A deep sea mining method includes providing a deep sea mining system for mining matter from a bottom of a body of water, the mining system including: a slurry line coupled with a pump system to transport the slurry from the bottom of the body of water; and a return line in fluid communication with the slurry line and distinguishable from the slurry riser, for transporting non valuable slurry part to the bottom of the body of water, the return line having a return line outlet proximate the bottom. The deep sea mining method further includes spreading the non valuable slurry part over the bottom of the body of water in a controlled manner.