Mineralized material from the Platosa Mine is shipped 220 kilometres to the Miguel Auza processing facility, which has operated two circuits for lead-silver and zinc-silver since 2009.
Report context
This technical report, dated June 17, 2021, addresses the Platosa Polymetallic Mine, part of Excellon Resources Inc. The report details recovery methods at the Miguel Auza mineral processing facility, which has been treating silver-, lead-, and zinc-rich carbonate replacement deposit (CRD) mineralization from Platosa since 2009. The facility was originally designed and constructed at 650 tonnes per day to process material from the historical lower-grade Miguel Auza Mine. Modifications made in 2009 upgraded flotation cells from a processing rate of 325 to 350 tonnes per day to 650 tonnes per day with a flexible flotation configuration to handle variable ore feed grade.
Processing route
Crushing and Grinding
Oversized run-of-mine ore greater than 200 millimetres is fed to a 900-tonne-per-day jaw crusher at Platosa. Any ore greater than 400 millimetres is reduced by a rock breaker before entering the jaw crusher. Sized ore is shipped in 38-tonne covered trucks to the Miguel Auza processing facility. At the facility, ore is blended in the stockpile area using a wheel loader with metallurgical criteria to provide more stable feed grade to the flotation circuit. Oversized ore reports to the crusher circuit at Miguel Auza, which comprises a jaw crusher, cone crusher, and double-deck grizzly. This crushing circuit reduces ore to 80% passing 9.5 millimetres, feeding a 600-tonne capacity fine material bin.
From the fine material bin, crushed material is fed into a 650-tonne-per-day ball mill, 3.0 metres in diameter and 3.2 metres in length, reducing material to 80% passing 45 micrometres. The ball mill operates in closed circuit with cyclones that separate fine particles and transfer cyclone overflow to the lead conditioning tank.
Lead Flotation
Ball mill product enters a lead conditioning tank where reagents including collector and frother are added ahead of lead flotation. Reagents added to the lead circuit are Aero 3407, a selective lead/silver collector; methyl isobutyl carbonyl (MIBC) Aero F-70, the foaming agent responsible for generating bubbles that allow stable froth formation; and zinc sulphate (ZnSO₄) as a zinc depressant.
Concentrate from the lead rougher enters a two-stage lead cleaning circuit. Tails enter the lead scavenger, where scavenger concentrate is pumped to the cleaning circuit and tails enter the zinc flotation circuit. Concentrate from the second lead cleaner constitutes the final lead concentrate and is pumped into the lead thickener. The lead concentrate contains approximately 80% of the lead and 81% of the silver from the mill feed.
Zinc Flotation
Tails from the lead scavenger cells enter zinc conditioner tanks where lime and copper sulphate are added. Material then enters two parallel zinc rougher banks. Tail is directed to the zinc scavenger, and rougher concentrate is directed to two-stage zinc cleaner banks. Concentrate from the second zinc cleaner constitutes the final zinc concentrate and is pumped to the zinc thickener. Tail from the second cleaner joins the rougher concentrate and scavenger concentrate to feed the first cleaner, enriching zinc grade and depressing insoluble components such as silicates. Final tailings from the zinc scavenger are directed to the tailings management facility. The final zinc concentrate contains approximately 80% of the zinc and 9% of the silver from the mill feed.
Reagents used in the zinc circuit are calcium oxide or lime (CaO), added to the first zinc conditioning tank to raise pH necessary for zinc flotation while working as an iron suppressant; copper sulphate (CuSO₄), added to the second zinc conditioning tank to activate zinc particles depressed upstream in the lead flotation circuit; and sodium isopropyl xanthate (X-343), used as a zinc collector.
Filtration
The processing facility has a filtration system, warehouse, and concentrate drying pads for each concentrate produced. Concentrate enters an 88-cubic-metre thickener tank, settles to the bottom, and is pumped to vacuum disk filters. After filtration, each concentrate is transferred into the corresponding storage warehouse where a wheel loader spreads it on a drying pad. From the drying pad, concentrate is transferred into a storage warehouse until loaded onto covered 38-tonne trucks for transportation to a concentrate sales facility.
Assay and Metallurgical Laboratories
The Miguel Auza mill has a chemical laboratory that receives samples from the processing facility, mine samples, geology samples, and mine truck samples. The laboratory can test up to 75 samples per day and has testing facilities for atomic absorption, granulometry, fire assays, and titration to test for gold, silver, lead, zinc, iron, copper, arsenic, antimony, cadmium, calcium, nickel, bismuth, lead oxide, and zinc oxide. In addition to analyzing samples from the mineral processing facility, the laboratory analyzes channel samples from the face, grab samples from stockpiles, and composite samples from mine trucks taken both at Platosa and Miguel Auza. The metallurgical laboratory can perform flotation tests before any ore campaign to confirm reagent dosage rates for Platosa or toll milling ore.
Key reported parameters
| Parameter | Unit | Design Basis | Historical Operating Data (2010-2020) |
|---|---|---|---|
| Processing rate (design) | tpd | 650 | , |
| Ball mill diameter | m | 3.0 | , |
| Ball mill length | m | 3.2 | , |
| Grind size (80% passing) | µm | 45 | , |
| Crushing product size (80% passing) | mm | 9.5 | , |
| Daily mill throughput (range) | tpd | , | 211 to 362 |
| Annual production (range) | tpa | , | 48,199 to 81,004 |
| Mill head silver grade (range) | g/t | , | 391 to 847 |
| Mill head lead grade (range) | % | , | 3.75 to 6.75 |
| Mill head zinc grade (range) | % | , | 5.12 to 11.83 |
| Silver recovery (range) | % | , | 85 to 93 |
| Lead recovery (range) | % | , | 68 to 83.7 |
| Zinc recovery (range) | % | , | 75 to 85 |
| Silver produced (range) | koz | , | 719 to 1,492 |
| Lead produced (range) | '000 lbs | , | 1,286 to 7,632 |
| Zinc produced (range) | '000 lbs | , | 1,689 to 10,703 |
| Laboratory capacity | samples/day | 75 | , |
Project website: https://excellonresources.com/news/details/index.php?content_id=126
Technical qualifications
This technical report describes a processing facility that was originally designed for 650 tonnes per day from the historical Miguel Auza Mine and subsequently modified in 2009. The report presents historical production data from 2010 through 2020 in Table 31, and the flowsheet is shown in Figure 33. The report notes that the metallurgical laboratory can perform flotation tests before any ore campaign to confirm reagent dosage rates for Platosa or toll milling ore. The report does not provide information on current operational status, ownership changes, economic analysis, or forward-looking production estimates beyond the presented historical data.
*Source: "Platosa Polymetallic Mine , 2021 Technical Report," Excellon Resources Inc., June 17, 2021, Section 16 Recovery Methods.*
