Dec 3 (Reuters) - Rio Tinto (LON:RIO) Ltd RIO.AX :
* PENTWATER CAPITAL MANAGEMENT LP SAYS WRITTEN LETTER TO RIO TINTO PLC
* PENTWATER - REQUEST RIO TINTO TO PRESERVE DOCUMENTS, ELECTRONICALLY STORED INFO RELEVANT TO INDEPENDENT INVESTIGATIONS OF OYU TOLGOI COST OVERRUNS
* PENTWATER - REQUEST RIO TINTO TO PRESERVE DOCUMENTS, ELECTRONICALLY STORED INFO RELEVANT TO TURQUOISE HILL ARBITRATION PROCEEDING AND NEGOTIATIONS