That's because access to that area is blocked for now. Meaning that you can enter into the Mines *from* the Feywood, but not from the Mines *to* the Feywood. You can't gain access to the area until you have gotten all the Espers except for Zordiak, who you obtain in that secret area. So you're better off just to travel to the Feywood via Paramina Rift or the way I did it, through Golmore Jungle.