This trip falls into the "Been There, Done That" category, I wasn't overly impressed.    The water is cold, it's dark in there, rock walls, no life, about 9 other divers bouncing into you, and the occasional piece of mining equipment.   After about the 4th ore cart, the magic was just gone.   If you insist on going, here's my advice...  Dive one day and check it out and spend the second day doing the above water tour.   The mine tour was more interesting than anything I saw under water.