The invention relates to a method and apparatus for producing high density slurry and paste backfills for use in mining operations and to associated backfill paste production facilities which incorporate the aforesaid method and apparatus. The high density slurry or paste is produced from a mill tailings mixture in a silo which includes a percolation/decant device for pecolating water out of the mill tailings mixture and for decanting clarified water from atop the settled tailings. While settling occurs, air is introduced from the bottom of the silo to agitate the mixture to ensure substantially homogeneous settlement of the solids. Once settled, the resultant high density slurry or paste is fluidized by air in order to give the paste more readily flowable characteristics. The flowable paste can then be mixed with a setting agent and pumped or transported to the mine site to be used as a settable backfill.