'core zone' is a correct and usable phrase in written English.
It is usually used to refer to a particular region that is of particular importance or significance to a larger area. For example, you could say, "The core zone of this city is a vibrant, bustling area full of businesses, restaurants, and shops."
We had barely entered the core zone at 6am when our guide stopped to look at some tiger tracks.
Our route crossed part of the core zone of Satpura National Park, among the largest of India's tiger reserves.
At 6am we are in a queue of about 50 jeeps at the park gates, awaiting entry to the "core" zone of the reserve.
Crossing the river into Satpura's core zone, we began climbing a gentle, part-cobbled track to the navel of India and soon reached the pretty Wainganga River.
Meanwhile Isis flaunts its activities outside its core zone: murdering anti-Isis Syrian activists in Turkey, claiming to destroy an airliner, raiding across central Libya and launching spectaculars in the Sinai and Yemen, and now in Paris.
The events would be held in two main zones: the Core Zone, which would include the Olympic Stadium, and the River Zone, a portion of the riverbank that would be reclaimed for public use.
The events will be held in two main zones: the Core Zone, which will include the Olympic Stadium, and the River Zone, a part of the riverbank which will be reclaimed for public use.
The core zone can only be reached by footpaths.
High-fidelity CFD models of gasification core zone is developed to obtain characteristics of flow field, temperature field and composition profiles within the gasification core zone.
In the core zone, the three target species were moderately rare tree species.
During our field work, signs of these activities were only rarely observed in the core zone.
