The Sepon copper operation produces approximately 80,000 tonnes of copper cathode (copper sheets) per year from the nearby Khanong and Thengkham ore bodies.

Crushing and milling

Run-of-mine (ROM) ore is crushed and then milled, which reduces the diameter of the pieces of rock from about 500mm to about 0.106mm (106 microns). 

The milling process at Sepon is unusual as it uses acidic solution instead of water to help grind and dissolve some of the copper.  The mixture of ore and acidic solution resembles a thick liquid or paste, and is called slurry. 90% of the copper in the slurry can be extracted by Sepon’s copper processing plant.

Leaching and thickening

The slurry is heated and leached at 80°C for five hours. It is then cooled and thickened, before being washed in a counter decantation circuit to remove soluble copper. The pregnant leach solution (a copper rich solution) from the counter decantation circuit is then clarified to remove the finer solids, before being pumped to a solvent extraction and electrowinning circuit.

Neutralisation circuit

After the copper has been extracted from the slurry, the slurry is mixed with limestone and lime to neutralise the acidic solution. Contaminants in the slurry are also made safe. Slurry from both the gold and copper plants are mixed together before being pumped to a tailings storage facility.

Autoclave circuit

A number of reagents (substances used to bring about a chemical reaction) are used in the leaching circuit. The reagents are expensive and required in large quantities, so instead of buying them and transporting them to Sepon, they are produced on site in an autoclave.

Tailings management

Tailings generated at Sepon are stored within two facilities, one for tailings generated during gold production (known as the Western Tailings Storage Facility) and a second (known as TSF1) for tailings generated during copper and gold production.

Following the completion of gold production at Sepon in 2013, TSF1 is now the primary facility.

The design of TSF incorporates a valley impoundment, earthfill embankments and natural topography. This facility is a valley impoundment with containment provided by engineered earthfill embankments and natural topography. The facility is also equipped with a seepage collection system.

Clarified process water, as well as rain captured in the facility, is returned to the process plant for re-use or treatment prior to discharge in accordance with environmental license conditions.

A long-term maintenance program commenced in 2014 to inspect, monitor and upgrade sections of the Western Tailings Storage Facility pipeline. 

Cell room where the sheets of Sepon copper are produced.


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