Citigold Corporation has installed a modern gold extraction plant that is located away from the populated areas of Charters Towers about 10 kilometres south west of the city centre along the Gregory Highway on the historically rich Black Jack mine site.
The plant is a conventional CIL (Carbon In Leach) plant with a capacity to process about 340,000 tonnes per year of gold bearing ore. There is also a gravity gold recovery circuit within the overall plant design to recover the coarse gold particles.
The plant outputs gold 'dore' bars (containing about 60% gold and 30% silver) which are then shipped by secure transport to a gold bullion refiner where the gold and silver are refined and the mine paid for these valuable metals.
Overall Plant Insfrastructure
The CIL plant is fully equipped with crushing and grinding circuits, gravity circuit for coarse gold, gold absorption and desorption leach circuits, electrowinning and gold pouring facilities. The plant has operated efficiently, recovering around 97% of the gold from the ore.
The plant is electric powered from the 66,000 volt Queensland State electricity grid and benefits from extensive Charters Towers city infrastructure including local industry, housing, skilled labour, sealed roads and community services.
The team at Charters Towers ensures the processing plant machinery is in satisfactory operational condition for the processing and extraction of gold from the ore. All equipment involved in the extraction process, including crushers, tanks and pumps is regularly examined for its durability and performance ability.
Gold Extraction Process
The mechanical and chemical gold extraction process has evolved to become a highly sophisticated, technical process. Today, modern processing plants commonly practice a chemical extraction method, whereby carbon is used to recover gold. As a direct result of large-scale advancements in technology, processing plants today have revolutionized the way gold was commonly extracted. Such plants have the capability to process ore at significantly higher efficiency levels than traditional methods, and while these have marked a new era of the recovery of gold, the process continues to undergo development.
The recovery of gold from Charters Towers type ore requires a relatively simple metallurgical process using well-established methods and equipment.
Citigold’s main gold recovery tool, the Black Jack gold plant, is an industry standard carbon-in-leach (CIL) plant. The stockpiled ore, comprising the large blasted rock from underground, is crushed to under 12 millimetres, and transported by conveyer to the grinding mill where water and lime are added prior to the ore being reduced in size by grinding to fine sand particles with a width of 0.1 millimetres. The slurry is then pumped through a series of six large tanks where additional chemical substances are added to further dissolve the gold. Carbon is added to the tanks to absorb and concentrate the gold, and later the gold is extracted from the carbon by a final chemical and electroplating process before it is smelted into gold ‘ dore ’ bars. The ‘ dore ’, which on average may consist of approximately 60 percent gold and 30 percent silver, is shipped by security transport to a specialist gold refinery, where it is made into pure gold bars that are readily sold on the international market.
Designed for Expansion
The plant layout was designed with provision for a second ball mill and additional leach tanks to cater for increased gold output in the future. There are plans to in future crush and use autosorters underground in the mines to remove the waste rock that dilutes the ore. This has the potential to lift ore grades to 20g/t and therefore the process plant upgrade will be through expanding the gravity gold recovery part. There may be no requirement to expand the mill or leach circuit.
Production in the future will derive from several reef structures at Charters Towers, namely the Warrior, Sunburst, Brilliant and Day Dawn, feeding this centrally-located processing plant. The existing two major declines that access the underground Central and South mines will supply the plant with ore to achieve our target of 320,000 ounces of gold per annum.
After the valuable metals are extracted the tailings residue, comprising principally granite rock ground into fine sand size particles, is deposited into a licensed storage facility on site. The stored tailings, after completion of mining operations, naturally neutralize themselves and will be capped with rock and soil for revegation.
The history of the Charters Towers goldffields production of 6,600,000 ounces means the goldfield averaged 145,000 ounces of gold per annum for 45 consecutive years to 1918, with a peak production performance of 320,000 ounces in 1899. With a modernised facility, latest equipment and highly specialised experts, Citigold Corporation may one day exceed this performance.
(Updated January 2012)