Section 150, The Mines and Minerals Act, 2009

(1) Where for any reason it is impracticable to assessthe amount of any royalty due, the Minister may assess a provisional royalty. (2) Where any royalty due has been ascertained, the holder of the mineral right concerned shall pay any sum which may be required to complete such ascertained royalty or be entitled to be repaid any sum paid in excess of the ascertained value.