Metallurgical Process

With the preliminary information obtained in the scoping study is possible to design a tentative recovery process. Under this consideration, ore types and master composites must be tested in order to know the restrictions of reduction size circuit. Since gold content is different, the variability of the feed to the open circuit or close-circuit must be evaluated. Ideally, the plant must receive an ore without much variability, but this rhetorical affirmation is valid only in theory. For this reason, the circuit is sensitive to the ore type and no matter how simple or complex is the design.

Basically, the ore tell us how it must be ground. If the ore breaks along grain boundaries easily, gold particles can be liberated and recovered easily. However, many ores need special liberation in order to liberate all valuable minerals. It is important to mention that the comminution circuit is responsible for most of the power consumption in a mill. Then, the need for better blending for feed homogeneity is obvious as well as the need for closes monitoring since the mine until the processing plant. Gold operations with comminution circuits know that the operative cost of this circuit is approximately 65-70% of the total cost. For this reason gold low grade deposits (e.g. 0.8 – 1.0 g/t Au) try to employ a heap leaching process which does not require a comminution circuit with SAG mill and Ball mills.

The geometallurgical model is based on metallurgical tests performed on exploration samples so that the characterization of each ore type includes several aspects such as recovery, reagent consumption, losses, grade concentrate. Preliminary tests must be done on lithological samples provided by the project geologist. The model will be constructed on each zone after analyzed the metallurgical tests results. Basically, the model is based on gold recovery and final product quality.

The metallurgist must be able to develop the metallurgical testing program based on global objectives, gold recovery, and common practices on similar ore deposits. It will be important to have an updated knowledge on metal prices in order to make a preliminary estimation of the profits. The impact of the process on environment must be studied in order to take appropriate solutions to the problem. For example, tails have free cyanide and the effluent has to be treated with any oxidation process, otherwise the project could be rejected by the authorities. Even, during the operation, the operation of the oxidation process must be monitored and improved.

If the metallurgical process was selected wrongly, the project could be approved, but the real operation could be a disaster. For this reason, the testing program must cover many possible combinations of recovery processes. In other words, the process must be selected under technical and economical considerations. Reserves and metallurgical process must be analyzed and probably the best way is to review and update the reserves so that the economy of the project can be optimized. Since mineralogy and gold content is variable, the plan must evaluate the order of treatment. Metallurgists want optimum recoveries and Project Managers want to improve the profitability of the project.

Next table shows the difference between two treatment options, gravimetric concentration + flotation+ concentrate cyanidation (Option 1) and direct cyanidation (Option 2). Both projects employ cyanidation, but Option 2 gives a better profitability.