§ 18. Mines in Saint Lawrence county. The proprietors of any mines or veins of lead or copper in the county of Saint Lawrence, may demise, lease, or rent the same for a period not to exceed twenty-one years from the date of any such lease, to any foreign individual or company, and such lessee may take, hold, work, use or convey the same during the said term, in the same manner and subject to the same liabilities as if such lessee were a natural born citizen.