The previous operator (Zacoro) contracted LeRoy SU Corporation (LeRoy SU) of New Glasgow, Nova Scotia to complete the crushing plant and mill rehabilitation started by Macocozac on the 2,250 t/d sulphide flotation plant. Macocozac initiated the rehabilitation work on the plant and the mine in early 2006. The rehabilitation work is currently ongoing and Aura plans additional upgrades and mill expansions.
Zacoro reported a preliminary mineral resource estimate for the Aranzazu project which was reported in its 2007 Technical Report. In addition, Zacoro contracted Process Research Associates (PRA) of Richmond, B.C. to perform metallurgical testwork on four mineralogical samples. The details of the samples and testwork conducted are reported in the 2007 Zacoro Technical Report and are quoted below.
“Four metallurgical samples were collected for the first round of analyses. One was from a mixed oxide and sulphide stockpile, two were collected from new stockpiled mineralization representing 2 separate mineralized zones, and one was collected from high sulphide material in a previously mined stope on Level 2100 in the Mexicana zone.
Table 16.1 is a summary of the characteristics for the metallurgical samples.”
Table 16.1
Metallurgical Sample Descriptions for the Aranzazu Property
Sample Description of Metallurgical Sample
Met-1 Sample from stockpile of mineralization from Level 2080 in the 53850 area on the east ramp of the open pit. The material is an igneous breccia with disseminated sulphide and a sulphide matrix. Sulphides consist of pyrite, chalcocite (primary (steely), and secondary (sooty and as coatings on pyrite), and chalcopyrite. Alteration consists of later clay alteration overprinting strong sericitic alteration of the feldspar minerals and some silicification. The zone is described as a quartz-sericite-pyrite altered breccia pipe.
Met-2 Sample from old stockpile of pyrite and chalcopyrite in garnet skarn. The sulphide minerals are coated by a strong oxide patina. The exact extraction location of this material is unknown but is assumed to be from the upper levels of the massive sulphide body in the Arroyos Azules open pit area.
Met-3 Sample is from newly mined and stockpiled material from the BW body on Level 2100. The rock consists of partially silicified garnet and pyroxene skarn with some chlorite along fracture surfaces. The sulphide mineralogy includes pyrite and chalcopyrite with chalcopyrite and sphalerite.
Met-4 Sample is from the 2100 stope of the D ore zone in the Mexicana area. The material consists of garnet skarn with pyrite, minor chalcopyrite, and minor sphalerite.
Table reproduced from the 2007 Zacoro Technical Report.
“Each sample was subjected to apparent specific gravity and solids specific gravity tests to determine these factors which ranged from 2.74 to 3.57 and 3.54 to 3.96, respectively.
Initial flotation testing was carried out on the stockpile material, as this would likely be the first material to be treated in the plant. However, after crushing and preparation for grinding it was found that the material required nearly 8 kg of lime to raise the natural pH to 6.0. With these levels of lime required it was apparent that the material was unlikely to be economically treated so testing was suspended.”
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“The remaining samples were ground to varying sizes in order to roughly determine grind / recovery relationships.”
“Following results from the preliminary scoping flotation tests, more work was carried out as indicated below:”
“Met - 1 Differential flotation to produce separate copper and zinc concentrates. The copper flotation results were excellent with an 87.8% recovery; however, the conditions employed did not adequately depress the zinc and different conditions will be employed for future tests.”
“Met - 2 The sample contained a high concentration pyrite and initial tests produced a highly acidic solution requiring 8 kg of lime per tonne of material. Initial flotation recoveries were very low even with the addition of a frothing agent.
Further work on this mixed oxide-sulphide stockpile will be postponed until phase 2 metallurgical testing.”
“Met - 3 Differential flotation produced excellent copper recovery but depression of the zinc was only partially successful as over 50% reported to the copper concentrate. Future testing will be designed to produce a bulk copper/zinc concentrate which will be followed by differential flotation to separate the minerals.”
Regarding Met – 3, Aura has noted that any future testing will be designed to produce a bulk copper/zinc concentrate followed by differential flotation testwork to determine whether it is feasible and economic to separate the minerals.
“Met - 4 This sample contains very low zinc and flotation was designed to optimize copper recovery. The results look very encouraging considering that the head was only 0.27% copper. PRA achieved an 82.5% recovery at a 34% copper concentrate grade. The gold and silver assays and recoveries in the concentrate were excellent. The final test for this sample will be a locked cycle test to define more exactly what can be expected under plant conditions. A standardized collector was used for all tests to avoid potential complications in the operation.”
“Table 16.2 is a summary of the comparison of the head assay values for the metallurgical samples from BSI and PRA. Table 16.3 is a summary of the rougher recovery for the metallurgical testing.”
Table 16.2
Metallurgical Sample Assays for the Aranzazu Property
Description Metallurgical Sample Assays
Sample #
Table reproduced from the 2007 Zacoro Technical Report.
Table 16.3
Metallurgical Rougher Recovery for the Metallurgical Samples from the Aranzazu Property
Rougher Recovery (%)
Table reproduced from the 2007 Zacoro Technical Report.
The Mexican owner of the Aranzazu project restarted mining operations on a limited scale in 2007 at approximately 600 t/d. According to the records the material mined for the period from July, 2007 through May, 2008 had an average head grade was 0.8% copper, 0.28 g/t gold and 12 g/t silver. A total of 5,650 t of copper concentrate were reported shipped to the Trafigura Smelting Company facility in Manzanillo. The copper concentrate averaged 24.3% copper, 4.2 g/t gold and 258 g/t silver. Associated recoveries averaged 84% copper, 40% gold and 61% silver.
Aura plans to conduct a very detailed and comprehensive metallurgical testwork program over the next several months. This work will be used to determine optimum copper and precious metal recoveries, reagent suites and associated concentrate grades.
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17.0 MINERAL RESOURCE AND MINERAL RESERVE ESTIMATES