This report describes the processing design, operating data, and testwork basis for the San Jose Mine concentrate plant as of December 31, 2023.
Report context
The San Jose Mine, located in Oaxaca, Mexico, is the subject of a technical report dated December 31, 2023. The processing plant described in this report was designed based on metallurgical testwork presented in Section 13 of the technical report and has been operating for 12 years. The report covers the current processing plant design, equipment characteristics, and specifications at each step of the process, with a focus on the crushing, milling, flotation, and tailings handling circuits.
Processing route
Crushing and milling circuits
The concentrate plant has a maximum throughput capacity of 3,000 dry tpd. The principal processing stages are crushing, milling, flotation, and thickening, filtering, and shipping.
The crushing process is a dry operation where ore extracted from the mine is reduced in size from 406 mm to 12.7 mm before feeding the mill. Ore is deposited into a reception hopper and fed via a plate feeder into a jaw crusher that reduces the ore to a 102 mm product. This material is transported by conveyors to a 2.44 m by 6.1 m primary screen deck equipped with a 35 mm mesh. Material not passing the 35 mm mesh is sent to a secondary crusher, reduced to 25 mm, and returned to the primary screen. Material passing the 35 mm mesh is conveyed to a 3 m by 7.3 m secondary screen deck with a 12.7 mm mesh. Oversize from this screen is sent to a tertiary crusher, reduced to 12 mm, and returned to the jig to close the circuit. Fine ore passing the 12.7 mm mesh is sent to fine ore storage, achieving a final product size of 12.7 mm before milling.
The milling circuit receives fine ore from storage via conveyor belts and feeds it to either a 3.96 m by 5.94 m or a 4.57 m by 6.6 m ball mill. The mills are filled to 25 to 30 percent of their volume with three-inch wrought steel balls for grinding. Mill product is pumped to a classification circuit consisting of hydro-cyclones, which generate two products: a fine ore overflowing from the top and a coarse ore exiting from the bottom, with the coarse ore recycled to the mills for further grinding. The fine ore must meet metallurgical conditions for metal recovery, specifying that 80 percent of the product must be under the 150-mesh size (105 µm), before being sent to flotation.
Flotation
The pulp (water plus mineral) from the hydro-cyclone fine ore is first sent to a flotation stage performed in ten mechanical cells: six cells of 14.2 m³ and four cells of 17 m³. These cells use a propeller and diffuser to distribute the pulp and inject air, allowing reagents to act on the elements of value, which adhere to bubbles that spill over the cell edges into a collection trough. The resulting product is the primary concentrate. After this first stage, the pulp flows by gravity to a second flotation stage.
The second flotation stage uses an additional four 17 m³ mechanical cells under similar conditions to generate a secondary scavenger concentrate. This concentrate is returned to the beginning of the 17 m³ cells. Mineral that does not float in the second stage is considered tailings and passes to the thickening process.
The primary concentrate from the first two 14.2 m³ cells is sent directly to the third cleaning stage. The remaining primary concentrate is sent to a first cleaning stage carried out in twelve 2.8 m³ mechanical cells, which remove impurities and increase concentrate grade. The product is a first clean concentrate, with the residue returned to the first of the 17 m³ cells. The first clean concentrate enters a second cleaning stage performed in three 2.8 m³ mechanical cells, where further impurities are removed to obtain a second clean concentrate, with residue returned to the first cleaning stage. The second clean concentrate is sent to a third cleaning stage performed in two 2.8 m³ mechanical cells, yielding a final concentrate for the thickening stage and a residue returned to the second cleaning stage.
Thickening, filtering, and tailings handling
The third cleaning concentrate is sent to a thickening tank where a flocculating reagent agglomerates particles and generates sediment. Solids and liquids are separated to recover water for recirculation to the process, while thickened solids are pumped to a two-press-type pressure filter with twelve tarpaulin-covered plates, where water is removed and re-circulated. The concentrate cake is discharged to concentrate storage for transportation.
The underflow from the final bank of the second flotation stage is sent to a thickening tank where solid-liquid separation is performed using a flocculating reagent. Recovered water is returned to the process, while the remaining pulp is pumped to a three-press-type pressure filter with 145 tarpaulin-covered plates, where most water is eliminated and re-circulated. The tailings cake is discharged to the tailings stock for transport to the dry stack disposal area.
Part of the pulp pumped to the pressure filter is diverted to the paste fill plant for backfilling purposes, with 30 percent of the mine's backfilling requirements supplied by the paste fill plant.
Requirements for energy, water, and process materials
Energy is supplied by a State power line of 115 kV serving two power transformers of 7 to 8 MVA capacity. These transformers cover the needs of the underground mine, mill plant, and facilities at the present 3,000 tpd production rate (8 MVA).
The plant requires 2.7 m³ of water to process one tonne of ore. Of this, 92 percent comes from recirculation, and the remaining 8 percent is sourced from the waste-water treatment plant in Ocotlan.
Reagent consumption is detailed in Table 17.1 of the technical report. The report notes a difference between plant design and functionality regarding sodium silicate usage. The CAM (2010) prefeasibility study recommended 100 g/t of sodium silicate reagent for the cleaning stages, but Cuzcatlan identified that this reagent is not necessary to obtain the desired product, resulting in significant cost savings. Two reagents, citric acid and aluminum sulfate, were added to reduce fluorine concentration in the final concentrate.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Plant maximum throughput | 3,000 dry tpd | Design |
| Ore feed size to crushing | 406 mm | Design |
| Crushed product size | 12.7 mm | Design |
| Primary screen dimensions | 2.44 m by 6.1 m | Design |
| Primary screen mesh opening | 35 mm | Design |
| Secondary screen dimensions | 3 m by 7.3 m | Design |
| Secondary screen mesh opening | 12.7 mm | Design |
| Jaw crusher product size | 102 mm | Design |
| Secondary crusher product size | 25 mm | Design |
| Tertiary crusher product size | 12 mm | Design |
| Ball mill dimensions | 3.96 m by 5.94 m and 4.57 m by 6.6 m | Design |
| Ball mill volume fill | 25 to 30% | Design |
| Grinding media | 3-inch wrought steel balls | Design |
| Flotation grind size | 80% passing 105 µm (150-mesh) | Metallurgical condition |
| Flotation cells, first stage | Six 14.2 m³ and four 17 m³ | Design |
| Flotation cells, second stage | Four 17 m³ | Design |
| First cleaning cells | Twelve 2.8 m³ | Design |
| Second cleaning cells | Three 2.8 m³ | Design |
| Third cleaning cells | Two 2.8 m³ | Design |
| Concentrate filters | Two-press-type, twelve tarpaulin-covered plates | Design |
| Tailings filters | Three-press-type, 145 tarpaulin-covered plates | Design |
| Water consumption | 2.7 m³ per tonne of ore | Design |
| Recirculated water | 92% of total | Design |
| Fresh water from Ocotlan | 8% of total | Design |
| Paste fill plant supply | 30% of backfill requirements | Design |
| Frother consumption (Ore Prep 507) | 1 g/t | Design |
| Collector consumption (Xantato Amilico de Potasio) | 4 g/t | Design |
| Collector consumption (Aeropromotor 404) | 10 g/t | Design |
| Collector consumption (Aerophine 3418) | 31 g/t | Design |
| Collector consumption (Pennfloat-3) | 2 g/t | Design |
| Collector consumption (Max Gold) | 5 g/t | Design |
| Flocculant consumption (Magnafloc 336) | 33 g/t | Design |
| Depressor consumption (Citric Acid) | 90 g/t | Design |
| Depressor consumption (Aluminum sulfate) | 100 g/t | Design |
| Sodium silicate consumption | 100 g/t recommended; not used in practice | Testwork, CAM 2010 prefeasibility study; actual operation |
| Alumina sulfate addition | Added to reduce fluorine in concentrate | Addition per design |
Project website: https://fortunamining.com/
Technical qualifications
The technical report notes that the processing plant was designed based on metallurgical testwork from Section 13 of the technical report. The QP considers processing requirements to be well understood and consistent with actual observed conditions in the operating plant. The report states there is no indication that the characteristics of the material being mined will change, and therefore the recovery assumptions applied for future mining are considered reasonable for the LOMP. The plant is described as conventional in design, using conventional equipment and consumables.
The report identifies a specific difference between plant design and functionality regarding sodium silicate usage in cleaning stages, with the CAM (2010) prefeasibility study recommending 100 g/t, while actual operation determined this reagent is unnecessary.
Source: San Jose Mine , 2023 Technical Report, Fortuna Silver Mines Inc., December 31, 2023, Section 17, Recovery Methods, pages 160–163.
