NEW DEVELOPMENTS IN PROCESS MINERALOGY, FROM QUANTIFYING GOLD IN AU-CU DEPOSITS TO HIGH-DENSITY GRAVITY SEPARATIONS

In this paper, we present new methods in process mineralogy that aim to improve gold and diamond recovery in the minerals industry.

Accurate methods of quantifying the distribution of gold in Au-Cu deposits have long been sought in order to assess the gold residing among different mineral components, and particularly to assist in the decision of whether pyrite is auriferous or not. In the former case, pyrite recovery by flotation is desirable; in the latter case, its rejection is desirable. Diagnostic leach tests are commonly applied and help to quantify the gold but do not distinguish among many sulfide minerals because they co-dissolve in nitric acid. Quantifying gold among sulfide species can be accomplished by a stepwise combination of physical separation methods and selective dissolution methods. We have used high-intensity magnetic separations of pyrite and chalcopyrite as a separation method based on the paramagnetic nature of chalcopyrite. The wide range of magnetic susceptibilities of chalcopyrite, however, means that separations are not always possible in some deposits. Mineral separations and quantifying gold require full knowledge of the sulfide mineralogy of the deposit, and of the physical characteristics of the minerals.

When mineral separation experiments are performed on samples obtained in diamond exploration, one difficult issue is the handling and disposal of toxic organic heavy liquids during processing. Tungsten-based inorganic heavy liquids are not toxic but are extremely expensive, and very-high-density thallium-based liquids that reach up to a density of 4 are extremely expensive and highly toxic. Heavy media separation using magnetite or ferrosilicon is a non-toxic method of gravity separation and has the added advantage that the media are recyclable. However, these media are awkward to use in the field and the media must remain in suspension by agitation. Magnetic fluids (Magstream) can be used at various density levels but require careful operation. We have conducted experiments creating non-toxic superdense media involving metal powders in aqueous solution. Separations were achieved at densities exceeding 4, allowing for non-toxic separation of an array of heavy minerals from diamond, for example.