A look at the processing flowsheet, recent circuit additions, and design parameters for the Los Gatos joint venture underground mine, in which First Majestic Silver Corp. holds a 70% interest and acts as operator in Chihuahua State.
The Los Gatos mine is a producing underground operation in Chihuahua State, Mexico, that processes silver-rich, lead and zinc bearing mineralization. Wholly owned by First Majestic Silver Corp., the mine has been in sustained commercial operation for several years. A centralized processing plant recovers silver, lead, zinc, and associated by-products from polymetallic epithermal mineralization. Throughput capacity and annual processing rates assumed in the life-of-mine plan are supported by historical operating performance. The effective date of the technical report supporting this description is August 25, 2026.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Plant design throughput | 2,500 | tpd | Original design, based on continuous operation and scheduled availability |
| Historical throughput range, post-commissioning | 2,570 to 3,400-4,000 | tpd | Sustained operation in recent years above 3,400-4,000 tpd |
| Primary crushing | Jaw crusher | Not applicable | Feeds coarse ore stockpile |
| Grinding circuit | SAG-ball mill | Not applicable | Closed circuit |
| Flotation type | Differential (bulk lead, then zinc) | Not applicable | Conventional |
| Fluorine leaching circuit commissioning | 2023 | Not applicable | Manages fluorine in zinc concentrate |
| Paste backfill plant commissioning | Late 2022/early 2023 | Not applicable | Diverts portion of thickened tailings |
| Lead-copper separation circuit | Planned, not yet installed at effective date | Not applicable | Installation timing aligns with mining of deeper, copper-rich domains |
| Coarse particle (flash) flotation circuit | Installation in progress at effective date | Not applicable | Not yet completed |
| Tailings disposal | Lined Tailings Storage Facility and paste backfill | Not applicable | Remaining tailings after paste backfill diversion sent to surface TSF |
| Concentrate types | Bulk lead, zinc; copper (future) | Not applicable | Lead concentrate the primary pathway for silver, gold, and copper |
Overview
Processing is based on conventional crushing, grinding, and differential flotation. The flowsheet produces separate bulk lead and zinc concentrates. Silver, gold, and copper are recovered predominantly to the bulk lead concentrate. At the effective date of the technical report, documented plant capacity and operating performance support the throughput assumptions applied in the Mineral Reserve mine plan. Throughput is constrained by mine production rather than installed plant capacity.
Key Process Stages
Run-of-mine material enters a primary jaw crusher and is conveyed to a coarse ore stockpile. From there, it feeds a SAG-ball mill grinding circuit. That circuit targets the flotation feed size. Ground slurry moves to differential flotation circuits. Bulk lead flotation occurs first, followed by zinc flotation. When needed, a fluorine leaching circuit manages the final fluorine concentration in the zinc concentrate. Zinc flotation tailings become the final tailings stream. A paste backfill plant, commissioned in late 2022 or early 2023, pulls a portion of the thickened tailings for underground placement. The rest goes to the lined Tailings Storage Facility.
Additional Interesting Data and Summary
The plant originally had a design throughput of about 2,500 tpd. Historical throughput after commissioning ran from approximately 2,570 tpd up to sustained rates above 3,400-4,000 tpd in recent years. The lead-copper separation circuit is planned for installation at a defined point in the life-of-mine schedule. Its timing aligns with mining deeper domains that have elevated copper grades and lower lead-to-copper ratios. A coarse particle flotation circuit, called flash flotation, was in the process of being installed as of the effective date. It is designed to recover liberated, high-density valuable minerals directly from the cyclone underflow stream before additional grinding. Process water comes primarily from mine dewatering and is extensively recycled. Final bulk lead and zinc concentrates are thickened, filtered, and stored before truck loading and shipment. These concentrates contain low levels of deleterious elements and are suitable for sale to third-party smelters. The reagent scheme includes collectors, frothers, depressants, activators, flocculants, and pH modifiers.
Key Processes
- Comminution: Primary jaw crushing followed by SAG-ball mill grinding
- Concentration: Differential flotation (bulk lead flotation, then zinc flotation)
- Leaching: Fluorine leaching circuit to manage fluorine levels in zinc concentrate
- Dewatering: Thickening and filtration of final concentrates; tailings thickened for disposal and backfill
- Recovery: Lead concentrate is the primary recovery path for silver, gold, and copper
- Process infrastructure: Includes crushing, grinding, flotation, fluorine leaching, concentrate storage, and paste backfill plant
- Reagents, water, tailings: Conventional flotation reagent scheme; process water from mine dewatering with recycling; tailings to lined TSF and paste backfill
Source: Technical Report on Mineral Resource and Mineral Reserve Estimates, NI 43-101 Los Gatos Silver Mine, August 25, 2026. Project website: Los Gatos Silver Mine
Additional process diagram from the technical report
