Rio Tinto RIO.AX, BHP Group BHP.AX advanced 2.5% and 3.6%, respectively, while Fortescue FMG.AX fell 0.9%. By Tejaswi Marthi September 20 (Reuters) - Australian shares on Tuesday recorded their best day in nearly two weeks with broad-based gains following a late rally on Wall Street, while focus remained squarely on the upcoming U.S. Federal Reserve meeting. Markets have priced in a 75-basis-point increase at the end of the two-day meeting on Wednesday but are worried whether aggressive tightening by the Fed to tame stubbornly high inflation will tip the economy into a recession.