The 2007 technical report for the Yanamina project defines a proposed 3,000 tonnes-per-day heap leach with Merrill Crowe recovery route, based on metallurgical testwork.
Report context
This report, dated 2007, documents the recovery method proposed for the Yanamina project. The proposed flowsheet was developed from Mineral Processing and Metallurgical Testing (Item 13.0) undertaken by JZW Mineral Processing Consultants. The report selects heap leaching with sodium cyanide and a Merrill Crowe plant as the preferred extraction option.
Processing route
The report considers two recovery methods: heap leaching with NaCN and a Merrill Crowe plant, and a combination of gravity concentration, flotation of sulphides, and NaCN leaching. Management selected heap leaching as the Best Available Technology (BAT) for the project, a designation supported by the report authors.
The proposed processing route is designed to treat 3,000 tonnes of ore per day using the following stages: run-of-mine ore delivered by truck, a three-stage crushing circuit reducing ore to ¼ inch, agglomeration with NaCN and CaO, deposition on prepared pads in 5-metre layers, irrigation with weak NaCN solution, collection of pregnant solution in a containment pond, and recovery of gold and silver in a Merrill Crowe plant.
Crushing circuit and agglomeration
Run of mine ore is dumped onto a grizzly with rails set at 18-inch centres. Material passing through the grizzly falls into a 1,000-tonne capacity coarse ore bin, while the oversize is broken using an impact breaker. Material from the coarse ore bin is transferred by a 48-inch by 12-foot apron feeder to a 4-foot by 8-foot vibrating grizzly with bars set at 4-inch centres. The plus-4-inch material passes under a metal detector into a 24-inch by 48-inch jaw crusher. The undersize from the grizzly and the jaw crusher discharge is conveyed on a 36-inch by 15-foot belt conveyor under a metal detector to feed a 6-foot by 12-foot double-deck vibrating screen with 1½-inch upper and 1-inch lower deck openings. The plus-1-inch material goes to a tertiary Symons cone crusher, while the minus-1-inch material is conveyed to a 6-foot by 14-foot rotary agglomerator where CaO and NaCN solution are added.
Pad preparation and NaCN leaching
The natural terrain is graded and sculptured with progressively finer aggregate and sand. Pads are double lined with 36-mil geomembrane and compacted daily, with leakage detection and removal provisions not requiring reinforcement for tear resistance. Perforated or corrugated plastic pipe is proposed to assist pregnant solution removal, transferring it by gravity to a collection ditch connected to the rich solution pond. PVC panels and High Density Polyethylene liners are noted as alternatives. Perimeter and diversion berms and ditches are required to remove rainfall and run-off water that would otherwise enter process streams.
Ore is transported by dump trucks to a fine ore bin near the pad area and distributed on the pad using a radial stacker with conveyor belts, forming layers 5 metres deep to minimise compaction. Heaps are irrigated by pressure emitters feeding leaching solution at 10 litres per hour per square metre, providing continuous dripping with minimal drop impact to reduce fines migration and channelling. A potential drawback identified is carbonate precipitation, which can be inhibited by descaling application as normal practice.
Merrill Crowe plant
Pregnant solution will be processed in a conventional Merrill Crowe Plant with a capacity of 105 m³, including a 96-inch by 20-inch deaeration tower, vacuum pumps, a zinc dust feeding system, lead acetate preparation and feeding systems, and pressure filters for precipitate recovery. A 6-foot by 6-foot preparation tank for diatomite pre-coating and body feeding is included. Barren solution from the precipitate recovery filters will be stored in a barren solution pond and recirculated to the leaching operation after NaCN concentration and pH adjustment.
Precipitate will be treated in a retort for drying and mercury recovery. The calcine will be mixed with borax, silica, and soda ash, and melted in an induction furnace, with bullion ingots and slag separated. A standard slag processing plant is considered, with a 3-foot by 3-foot ball mill included for effective liberation of gold blebs. Gravity separation tailings will be recirculated to the agglomeration stage together with solids recovered in clarification stages.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Design throughput | 3,000 tonnes per day | Proposed design |
| Crushed product size | ¼ inch | Proposed design |
| Heap layer height | 5 metres | Proposed design |
| Irrigation rate | 10 litres per hour per square metre | Proposed design |
| Pregnant solution tank capacity | 105 m³ | Proposed design |
| Filter area (Scheibler) | 300 m² | Proposed design |
| Filter feed pressure (Scheibler) | 12 PSI | Proposed design |
| Alternative filter feed pressure (US Filters) | 65 PSI | Alternative proposal |
| Leaching reagent | NaCN | Testwork basis |
| Agglomeration reagent additions | NaCN and CaO | Proposed design |
| Liner type | 36-mil geomembrane, double lined | Proposed design |
Project website: https://www.mining.com/coronet-metals-announces-closings-of-the-yanamina-gold-project-acquisition-and-10-8-million-financing/
Technical qualifications
The report presents a proposed flowsheet rather than confirmed operating data. Design details such as the 5-metre heap layer height, irrigation rate, filter areas, and the crushing circuit equipment sizes form part of the proposed design and have not been validated by full-scale operating results. The report notes that filter performance assumptions differ between the Scheibler and alternative US Filters options, with the latter requiring higher feed pressure and increased power and filtering aid consumption. The process flowsheet is presented as a figure, with the report indicating that gravity separation tailings and solids from clarification are recirculated to agglomeration.
Source: Yanamina Project , 2007 Technical Report, Sections 17, 17.1, 17.2, and 17.3.
