The Juanicipio processing plant in Zacatecas, Mexico, has achieved its designed 4,000 tpd throughput and demonstrated metallurgical performance above plan for zinc, lead, and silver recoveries during its first year of operation.
Article Body
The Juanicipio project, operated by MAG Silver Corp., includes a processing facility designed for a nominal capacity of 4,000 tonnes per day. The plant has been in operation since March 2023, with ramp-up and optimization continuing through the reported operating period. The process flowsheet comprises a comminution circuit with primary crushing and milling, followed by sequential flotation to produce three concentrate products: a silver-rich lead concentrate, a zinc concentrate, and a gold-silver-bearing pyrite concentrate.
Ore is delivered from the underground mine to an underground primary jaw crusher designed to reduce run-of-mine material from a nominal 500 millimetres to a 100 per cent passing size of 178 millimetres, with an 80 per cent passing size of 87 millimetres. The crushed material is conveyed to a surface stockpile with a live capacity equivalent to two days of mill operation, or 8,000 tonnes. This stockpile is intended to provide operational continuity and allow blending of different ore types to achieve the targeted plant feed grade and consistent material sizing.
The grinding circuit comprises a semi-autogenous grinding mill followed by a ball mill. The SAG mill discharge flows over a vibrating screen, with oversized material returned to the SAG mill via a conveyor belt. Screen undersize flows by gravity to a pump-box, where it combines with the ball mill discharge before entering hydrocyclones. The hydrocyclone underflow returns to the ball mill for further grinding, while the overflow reports to flotation. A minimum grind size is required to achieve the metal recoveries determined during metallurgical test work, and an automated process control system is part of the design to ensure consistent grinding. The closed grinding circuit achieves a product size with an 80 per cent passing size of 60 micrometres.
Flotation proceeds sequentially through lead, zinc, and pyrite circuits. The lead flotation circuit produces a silver-rich lead concentrate, with the circuit tails passing by gravity to the zinc flotation circuit. The zinc circuit consists of two rougher stages, a scavenger stage, and three stages of cleaning of rougher concentrate. Concentrate handling includes surge tanks designed to keep the feed to the respective filters constant; the zinc concentrate surge tank has capacity to store 12 hours of zinc concentrate production. The pyrite circuit has been in an optimization phase since initial operation, with first delivery to an off-shore purchaser. If the pyrite circuit is not operated, the tails of the scavenger bank become the final tails and are pumped to the tails thickener, where the maximum amount of process water is recovered.
Operational performance data from March 2023 to January 2024 demonstrate that the plant feed rate has tightened around the nominal 4,000 tpd design figure, with the range of daily averages narrowing and average production increasing as operators conduct optimization work. The qualified person notes that the throughput data demonstrate achievement of the designed performance. Total plant feed for the operating period from March to December 2023 was 956,914 tonnes.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Nominal plant capacity | 4,000 | tpd | Design figure |
| Primary crusher feed top size | 500 | mm | Nominal |
| Primary crusher product, P100 | 178 | mm | |
| Primary crusher product, P80 | 87 | mm | |
| Stockpile live capacity | 8,000 | t | Two days of mill operation |
| Grinding circuit product, P80 | 60 | µm | |
| Zinc concentrate surge tank capacity | 12 | h | 12 hours of zinc concentrate production |
| Total plant feed, Mar-Dec 2023 | 956,914 | t | |
| Average gold recovery | 71.4 | % | December 2023 |
| Average silver recovery | 87.6 | % | Excluding ramp-up period |
| Average lead recovery | 89.9 | % | Excluding ramp-up period |
| Average zinc recovery | 90.5 | % | Excluding ramp-up period |
Overview
The Juanicipio processing plant was designed and constructed as part of the larger Juanicipio project. The comminution and flotation circuits were sized and specified based on metallurgical test work that established the required grind size and expected metal recoveries. The plant design incorporates an automated process control system for the grinding circuit to maintain consistent performance.
The flowsheet was arranged to produce three concentrates sequentially, with the lead circuit producing a silver-rich product, followed by zinc and pyrite circuits. The pyrite circuit was initially operated in an optimization phase, and the plant was designed so that the pyrite circuit could be bypassed, with scavenger tails becoming the final tails and directed to the tails thickener for water recovery.
Key Process Stages
The process plant comprises several integrated stages designed to treat the full throughput of underground ore. The primary crushing stage involves a jaw crusher located underground, reducing the ore from a nominal 500 millimetres to a 100 per cent passing size of 178 millimetres. A surface stockpile with a live capacity of 8,000 tonnes, representing two days of mill feed, provides buffer capacity and ore blending capability.
The grinding circuit operates as a closed circuit, with the SAG mill discharge screened and oversize returned for further grinding. The screen undersize combines with the ball mill discharge in a pump-box and is fed to hydrocyclones. The hydrocyclone underflow returns to the ball mill, while the overflow continues to flotation at a product size with an 80 per cent passing size of 60 micrometres.
Sequential flotation follows, with the lead circuit producing the first concentrate. The lead flotation tails feed the zinc circuit by gravity. The zinc circuit comprises two rougher stages, a scavenger stage, and three cleaning stages. Concentrate from the zinc roughers is cleaned in three stages, with the first cleaner tails returning to the head of the rougher bank and the second cleaner tails returning to the first cleaner. The final zinc concentrate reports to a surge tank before filtering.
The pyrite circuit, when in operation, treats the zinc scavenger tails and produces a pyrite concentrate for gold recovery. The circuit uses two banks of flotation cells for rougher and scavenger flotation, with cleaner stages, and the final tails are pumped to the tails thickener. If the pyrite circuit is not operating, the zinc scavenger tails are the final tailings.
Additional Interesting Data and Summary
Metallurgical performance during the first operating period exceeded the planned design values for several metals. Zinc recovery averaged 90.5 per cent compared to the planned value of 74.5 per cent, a significant outperformance. Lead recovery averaged 89.9 per cent compared to the planned value of 86.3 per cent. Silver recovery averaged 87.6 per cent compared to the planned value of 87.1 per cent. Gold recovery was lower than planned, and the qualified person recommends continuing the optimisation program aimed at improving all processing aspects, including gold recovery.
The qualified person acknowledges the continuing testing and process development being conducted by the plant’s operators. The ramp-up phase has demonstrated that the daily feed rate has tightened around the nominal 4,000 tpd design figure, with the range of daily averages narrowing as operators optimise operations. The zinc and lead circuits have performed particularly well, achieving recoveries well above the design basis. The pyrite circuit achieved its first concentrate delivery to an off-shore purchaser during the optimisation phase.
The processing philosophy incorporates features to maintain operational flexibility, including the surge tanks that stabilise feed to the filters and the ability to route final tails directly to the tails thickener when the pyrite circuit is not operating. These design characteristics, combined with the successful ramp-up, position the plant to achieve its full production potential, subject to completion of the ongoing optimisation programs.
Key Processes
- Comminution: single-stage jaw crushing to 178 millimetres P100, followed by SAG and ball milling in closed circuit with hydrocyclones to achieve a product size of 60 micrometres P80
- Lead flotation: produces a silver-rich lead concentrate
- Zinc flotation: two rougher stages, a scavenger stage, and three stages of cleaning of rougher concentrate
- Pyrite flotation: recovers gold-silver-bearing pyrite concentrate; can be bypassed with tails sent directly to final tailings
- Tails thickening: final tails pumped to thickener to recover maximum process water
Source: Juanicipio , NI 43-101 Technical Report, 2024, MAG Silver Corp.
Editorial note: The source material includes contradictory statements regarding silver and gold recovery performance, with quoted values differing between the summary section and the operational data tables. Specifically, the QP's narrative reports silver recovery averaging 87.6 per cent against a plan of 87.1 per cent, consistent with the tabulated data, while gold recovery is described as below plan without a quantified variance. Additionally, the planned zinc recovery is stated as 74.5 per cent in the operating data section but the QP's summary refers to a planned value that is inconsistent with the tabulated data. The technical report also contains an apparent inconsistency in the description of the flotation circuit configuration, with the text describing both two and three cleaner stages in different sections.
Project website: Juanicipio, NI 43-101 Technical Report
