The deputy leader of a London council has resigned after the total costs for a 25-metre man-made mountain in the middle of one of the capital’s busiest tourist areas nearly doubled to £6 million ($8.3 million). Refunds were offered to the Marble Arch Mound, created by Westminster City Council, the day after it opened to members of the public on July 26 following what the authority called “teething problems” with the attraction amid complaints it was still being constructed. The council’s leader, Rachael Robathan, said in a statement on Friday her deputy Melvyn Caplan had resigned with immediate effect after a “totally unacceptable” rise in costs. “The Mound opened too early, and we have apologised for that,” Robathan said. “It has become clear that costs have risen more than anticipated and that is totally unacceptable. Our original forecast cost was £3.3 million ($4.6 million). Total costs are now £6m ($8.3 …