An extensive laboratory testwork campaign was undertaken to evaluate metallurgical performance of the Constancia deposit at a DFS level of detail. In addition, a 25 t pilot campaign was conducted to provide concentrate for molybdenum flotation evaluation, settling, regrind and filtration tests. The sample collection and testwork were directed by GRD Minproc with assistance from Transmin Metallurgical Consultants (Lima).
1.5.1 Testwork sample selection
Representative samples were selected for metallurgical testwork, taking into account variations in lithology, mineralisation type, grade and three-dimensional location.
To facilitate location and depth discrimination, the ore body was divided into “metblocks”, each metblock being a 100 m cube. Continuous core runs within the metblocks that met the sample selection criteria were then identified. From the available suitable core, a sample set that provided broad spatial representation and was relevant to the likely mine plan for the ore body was selected. 1.5.2 Comminution testwork
Comminution testwork was conducted on samples representing Supergene, Skarn and Hypogene ore types. The testwork campaign was conducted at SGS Lakefield Research in Chile during 2008, and included Bond abrasion, rod mill and ball mill work index, SMC and JK Drop Weight Index tests.
Supergene material was classified as the least competent ore type at Constancia with an 80th percentile DWi of 3.7 kWh/m3. In terms of ore hardness for ball milling, Supergene ore is of moderate hardness with an 80th percentile BWi of 13.1 kWh/t.
Hypogene ore is classified as the most competent ore type at Constancia with an 80th percentile DWi of 7.5 kWh/m3. In terms of ore hardness for ball milling, Hypogene ore is also the hardest with an 80th percentile BWi of 16.3 kWh/t.
Skarn samples were analysed as two groups, medium-zinc Skarn (soft) and high-zinc Skarn (hard). The soft Skarn is located in the upper part of the orebody and the hard Skarn is deeper. There were eight samples representing medium-zinc Skarn (soft) and only three representing high-zinc Skarn (hard). Soft Skarn is classified as the least competent ore type at Constancia with an 80th percentile DWi of 3.8 kWh/m3. In terms of ore hardness for ball milling, Skarn is the softest with an 80th percentile BWi of 10.6 kWh/t. Hard Skarn is classified as competent as hypogene with an 80th percentile DWi of around 7.5 kWh/m3. In terms of ore hardness for ball milling, hard Skarn is slightly harder than soft Skarn with an 80th percentile BWi of around 11.5 kWh/t.
1.5.3 Flotation testwork
The first flotation testwork campaign focused on identifying optimum processing parameters to produce a bulk copper / molybdenum concentrate. It evaluated the impact of grind size, reagents and pH on recovery, flotation kinetics and concentrate grades for the three main ore types. Variability and locked cycle tests were conducted and deportment of zinc and other impurities investigated.
Supergene ore had a low metallurgical complexity with moderate variability. The locked cycle test produced concentrate grades of 28.6% to 30.2% Cu, at 86% recovery. Deleterious elements, including zinc, were all below penalty levels, however, zinc was present in sufficient quantity to have a material affect on transport and smelting charges.
Hypogene ore had a low metallurgical complexity with moderately high variability. Copper recovery decreased at depth and recoveries are based on upper Hypogene ore and lower Hypogene ore, respectively. Upper Hypogene ore exhibited low variability, while lower Hypogene ore exhibited moderately high variability. The locked cycle test produced concentrate grades of 23.1% to 25.7% Cu, at 88% recovery. With the exception of zinc and lead, other elements were well below possible penalty limits. Zinc (1.62 % of concentrate) and lead (0.2 % of concentrate) were below expected penalty levels, but comprise a sufficient portion of the concentrate to have a material effect on transport and smelting charges.
Skarn ore had a moderate metallurgical complexity with high variability. The locked cycle test produced concentrate grades of 18.9% to 24.7%Cu, at 85% recovery, depending on the zinc to copper ratio in the feed. Cadmium and bismuth were at values close to their penalty limits at 0.0325% Cd and 0.029% Bi, and will require monitoring during operation. Zinc at 9.9%-19.9% of concentrate weight is well above penalty limits. Depression tests showed that zinc sulphate could be used to lower the zinc content of the concentrate, with some loss in copper recovery.
Table 1.8
Expected Elemental Recoveries
Copper Concentrate Cu % 87.00% After yr10
Hypogene Cu % 91.40% Up to yr10 Zn % 30.00% Ag % 80.00% Au % 60.00% Pb % 25.00% Supergene Cu % 89.00% Zn % 80.00% Ag % 80.00% Au % 60.00% Pb % 25.00% Skarn Cu % 89.00% Zn % 30.00% Ag % 80.00% Au % 60.00% Pb % 25.00%
Samples were also generated to evaluate the effect of blending and treating different ore lithologies within the concentrator. The blending of Supergene and Skarn ore produced a blend that had a high metallurgical complexity with high variability. Activation of sphalerite by soluble copper or sulpho-salts was suspected, leading to high levels of zinc content in the copper concentrate. Depression tests showed that sodium cyanide could be used to lower the zinc recovery, however, the loss in copper recovery was significant. Other ore blends showed no detrimental effects on grade or recovery.
All ore types require a regrind of rougher concentrate, with P80 varying from 25 µm to 40 µm. Rougher
concentrate mass recoveries varied from 10% to 20%, depending on ore type.
Recovery of molybdenum was simulated using floatability component modelling. This indicated a recovery to molybdenum product of 55% at a grade of 40% Mo. The presence of talc resulted in lower grade molybdenum concentrates.