IRONORE/ With an exception of Rio Tinto RIO.AX, which closed 0.2% higher, BHP Group BHP.AX and Fortescue Metals FMG.AX fell 0.5% and 0.3%, respectively. By Savyata Mishra Dec 15 (Reuters) - Australian shares ended lower on Wednesday as cautious investors refrained from placing big bets ahead of outcome of the U.S. Federal Reserve's two-day policy meeting, possibly adding to the pressure on its peers for further tightening. "The dual threat of increasing virus cases and inflation dampened expectations of the Australian economy entering 2022 on a firm footing," said Kunal Sawhney, chief executive officer, Kalkine Group.