The term "hollow core" is not a standard geological term, so it's difficult to understand what you mean.

It's possible you're referring to:

* A hollow core in a specific mine: If you provide the name of the mine or its location, I might be able to help.

* A specific type of geological formation: If you can describe what you mean by "hollow core" in terms of its geology, I might be able to understand what minerals are mined there.

Please provide more information about what you mean by "hollow core."