The July 2015 technical report on Pan American Silver's San Vicente property describes a 350,000 t/y mill with one-stage jaw crushing, SAG and ball milling to 106 µm, selective flotation, and 2014 silver recovery of 93.2%.
San Vicente is a silver mine in Potosí, Bolivia, owned by Pan American Silver Corp. through its 95% interest in the operating company PASB. Pan American prepared the Technical Report for the San Vicente Property, with an effective date of 31 December 2014 and dated July 2015. The mine operates a process plant with a capacity of approximately 350,000 tonnes per year, using selective flotation technology to produce silver in silver-lead and zinc-silver concentrates. The mill flowsheet consists of one-stage crushing, a semi-autogenous grinding and ball mill grinding circuit, and selective flotation followed by filtration of concentrates. In 2014, the mill processed around 330,000 tonnes of ore at average metallurgical recoveries of 93.2% for silver, 82.3% for lead and 78.0% for zinc.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Plant capacity | About 350,000 | t/y | Selective flotation |
| 2014 mill feed | About 330,000 | t | Pan American's reporting |
| 2014 recoveries | 93.2 / 82.3 / 78.0 | % Ag / % Pb / % Zn | Average |
| Crushing circuit capacity | 80 | t/h | Close setting 4 in |
| Jaw crusher | 800 x 600 | mm | After a 3 in static screen |
| Crushed ore stockpile | 2,000 | t live | Ahead of grinding |
| SAG mill | 14 ft x 5 ft | 525 hp | Closed circuit with vibratory screen |
| Ball mill | 9 ft x 14 ft | 525 hp | Closed circuit with a 15 in cyclone |
| Grind size | 75 | % passing 106 µm | 140 mesh |
| Rougher cells, silver-lead | 5 | x 10 m3 | Plus a 10 m3 flash cell |
| Zinc rougher cells | 7 | x 10 m3 | Followed by six scavenger cells |
| Concentrate thickeners | 2 | 6 m x 3 m | One per concentrate |
| Filter cake moisture | 6 / 7 | % | Silver-lead / zinc-silver |
| Tailings thickener | 15 | m diameter | High-efficiency |
| Annual power use | About 20.3 | million kWh | 12.2 million at the plant |
| Fresh water | About 190,000 | m3/y | Plus 576,000 m3 recirculated |
Overview
Trucks haul ore to a 5,000 t stockpile beside the crushing plant. The ore is crushed in one stage, ground in a SAG mill and a ball mill, and floated. Silver-lead flotation comes first. Sphalerite and pyrite are depressed, silver and lead float, and the silver-lead concentrate is cleaned in two stages. The sphalerite is then reactivated to float and clean a zinc-silver concentrate. Both concentrates are thickened and filtered in press filters, and tailings are thickened and sent to a centreline-raise tailings storage facility.
Key Process Stages
Crushing
Ore passes a static screen with 20 inch openings into a bin, and an apron feeder discharges onto a three inch static screen. Oversize goes to an 800 by 600 mm jaw crusher, and the product joins the screen undersize on two conveyors. The circuit has a capacity of 80 t/h with a crusher close setting of four inches and feeds a 2,000 t live stockpile ahead of the grinding circuit.
Grinding
Primary grinding is a closed circuit 14 ft by 5 ft SAG mill with a 525 hp motor discharging onto a vibratory screen. Secondary grinding is a 9 ft by 14 ft ball mill with a 525 hp motor in closed circuit with a 15 inch hydrocyclone. The product is 75% passing 106 microns. Cyclone overflow goes through an automated sampler before being pumped to flotation.
Flotation
Depressants are added in the ball mill. Silver-lead flotation uses a 10 m3 flash cell, a conditioning tank and five 10 m3 rougher cells. Cleaning is in two stages in 1.5 m3 cells, and cleaning tails recirculate to the second rougher cell. In the zinc-silver circuit, two conditioning tanks activate the sphalerite, seven 10 m3 rougher cells float it and six 10 m3 scavengers make the final tails. The rougher concentrate is cleaned in three stages in five 5 m3 cells.
Thickening, filtering and tailings
Each concentrate is pumped to its own high-efficiency thickener, six metres in diameter. Press filters of 1,200 by 1,200 mm, with 26 plates for silver-lead and 68 plates for zinc-silver, make cakes of about 6% and 7% moisture. Flotation tails go to a 15 m high-efficiency thickener, and overflow is recirculated to the plant. Underflow goes by gravity through an approximately 3 km HDPE line to the tailings storage facility, a centreline raise facility with tails discharged from spigots along the primary embankment. A 120 hp pump recirculates clarified water.
Additional Interesting Data and Summary
Metal production in 2014, for Pan American's 95% share, was about 3.9 million ounces of silver, 5,800 tonnes of zinc and 510 tonnes of lead. Annual milled tonnes rose from 270,000 in 2010 to 320,000 in 2013 and 2014, and silver production was 3.0 million ounces in 2010 and 3.7 to 4.0 million ounces from 2012 to 2014. Before 2012 the silver-lead concentrate was sold as a silver-copper concentrate, with 600 tonnes of copper in 2011 and 500 in 2010.
Power comes from the Bolivian grid at 34.5 kV, reduced from 69 kV at the Portugalete substation. Fresh water comes from wells at the plant site and from the Angosto Mica river about 18 km away, and about 120,000 m3 of mine discharge water is available after neutralization with lime. Annual consumables are 320 tonnes of grinding media, 1,400 tonnes of lime, 350 tonnes of zinc sulphate, 250 tonnes of copper sulphate and 30 tonnes of flotation collectors.
Key Processes
- One-stage jaw crushing with static screens
- SAG and ball milling in closed circuit
- Silver-lead rougher and two-stage cleaner flotation
- Zinc-silver activation, rougher, scavenger and three-stage cleaner flotation
- Thickening and press filtration of concentrates
- Tailings thickening and centreline-raise storage
Source: Technical Report for the San Vicente Property, Potosí, Bolivia, July 2015.
Project website: San Vicente Mine
