The Rio Tinto subsidiary’s share of the output fell 20% from the December quarter to 4.22Mt.

The open cut miner’s wholly owned Hunter Valley Operations produced 2.58Mt, falling 15% from the previous three months, while output was roughly 27% semi-soft coking coal and the remainder thermal coal.

Low levels of pit inventory hampered the mine while geotechnical issues in the West Pit along with higher rainfall halted mining for three weeks.

Further south to the company’s 80%-owned Mount Thorley Operations, December quarter output dived 58% from the previous quarter to 495,000 tonnes while the nearby 55.6%-owned Warkworth mine improved 3.5% to 1.35Mt.

Both operations were affected by low in-pit inventories and were also mining through areas with a higher stripping ratio.

Coal & Allied’s 40%-owned Bengalla thermal coal mine near Muswellbrook produced 1.23Mt in the past three months, 14% down from the December quarter.

The company attributed the fall to a less productive mine sequence.

Coal & Allied’s coal sales were also 28% down from the December quarter due to lower production.

But the major Hunter Valley producer shifted its port allocation from the March quarter to the second half of the year and expects full-year sales will still increase on 2009 levels.

While the company noted its semi-soft coking coal production increased year-on-year, the March quarter of 2009 was a rough time for the coal industry due to the impact of the global financial crisis.

Rio owns 76% of Coal & Allied.

The company’s shares are down 1% this morning to $97.01.