In the event any part of such lands, as are described in Section 59-9-29, are not used for port purposes, and navigation, commerce and fishing will not be impeded thereby, such county port authority may lease or sell the same to individuals, firms, or corporations, public or private, for industrial operations, on such terms and conditions and with such safeguards as will best promote and protect the public interest, and they are hereby authorized to transfer possession of, lease or sell any part or all of such lands by lease, deed, contract, or other customary business instrument. However, no such lease shall be executed for a term in excess of ninety-nine years from its date, and before execution of same any such lease, deed, or contract or other disposition shall be authorized by the affirmative vote of at least two-thirds (2/3) of the membership of such county port authority by order or resolution entered upon its minutes, which order or resolutions shall set forth the substantial terms of such lease, deed, contract, or other disposition. No such transaction shall be consummated until and unless the same be authorized by proper resolution of the board of supervisors, who shall join in the execution of any such instrument.