The current release of ZBrush and ZBrushCore also came out before ZBrushCoreMini introduced the iMage3D file type, which means that they cannot yet read such files.
This will change with the next update of ZBrush and ZBrushCore. We do not yet have an ETA for this, however.
Until the update can be released, you are still able to get geometry from ZBrushCoreMini into the other ZBrush versions simply by exporting as .OBJ. This file format will work with almost all other 3D software, including both ZBrush and ZBrushCore.