GMC Cata Processing Plant — 2017 Technical Report

The GMC Cata processing plant treats approximately 973 tonnes per operating day through crushing, milling, flotation, thickening and filtering to produce an iron sulphide (pyrite) concentrate containing gold and silver.

Report context

This technical report describes the mineral processing facilities at the GMC Cata plant as of the effective date of August 31, 2017. The plant processes ore delivered by truck from GMC's mines to the Cata ore processing yard. The report presents the designed processing route, historical production data from 2006 through the first eight months of 2017, and results from metallurgical testwork completed internally during November and December 2015.

Processing route

Crushing and grinding circuits

Ore is delivered to a processing yard with 1,500 tonnes storage capacity and fed onto a gravity fed grizzly with 12 inch steel grid openings, falling into a 1,000 tonne capacity hopper. Material is transferred along a 48 inch wide belt to a 24 inch by 36 inch PettiBone jaw crusher that reduces 12 inch feed to less than 3 inch diameter. Crusher discharge exits along a 36 inch wide belt to a 6 ft wide by 20 ft long double bed vibrating Ludowici screen.

The Ludowici screen separates material by size. The upper bed removes material greater than 1 inch; the lower bed separates material less than ¼ inch. The ¼ inch fine material is fed along a 24 inch belt to a hopper prior to grinding. Current feed to the mill averages 88% less than ¼ inch. Oversize from the screen feeds a Metso (300HP) secondary cone crusher for further size reduction and is returned to the Ludowici screen along a 24 inch belt. A backup Simmons 5½ short head cone crusher is available as needed.

After crushing, ore is stored in a series of fines hoppers with 1,800 tonnes total capacity. Material passes through chutes to three 24 inch wide belts with continuous weighing scales, feeding three twin Denver 7 ft by 14 ft ball mills. The mills are coated inside with a chromium-molybdenum alloy shield on the cylinder surface and natural rubber on the heads. Grinding media are 2.5 inch diameter high chrome alloy cast balls. The ¼ inch crushed material enters the ball mills where wet pulverization produces a thick mineral pulp approximately 70% solids by weight and 30% water. This pulp is diluted with water and feeds 4 inch by 3 inch Krebs pumps, then a series of Gmax G10 hydrocyclone classifiers (two cyclones per mill) that classify fines before flotation, achieving 75% passing minus 200 mesh with automatic sampling. The average content at this stage is 28% solids by weight and 72% water. Oversize returns to the mill in closed circuit with a circulating load of 350%. Reagents added as ore enters the mills include promoter MaxGold 900 and promoter 7310 (Cyteg brand) to promote gold and silver recovery.

Flotation circuits

After grinding and initial reagent conditioning, material enters a 20 cubic metre capacity tank where additional reagents are added: promoter 7310, Aerophine 3416 (both Cyteg) and cc-1065 SF surfactant (PQM brand). Agitation incorporates these reagents into the mineral pulp. Material then enters primary rougher flotation cells consisting of two stirred cell tanks of 5 cubic metres each (Outotec), where a primary concentrate is paddled and spills over the edge of both cells for collection. Two stages of cleanup occur in primary and secondary cleaner flotation cells, consisting of two banks of Wemco-type cells (6 cubic metres each, three cells per bank). Cell discharge cascades toward secondary rougher flotation cells of three Outotec No. 5 cells, each 5 cubic metres capacity. Spills from these cells feed a medium grained material tank that partially returns to flotation after a regrind stage.

Discharge from the Outotec No. 5 cells feeds a bank of 8 Wemco type scavenger cells with total capacity of 20 cubic metres. Spills from this bank join spills from the previous 3 Outotec No. 5 cells and are sent to a 4 ft by 5 ft regrind mill, then to a hydrocyclone classifier, with the spill entering the 20 metre conditioning tank along with the grinding product in closed circuit to the regrind mill.

The material then enters an automatic filter press with 30 plates. The final concentrate has an average water content of 8% by weight.

Additional reagents necessary for flotation are introduced at the beginning of the bank of scavenger cells. The current modular system of cells allows changes to flows depending on head grades feeding the mill. Discharge of the scavenger bank, containing on average 28% solids, is sent through a series of pumps to the tailings dam after automatic sampling, transported a distance of 984 metres using 2 by 6 inch by 4 inch Warman 100 hp pumps.

Thickening and filtration

Product from the secondary cleaner flotation cells is sent via a 15 hp Gallagher pump through an automatic sampler before entering a 230 cubic metre settling tank. Thickening results in material containing 50% to 70% solids by weight, which is then sent to the filtering stage. Water recovered during thickening is recirculated and utilized at the beginning of the milling stage.

For filtration, a Clever filter press with 30 plates is used (63 cm by 63 cm each plate). Material from the thickener is fed into the filter pack through an Abel piston pump where maximum possible water is removed by compressive pressure. The resulting filtered concentrate contains on average 12% humidity. The concentrate is then sampled, weighed and stored in the concentrate yard prior to sale and shipment.

Production history

Table 17.1 in the report summarizes GMC production from 2006 through August 31, 2017. Tonnes and ounces of silver and gold include the San Ignacio mine from 2013 onward. Total production over this period was 2,406,046 tonnes, yielding 11,927,387 ounces of silver and 129,333 ounces of gold.

Metallurgical testwork

Metallurgical tests are completed internally to optimize reagent consumption and overall milling process for maximum recovery and required concentrate grades. The report presents results for November and December 2015 tests under various feed blends and conditions.

A 70%-30% blend test (concentrate 3.40% weight, scavenger 4.20% weight, tails 92.40% weight) produced concentrate grades of 56.96 g/t Au and 5,351 g/t Ag, with head grade of 2.72 g/t Au and 255 g/t Ag. Recoveries were 83.18% Au and 85.50% Ag.

A 60%-40% blend test (concentrate 4.10% weight, scavenger 2.80% weight, tails 93.10% weight) produced concentrate grades of 44.66 g/t Au and 3,861 g/t Ag, with head grade of 2.79 g/t Au and 221 g/t Ag. Recoveries were 85.01% Au and 83.54% Ag.

A 50%-50% blend test (concentrate 4.00% weight, scavenger 2.50% weight, tails 93.50% weight) produced concentrate grades of 56.97 g/t Au and 4,163 g/t Ag, with head grade of 3.29 g/t Au and 238 g/t Ag. Recoveries were 83.01% Au and 81.16% Ag.

A test using Xantato Isopropilico (concentrate 0.30% weight, scavenger 1.85% weight, tails 1.40% and 0.35% weight) produced concentrate grades of 1,341.93 g/t Au and 37,912 g/t Ag, with head grade of 5.39 g/t Au and 185 g/t Ag. Recoveries were 86.40% Au and 78.14% Ag.

San Ignacio low grade material testing (concentrate 4.10% weight, scavenger 4.40% weight, tails 91.50% weight) produced concentrate grades of 55.41 g/t Au and 1,737 g/t Ag, with head grade of 3.05 g/t Au and 119 g/t Ag. Recoveries were 70.69% Au and 78.66% Ag.

A test using Xantato Amilico (concentrate 2.90% weight, scavenger 2.50% weight, tails 94.60% weight) produced concentrate grades of 89.44 g/t Au and 2,881 g/t Ag, with head grade of 3.59 g/t Au and 124 g/t Ag. Recoveries were 76.35% Au and 83.27% Ag.

San Ignacio 100% material at 75% passing minus 200 mesh (concentrate 4.00% weight, scavenger 3.40% weight, tails 92.60% weight) produced concentrate grades of 57.16 g/t Au and 1,903 g/t Ag, with head grade of 3.34 g/t Au and 126 g/t Ag. Recoveries were 72.05% Au and 82.71% Ag.

San Ignacio 100% material at 82% passing minus 200 mesh (concentrate 4.10% weight, scavenger 4.90% weight, tails 91.00% weight) produced concentrate grades of 72.01 g/t Au and 2,301 g/t Ag, with head grade of 3.69 g/t Au and 128 g/t Ag. Recoveries were 80.08% Au and 86.38% Ag.

San Ignacio 70% material (concentrate 6.00% weight, scavenger 5.20% weight, tails 88.80% weight) produced concentrate grades of 45.39 g/t Au and 1,495 g/t Ag, with head grade of 3.57 g/t Au and 126 g/t Ag. Recoveries were 79.54% Au and 87.55% Ag.

San Ignacio 75% material (concentrate 3.00% weight, scavenger 3.10% weight, tails 93.90% weight) produced concentrate grades of 102.75 g/t Au and 3,017 g/t Ag, with head grade of 3.95 g/t Au and 131 g/t Ag. Recoveries were 77.11% Au and 89.21% Ag.

A second San Ignacio 75% test (concentrate 6.30% weight, scavenger 5.10% weight, tails 88.60% weight) produced concentrate grades of 34.09 g/t Au and 1,004 g/t Ag, with head grade of 2.74 g/t Au and 96 g/t Ag. Recoveries were 74.15% Au and 83.93% Ag.

Santa Margarita material (concentrate 5.00% weight, scavenger 2.80% weight, tails 92.20% weight) produced concentrate grades of 68.03 g/t Au and 2,171 g/t Ag, with head grade of 4.31 g/t Au and 151 g/t Ag. Recoveries were 87.17% Au and 79.90% Ag.

Key reported parameters

Technical qualifications

This article is based solely on the original technical report evidence provided. The report does not disclose flowsheet diagrams, detailed mass balances for the full plant, or specific equipment capacities beyond those stated. No information is available on plant ownership, current operational status, economic performance, or post-2017 developments. Metallurgical testwork was completed internally and the report does not indicate independent verification of results. The production history data from 2013 onward includes material from the San Ignacio mine and is not separated by source in the table. No qualified persons or report authors are identified in the source material provided.

*Source: GMC 43-101 Technical Report, Effective Date August 31, 2017, Sections 17.0 Recovery Methods*