Upon showing to the satisfaction of the Secretary of the Interior that valuable deposits of one of the substances enumerated in this subchapter has been discovered by the permittee within the area covered by his permit, and that such land is chiefly valuable therefor, the permittee shall be entitled to a lease for any or all of the land embraced in the prospecting permit, at a royalty of not less than 2 per centum of the quantity or gross value of the output of potassium compounds and other related products, except sodium, at the point of shipment to market, such lease to be taken in compact form by legal subdivisions of the public land surveys, or if the land be not surveyed, by survey executed at the cost of the permittee in accordance with regulations prescribed by the Secretary of the Interior.