坑口[koukou] pithead
坑道[koudou] tunnel
坑内[kounai] within a pit or (mine) shaft
坑内事故[kounaijiko] mine accident
入坑[nyuukou] entrance into drift or pit

廃坑[haikou] abandoned mine
金坑[kinkou] gold mine
坑夫[koufu] miner
炭坑[tankou] coal mine
銀坑[ginkou] silver mine