As previously mentioned, the project came to within two months of commissioning when it succumbed to the 1998 Asian Financial crisis. The gold price recovered in the mid 2000s, and the project was revisited. Luckily, 10 years in the Borneo jungle had no serious effect on the plant and it’s equipment - a testament to the quality of construction and equipment selection. The Mirah Gold/Silver project was finally commissioned in 2012, but the cyanide recovery section was not brought online until 2015. Again, this demonstrates the focus on production over new technology. SMBS was used as the detox method. This proved expensive and destroyed not only the cyanide, but also the steel work. The incentive to commission the resin plant became imperative. The cyanide recycle plant was commissioned in early 2015 and has operated continuously ever since, recovering on average 1t/d of NaCN. No detox has been necessary since commissioning the cyanide recovery plant The Mirah project has relatively low soluble copper levels and the compliance level for discharge into the TSF is <50ppm WAD Cyanide. Although a metal recovery section is included as part of the resin plant, it has not been utilized after commissioning due to soluble copper levels being less than 30ppm. Removal of free cyanide is sufficient to meet compliance levels. A programme to recommission the metals section is now underway to test the base metal recovery efficiency with different eluants. A major benefit of recycling cyanide has been the ability to increase levels in the leach to 1000ppm NaCN resulting in a substantial increase in silver recovery, up to 90%. Gold recovery averages 96% from a 2.5g/t head grade. Classic advice states that a high silver ore requires a Merrill-Crowe recovery circuit. This is attributed to the much higher carbon treatment levels for the high metal content. Signet Engineering built several process plants, including the Mirah Project, using carbon for metal recovery where silver levels were over 100g/t. The application has proven to be very successful and has shown increased silver recovery where preg-robbing occurs. The Mt. Muro Project Following its success at the Mirah project, the RECYN Technology has now been applied to a second project: the reborn Mt. Muro project which is also located in Central Kalimantan. This project has a similar mineralization to Mirah being a high silver, low sulphidation, epithermal, narrow vein ore body. Many of the lessons learned with the Mirah RECYN plant have been applied at Mt. Muro, which has a 50% larger throughput than Mirah, for recycling 1.5t/day of NaCN. A note for the record: Part of the plant modification at Mt. Muro entailed converting the recovery circuit from Merrill-Crowe to carbon, in spite of the +100g/t silver levels. Also, a much simpler electrowinning circuit has been installed, another myth overturned. The Third RECYN Project This is for a large gold project located in Sumatra, Indonesia. It has been operating for several years using a conventional sulphide detox process to achieve a WAD compliance level of <50ppmm WAD CN for discharge to the tailings dam. It also has a sophisticated detox plant for water discharge to the environment. The mine is discussing with GreenGold the possibility of providing a RECYN process plant to replace the existing detox system and to be expandable to replace the water treatment facility. The economics show a 12 month payback period for capital investment. Some of the existing equipment is reutilized in the RECYN Plant. Most interestingly, a new potential advantage has emerged for this project, which may be applicable to other projects.
ALTA 2017 Gold-PM Proceedings
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