SYDNEY (Dow Jones)--Australia's proposed Mineral Resources Rent Tax may dent investment but won't much affect the profitability of the largest mining companies, such as Rio Tinto Ltd. (RIO.AU) or BHP Billiton Ltd. (BHP.AU), Steven Hess, senior credit officer in the sovereign risk group at Moody's Investors Service, said Wednesday. While the proposed tax may impact profits to some degree, it won't be significant, he said. "It's not going to be a huge hit to their profitability," Hess said. -By Enda Curran, Dow Jones Newswires; 61-2-8272-4687; [email protected] (END) Dow Jones Newswires July 28, 2010 02:02 ET (06:02 GMT)