(Corrects year ago figure in paragraph two to 41.1 million tonnes from 39.8 million tonnes)
SYDNEY, Jan 23 (Reuters) - BHP Billiton , the world's biggest mining company, reported that its quarterly iron ore output rose 3 percent, slightly under analysts' estimates.
Iron ore production climbed to 42.2 million tonnes in the three months ended Dec. 31 from 41.1 million in the same period a year ago.
BHP is one of three mega-iron ore miners along with Brazil's Vale and Rio Tinto that together account for two-thirds of the global seaborne iron ore trade.
Analysts had pegged BHP's December-quarter production at between 45 million and 49 million tonnes, based on shipping export data from the Port Authority of Port Hedland. (Reporting by James Regan; Editing by Gary Hill and Paul Tait)