First Quantum Minerals LtdFM.TO shares remained volatile after Panama's government on Thursday ordered the company to pause operations at its flagship copper mine. By Fergal Smith TORONTO, Dec 16 (Reuters) - Canada's main stock index fell to a five-week low on Friday, pressured by lower oil prices and concern about the economic outlook following interest rate hikes this week by some major central banks. U.S. stocks also ended lower as fears grew that the Federal Reserve's quest to stifle inflation would push the economy into a recession.