The process plant design for the Loma Larga Project is based on testwork, vendor data, and design criteria to produce separate gold-copper and pyrite gold concentrates from a nominal 3,000 t/d of run-of-mine ore.
Report context
The Feasibility Study Update for the Loma Larga Project, located in Azuay Province, Ecuador, is documented in Technical Report document number LLP110-0000-1000-RPT-1011, Revision 0, dated October 2025. The recovery methods section describes the process plant design derived from data and design criteria provided by DPM, DRA, vendor data, testwork, and regulatory permitting requirements.
Processing route
Comminution and classification
ROM ore from the underground mine is crushed on surface in a one-stage open circuit primary jaw crusher. The material is then fed to a 1,000-t live capacity crushed ore storage bin. Material is withdrawn via an apron feeder and conveyed to a single SAG mill operating in a single-stage closed milling circuit with a bank of hydro-cyclones. The SAG mill has a Variable Frequency Drive (VFD) and dimensions of 6.9 m length by 6.9 m EGL, with 5,500 kW installed power. Pebbles separated from the mill discharge by a trommel have oversize conveyed back to the SAG mill, and undersize gravitates to the mill discharge pumpbox. No pebble crushing is required as per the mill circuit simulation results. Process water is added to the SAG mill feed chute, and milk of lime is added to the mill discharge pumpbox to maintain target mill pulp pH. Hydrocyclone underflow material returns to the SAG mill. Hydrocyclone overflow pulp reports to a grinding product buffer tank through a linear trash screen, providing 15-minute slurry residence time.
Flotation circuits
Copper flotation feed is conditioned with milk of lime, MIBC, 3418A, and process water in a copper rougher flotation conditioning tank. The conditioned slurry flows by gravity to the copper rougher Jameson cell. Copper rougher tails are pumped to the copper rougher scavenger Jameson cell. Copper rougher and scavenger concentrates are both sent to regrind. Copper rougher scavenger tailings are pumped to the pyrite rougher conditioning tank.
Gold-copper rougher and rougher scavenger concentrates are combined as copper regrind feed and reground in a VFD driven ceramic media vertical stirred mill operating in open circuit with a scalping cyclone cluster which removes fines of 30 µm d80 to overflow, with underflow pumped to the regrind mill. The regrind mill discharge is combined with cyclone overflow and pumped to copper cleaning flotation, which uses single-stage cleaning with one cleaner and one cleaner scavenger Jameson flotation cell of the same size. Tails from the cleaner cell are pumped to the cleaner scavenger cell. Tails from the cleaner scavenger cells are directed to the pyrite rougher conditioning tank, and concentrate from the cleaner scavenger is returned to the cleaner cell feed box. Gold-copper cleaner concentrate reports to final concentrate thickening, filtration, and loadout.
In the pyrite rougher conditioning tank, the copper rougher scavenger tails slurry pH is reduced from 11–11.5 to 7 with sulphuric acid addition. The slurry is conditioned with PAX collector, and process water is added for density control. MIBC frother is added to the pyrite rougher cell feed box. The conditioning tank overflows to the pyrite rougher feed box and discharges into the pyrite rougher Jameson flotation cell. Pyrite rougher tails are pumped to the pyrite rougher scavenger Jameson cell. Pyrite rougher and scavenger concentrates are both sent to regrind. Pyrite rougher scavenger tailings gravitate to the tails pumpbox and are pumped to tailings thickening, filtration, and paste backfill plant within the Paterson & Cooke battery limit.
Pyrite rougher and rougher scavenger concentrates are combined as pyrite regrind feed and reground in a VFD driven ceramic media vertical stirred mill operating in open circuit with a scalping cyclone cluster which removes fines of 30 µm d80 to overflow, with underflow pumped to the regrind mill. The regrind mill discharge combined with cyclone overflow is pumped to pyrite cleaning flotation. Pyrite cleaning comprises two sequential stages. The first stage consists of one first cleaner and one first cleaner scavenger Jameson flotation tank cells. Tails from the first cleaner cell are pumped to the cleaner scavenger tank cell. Tails from the first cleaner scavenger are combined with pyrite rougher scavenger tails and pumped to tailings thickening. The first cleaner concentrate is pumped to the second cleaner Jameson cell, while concentrate from the first cleaner scavenger is returned to the first cleaner cell feed box. The second cleaner bank consists of a single Jameson flotation cell. Second cleaner concentrate reports to the pyrite concentrate thickener, and second cleaner tails report to the first cleaner cell feed box.
Concentrate dewatering
Gold-copper concentrate is thickened and dewatered with pressure filters and stored in bulk in the concentrate storage area prior to being loaded into containers and shipped. Pyrite concentrate is thickened and dewatered with pressure filters and stored in bulk in the concentrate storage area prior to container loading and shipment. The filtration circuit design is based on common design practices for the concentrate, as no testwork data are yet available. Tailings dewatering is outside of the DRA scope and is addressed by Paterson & Cooke and NewFields for the tailings facility design.
Water systems
Three types of water are defined for the process: process water, fresh water, and gland seal water. Process water is recovered as overflow from the concentrate thickeners and final tailings thickener. The process water circuit also receives water from the mine and fresh water for make-up. Fresh water is sourced from the local environment. Gland seal water is produced by filtration from the freshwater tank. Plant fire protection uses fresh water from the plant freshwater tank. Potable water is sourced from the plant fresh water source and treated within the plant envelope as per local regulations.
Sampling and process control
The plant uses Blue Cube slurry analysers employing diffuse reflectance spectroscopy to measure mineral grades of slurries directly in the process, sampling for Cu, As, Fe, Au, Ag grades and particle size distribution. The system does not require a sample delivery and dispatch system.
The process control system is a PLC-based SCADA system controlling process interlocks and PID control loops for non-packaged equipment. Two modes for loop-controlled control variables are available: Auto-Mode and Manual Mode.
Key reported parameters
| Parameter | Unit | Nominal | Design |
|---|---|---|---|
| Plant throughput | t/d | 3,000 | 3,400 (Year 2) |
| Crushing Work Index (CWi) | kWh/t | 11.5 | – |
| Abrasion Index (Ai) | – | 1.08 | – |
| Bond Ball Mill Work Index (BWi) | kWh/t | 18.5 | – |
| SAG mill installed power | kW | 5,500 | – |
| SAG mill dimensions (L x EGL) | m | 6.9 x 6.9 | – |
| Primary grinding product P80 | µm | 75 | – |
| Regrind product P80 | µm | 30 | – |
| Copper rougher feed design flow | m³/h | – | 498.9 |
| Copper rougher scavenger feed design flow | m³/h | – | 497.1 |
| Copper cleaner feed design flow | m³/h | – | 49.2 |
| Copper cleaner scavenger feed design flow | m³/h | – | 30.5 |
| Pyrite rougher feed design flow | m³/h | – | 510.7 |
| Pyrite rougher scavenger feed design flow | m³/h | – | 504.1 |
| Pyrite 1st cleaner feed design flow | m³/h | – | 208.5 |
| Pyrite 2nd cleaner feed design flow | m³/h | – | 108.6 |
| Copper concentrate thickener settling rate | t/h/m² | – | 0.14 |
| Pyrite concentrate thickener settling rate | t/h/m² | – | 0.11 |
| LOM gold recovery (total) | % | – | 89.6 |
| LOM gold recovery to gold-copper concentrate | % | – | 15.8 |
| LOM gold recovery to pyrite concentrate | % | – | 73.8 |
Project website: https://dpmmetals.com/assets/development/loma-larga-gold-project/
Project website: https://miningwatch.ca/blog/2021/8/6/inv-metals-loma-larga-project-acquired-canadian-company-toxic-environmental-record
Technical qualifications
The process plant design is based on data and design criteria provided by DPM, DRA, vendor data, testwork, and regulatory permitting requirements. The SAG mill sizing is based on achieving the grind size required to obtain required flotation performance as well as outcomes of metallurgical testwork and mill simulations. The flotation circuit design is based on 2017–2018 SGS testwork results, with 2022 and 2023 testwork programs designed to confirm those results and update the flowsheet to incorporate Jameson cell technology. Results of the 2017–2018 locked cycle testwork and 2022 and 2023 programs provided the basis for recovery and grade calculations and enabled sizing of the Jameson cell flotation circuit equipment. The filtration circuit design is based on common design practices for the concentrate, as no testwork data are yet available. Recovery estimates were derived from sequential flotation locked cycle tests completed during the 2014 metallurgical program and locked cycle tests #3 and #4 from the 2017 metallurgical program. Copper recovery formulas are considered accurate for copper head grades greater than 0.1% and less than 1.0% (for the original concentrate model) and greater than 0.17% and less than 0.47% (for the gold-copper concentrate model). Gold recovery formulas are considered accurate for Au head grades greater than 3.71 and less than 7.17 g/t as per the mine schedule. The copper concentrate production schedule formulas use fixed LOM recovery of 86.90% and fixed LOM grade of 8.80%, with adjustments based on copper head grade variation. For gold, a fixed LOM recovery of 15.88% to gold-copper concentrate is used. The paste backfill plant design is by Paterson & Cooke, and the filtered tailings storage facility design is by NewFields.
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Source: Technical Report, Feasibility Study Update, Loma Larga Project – Azuay Province, Ecuador, Document #LLP110-0000-1000-RPT-1011 – Rev 0 – FINAL, October 2025, Section 17, Recovery Methods.
