The materials sector fell on a retreat in oil, iron ore and lithium prices. BHP Group is down 3.4 per cent to $45.01 per share. Rio Tinto fell 3.3 per cent $117.28 per share. Lithium lossesLithium producer Mineral Resources retreated 6.2 per cent to $83.50 per share. Pilbara Minerals also tumbled 7 per cent to…