Joe Steffen, 51, came to Bell Island to help explore the flooded mine's tourism potential. ((CBC))

An American adventurer died suddenly Sunday while diving in a flooded iron ore mine near St. John's.

Joe Steffen, 51, a resident of Ohio, was a member of an international dive team that had come to explore the flooded mine on Bell Island in Conception Bay.

RCMP are investigating after he died Sunday afternoon.

Ocean Quest Adventures invited Steffen and other cave divers to explore the flooded No. 2 mine to help promote it as an adventure tourism destination.

The company said in a news release that other divers brought Steffen to the surface and their attempts to revive him were not successful.

RCMP Const. Sean Tipple said Steffen died suddenly, but would not comment on specifics.

He said, though, the rest of the diving team was taking Steffen's death hard.

"The people were shaken up, as you would expect— a fellow diver suddenly passing away," Tipple told CBC News.

"The appropriate people were called in, to speak to the individuals involved, to make sure everybody was OK."

Steffen, a career police officer, was an experienced cave diver and often spent time cave-diving in Florida.

Last week, as he and others began laying guide ropes and mapping the shafts of the underwater maze, he told CBC News why he was attracted to the Bell Island dive.

"It's a virgin mine. There's been no divers in it since they shut down," Steffen said last week. "There's a lot of adrenaline flowing for me."

The No. 2 mine was closed in 1949. The rest of the mine was shut down and flooded in 1966.

No one from Ocean Quest Adventures was available for interviews on Sunday.