In cases in which an interest in fixed property vests in the Board, whether without option or by viture of the exercise of an option, and the owner of that interest has also an interest in land used partly (but not exclusively or mainly) for coal industry or transferred allied activities for which that property is used, or an interst in land owned by him partly (but not exclusively) for the purpose of having land available for use for such activities or an extension thereof, the interest of that owner in that land.