A federal agency began its investigation Monday into the death of a miner who spent almost two days inside a Sweetwater County trona mine.

Kathy Snyder, a spokeswoman for the federal Mine Safety and Health Administration in Arlington, Va., said Monday that investigators had started to look into the death of Mike Anderson, 26, who died Sunday as rescuers tried to bring him to the surface of the Solvay Minerals mine."We investigate every mining death," Snyder said. "We will be conducting an investigation into the tragedy this weekend."

Anderson and Dan Jereb had been reported missing in the mine after an earthquake with a magnitude of 5.4 shook southwestern Wyoming on Friday morning.

Jereb was found Saturday evening, and the rescue teams that searched the mine for two days found Anderson about 12 hours later.

However, the man's heart stopped as the rescue teams transported him the 1.5 miles from the point he was found to the mouth of the mine.

Jereb was released from a Rock Springs hospital Sunday.

Sweetwater County Coroner Dale Majhanovich said a preliminary investigation indicated Anderson died because he was over-come by poisonous gases.

Funeral services for Anderson were scheduled for Thursday morning at Immaculate Conception Catholic Church in Green River, mine officials said.

Methane gas is common in trona mines, and the ventilation system that prevents buildups of the gas was damaged by the earthquake. A buildup of the gas prevented rescue teams from entering the mine for several hours immediately after the earthquake.

Snyder said investigators will try to determine what led to Anderson's death.

"In the aftermath of any kind of mining tragedy, there are always questions about exactly what happened, (and) why things happened the way they did," she said.

Repairs on the ventilation system were the focus of work Monday as Solvay continued its efforts to resume operations at the mine.

Solvay, in a news release, said mine workers were assessing the status of the ventilation system to determine what work was needed to put it back into operation.

"After initial evaluation of this information, reconnaissance teams will begin a systematic exploration," the release said. "Damage to ventilation structures will be repaired and roof support installed as necessary. After operating areas are adequately ventilated and roof conditions corrected, plans will be formulated to begin mining."

The release said Solvay believed parts of the mine could be back in production by the end of this week, but it added two weeks could be required to bring the mine's production to 80 percent to 90 percent of what it was before the earthquake.