The Hellyer deposit is a volcanic hosted polymetallic massive sulphide deposit located within the Mount Read volcanic arc of western Tasmania. Mineralisation is sulphide hosted and comprised predominantly of pyrite, with lesser sphalerite, galena and arsenopyrite. The pyrite must be carefully managed when exposed to air to prevent its oxidation and potential to form acid mine drainage issues. The economic metals mined at Hellyer were lead, zinc, copper, gold and silver. The Hellyer deposit was mined by underground methods during the period 1989 to 2000. The Fossey deposit extends down plunge from the Hellyer deposit and was mined by Bass Metals between 2010 and 2012.

Tailings from the mill were deposited in a depression approximately 1 km to the west of the Hellyer mill. The tails were inundated with water to prevent oxidation of the sulphide species present in the tails. The tails are typically stratified, having been deposited from discharge pipes set around the dam. The sedimentary stratification is also reflected in a mild gradient in grades of Zn and Pb, with grades typically higher in the deeper parts of the tails and decreasing as the depth of the tails sediments shallow. The tails sediments are unconsolidated.

Dredging is the major mining method for the extraction of Hellyer tailings. Hydraulic mining with slurry pumps mounted on a platform and water cannon wash are the other mining methods to be used.

The planned reprocessing of Hellyer Tailings is designed to produce three saleable products:
• Lead concentrate
• Zinc concentrate
• Gold/silver/pyrite concentrate.

The processing plant is expected to operate at an average tailings feed rate of 154 dmt/hr with availability of 92%, which was achieved during the previous dredging operations in 2006 to 2008. The plant is already equipped with a high degree of instrumentation and process control equipment with a high level of automation and on line, real-time
measurement and recording.

The rate of 154 dmt/hr has also to be achieved by the feed pumps of the surge tanks near the Main Dam via the 2,000 m pipeline to the mill.

There are two mill feed tanks outside the mill. Each of them has 12,000–13,000 m3 capacity or 26,000 m3 in total. Both filled can allow a 12 hours work of the processing plant when the dredge moves to another location.

The metallurgical processing char ........