"Concession" under this Act shall mean the granted special right to use objects which are public state property, as well as the granted permission to carry out activities for which a state monopoly is established by law. Concessions shall be granted for periods up to 35 years. The term of a concession may be extended but the overall term may not exceed 50 years. Concessions may be granted for objects such as: the waterfront beach strip, biological, mineral and energy resources of the continental