* Small sheen found, likely not a leak - government
* U.S. investigators have boarded the facility
* Mariner shares close up nearly 2 percent
* Mariner fire an "industrial accident"-Salazar (Adds closing share price, Salazar comment, changes byline)
By Bruce Nichols
HOUSTON, Sept 3 The U.S. government on Friday launched an investigation into Mariner Energy Inc's ME.N Gulf of Mexico platform fire, according to the U.S. Coast Guard.
A light oil sheen spotted near the offshore facility was not believed to be a leak and is thought to be related to Thursday's efforts to extinguish the fire, an agency spokesman said. [ID:nWEN9400]
Investigators have boarded the damaged facility and were working to verify it is not leaking crude oil into the Gulf. No additional information was immediately available.
The cause of the fire, which forced the evacuation of the oil and gas production platform's 13-member crew, is not yet known.
On Thursday, Mariner's platform burst into flames. The accident follows BP Plc's (BP.L) (BP.N) disastrous Macondo well rupture on April 20 which caused the death of 11 workers and unleashed the world's worst offshore oil spill.
Interior Secretary Ken Salazar told reporters in Anchorage on Friday the Mariner fire appeared to be "another industrial accident," and was not comparable to the BP spill. [ID:nN02247473]
Even so, the U.S. government promised a vigorous probe.
"We will use all available resources to ensure that we find out what happened, how it happened, and what enforcement action should be taken if any laws or regulations were violated," Michael Bromwich, director of the Bureau of Ocean Energy Management, said in a statement.
Take a Look on Mariner platform fire [ID:nN02243726]
Graphic showing location of Mariner platform
Factbox on comparisons between Mariner and BP accidents
Reuters Insider video on Coast Guard finding no leak
The platform is located about 100 miles (160 km) south of Vermilion, Louisiana, in shallow water. The facility is not affected by the U.S. government's six-month deepwater drilling moratorium, which only applies to rigs, not production platforms.
Automated shut-off equipment turned off the flow of oil and gas from the platform's seven producing wells, according to the company.
The fire was the fifth reported at offshore sites operated by Mariner since October 2006, according to government data.
None of the earlier fires caused fatalities, although workers were injured in two of the accidents. The company also suffered a blowout while drilling a well about 90 miles (145 km) off the Louisiana coast in May 2008, but the situation was brought under control within a few hours.
The Vermilion platform was last inspected in January and was found to have three minor compliance violations, government data showed.
Shares of Mariner closed nearly 2 percent higher at $23.16 on the New York Stock Exchange. (Additional reporting by Kristen Hays in Houston and Yereth Rosen in Anchorage, writing by Anna Driver; Editing by Sofina Mirza-Reid)