THE value of the Zimbabwean dollar has suffered its worst crash in memory, sparking a run on US dollars and forcing stores to close early to put new prices on what little they could afford to stock. Black-market exchange rates -- fuelled by the central bank buying at the illegal rates to pay the mounting debts of crumbling state fuel and power utilities -- rose to more than $Z300,000 ($1450) to one US dollar in large offshore deals, one trader said yesterday. The official exchange rate is 15,000:1. "It's gone crazy," said the trader, who spoke on condition of anonymity....