(New throughout, adds market impact)
By Nia Williams
CALGARY, Alberta, March 16 (Reuters) - The fire at Syncrude Canada's oil sands plant in northern Alberta was extinguished on Thursday morning, the company said in a statement, as parts of the mining and upgrading facility ran at reduced rates.
Concerns about tighter supply sent synthetic crude soaring to its highest premium over U.S. crude since June.
Syncrude said crews were still working to fully isolate the affected area of the Mildred Lake upgrader to allow safe entry to assess damage and develop a repair strategy.
"In addition, this will enable both Syncrude and agencies, including Alberta Occupational Health and Safety, to conduct full investigations to understand exactly what happened and help prevent future incidents," the company said.
Other operations remained stable at the 350,000 barrel per day mining and upgrading facility, which processes mined bitumen into refinery-ready synthetic crude and is situated roughly 40 kilometres north of the oil sands hub of Fort McMurray.
The fire broke out on Tuesday afternoon and one worker was injured. Firefighters brought the blaze under control within hours but it was allowed to burn through Wednesday to get rid of residual fuel. Several upgrader units were shut or running at reduced rates, while mining and extraction were being paced to balance lower bitumen demand, the company said.
Syncrude spokesman Will Gibson said he did not have details of the impact on production volumes.
Light synthetic crude from the oil sands for April delivery surged to $3.10 a barrel over the West Texas Intermediate benchmark in illiquid trade, according to Shorcan Energy brokers. It was the highest since last June, when the premium spiked as uncontrolled wildfires in the region forced a number of oil sands plants to shut down as a precaution.
It had settled on Wednesday at $1.90 a barrel over U.S. crude, after rallying after the market learned of the Syncrude plant fire.
On Thursday, volumes were thin as the Canadian crude market's so-called trade window, which lasts from the first of the month until the day before pipeline nominations are due, had closed.
The fire broke out on Tuesday after a line failure caused a treated naphtha leak, prompting an evacuation of the Syncrude site. The injured worker was in stable condition at an Edmonton hospital.
Syncrude is majority-owned by Suncor Energy SU.TO , while Imperial Oil IMO.TO provides operational, technical and business management support. (Editing by David Gregorio)