Tills paper is the outcome of experiments carried on and experience gained at the Waihi-Paeroa Gold Extraction Company's tailings plant at Waihi, New Zealand. The plant was erected to treat accumulated tailings which had been discharged into the Ohinemuri River by the Waihi batteries. The Ohinemuri River is a common sludge channel for all mining debris, tailings, and ashes from the power plants, the last being the cause of occasional high residues, which gave so much trouble to the management. . The tailings were dredged from the bed of the river into barges by means of a Pohle air lift, the power being supplied by a 13 b.h.p. Tangye oil engine driving an air compressor and a centrifugal pump. The sands were elevated from the barges by bucket-belt elevators over screens, to eliminate large particles and rubbish, into .storage hoppers, and from there fed direct into four C. Judd Ltd. tube mills. The method of treatment was fine grinding in a weak cyanide solution, agitation in B. and M. tanks, filtration with turn-over vacuum filters, and precipitation with zinc shavings.