Anglo-Australian mining giant Rio Tinto posted a fall in first-quarter iron ore production on Tuesday, blaming bad weather over western Australia. January-March output of 66.4 million tonnes of ore was below most forecasts and six percent, or four million tonnes, down on the last three months of 2013. The world's second largest mining company pointed to cyclone activity, which often plagues first-quarter figures from the resource-rich Pilbara region in Western Australia. "Production in the first quarter was below fourth quarter levels due to disruption caused by seasonal weather patterns," the company said.