By David Stanway ULAN BATOR, Jan 29 (Reuters) - Mongolia's new Prime Minister Norov Altanhuyag starts 2013 with investors increasingly worried about the outlook for the all-important mining sector. The giant Tavan Tolgoi coal project is facing financial problems and an up to $3 billion initial public offering for the mine will not go ahead this year as originally scheduled, the firm said in January, despite a government handout of $250 million.