(Reuters) -Battered Canadian mining company First Quantum Minerals is bracing for a rocky road ahead as Panama moves to strike down its contract to operate one of the world's largest copper mines. Panama's shock decision on Sunday to call a binding vote on whether to scrap the mine's recently struck 20-year contract sparked a sell-off in Vancouver-based First Quantum shares. Investors wiped out about C$8.35 billion ($6 billion), or 48%, from the company's market value this week, registering doubts about First Quantum's ability to operate its crown jewel.