The ore materials produced by PT Nusa Halmahera Minerals (NHM) mining activity, both from Kencana dan Toguraci underground mines, are sent to the processing area or the Mill and the grouped based on their grades, and origins of extraction. Their grades will be blended based on the target of the production plan, for the ore materials to be ready as Mill Feed, which will be fed to the next milling process.
They will be fed to the SAG Mill circuit using conveyor by wheel loader. The SAG Mill, is a rotating cylinder containing steel balls to crush the chunks so that they have the ideal size for the process ahead. NHM currently operates two SAG Mill circuits with a total capacity of around 100 tons per hour.
The crushed ore produced will be separated by size to separate fine ore, from the coarse ones which will be fed back to SAG Mill for regrinding. The fine ore, will be sent to further milling, so that they are ideal for the leaching process.
The ore, which is in slurry form, will be contacted with cyanide solution to dissolve its gold content. The solids that have been separated from the gold undergo a detoxification process to reduces the free-cyanide content level, to less than 50 ppm. The tailing material is then pumped to the Tailing Storage Facility to undergo a natural sedimentation and cyanide degradation process, which can reduce the cyanide contained in the tailing to less than 0.5 ppm.
The run off liquid is pumped into the Polishing Pond for further purification. Samples will be analyzed every day to check for their levels of dissolved metal, and free cyanide content. If the water samples have met the environmental quality standards, the water will be released into the environment by pump connected to a river.
Meanwhile, the harvested gold sediment materials go through a mixing and drying process to reduce moisture and evaporate their heavy metals. Furthermore, they will be melted in a high temperature furnace.
The gold and silver contents, will be separated from the slag which contains and unwanted materials, and are processed to produce the final product, called Dore Bullion, which contains about 45% gold, 45% silver, and only 10% of other metals.
NHM’s bullion bar products, are then shipped to the refining facility owned by PT Antam Logam Mulia. Where they are going to be refined, into pure gold bars or granules, with a grade of 99.99%, before being marketed, to meet the world’s demand for gold.
