The coal price slump that brought Australian tycoon Nathan Tinkler down last year has also sown the seeds for his comeback, with the former electrician snapping up a closed coal mine from Peabody Energy for next to nothing. Tinkler's Singapore-based firm Bentley Resources agreed to buy the Wilkie Creek mine from Peabody for $70 million in cash, plus the assumption of $60 million in various obligations and liabilities, in a deal announced on Tuesday. The sale came as a surprise to bankers and analysts, who knew that Peabody had wanted well over $500 million for the mine when it was put on the block two years ago. After failing to attract a buyer…