RIO Tinto Off-market buybackRIO has announced it will strengthen its portfolio by divesting non-core assets, including Australian coal assets for $4.2b US. Part of these proceeds will be returned through the launch of an off-market buy-back tender targeting up to 41.2 million Rio Tinto Limited shares (approximately A$2.7 billion1 (US$1.9 billion2)) with the balance of proceeds being allocated to further on-market purchases of Rio Tinto plc shares.