0000 GMT - Rio Tinto's valuation is beginning to look more attractive, with shares in the miner having lagged peers year to date, says Citi. Yet Rio's relatively low exposure to copper and a growth pipeline concentrated in higher-risk jurisdictions is likely to prevent outperformance, the bank says. It keeps a neutral rating on the stock. Citi has a A$171 target on Rio's Sydney-listed shares. The stock last traded at A$172.39, up 17% year to date. Peer BHP is up 33% over the same period.