The August 2022 technical report on the Minera Florida mine in Chile describes a 900 ktpa plant that classifies ore, crushes it in three stages, grinds in three ball mills, leaches a concentrate and treats flotation tailings in a separate leach and carbon-in-pulp circuit.
Minera Florida is a gold, silver and zinc mine in Chile's Metropolitan Region. The NI 43-101 technical report has a signature date of August 31, 2022, and the mine was reported by Yamana Gold Inc. The processing plant and associated facilities treat run-of-mine and stockpiled ore. The main processes are reception and classification of ore, crushing, grinding, gold bulk flotation, a concentrate leaching plant (PLC), electrowinning of rich solution, doré melting, a zinc-lead flotation plant, a tailings treatment plant (PTR), and tailings thickening and disposal. The plant has a nominal production capacity of approximately 900 ktpa at 95% availability. It processes ore from Minera Florida and also from third-party mines.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Nominal capacity | About 900 | ktpa | 95% availability |
| Milling target | 100,000 | t per month | Average |
| Classification sizes | Over 90, 10 to 90, under 10 | mm | Oversize / intermediate / undersize |
| Primary crusher product | 3.5 | in P80 | Jaw crusher |
| Grizzly | 6 | openings | 2.5 to 3.5 in each |
| Secondary screens | 75 / 50 | mm | Double deck |
| Tertiary screens | 19 / 10 | mm | Upper / lower deck |
| Ball mill 2 | 8 x 9 | ft | 536 hp |
| Ball mills 3 and 4 | 12 x 14 | ft | 1,320 hp each |
| Grind | 65 | % below 75 µm | Three cyclone batteries |
| Bulk flotation | 4 | stages | Pre-rougher, rougher, cleaner, scavenger |
| Concentration | About 15 | times | Mass ratio of bulk flotation |
| Concentrate leach oxygen | 7 | ppm | Dissolved O2 |
| Leach tailings filter | About 10 | % moisture | LAROX filter |
| Electrowinning pregnant solution temperature | 70 | °C | Five cells in series |
| Tailings leach | 5 | tanks | Followed by 8 CIP tanks |
| Doré melting | 1200 to 1400 | °C | Two induction furnaces |
Overview
The Minera Florida plant is a hybrid flowsheet. Gold bulk flotation takes gold and the gold-silver-zinc-lead minerals into a small concentrate, which is leached with cyanide in a concentrate leaching plant. The pregnant solution is electrowon and the solids are filtered and become feed for a zinc flotation plant. Flotation tailings go to a separate tailings treatment plant with agitated leaching, carbon-in-pulp (CIP) adsorption, elution and detoxification, to raise overall gold recovery.
Key Process Stages
Reception, classification and crushing
Ore is weighed at the plant gate and unloaded into classification stockpiles, third-party ore stockpiles or directly into the primary crusher. It is classified into oversize above 90 mm, intermediate from 10 to 90 mm and undersize below 10 mm. The oversize goes to the primary jaw crusher, the intermediate to a stockpile feeding the secondary and tertiary crushers, and the undersize to the fine stockpile for grinding. A one metre vibrating grizzly with six openings of 2.5 to 3.5 inches pre-sorts feed to the primary jaw crusher, which crushes to a P80 of 3.5 inches. Secondary double deck screens of 75 and 50 mm send plus 50 mm to the secondary crusher and the rest to the tertiary crushers, and tertiary screens of 19 and 10 mm make a 100% minus 10 mm product in closed circuit.
Grinding and bulk flotation
Three ball mills, an 8 by 9 foot Denver mill and twin 12 by 14 foot Dominion mills, aim to produce 100,000 tonnes a month at 65% below 75 microns. Three hydrocyclone batteries classify the product. Overflow is sampled and conditioned in a 50 m3 tank with RC 800 primary collector, CIBXS secondary collector, D-400 and MIBC frothers and copper sulphate zinc activator. Four flotation stages follow: pre-rougher, rougher, cleaner and scavenger. Bulk flotation concentrates gold about 15 times, so the concentrate mass is about 15 times lower than mill feed.
Concentrate leaching and electrowinning
Concentrate passes a linear screen and thickeners to about 1.5 g/cm3 density, is conditioned with sodium cyanide and caustic soda, and leached in tanks in series with low-pressure air to hold 7 ppm dissolved oxygen. A second thickener circuit makes the pregnant solution, and the underflow is filtered on a LAROX filter to about 10% moisture with successive washing stages. This leached tailing is the feed to the zinc flotation plant. Pregnant solution is clarified, heated to 70 °C and electrowon in five stainless steel cells in series. Cathode mud is filtered, retorted, and melted in two electric induction furnaces with silica, borax and sodium nitrate fluxes to make doré.
Zinc-lead flotation and tailings treatment
The zinc flotation plant treats washed, filtered cyanidation tailings in an 11 m3 conditioning tank with CIBXS collector, frother and copper sulphate. The tailings treatment plant (PTR) processes bulk flotation tailings. Pulp is thickened and leached in a conditioner and five agitated tanks with sodium cyanide, with poor solution from electrowinning added. Leach pulp goes to eight CIP tanks, and loaded carbon is screened out, eluted in a high pressure, high temperature column with concentrated cyanide solution, and acid washed with hydrochloric acid when impurities are high. The effluent pulp is detoxified to destroy free cyanide, then thickened and disposed of.
Additional Interesting Data and Summary
The doré fluxes are mixtures of silica, borax and sodium nitrate. Silica forms the slag base but melts at 1723 °C and tends to make a viscous slag that could trap precious metals, while borax lowers the melting point and viscosity. The melting system also has doré casting equipment, a gas extraction system connected to a baghouse and slag pots.
Poor solution from electrowinning goes to the PTR so that its residual cyanide is reused in tailings leaching. Overflow from the concentrate thickeners is also sent to the PTR for reuse.
Key Processes
- Ore classification and three-stage crushing
- Three ball mills with hydrocyclone classification
- Four-stage gold bulk flotation
- Cyanide concentrate leaching with LAROX filtration
- Electrowinning and induction furnace smelting
- Zinc-lead flotation of leach residue
- Tailings leaching with eight-tank CIP and elution
- Cyanide detoxification and tailings thickening
Source: NI 43-101 Technical Report, Minera Florida Gold-Silver-Zinc Mine, Metropolitan Region, Chile, August 31, 2022.
