All economic mineralisation at Gosowong is of low sulphidation epithermal type occurring as mineralised fault systems resulting from high temperature gold and silver bearing hydrothermal fluids. The ore shoots are narrow and approximately planar although irregular and complex in local detail. The deposits are relatively moderate to low in dip averaging around 40-50 degrees in the Kencana – Gosowong structural corridor and sub-vertical in the Toguraci corridor. Silver to gold ratio in the ore is approximately 1:1.

The Toguraci low sulphidation epithermal gold vein deposits are located 2 km south west of the Gosowong mine and form part of the Gosowong Goldfield. The vein structures at Toguraci are narrow with horizontal widths typically ranging between 0.1m and 5m.

The Kencana mineralised system is a complex intersecting network of structures consisting of well-developed epithermal vein zones (K1 and K2) and link structures.

The open-pit method mining operation in Gosowong has been completed, and currently Gosowong Gold Mine is actively conducting mining activities on its two underground production areas; Kencana, and Toguraci, by combining the mining methods of overhand cut and fill, and stoping.

Kencana Underground Mine commenced its operations in July 2005 and has been productive until today. While Toguraci is another active production area in Gosowong with characteristics unlike other underground mining operations, as the underground area of Toguraci contains geothermal manifestation in the form of hot water source.

The underground mining department of PTNHM operates this mining unit by an extra-effort management. In addition to dewatering procedure, or to pump the resulted hot water out of the mine, it needs to conduct air cooling using an underground air cooler unlike the typical one found in most mines.

These dewatering and air cooling activities are conducted around the clock. The hot water is pumped out of the mining site and stored at a settlement pond for cooling process before channeled into nature.

The processing plant at Gosowong, which has a capacity of 800,000 tonnes per year, comprises a
primary jaw crusher followed by a SAG and ball mill circuit and a Vertimill circuit. The ore then
undergoes a conventional cyanide leaching process. Gold and silver is recovered from the cyanide
solution using the Merrill-Crowe Zinc Precipitation Process and is then smelted to produce gold and
silver ore. The gold ore is then refined at Logan Mulia which is owned by PT Aneka Tambang.

Processing technologies at the Mill include:
• Gravity separation
• Counter current decantation (CCD)
• Agitated tank leaching
• Merrill Crowe zinc precipitation
• Cyanide leaching

The ore then undergoes a conventional cyanide leaching process. Gold and silver is recovered from the cyanide solution using the Merrill-Crowe Zinc Precipitation Process and is then smelted to produce gold and silver ore. The gold ore is then refined at Logan Mulia which is owned by PT Aneka Tambang.