Mining giant Rio Tinto has reported that some customers have asked for deliveries of metals to be delayed, signalling that global economic weakness is hitting demand for commodities."It is noticeable that markets are somewhat weaker," Rio Tinto chief executive Tom Albanese is quoted as saying in the Financial Times."In a few cases, customers are asking to reschedule deliveries."Analysts at Citigroup said that, while Rio Tinto's order books are full and it is shipping "flat out", customer sentiment has become more cautious due to concerns over industrial economies and volatility in financial markets."We believe the real catalyst is resolution (or otherwise) of the current macro uncertainty in Europe," Citi said.---RG