You will require this lease if you intend to hold the title to a mineral deposit for further assessment after an exploration or prospecting licence has expired. An assessment lease allows you to retain title of minerals you have discovered but are currently unable or uncertain if you will commence mining. For example, a mineral resource has been proven and the feasibility of mining established, but where for various reasons, the project is not viable, although it has potential to be developed in the foreseeable future.
There are areas of mineral potential which are natural extensions to existing operations or projects, but where it is currently impractical to apply for a mining lease.