Nevsun Resources' 2018 prefeasibility study for the Upper Zone of the Timok copper-gold project in Serbia (Čukaru Peki) staggers the cleaner circuit, using rougher flotation alone for the first two years of high-grade feed.
The NI 43-101 Technical Report on the Timok Copper-Gold Project, Serbia: Upper Zone Prefeasibility Study and Resource Estimate for the Lower Zone, was prepared by Hatch and others for Nevsun Resources Ltd. with an effective date of June 19, 2018 and a report date of August 7, 2018. The Upper Zone copper mineralogy is mainly covellite with lesser enargite. The flowsheet was first designed to make two concentrates, one below and one above 0.5% arsenic. The study is based on a simpler single bulk concentrate route, with all pyrite going to the bulk tailings.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Report effective date | June 19, 2018 | Not applicable | Hatch for Nevsun Resources Ltd. |
| Plant capacity | 3,250,000 | t/a | About 8,900 t/d nominal |
| Primary crushing | Underground jaw crusher, to minus 150 | mm | Overland conveyor to the plant |
| Coarse feed storage | Two bins of 4,500 t live | Not applicable | 24 hours of storage combined |
| Grinding | Variable-speed SAG mill and ball mill | Not applicable | Cyclone overflow 80% passing 75 µm |
| Regrind | 80% passing 25 | µm | Vertical ball mill |
| Rougher flotation | Six forced-air tank cells | Not applicable | pH 10.0, MIBC and Aerofloat 211 |
| Cleaners | Two counter-current stages and a cleaner scavenger | Not applicable | First cleaner of seven cells at pH 11.0 |
| Availability | 75 crushing, 92 grinding and flotation, 80 concentrate filtration | % | Three 8-hour shifts, 365 days |
| Concentrate dewatering | Two 15 m high-rate thickeners, two Larox PF60M132 filters | Not applicable | Underflow 60% solids |
Overview
The plant comprises underground primary crushing, overland conveying, coarse feed bins, a SAB grinding circuit, copper rougher flotation with concentrate regrind and two-stage cleaning, and concentrate thickening, filtration and load-out. Tailings storage with water reclaim, effluent treatment, reagent, water and air services complete the site. There is provision for future flotation of a separate high-arsenic complex concentrate.
For the first two years, rougher flotation alone gives an acceptable concentrate because the feed grade is high. A first cleaner stage is then added, and later a second, as the feed grade declines. The process description in the report is for the completed plant.
Key Process Stages
Crushing and storage. A vibrating grizzly feeder feeds an underground jaw crusher that crushes to minus 150 mm. A decline conveyor and an overland conveyor carry the feed to a shuttle conveyor over two 4,500 t live coarse feed bins, with a chute to an emergency stockpile.
Grinding. A single variable-speed SAG mill with discharge grates is followed by a ball mill in closed circuit with a cyclone cluster, producing cyclone overflow at 80% passing 75 µm. Pebbles are recycled to the SAG feed conveyor, and space is left for a pebble screen and crusher if the ore becomes harder. Lime is added at the cyclone feed hopper to raise the pH to about 10.
Rougher flotation. After a trash screen and conditioner, where the pH is set to 10.0 with slaked lime, the feed passes through one bank of six forced-air mechanical tank cells dosed with MIBC frother and Aerofloat 211 collector. After the first two years, rougher concentrate needs further liberation and upgrading to remove arsenic.
Regrind and cleaning. Rougher concentrate is reground to 80% passing 25 µm in a vertical ball mill with small cyclones. The first cleaner, of seven tank cells at pH 11.0, feeds a second cleaner. Cleaner scavenger concentrate returns to the conditioner, or in future to copper-arsenic retreatment cells. An on-stream analyzer tracks copper and arsenic.
Concentrate dewatering. Concentrate is split between two circuits, each with a 15 m high-rate thickener producing 60% solids underflow and an Outotec Larox PF60M132 pressure filter. If a separate complex concentrate is made later, one circuit would handle each concentrate.
Additional Interesting Data and Summary
The report gives different grind sizes in different places. The text states a grinding product of 80% passing 75 µm and a regrind of 80% passing 25 µm, while the bulk concentrate flowsheet figure from SGS shows P80 of about 106 µm and about 35 µm. This article reports the figures as the text states them.
In summary, the 2018 Timok Upper Zone PFS is a conventional SAG-ball and copper flotation design for 3.25 Mt/a. It makes one bulk concentrate from covellite-rich ore, starts with roughers only during the high-grade early years, and leaves room for a separate arsenic-rich concentrate if that later proves better.
Key Processes
- Underground jaw crushing and overland conveying
- SAG and ball milling to 80% passing 75 µm
- Rougher flotation at pH 10 with MIBC and Aerofloat 211
- Vertical ball mill regrind to 80% passing 25 µm
- Two-stage counter-current cleaning and cleaner scavenging
- Concentrate thickening and pressure filtration
- Tailings storage with water reclaim
Source: NI 43-101 Technical Report – Timok Copper-Gold Project, Serbia: Upper Zone Prefeasibility Study and Resource Estimate for the Lower Zone, prepared by Hatch for Nevsun Resources Ltd., effective date June 19, 2018.
Earlier report summaries
Earlier versions of this profile, based on older technical reports, are retained below for source traceability. Dates and figures reflect each report’s own effective date and are superseded by the current information above.
Cukaru Peki PEA Report — 2016
A staged processing route is proposed for the Cukaru Peki project, progressing from direct-sale ore to flotation concentrate production.
Report context
This report presents a Preliminary Economic Assessment (PEA) for the Cukaru Peki project, dated March 2016. The processing sections describe a developmental approach to provide processing facilities that accommodate the mine plan, using capital-efficient staging from a direct shipping ore (DSO) starter mine through to a 2.0 Mtpa flotation plant for upper zone material.
Processing route
DSO Starter Mine Phase
For the initial three to four years of production, an oversized 1.0 Mtpa crushing, open-circuit grinding and filtration plant is constructed to reduce the 0.5 Mtpa DSO to a size acceptable to smelters and also to allow representative samples to be taken. The DSO product is described with a copper grade of 12-14%, a gold grade of 9-15 g/t and an arsenic grade of 0.13-0.25%. This material could be smelted directly after crushing and milling. It is assumed that DSO will be crushed to a nominal size in the order of P100 less than 2 mm before being bagged or trucked directly to smelters. The DSO crushing and screening plant will be located near to the underground access decline.
Flotation Expansion Phase
The DSO plant is later expanded by the addition of a rougher and cleaner flotation plant to result in a 1.0 Mtpa crushing, closed-circuit grinding, flotation and concentrate filtration plant. The PEA assumes that copper will be recovered by rougher and cleaner flotation either into “low arsenic” and “high arsenic” concentrates, or into a single arsenic-containing copper concentrate. The copper mineralogy consists primarily of covellite with lesser enargite, and minor colusite, bornite and chalcopyrite. Enargite and colusite contain arsenic and therefore the arsenic grade of any copper concentrate will be a key consideration for smelter choice, terms and charges.
Final Expansion Phase
The 1.0 Mtpa plant is duplicated, to provide 2.0 Mtpa capacity to treat the lower grade upper zone material in order to maintain a similar level of copper production.
Concentrate Products
Two copper concentrates are envisaged for subsequent production:
- Up to 100 ktpa of a ‘Low Arsenic’ high copper concentrate with a copper grade of 52-58%, a gold grade of 3.9-6.3 g/t and an arsenic grade of 0.48% after blending.
- 50-100 ktpa of a ‘High Arsenic’ relatively high copper concentrate with a copper grade of 37%, a gold grade of 3.4-12.8 g/t and an arsenic grade of 2.5-5.5% after blending.
Both concentrates are within marketable ranges, with no other significant deleterious elements identified.
Gold Distribution
The majority (60%) of the gold in ROM reports to a pyrite concentrate which is considered as a waste product in the PEA; this will be stored separately and will be targeted for additional processing testwork in future technical studies. DSO product contains approximately a third of the gold and a quarter of the copper life of mine mill feed (ROM), all of which will derive revenue in the first four years of the mine life according to the smelter payment terms assumed in the PEA.
Processing Alternatives Considered
The report briefly discusses two processing alternatives. A third concentrate from the rougher and/or cleaner tails containing pyrite and gold might be considered; this has not been included in the PEA, but could provide additional revenue. No treatment route has been identified as yet for the pyrite concentrate, but a pyrite roasting, cyanide leaching of the calcine and “SART” will be considered. A dedicated study will be required into metallurgical behaviour and recovery of the gold from the pyrite concentrate.
A hydrometallurgical treatment route is also considered, based on oxidation of the sulphides (covellite and enargite) in a high pressure and temperature autoclave, followed by neutralization of dissolved metals, recovery of copper by SX/EW and gold by CIL.
Key reported parameters
| Parameter | Unit | Design / Actual / Basis |
|---|---|---|
| DSO starter mine throughput | Mtpa | 0.5 (DSO), plant oversized to 1.0 (design) |
| Flotation plant throughput (initial) | Mtpa | 1.0 crushing, closed-circuit grinding, flotation and concentrate filtration (design) |
| Flotation plant throughput (final) | Mtpa | 2.0 (design, duplicated from 1.0 Mtpa) |
| DSO copper grade | % | 12-14 (testwork basis) |
| DSO gold grade | g/t | 9-15 (testwork basis) |
| DSO arsenic grade | % | 0.13-0.25 (testwork basis) |
| Low arsenic copper concentrate grade | % Cu | 52-58 (testwork basis) |
| Low arsenic concentrate gold grade | g/t | 3.9-6.3 (testwork basis) |
| Low arsenic concentrate arsenic grade | % | 0.48 after blending (testwork basis) |
| High arsenic copper concentrate grade | % Cu | 37 (testwork basis) |
| High arsenic concentrate gold grade | g/t | 3.4-12.8 (testwork basis) |
| High arsenic concentrate arsenic grade | % | 2.5-5.5 after blending (testwork basis) |
| Low arsenic concentrate production | ktpa | Up to 100 (design) |
| High arsenic concentrate production | ktpa | 50-100 (design) |
| Copper recovered in concentrate (life of mine) | kt | 702 (design estimate from Table 17-1) |
| Gold recovered in concentrate (life of mine) | koz | 277 (design estimate from Table 17-1) |
| DSO copper (life of mine) | kt | 248 (design estimate from Table 17-1) |
| DSO gold (life of mine) | koz | 649 (design estimate from Table 17-1) |
| Gold reporting to pyrite concentrate | % | 60 (testwork basis) |
Project website: https://www.zijinmining.com/global/program-detail-71735.htm
Technical qualifications
The PEA assumptions for concentrate production are based on preliminary metallurgical testwork and mineralogical work completed on Cukaru Peki upper zone samples. No treatment route has been identified as yet for the pyrite concentrate, and a dedicated study will be required into metallurgical behaviour and recovery of the gold from the pyrite concentrate. For capital cost estimation, a cost was obtained for a similar crushing, grinding, flotation and concentrate filtration plant that was recently estimated at feasibility level by a reputable Australian engineering company; costs were adjusted using the “six tenths rule” and typical factors were added for construction indirect costs, EPCM and contingency. For the tailings storage facility, little definition exists on possible tailings disposal sites or dam design, and a mid-range value of USD2/t has been used to cover the cost of dam raises during the life of the mine. Operating costs were calculated from a combination of first principles and typical benchmarks for similar plants.
Source: U6782 Cukaru Peki PEA Report v30.docx, March 2016, Sections 17.1-17.5.2.
