I'm new at this, but the new terrainbuildings file in c3c have this addition column of gfx for fortress with barricades. Using the old file which does not have that addition column will result in an error when launching the game.
The first time i tried to copy the mine gfx over, i ended up with patchs of pink instead of mines, heehee. But i just tried it again by converting over to bmp format first as advised in a thread here, and it worked.
Attaching the file here. Hope i am not voiding any rules by redoing and posting the file here.
Thanks Buk. I really liked the mine.