validate the thickness and continuity of rare earth mineralization previously found through auger drilling.

The project has a conceptual exploration target ranging between 30 million tonnes and 50 million tonnes at a grade range of 1,100 to 1,600 parts per million, the filing said.

Shares fell 10% in afternoon trade Friday.