Aura Minerals' 2014 technical report for the San Andrés gold mine in Copán, Honduras, covers a ten-year mine plan of 68.1 Mt at 0.52 g/t Au. It uses gold recoveries of 76% for oxide ore and 57% for mixed ore.
The Mineral Resource and Mineral Reserve Estimates on the San Andrés Mine in the Municipality of La Unión, Department of Copán, Honduras, NI 43-101 Technical Report was prepared for Aura Minerals Inc. It is dated July 2, 2014, with an effective date of December 31, 2013. San Andrés is an open pit heap leach mine. Ore is hauled by contract trucks to two jaw crushers, crushed in two stages, agglomerated with cement and lime, and conveyed to the leach pads. The life-of-mine schedule of 68.1 Mt contains about 1,129,000 oz Au. Annual gold output depends on grade and on the blend of oxide and mixed ore. The ADR plant was being upgraded for 7 Mtpa.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Report effective date | December 31, 2013 | Not applicable | Report dated July 2, 2014, for Aura Minerals Inc. |
| Mine plan | 68.1 Mt at 0.52 g/t Au | Not applicable | Ten years, about 1,129,000 oz contained |
| Recovery basis | 76 oxide, 57 mixed | % | Used for reserves and economics |
| Crushing capacity | 1,100 t/h nominal | Not applicable | Expanding to 24 h/d at 74% utilization |
| Primary crushers | 55 x 66 inch Telsmith jaw and 44 x 48 inch Svedala jaw | Not applicable | Water Tank and Twin Hills stations |
| Secondary crusher | Symons 7 ft standard cone at 2.5 inch | Not applicable | Second unit planned for 2014 |
| Final crush size | 80% passing 2.5 inch | Not applicable | Stacked product |
| Agglomeration | Two 10 m x 3.5 m drums, 5 min | Not applicable | Cement 2.5 to 4.0 kg/t, lime 1.5 to 4.0 kg/t |
| Leach cycle | 72 h cure, about 90 days leach | Not applicable | 8 m lifts |
| Pads I to IV | About 23.5 Mt | Not applicable | Designed by SRK |
| Phase V pad | 32 ha, about 19 Mt | Not applicable | Designed by AMEC, hydraulically separate |
| ADR | 12 carbon columns, 1,000 m³/h | Not applicable | About 96% extraction from solution |
Overview
Ore from the East Ledge and Twin Hills pits is crushed to 6 inches in a jaw crusher and conveyed to an intermediate stockpile. It is reclaimed and crushed in a secondary cone crusher to 2.5 inches. Cement and lime are added, and the ore is agglomerated with intermediate solution to 18% moisture. It is sprayed with 400 ppm cyanide solution on the conveyors and stacked in 8 m lifts on ripped, previously leached ore. After curing, the heap is irrigated with barren solution from the ADR plant. Gold is recovered on carbon in 12 columns that can run as two or three trains of 500 m³/h each. It is then stripped and refined at the site.
Key Process Stages
Crushing. The Water Tank primary crusher feeds a 490 m conveyor to the intermediate stockpile, followed by 510 m of conveyors from the reclaim tunnel. A Svedala jaw and conveyor system at Twin Hills was commissioned in the second quarter of 2010, and stacking changes made in late 2010 allow up to 1,100 t/h of rocky ore. The secondary crusher and its scalping wobbler were a bottleneck with wet ore. The wobbler was replaced by a double-deck vibrating screen in late 2013, and a parallel secondary crusher was planned for the second half of 2014.
Agglomeration and stacking. The two drums hold the ore for five minutes. Cyanide solution is sprayed at three points on the conveyor belts before the stacker.
Leach pads. The monolithic pad was built in phases: I, II-A (2002), II-B (July 2005), and III and IV, which were being loaded and were due to fill in early 2015. Phase V was designed by AMEC and started in November 2012, with completion expected by May 2015. It partly overlaps Phases II to IV, and a geomembrane liner keeps it hydraulically isolated from them.
ADR and refining. The 12 columns were enough for the expanded adsorption capacity. Planned upgrades added parallel basket strainers on the strip vessel, a new dilute caustic tank in the acid wash system and a new neutralization tank. More cathodes and anodes and new rectifiers raise refining capacity.
Additional Interesting Data and Summary
Historical production recovery from the East Ledge pit averaged 82.1% from 2003 to September 2006. About 6 Mt of mixed ore from Twin Hills treated from 2009 to 2013 recovered 40% to 62%, depending on the share of fresh sulphide. Aura began using hot soluble cyanide gold assays on blast holes and for plant control to gauge oxidation and expected recovery.
In summary, the 2014 San Andrés report describes a two-stage crushing, drum agglomeration and multi-lift heap leach operation with a carbon ADR plant. Its crushing, ADR and pad capacity were being expanded toward 7 Mtpa, and mixed ore recovers markedly less gold than oxide ore.
Key Processes
- Jaw and cone crushing to 80% passing 2.5 inch
- Cement and lime addition with drum agglomeration
- Cyanide heap leaching in 8 m lifts
- Carbon-in-column adsorption, stripping and electrowinning
- Phased lined leach pad expansion
Source: Mineral Resource and Mineral Reserve Estimates on the San Andrés Mine, Municipality of La Unión, Department of Copán, Honduras, NI 43-101 Technical Report, prepared for Aura Minerals Inc., effective date December 31, 2013.
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.
San Andrés Mine — NI 43-101 Technical Report
The San Andrés Mine processes open-pit oxide and mixed ore through a two-stage crushing circuit, agglomeration, and heap leaching with gold recovery via an ADR plant.
Report context
This technical report presents the San Andrés Mine process facilities based on a life-of-mine schedule generated from December 31, 2011 Mineral Reserves. The project has a 9-year life, with total run-of-mine production of 45.8 Mt containing approximately 784 k oz Au at an average grade of 0.53 g/t.
Processing route
Mining and ore delivery
Mining is by conventional open pit methods with 6 m high benches. Operating phases (push-backs) support mine production from the initial topography of December 31, 2010 to the final pit geometry. Ore is hauled to the jaw crusher using a contract haul fleet.
Crushing circuit
All ore passes through a two-stage crushing circuit before being transported on conveyors and stacked. The circuit was designed for a daily operating time of 18 hours and a throughput capacity of 1,100 t/h. Final product size is 80% passing 2.5 in.
The primary crusher is a 55 in x 66 in Telsmith Jaw crusher producing a 6 in product, which is transported by a 490 m long conveyor to an intermediate stockpile. Material is fed from the stockpile via a reclaim tunnel to a second series of conveyors totaling 510 m. A new primary crusher and conveyor system was constructed during 2009, with commissioning completed in the second quarter of 2010. Modifications to the stacking system were completed during the fourth quarter of 2010, allowing crushing and stacking of up to 1,100 t/h of rocky ore.
From the reclaim tunnel, ore passes through a Symons 7 ft Standard Cone crusher set at 2.5 in.
Agglomeration and cyanide addition
After crushing, cement is added at 2.5 kg/t to 4.0 kg/t before the ore reaches the agglomeration circuit. Lime is added for pH control, averaging 1.5 to 4.0 kg/t. In two 60-ft long x 12 ft diameter agglomerators, ore is retained and mixed for five minutes while intermediate solution is added to achieve optimum moisture of 18%. Before reaching the stacker, 350 ppm cyanide solution is sprinkled at three different points on the conveyor belts.
Heap leaching
Ore is stacked on the leach pad in 8 m lifts on previously leached ore that has been ripped and prepared. The ore is left for 72 hours to cure before any solution is applied. The ore is leached for an average of 60 days before the area is allowed to dry and prepared for the next lift. Solution for leaching comes from the ADR plant after cyanide concentration has been replenished.
The leach pad facility is a monolithic pad constructed in three phases. Phase I was completed during initial construction and start-up. Phase II-A was an expansion constructed in 2002. Phase II-B was another expansion completed in July 2005. Total capacity of the three phases is approximately 23.5 Mt. A vertical expansion followed by two horizontal expansions is currently being evaluated. The leach pad facility was designed by the consulting firm SRK, with engineering for stability, water balances, liner specifications, and earth work specifications completed. SRK was also involved during construction as the Quality Assurance inspector.
Carbon ADR plant
Gold recovery is achieved through the ADR plant. The plant has three trains of carbon columns, each capable of processing 350 m³/h. The trains each contain six carbon columns that can hold a total of 80 t of carbon. The plant has two 7-t pressure strip vessels.
The acid wash vessel processes approximately 10 t of carbon per day in 2.5-tonne batches using 30-33% hydrochloric acid. The volume ratio during wash is 1 to 4 of carbon to acid. This acid solution dissolves carbonates in the carbon micropores before the carbon is sent for regeneration in the carbon reactivation circuit. The carbon reactivation system consists of one 5-t carbon reactivation kiln, operating at approximately 10 tonnes per day.
The fine recovery system includes an electro-winning circuit with capacities of 70 gpm. The refinery has two parallel electro-winning cells with 16 cathodes and 14 anodes, running at a current of 1000 to 2500 A and a voltage of 15 V, and two parallel mercury retort systems.
The assay laboratory is located in the same complex as the ADR plant. Gold produced at the ADR plant is analyzed prior to shipment to Johnson Matthey Inc. for refining and sale. Comparison of ore recovered shipment shows gold ounces as measured at the ADR plant are no more than 1% above the Johnson Matthey measurements.
Energy, water, and process materials
A steady circulation of 18 to 20 tpd of solution is kept within the system at all times. The water balance is always positive from high local precipitation and the recycling water system. When required, water make-up is supplied by the booster pond into the heap leach operation.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Crushing circuit design throughput | 1,100 t/h | Design |
| Crushing circuit daily operating time | 18 hours | Design |
| Final product size | 80% passing 2.5 in | Design |
| Agglomeration retention time | 5 minutes | Design |
| Optimum agglomeration moisture | 18% | Design |
| Cement addition rate | 2.5 – 4.0 kg/t | Design |
| Lime addition rate | 1.5 – 4.0 kg/t | Design |
| Cyanide solution concentration | 350 ppm | Design |
| Cure time before leaching | 72 hours | Design |
| Average leach time | 60 days | Design |
| Leach pad total capacity | 23.5 Mt | Historical |
| ADR plant design capacity | 830 t/h | Design |
| ADR plant operational gold extraction | 96% | Testwork/actual |
| Carbon column capacity per train | 350 m³/h | Design |
| Total carbon per train | 80 t | Design |
| Acid wash throughput | 10 t carbon/day | Design |
| Carbon reactivation kiln throughput | 10 t/day | Design |
| Estimated metallurgical recovery – oxide ore | 76% | Testwork/estimated |
| Estimated metallurgical recovery – mixed ore | 57% | Testwork/estimated |
| Estimated gold in solution feed grade to ADR | 0.30 g/m³ | Testwork/estimated |
| Estimated gold production rate | 8 oz Au/h | Testwork/estimated |
| Power consumption | 18,187 MWh | Historical/actual |
| Specific power consumption | 0.004 MWh/t feed | Historical/actual |
| Average power price | US$338.57/MWh | Historical/actual |
| Power unit cost | US$1.43/t feed | Historical/actual |
| Lime consumption | 16,759,910 kg | Historical/actual |
| Lime specific consumption | 3.897 kg/t feed | Historical/actual |
| Cyanide consumption | 1,709,000 kg | Historical/actual |
| Cyanide specific consumption | 0.397 kg/t feed | Historical/actual |
| Cement consumption | 17,936,120 kg | Historical/actual |
| Cement specific consumption | 4.167 kg/t feed | Historical/actual |
| Chemical products consumption | 264,881 gallons | Historical/actual |
Project website: https://bmrcorp.com/projects/copper/punitaqui-san-andres/
Technical qualifications
This report presents a life-of-mine schedule based on December 31, 2011 Mineral Reserves within designed pit phases and has considered restrictions of the cemetery. Estimated metallurgical recoveries are 76% for oxide ore and 57% for mixed ore; annual gold production depends on average grade and the blend of oxide and mixed ores processed. An engineering study is currently underway to develop an optimum plan for leach pad expansions. The leach pad facility was designed by the consulting firm SRK. The process flow sheet for San Andrés is presented in the original report as Figure 17-1.
Source: San Andrés Mine , NI 43-101 Technical Report, relevant sections 17.0, 17.1.1, 17.2.1, 17.2.2, 17.2.3, and 17.2.4.
