With railway damage in the state widely known, the mining major said the constraints on its Queensland coal operations included weather impacts on third-party infrastructure.

“Limited operations are underway but Rio Tinto is currently unable to provide an estimate of the full impact of this adverse weather or the duration of the force majeure declaration,” the company said.

While the production report for the March quarter will be grimmer for its coal operations, the wet weather in the last months of 2010 has already affected production at Rio’s coal mines in Queensland.

Kestrel produced 844,000 tonnes of coking and thermal coal in the December quarter, 22% lower than the previous three months and 12% down year-on-year.

The Blair Athol mine is continuing to wind down as the nearby Clermont mine ramps up.

Blair Athol produced 691,000t of thermal coal for the December quarter compared to 1.77 million tonnes in the previous quarter.

In the same period, the Clermont mine nearly doubled production to 2.12Mt in the December quarter.

The Hail Creek mine produced 2.08Mt of coking coal in the December quarter, in line with the previous quarter but up 13% year-on-year.

Rio said its hard coking coal production in Queensland was benefiting from the recent investment in two additional shovels and two new truck fleets.

The company’s share of hard coking coal production reached 2.23Mt in the recent quarter, up 8% year-on-year but down 6% from the September quarter due to the heavy rain in Queensland.

Rio’s semi-soft coking coal output reached 800,000t in the December quarter, down 20% year-on-year but up 70% from the previous three months due to the sequences mined.

Total thermal coal production from its mines in New South Wales and Queensland in the December quarter reached 5.15Mt, up 10% from the previous quarter and a 3% gain year-on-year.

On the corporate front, Rio divested its remaining 48% stake in the Cloud Peak Energy coal business in the US in mid-December for $573 million of gross proceeds.

Rio made a takeover offer for Riversdale at $16 per share two days before Christmas and dispatched its bidder’s statement last week.

The diversified miner approved $5.5 billion of major capital projects in the final quarter of the 2010 calendar year, taking its full-year investment to $10.8 billion.

Rio’s overall December quarter results were boosted by strong performances from its iron ore mines.

“Running our operations at full capacity was a priority for Rio Tinto in 2010, in an environment of strong prices for most of our commodities,” Rio chief executive Tom Albanese said.

“Our success is clearly demonstrated in iron ore, where we set new quarterly and annual production records.”

Rio’s shares were up 11c this morning to $86.91.