The Asia Miner

SEP-OCT 2014

The ASIA Miner - Reporting Important Issues to Mining Companies in the Asia Pacific Region

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Page 38 of 91

September/October 2014 | ASIA Miner | 37 Malaysia MONUMENT Mining continues to consider various options to treat transitional and sulphide material at the Selinsing Gold Project as part of the proposed phase IV development. In the meantime, the Selinsing plant is being fed with low grade oxide ore and stockpiled materials discharged from the mill in the early stage of production. Independent metallurgical testing by Inspectorate Exploration and Mining Services in Canada has been performed on refractory sulphide ore samples from the Selinsing Deeps and Buffalo Reef projects. This work encompassed a variety of methods including pressure oxidation, ultrafne grinding, roasting and acid leaching techniques. The best recoveries for sulphide ore were achieved in the mid to upper 80% range with a biological oxidation approach through a combined fotation and tank bioleach treatment approach. The pro- cessing facilities would require a capital investment of about US$50 million, according to an engineering study carried out by Lycopodium of Australia, and an additional estimated cost of US$10 million for a new power line being built with an estimated completion time of 2 to 3 years. A follow-up engineering study by Tetratech in Canada shows that some savings could be realized by incorporating a modifed design. Monument's management is continuing its research and develop- ment work in evaluating less capital intensive alternatives. One such option is biological heap leaching, which aims to use acid produced from sulphide minerals in the ore to stimulate the natural occurrence of soil microbes in dissolving sulphides contained in the ore materials. Once sulphides are dissolved in the leach pads, the oxidized sulphide ore would be further leached in the same pads or in the existing comminution and CIL circuit. This would be followed by smelting into dore bars for shipping to a refnery as is done for oxide ore. This method has the advantage of low capital investment. A sulphide concentration plant and alterations to crush ore feed would not be required. Potentially crushed ore from the present crushing circuit can be directly treated though permanent heap leach pads. These permanent re-usable heap leach pads can be built and operated in-house by the present staffng at Selinsing with low capital expenditure that require multiple cells, suitably lined liquor ponds and a network of reticulation piping, pumps and metal recovery systems. While recoveries of gold product can be lower than bioleach treat- ment plant, potential heap leach issues such as heap blinding and slumping can be minimized by methods such as whole ore stack- ing, de-sliming, eliminating agglomeration and other approaches being considered. There is an adequate area of suitable land to construct heap leach cells and ponds on site and a plentiful supply of limestone is available for neutralizing the solutions prior to discharge to the tailing facility. Research and development programs on various alternate oxida- tion processes will continue to completion in parallel with the heap leach trials before a fnal commercial decision is made. Monument considers sulphide options

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