By definition, refractory gold ores contain gold that is resistant to extraction by conventional chemical processing and as a result responds poorly to traditional gold cyanidation techniques such as Carbon-in-Leach (CIL), yielding less than 80% of the contained gold.
Refractory gold consists of extremely fine grained gold particles that are either physically encapsulated within, or chemically bound within, a host mineral. In addition, the host mineral proves impervious to cyanide leaching, which prevents gold extraction.
Refractory gold deposits are metallurgically complex and are therefore often difficult and expensive to develop and operate. Refractory gold ores require either or both physical and chemical pre-treatment, prior to cyanidation.
The proportion of known refractory gold resources relative to overall gold resources, is increasing year on year throughout the world.
Albion Oxidation Process
The Albion Oxidation Process which was developed in Australia and is patented by a subsidiary of global mining group, Glencore PLC.
The Albion Process is an atmospheric leaching process used to oxidise refractory gold sulphide mineral concentrates. Such sulphide minerals are typical of the refractory gold mineralisation found worldwide and in particular throughout China, the Iberian Peninsula, and various regions in Latin America.
The Albion Process ensures efficient downstream extraction of contained gold from concentrates by conventional gold processing methods.
The Albion Process treats gold froth flotation concentrates in two stages:
within an IsaMill
The IsaMill grinds the gold concentrate down to a size (approximately 10 microns) to maximise the rate and efficiency of subsequent oxidation and gold extraction chemistry.
Albion Oxidation Reactors
Oxidation of the ultra-fine concentrate through the injection of oxygen into a leach slurry within reactors. The process runs at atmospheric pressure, and operates at near neutral pH conditions, controlled by the addition of an acid neutralising substance (limestone slurry).
The Albion Process produces a slurry suitable for gold recovery by cyanidation, ultimately producing high value gold doré bars.
ECONOMICS OF THE ALBION
Relative to other available refractory gold processing technologies, the Albion Process will be more profitable for:
- Highly refractory gold mineralisation – including double refractory ores, i.e. gold associated with both sulphide and carbonaceous mineralogy.
- Low to middle-tier resources that target a gold production of less than 150,000 oz per annum.
- Ore containing toxins such as arsenic, antimony, mercury, etc., as these toxins do not influence Albion Process performance or result in toxic offgases. They are neutralised within the Albion Process, and converted into compounds that are non-reactive within a tailings environment.
Importantly, the specific economics for a refractory gold resource are case sensitive, and strongly influenced by the geological, geographical, environmental, and community settings.