Is Metal Detecting allowed in New Jersey State parks: YES, with permits issued by Park Superintendent.
The State park service code can be found HERE:
State park service code Title 7 of the New Jersey Administrative code.
7:2-2.16 Metal detectors
A person shall not use metal detectors or similar devices without a permit issued by Superintendent or designee. The permit may limit the location, hours, and days of use. A permit will not be issued for use in areas of significant historical or other value, or where such use would be incompatible with protection of the resource and/or interfere with public use of the facility.