The Preliminary Economic Assessment describes a proposed 1,500 t/d concentrator using crushing, grinding, bulk and zinc flotation, and gravity gold recovery to produce lead-silver, zinc, and coarse gold concentrates.
Report context
This article is drawn from the Tangana Project Preliminary Economic Assessment dated April 2023. The report presents a proposed processing plant design for the Tangana project, with process design criteria largely assumed based on experience at the existing Nueva Recuperada concentrator located 22 km south of the future Tangana site, and on experience with operations treating similar mineralization at a similar scale.
Processing route
Crushing and ore preparation
Run-of-mine material will be reclaimed from a ROM bin using a vibrating grizzly feeder. Process water will be added at a trommel to remove clays, with the fine material and water flowing directly to the mill pump box. Coarse material will be fed to a primary jaw crusher via conveyor, with a metal detector fitted to protect downstream equipment. Primary crusher discharge will report to a vibrating screen; oversize will feed a secondary cone crusher, with screen undersize collected and returned. Secondary crusher product will report to a fine feed bin.
The milling feed bin will discharge onto conveyors feeding the rod mill. Surplus material will overflow to a crushed material stockpile, which can be reclaimed if the crushing area is not functioning. The nominal milling feed bin capacity will be calculated for two days of continuous milling operation while the crushing area is down for maintenance.
Grinding, classification, and gold recovery
The primary grind size feeding flotation will be P80 = 90 µm. The rod mill will reduce material from 45 mm to 2.2 mm and will be provided with a screen to remove metallic materials. Rod mill product will discharge into the mill pump box, which will also receive fines and water from the trommel. The combined material will feed a cyclone battery for classification at P80 = 74 µm. The coarse fraction will return to the ball mill, which will reduce material from 3.3 mm to 75 µm, with product size controlled by a particle size analyzer.
A gravity bowl concentrator will scalp coarse gold from the grinding circuit. A shaking table will clean the bowl concentrate to commercial quality, after which it will be stored in a secure area until shipment. Gravity tailings will be directed to the flotation process.
Flotation process
The bulk flotation circuit will process material to recover copper, lead, and silver, comprising rougher, cleaner, and scavenger stages. The rougher stage involves conditioning grinding circuit product with reagents followed by flotation. Rougher concentrates will transfer to the cleaner stage for further concentration, then to the scavenger flotation cell. Final concentrate from the scavenger stage will be thickened and filtered.
The zinc flotation circuit involves multiple stages of activation, conditioning, rougher, cleaner, and scavenger flotation. Bulk tailings will be subjected to activation using copper sulfate to activate sphalerite minerals. The conditioned material will undergo rougher flotation. Rougher concentrate will be reground to P80 = 54 µm to improve liberation. Reground concentrate will then be subjected to cleaner flotation to produce a final concentrate. Tails from cleaner flotation will be subjected to scavenger flotation, with concentrate combined with rougher concentrate for further cleaning. Flotation circuit control will be aided by an inline analyzer.
Concentrate dewatering
The plant will produce three concentrates: a lead-silver concentrate anticipated to assay 55% Pb and between 51 and 99 oz/t Ag, a zinc concentrate anticipated to assay 52% Zn, and a coarse gold concentrate that will be sold to a third party refinery. Concentrates from flotation will be thickened using a high-rate thickener to 60-70% solids, then filtered using a filter press. Filter cake will be stored in a covered storage area. Overflow and filtered water will be recycled. Concentrates will be loaded onto trucks by front-end loader for transport.
Tailings dewatering and disposal
Tailings from the zinc scavenging flotation bank will feed a tailings thickener to be dewatered to about 57% solids. Thickener underflow will report to a tailings filter where 12% moisture will be achieved by pressure filtration. Disc filters will use fresh water. Dry tailings will be transferred to a tailings storage facility or used as underground mine backfill. Thickener overflow and filtering water will be recycled.
Utilities and consumables
Installed power requirement is estimated at 3,015 kW. The incoming power line will feed the main electrical substation from the Peruvian national grid, with emergency diesel generators for critical standby instances.
Two potential fresh water sources have been considered: rainfall and runoff courses, and underground mine dewatering. Borehole wells could also be a source. It has been assumed that 1.9 m³/t of water will be required for the process. Dewatering water from the mine at approximately 20 l/s (72 m³/h) will mainly be used for mine operation, with an additional 67 m³/h makeup water needed for the processing plant.
Major reagents include lime for pH control, zinc sulphate and sodium cyanide as depressants, copper sulphate as a zinc activator, MIBC as frother, and collectors including sodium isopropyl xanthate, potassium amyl xanthate, thionocarbamate, Aerophine, and dithiophosphate. Steel rods and balls for grinding and flocculant for thickening are also required. Consumables estimation is based on the current operation at the existing Nueva Recuperada process plant.
Key reported parameters
| Classification | Description | Value | Units | Data Source |
|---|---|---|---|---|
| Feed characteristics | Processing rate | 1,500 | t/d | Design |
| Feed characteristics | Head grade Ag | 2.37 | oz/t | Existing plant data |
| Feed characteristics | Head grade Pb | 1.47 | % | Existing plant data |
| Feed characteristics | Head grade Zn | 1.48 | % | Existing plant data |
| Feed characteristics | ROM moisture | 3 | % | Existing plant data |
| Feed characteristics | Clay in ROM | <5 | % | Client estimation |
| Feed characteristics | Abrasion index | 0.3 | g | Estimated |
| Feed characteristics | Wi rod mill | 22 | kWh/t | Estimation from existing plant |
| Feed characteristics | Wi ball mill | 17 | kWh/t | Estimation from existing plant |
| Feed characteristics | Wi crushing | 18 | kWh/t | Estimation from existing plant |
| Feed characteristics | SG ROM | 2.74 | g/cm³ | Existing plant data |
| Product specifications | Ag grade in Pb concentrate | 53 | oz/t | Existing plant data |
| Product specifications | Pb grade in Pb concentrate | 55 | % | Existing plant data |
| Product specifications | Zn grade in Zn concentrate | 52 | % | Existing plant data |
| Grinding | Primary grind size (flotation feed) | P80 = 90 | µm | Design |
| Grinding | Classification size | P80 = 74 | µm | Design |
| Grinding | Zinc regrind size | P80 = 54 | µm | Design |
| Operations | Operating hours per shift | 12 | hours | Existing plant data |
| Operations | Operating days per year | 365 | days | Existing plant data |
| Operations | Shifts at plant | 2 | shifts | Existing plant data |
| Operations | Availability crushing area | 85 | % | Estimated |
| Operations | Availability rest of plant | 90 | % | Estimated |
| Energy | Total installed power | 3,015 | kW | Design |
| Water | Process water requirement | 1.9 | m³/t | Assumed |
| Water | Mine dewatering flow | ~20 | l/s | Assumed |
| Water | Additional makeup water needed | 67 | m³/h | Assumed |
Project website: https://www.silverxmining.com/projects/production/tangana-mining-unit/
Technical qualifications
The report states that much of the process design criteria have been assumed, based on experience at the existing Nueva Recuperada concentrator and on experience with operations treating similar mineralization at a similar scale. The plant has been designed on a fit-for-purpose basis considering a project life of about 15 years, with no consideration or allowance for any expansion. The report notes it has been prepared based on assumed information and limited metallurgical testwork. For water systems, only high-level evaluations have been made, and the report recommends quality testing of different sources for future studies to reduce processing risk in terms of metal recovery and concentrate grades.
The report provides specific recommendations before completing a prefeasibility study, including obtaining representative core samples for mineralogical and metallurgical testing for the main mineral types, optimizing the process with respect to flowsheet and equipment sizing, evaluating geometallurgical variability, validating the process flowsheet using bulk pilot testing at the Nueva Recuperada plant, and determining engineering design criteria through testwork for materials handling, tailings management, and water management.
Source: SilverX: Tangana Project, Preliminary Economic Assessment, April 2023, Sections 17.1-17.6.
