Guanajuato Mine Complex — 2020 Technical Report

The GMC processing plant uses crushing, milling, flotation, thickening, and filtering to produce a gold-silver-bearing iron sulphide concentrate.

Report context

This technical report for the Guanajuato Mine Complex (GMC), dated December 22, 2020, and prepared under NI 43-101, describes the mineral processing plant that treats ore from GMC's mines. The processing section reports historical operating data for the period August 1, 2019, to July 31, 2020, and summarizes metallurgical testwork from November and December 2015.

Processing route

Crushing and Grinding Circuits

Ore delivered by truck to the Cata ore processing yard, which has a storage capacity of 1,500 tonnes, is fed onto a gravity-fed grizzly with 12-inch steel grid openings and falls 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. The jaw crusher discharge feeds a 6 ft wide by 20 ft long double-bed vibrating Ludowici screen via a 36-inch-wide belt. The upper bed separates material greater than 1 inch; the lower bed separates material less than 1/4 inch. This fine material (currently averaging 88% less than 1/4 inch to the mill) is fed along a 24-inch belt to a hopper prior to grinding. Oversize from the screen is fed to a Metso (300 HP) secondary cone crusher and then returned to the Ludowici screen. A backup Simmons 5½ short head cone crusher is available as needed.

Milling

Crushed ore is stored in a series of fines hoppers with a capacity of 1,800 tonnes. Material passes through chutes to three 24-inch-wide belts with continuous weighing scales and feeds 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 uses 2.5-inch diameter high chrome alloy cast balls. The 1/4-inch crushed material enters the ball mill for wet pulverization and is discharged as a thick mineral pulp with approximately 70% solids and 30% water by weight. The pulp is diluted and feeds 4 by 3-inch Krebs pumps, then a series of Gmax G10 hydro-cyclone classifiers (two cyclones per mill) that classify fines before the flotation circuit, with 75% of material passing minus 200 mesh. The average content of classified material is 28% solids and 72% water by weight. Oversize material is returned to the mill in a closed circuit with a circulating load of 350%. Two reagents are added as ore enters the mills: promoter MaxGold 900 and promoter 7310, both Cytec brand products.

Flotation Circuits

After grinding and initial reagent conditioning, material enters a 20 cubic meter capacity tank where additional reagents are added (Promoter 7310, Aerophine 3416, and cc-1065 SF surfactant). The material then enters primary rougher flotation cells consisting of two stirred Outotec cells of 5 cubic metres each, where a primary concentrate is collected. Two stages of clean-up occur in primary and secondary cleaner flotation cells: two banks of Wemco-type cells (6 cubic metres each, three cells per bank). Cell discharge cascades toward secondary rougher flotation cells consisting of three Outotec No. 5 cells of 5 cubic metres each. 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 eight Wemco-type scavenger cells with a total capacity of 20 cubic metres. Spills from the scavenger bank and the three Outotec No. 5 cells are sent to a 4 ft by 5 ft regrind mill and a hydro-cyclone classifier, with the spill then entering the 20 cubic metre conditioning tank. The material then enters an automatic filter press with 30 plates. The final concentrate has an average water content of 8% by weight. The discharge of the scavenger bank, containing on average 28% solids, is sent through pumps to the tailings dam 984 metres away, using two 6-inch by 4-inch Warman 100 hp pumps.

Thickening and Filtration

The product from the secondary cleaner flotation cells is sent via a 15 hp Gallagher pump through an automatic sampler to a 230 cubic metre settling tank. Thickening results in material containing 50% to 70% solids by weight, which is then sent to filtration. Water recovered during thickening is recirculated to the milling stage. For filtration, a Clever filter press with 30 plates (63 x 63 cm each) is used. Material from the thickener is fed into the filter pack through an Abel piston pump, and water is removed by compressive pressure. The resulting filtered concentrate contains on average 12% humidity. The concentrate is sampled, weighed, and stored in the concentrate yard.

Key reported parameters

Technical qualifications

The report states that operations at the GMC were suspended from April 2, 2020, through June 3, 2020, due to the Mexican Federal Government directive to mitigate the spread of COVID-19. All metallurgical tests described are completed internally, with a summary of results from November and December 2015 testwork provided. The processing description notes that the current modular system of cells allows flowsheet changes depending on head grades feeding the mill. The report does not present a detailed flowsheet for the proposed design beyond the existing plant configuration, and no metallurgical testwork results beyond 2015 are included.

Source: Guanajuato Mine Complex, NI 43-101 Technical Report, December 22, 2020, Section 17.0 Recovery Methods.