(ShareCast News) - Mining giant Rio Tinto said it was buying back $1.74bn in debt securities as part of its plan to reduce gross debt and shore up its balance sheet against a backdrop of low iron ore prices.The company said it had accepted $943m in 6.5% notes due 2018 which will be purchased at a price of $1,108.33 per $1,000 principal amount of notes and $804m in 2.25% notes due 2018 will be bought at $1,024.36 per $1,000 principal amount of notes.The notes will be cancelled after purchase, Rio Tinto said.