(January 2009)

Maelgwyn Mineral Services Ltd (MMS) announces that it has licenced its proprietary Leachox refractory gold recovery process to JSC Vasilkovsky MMC for use at the Vasilkovskoye gold mine near Kokshetau in Northern Kazakhstan. The Leachox plant, with a nominal capacity of 50 tons per hour of gold contained in sulphide concentrate, will be one of the largest refractory gold treatment plants in the world and will have a throughput over 50% greater than the largest gold bio-oxidation plant currently operating worldwide. The MMS Leachox process is a major breakthrough in the treatment of difficult to process refractory gold ores. It offers a low capital and operating cost process route but with high gold recoveries, comparable to bio-oxidation. The Vasilkovskoye gold mine is a joint venture between Floodgate Holdings BV and the Kazakhstan state-owned Ministry of Finance of the Republic of Kazakhstan. The mine has one of the largest undeveloped gold reserves in the world however the gold is mostly contained in hard to recover refractory gold ore. Commissioning is planned for later in 2009.

Aachen Reactors in manufacture for Vasilkovskoye

Aachen Reactors in manufacture for Vasilkovskoye


The Leachox process, which has been patented world-wide, has been jointly developed over a number of years by MMS and Maelgwyn Mineral Services Africa (Pty) Limited. It utilizes proprietary MMS Aachen Reactor™ technology in conjunction with a specific process flowsheet that includes ultra fine grinding. The process has previously been trialled by MMS Africa over a number of gold operations in the Mpumalanga greenstone belt of South Africa.

The Vasilkovskoye operation will initially mine 5 million tons per year of a pyrite/ arsenopyrite refractory gold ore. The Leachox plant has been designed to treat 7800 tons per week of a gold contained in sulphide concentrate with over 93% leach recovery expected. Vasilkovskoye chose the Leachox process after extensive pilot plant testwork in South Africa as it gave high gold recoveries with low capital investment cost and low predicted operation cost compared to bio-oxidation, pressure oxidation and other processes. The Vasilkovskoye flowsheet is one of the most innovative in the gold industry where, apart from the introduction of Leachox, it also utilizes high pressure grinding rolls in the comminution circuit and a differential pyrite/ arsenopyrite flotation circuit.

The Leachox process involves the ultra fine grinding of mineral concentrate followed by low pressure partial oxidation of sulphides using a series of Aachen Reactors in a proprietary flowsheet configuration including MMS Leach Columns. The Leachox process can also be designed to treat carbonaceous “preg robbing” ores. One of the issues that had previously been encountered in trying to treat refractory gold ores by ultra fine grinding has been that, almost universally with such ores, there comes a point where further ultra fine grinding results in an appreciable drop in gold recovery. It is thought that this is due to passivation of the gold at extremely fine sizes. A further major problem encountered with the treatment of sulphide ores at grind sizes generally less than 20 microns is that the consumption of reagents required to leach the gold – typically cyanide, lime and oxygen, increases exponentially in open tank leaching. This may be so high as to make the process uneconomic even at the current high price of gold. The Leachox process negates both the passivation effect and the great increase in reagent consumption making the process economically attractive.


Vasilkovskoye Leachox plant building and construction