Refractory Gold

 

The recovery of gold from refractory material plays an important role as part of the mine plan and reserves, and more even when is necessary to compare cyanidation results on amenable ore that gave high recovery by direct cyanidation. It is believed that gold operations of the western United States such as those located in Nevada and California are using several different processes to treat a variety of refractory gold ores. Without any doubt, more refractory material will be mined in next years. The importance on refractory ore treatments is based on the fact that gold deposits of easy treatment are almost disappeared in the world and this is a concern of many gold mining companies. The idea of these lines is to show the main considerations that all metallurgists must keep in mind at the moment of evaluating the degree of refractory of any gold ore.

It is common to define a refractory ore as an ore containing gold that is not recovered by basic gravity concentration or by simple leaching. According to many cyanidation results, gold ores that give gold recoveries of less than 75-80% are refractory. Such ores are typically pyrite, arsenopyrite and carbonaceous material. Normally, gold is detected as very fine particles locked in the host minerals (e.g. arsenopyrite). Usually, refractory parameters are related to the association or interlocking of gold with pyrite and microcrystalline quartz, and the presence of different forms of carbon. Probably, silica locking has been considered to as size that influences refractoriness and can be noted or detected in some processes like heap leaching when the ore is leached in a coarse fraction. Basically, the main reasons of refractoriness are

-       Presence of carbonaceous compounds that cause pre-robbing

-       Encapsulation in pyrite and arsenopyrite

-       Coatings on gold particle surfaces

-       Cyanide is consumed in secondary reactions

-       Presence of insoluble gold compounds, mainly tellurides

The problems to solve are not unique and there is not a unique reason for refractoriness in many gold ores. It is believed that the deeper reserves consist of ores which have complex mineralogical characteristics creating different metallurgical problems other than just encapsulation or pre-robbing. Next table shows some types of refractoriness in gold ores