A non-executive director in Rio Tinto splashed out to buy shares as the mining giant confirmed details about its recently unveiled plans for a $2bn share buyback.Megan Clark purchased 1,550 shares for an individual price of 3,228.6p, spending a total of £50,044 in the transaction.Clarke, who has been a member of the board since November last year, holds now 1,715 shares in Rio Tinto.The group revealed last week that despite a sharp drop in commodity prices, higher production and lower costs drove full-year profits past expectations.Looking ahead, the company said it is targeting further cash-cost improvements of $750m to be realised in 2015.Top Director BuysRio Tinto (RIO) Director name: Ms Megan ClarkAmount purchased: 1,550 @ 3,228.64p Value: £50,044Catco Reinsurance Opportunities Fund Ltd (DI) (CAT) Director name: Mr Alastair Barbour Amount purchased: 38,737 @ $1.15 Value: $44,451Helios Underwriting (HUW) Director name: Mr Nigel HanburyAmount purchased: 17,188 @ 145.00p Value: £24,923Fulcrum Utility Services Ltd. (DI) (FCRM) Director name: Mr Phil HolderAmount purchased: 250,000 @ 9.35p Value: £23,375Vianet Group (VNET) Director name: Mr James DicksonAmount purchased: 25,000 @ 82.00p Value: £20,500PHSC (PHSC) Director name: Mr Stephen A KingAmount purchased: 66,597 @ 27.20p Value: £18,114Murray International Trust (MYI) Director name: Mr David HardieAmount purchased: 1,439 @ 1,037.00p Value: £14,922Top Director SellsSt. Modwen Properties (SMP) Director name: Mr William (Bill) OliverAmount sold: 456,703 @ 463.90p Value: £2,118,645St. Modwen Properties (SMP) Director name: Mr William (Bill) OliverAmount sold: 272,160 @ 463.90p Value: £1,262,550St. Modwen Properties (SMP) Director name: Mr Steve BurkeAmount sold: 272,160 @ 463.90p Value: £1,262,550St. Modwen Properties (SMP) Director name: Mr William (Bill) OliverAmount sold: 205,085 @ 463.90p Value: £951,389St. Modwen Properties (SMP) Director name: Mr Michael DunnAmount sold: 205,085 @ 463.90p Value: £951,389China Nonferrous Gold Limited (DI) (CNG) Director name: Mr Abuali IsmatovAmount sold: 1,500,000 @ 26.04p Value: £390,600PHSC (PHSC) Director name: Mr Stephen A KingAmount sold: 66,597 @ 27.00p Value: £17,981