UPDATE 2-Court blocks Cosette's attempt to drop $438 million Mayne deal; shares jump

(Updates with shares in paragraph 3, background and details in paragraphs 5, 8-10) Oct 16 (Reuters) – An Australian court on Wednesday stopped U.S. drugmaker Cosette from abandoning its A$672 million ($437.6 million) takeover of Mayne Pharma, which now awaits clearance from the Foreign Investment Review Board (FIRB). The ASX-listed pharmaceutical company said on Thursday it would take all steps within its scope to implement the deal. Shares in Mayne Pharma jumped as much as 14.8% to A$6.5 at open in Sydney, but were still trading way below the A$7.40 apiece that Cosette had offered. Cosette has been trying to terminate its offer, after saying in May that it was reviewing the deal because of a "material adverse change" in Mayne's performance. The stock had fallen to A$4.31 in its weakest tr