All prospecting permits and leases issued prior to the effective date of this act which have not expired, or which have not been canceled legally for nonperformance, are hereby declared to be valid and existing contracts with the state of New Mexico according to their terms and provisions, and the commissioner is hereby directed to accept and recognize all such permits and leases according to their terms and provisions. Provided, further, that no such existing prospecting permits shall be extended, renewed or otherwise prolonged or enlarged as to length of term.