By Georgia Diebelius A major hunt has been launched for a fisherman who vanished on a drifting ice floe in Siberia. The missing pensioner, 77, was marooned on the giant slab of ice on the giant Yenisei River in Siberia. He was last seen floating downstream after the ice became detached from the river bank. There is deep concern for the angler who has been missing since early Saturday, in night temperatures of -20C. He had been fishing on the ice on the semi-frozen river when it became detached and began floating. A woman said she had witnessed an unknown angler on the ice as it drifted downstr…