Treating Refractory Gold Ores

The Leachox^TM Process

First Operational Leachox^TM System

Leachox^TM Developments

Refractory gold ores are generally defined as those ores that do not give economical recoveries in conventional cyanide circuits where the ore has been ground to around 53 to 75 microns. The gold is normally present in refractory gold sulphide ores containing mainly pyrite, arsenopyrite or pyrrhotite and occurs in both the chemically bonded state and as micro or nano-size grains of metallic gold.

There have been a number of commercially successful processes developed over the years to treat such refractory gold ores – roasting, pressure oxidation and bacterial oxidation process are all aimed at destroying the sulphide matrix. The liberated gold is then easily dissolved in cyanide and recovered by conventional methods such as carbon-in-leach or carbon-in-pulp. All these processes can achieve very high gold recoveries with possibly greater than 95% gold recovery.

The above processes, whilst resulting in high gold recoveries, do have issues. Roasting, is an environmentally unfriendly process. Pressure oxidation requires a fairly high degree of operator skill and control, and the bacteria used in bacterial leaching, in tanks or on a heap, are susceptible to changes in environmental conditions and require careful control. However the biggest issue is that all these processes have, in various degrees, very high capital and operating costs. This means that they are economic only on a high grade deposit or one that has generated enough reserves to justify the return on capital. There are not many occurrences of these “world class” gold deposits that will sustain such processes. The vast majority of refractory gold deposits are of lower grade and whilst many could contain enough reserves to sustain a high cost extraction process, invariably extensive drilling to determine this does not justify the risk/reward scenario.

Leachox^TM is a low cost refractory gold process developed by Maelgwyn Mineral Services (MMS) based in Wales, UK and Johannesburg, RSA. It is a process that whilst not claiming to achieve the high recoveries obtained by roasting, pressure oxidation or bacterial leaching can achieve gold recoveries in the high 80’s percent that are significantly high enough with low capital and operating cost to make treatment of lower grade deposits justifiable and economic.