La Colorada Silver Recovery: Flotation & Cyanide Leach

Source: Pan American Silver Corp (2026)
Website: https://panamericansilver.com/operations/silver-segment/la-colorada/

Critical Data

Overview

Pan American Silver Corp. operates the La Colorada Property processing plant in Zacatecas, Mexico, a facility designed to handle two distinct ore types through separate circuits. The plant, which has been in operation with established nominal capacities of 2,000 tpd for sulphide ore and 400 tpd for oxide ore, employs conventional yet highly effective silver recovery methods tailored to each ore’s mineralogy. The sulphide circuit utilizes selective lead-zinc froth flotation to produce high-grade lead and zinc concentrates, capturing 90.6% of the silver in the lead concentrate and 3.5% in the zinc concentrate. The oxide circuit relies on a conventional cyanide leach process followed by Merrill-Crowe zinc precipitation and smelting to produce doré bars. In 2025, overall plant recoveries reached 92.9% for silver, 64.8% for gold, 86.7% for lead, and 84.6% for zinc, underscoring the efficiency of these recovery methods. The significance of La Colorada lies in its dual-circuit design, which allows simultaneous treatment of sulphide and oxide ores from the same mine, maximizing metal extraction and economic returns. Water sustainability is a key feature, with 83% of process water recirculated from the tailings storage facility and the remainder sourced from underground dewatering. Power is supplied from the national grid, supplemented by backup generators, with annual consumption of 17 GW-hr.

Key Process Stages

• Stage 1: Sulphide Ore Crushing & Grinding – Ore from an 8,000 t stockpile is fed via apron feeder to a C-100 jaw crusher, reducing material to minus 6 inches. The crushed ore passes over a double-deck 2.4 × 6.1 m screen; oversize reports to a short head crusher in closed loop, while undersize is stored in two 800 t fine ore bins. Material is then ground in a 4.0 × 5.7 m ball mill in closed circuit with cyclones to achieve the target particle size for flotation.
• Stage 2: Lead Flotation Circuit – Cyclone overflow enters a lead flotation bank of six 30 m³ tank cells (four rougher, two scavenger). Rougher concentrate is cleaned in six 10 m³ cells across two stages. Cleaner concentrate reports to a 7.0 m diameter thickener; underflow is filtered in a filter press to produce a lead concentrate cake averaging 44.4% Pb. Thickener overflow returns as process water.
• Stage 3: Zinc Flotation Circuit – Lead scavenger tailings are conditioned with reagents in a 4.3 m diameter tank, then fed to six 30 m³ zinc flotation cells (four rougher, two scavenger). Rougher concentrate is cleaned in six 10 m³ cells. Cleaner concentrate thickens in an 8.0 m diameter thickener and is filtered to produce a zinc concentrate cake averaging 57.4% Zn. Tailings from the scavenger circuit proceed to classification for backfill or disposal.
• Stage 4: Oxide Ore Crushing, Grinding & Leaching – Oxide ore is jaw-crushed (600 × 900 mm), screened, and secondary cone-crushed in closed loop. Fine ore is ground in a 2.9 × 3.4 m ball mill in closed circuit with cyclones; a second 2.4 × 3.0 m ball mill provides additional grinding. Dilute cyanide solution initiates gold and silver leaching in the grinding circuit. Cyclone overflow reports to two 7.9 × 2.4 m primary leach thickeners, then passes through seven agitated leach tanks, an intermediate thickener, four more leach tanks, and four countercurrent rinse thickeners to maximize metal recovery and minimize cyanide in tailings.
• Stage 5: Merrill-Crowe Precipitation & Doré Smelting – Pregnant leach solution is clarified and deoxygenated in a vacuum tower. Zinc dust is added to precipitate gold and silver. The metal precipitate is separated via filter presses; barren solution returns as process water. The precipitate is mixed with fluxes and smelted in a gas-fired furnace, then cast into doré bars for shipment.

Additional Interesting Data and Summary

The La Colorada processing plant’s dual-circuit design provides operational flexibility to handle varying ore types from the same deposit, optimizing overall silver recovery methods. While head grades are not detailed in Section 17, the 2025 recovery performance—92.9% for silver, 64.8% for gold, 86.7% for lead, and 84.6% for zinc—demonstrates high efficiency. The sulphide circuit achieves 90.6% of silver into the lead concentrate (44.4% Pb grade) and 3.5% into the zinc concentrate (57.4% Zn grade), highlighting the selectivity of the flotation circuit. Reagent consumption is well-documented: sulphide ore uses 0.56 kg/t grinding media and 1.0 kg/t lime; oxide ore uses 0.80 kg/t grinding media, 4.6 kg/t lime, and 3 kg/t sodium cyanide. Environmental considerations include a lined tailings storage facility for fine tailings and hydraulic backfill for coarse material from the sulphide circuit, reducing surface disposal. Water conservation is a major sustainability initiative: 83% of the plant’s water (approximately one million cubic metres per year) is recirculated from the tailings storage facility, and the remaining 17% (200,000 m³) comes from underground dewatering, fully meeting process requirements. Energy consumption of 17 GW-hr annually is supplied by the national grid with backup diesel generators. Economic impact is driven by the production of high-grade lead and zinc concentrates and doré bars shipped to smelters and refineries. Future outlook for the La Colorada property includes continued optimization of the flotation circuit and leaching parameters to further improve recoveries, especially for gold. The facility’s robust design and sustainable water management position it well for long-term operation, contributing significantly to Pan American Silver’s portfolio as a major silver producer in Zacatecas, Mexico.

Key Processes: Flotation, Cyanidation, Ball Mill, Crushing

Target Commodities: Gold, Silver, Zinc, Lead