Falkland Basin oil explorer Rockhopper has wasted little time in tapping shareholders after its recent discoveries in the South Atlantic.The firm is to raise £48.5m through a placing of 17.3m new shares at 280p apiece, a small discount to last night's close of 290p.Last Friday, Rockhopper upgraded its estimate of recoverable reserves at the Sea Lion prospect in the North Falkland Basin from 170m barrels to 242m barrels, adding it has 'significant upside potential'. Three quarters of the money raised in the placing will go towards flow testing the Sea Lion well and other operational costs.Rockhopper shares have risen by more than 600% over the past year on hopes for big oil finds in in the South Atlantic region.