Sand leaching or percolation may be practiced wherever the ore is coarse enough to permit free passage of the solvent through the voids. The ore is loaded into large vats or tanks that are then filled with leaching solution. After the solution has been in contact with the ore for a certain time, it is withdrawn, and fresh solution is added. Liquid may 2755 be added from the top (downward percolation) or from the bottom (upward percolation).