This report describes the multi-stream heap leaching and flotation processing facilities at Zaldívar as of March 2012.
Report context
The Zaldívar Mine Technical Report NI 43-101, Project #1683, dated March 16, 2012, was prepared for Barrick Gold Corporation. This article summarises the recovery methods section (Section 17) of that report.
Processing route
Overview
Ore is processed primarily through a heap leaching system using sulphuric acid leaching solutions with copper recovery in a solvent extraction/electrowinning (SX/EW) process in the form of copper cathode. There are multiple stages and routes of heap leaching to treat various ore streams depending upon material characteristics.
Dynamic pad leach process
Run-of-mine (ROM) ore is primary crushed to 50 mm and secondary crushed to 35 mm at a rate of 65,000 tpd. Product from the secondary crushers is transported via overland conveyor to a covered stockpile with a capacity of 10,000 tonnes. Reclaim from the stockpile is tertiary crushed to 13 mm and screened, producing leach pad feed and a small fraction (3%) that is thickened for feed to flotation.
The finely crushed leach feed is placed in 10 m lifts with a RAHCO Stacker on the pad. A bucket-wheel excavator removes the spent ore after leaching for rehandling to the Ripios Alto Ley (RAL) or permanent secondary leach dump. The residence time on the dynamic pad is approximately 360 days. Acid leach solution is applied to the surface of the ore, with pregnant solutions collected at the base of the pad.
The dynamic heap leach facility is based on a nominal 65,000 tpd operation (22 Mtpa).
ROM leach pad
The ROM dump leach processes low grade material directly from the mine. The material is not crushed and is placed on the ROM pad directly from haulage trucks. Acid leach solution is applied to the surface of the ore, with pregnant solutions collected at the base of the pad. The ROM dump leach facility is based on the dynamic heap leach capacity and ore availability in the mine and will average a nominal 15 Mtpa over the remaining mine life.
SX/EW copper recovery circuit
The pregnant solutions from both the heap and dump leach are directed to the SX/EW process. The plant includes four trains of low-head mixer-settler units, each followed by a two-series extraction stage – a wash stage and a strip stage. Cathodes are bundled in 3,000 kg lots for shipment by rail to the port of Antofagasta.
Flotation concentration process
The thickened fines slurry is treated in the 1,850 tpd flotation plant. The final concentrate, containing approximately 35% Cu, is thickened, filtered, and shipped by truck to Xstrata's La Negra smelter near Antofagasta. The tailings from the flotation plant are transported by gravity through a four kilometre pipeline to a disposal site in the northeast corner of the property.
Copper recovery algorithms
Zaldívar has been using copper recovery algorithms for reserve estimation developed from the results of Lift #6 in 2006. Sequential copper assay data (total copper, acid soluble copper, cyanide soluble copper, and insoluble or residual copper) is used to calculate and reconcile leach recoveries.
For the 2011 recovery model, a modification to the dynamic heap leach insoluble copper recovery was made, limiting maximum insoluble copper recovery to 55%. With this change, the average calculated recovery for the remaining resources at Zaldívar decreases by approximately 9%. This is a direct result of the recovery capping of 55% applied to the insoluble copper component of the dynamic leach pad ore as well as the impact of an approximate 8% reduction in average grade of the insoluble copper included in the current geological model.
In 2012, a revision will be made to the recovery model to account for current operational parameters and results.
Key reported parameters
| Parameter | Unit | Design | Historical Operating | Testwork Basis |
|---|---|---|---|---|
| Dynamic heap leach feed rate | tpd | 65,000 | , | , |
| Dynamic heap leach throughput | Mtpa | 22 | , | , |
| ROM dump leach throughput (average remaining mine life) | Mtpa | 15 | , | , |
| Dynamic pad leach residence time | days | 360 | , | , |
| Tertiary crushed product size | mm | 80% passing 13 | , | , |
| Fines fraction to flotation | % of crushed material | 3 | , | , |
| Flotation plant capacity | tpd | 1,850 | , | , |
| Flotation concentrate grade | % Cu | 35 | , | , |
| Average metallurgical recovery – Dynamic heap leach | % | 62.6 | , | , |
| Average metallurgical recovery – Dump heap leach | % | 36.0 | , | , |
| Average metallurgical recovery – Overall | % | 59.7 | , | , |
| Recovery algorithm parameters (F1, F2, F3) | % | 96, 78, 40 | , | Proposed values from 2006 study |
| Maximum insoluble copper recovery (dynamic leach, 2011 model) | % | 55 | , | , |
| Insoluble copper recovery (flotation) | % | 70 | , | Design algorithm |
| Acid soluble copper recovery (flotation) | % | 13 | , | Design algorithm |
Project website: https://www.barrick.com/English/operations/zaldivar/default.aspx
Technical qualifications
The report states that the recovery algorithms adequately represented the data obtained for Lift #6, as the equations were forced to fit the data. However, when used to calculate recoveries from other lifts, the fit was less precise. This is because the methodology used does not recognise that sulphide copper occurs in several different mineralogical species which do not have the same leaching kinetics.
The report notes that in 2012, a revision will be made to the recovery model to account for current operational parameters and results.
Source: Barrick Gold Corporation – Zaldívar Mine, Technical Report NI 43-101, Project #1683, March 16, 2012, Section 17 Recovery Methods.
