This 2012 technical report presents a proposed gold recovery process for the Trinidad/Taunus project using heap leaching, crushing, agglomeration, and an ADR plant.
Report context
The Trinidad/Taunus Project 2012 Technical Report, dated June 1, 2012, describes the proposed recovery methods for gold from the Trinidad project. The processing approach is based on heap leaching with a weak cyanide solution, supported by a three-stage crushing circuit, agglomeration, and an adsorption-desorption-recovery (ADR) plant. The report presents design criteria, major equipment specifications, manpower estimates, and consumable requirements for the proposed process facilities.
Processing route
Crushing circuit
Run-of-mine ore will be truck-dumped into a feed hopper and fed to a vibrating grizzly feeder with 1.5 inch openings. Grizzly oversize will be crushed by a 30 inch x 42 inch jaw crusher with a 4 inch closed-side setting. Both grizzly undersize and jaw crusher discharge will be combined and conveyed to the secondary crushing circuit.
The secondary crushing circuit comprises a 7 ft x 20 ft double deck screen with 1.5 inch top deck and 3/8 inch bottom deck cloth, and an MVP 380 cone crusher operated in open circuit with a 3/4 inch CSS. The tertiary crushing circuit consists of an MVP 380 cone crusher in closed circuit with a 7 ft x 20 ft double deck screen fitted with 3/4 inch top deck and 3/8 inch bottom deck, producing a final -3/8 inch crushed product.
Agglomeration
Final crushed product will be agglomerated in an agglomerating drum with approximately 2 kg/t Portland cement. Water or barren solution will be added for proper slurry consistency. A belt scale will control ore feed rate and cement addition. Dust control will use an engineered wet dust suppression system.
Heap leaching
Agglomerated ore will be conveyed to a lined heap leach pad by 36 inch wide x 100 ft long grasshopper conveyors feeding a 36 inch x 140 ft telescopic radial stacker. Cyanide solution at approximately 300 g/L NaCN will be pumped from the barren pond and distributed by pipes and emitters. The leach cycle is estimated at 60 days, consisting of two 30-day cycles: the first at 10 L/hr/m² application rate, the second at 5 L/hr/m². Total area under irrigation is estimated at 55,000 m².
The current design is for a conventional multi-lift heap leach with a maximum of six 8 m high lifts. The report notes that material from the Taunus pit is expected to have a high percentage of fines, and it is uncertain whether heap leaching will best be accomplished with a conventional multi-lift dedicated heap or an on/off heap leach strategy. Additional studies will be required to assess ore stacking and leaching while maintaining adequate percolation rates.
The pregnant solution pond is designed with a holding capacity of 20,182 m³, providing 60 hours storage at a nominal flow of 338 m³/hr. The barren solution pond has a holding capacity of 15,353 m³, providing 40 hours storage at a nominal flow of 383 m³/hr. An emergency pond with a capacity of 27,667 m³ provides an additional 82 hours storage at nominal flow of 338 m³/hr.
ADR plant
A carbon ADR circuit will recover gold and silver from pregnant leach solution. The plant includes a 5-stage carbon-in-column circuit consisting of five 12 ft diameter cascading columns, each with 2 t carbon capacity. Pregnant solution will be pumped to the first adsorption column and cascade sequentially through the remaining columns. Discharge from the fifth column will be barren and flow to the barren pond. Carbon will be transferred counter-current to solution flow.
Loaded carbon from the first column will be transferred to an acid wash vessel, acid washed, neutralized, and transferred to the strip vessel. Gold and silver will be stripped from carbon by circulating a hot NaOH/NaCN solution maintained at about 150°F for approximately 16 hours per batch. Stripped carbon will be transferred to a 2 t/d regeneration kiln or sent directly to washing and sizing circuit. Reactivated carbon will be recycled to the CIC circuit.
The gold-bearing strip solution will be pumped at approximately 1.5 m³/h to electrolytic cells where gold will be recovered as sludge on cathodes. The gold sludge will be collected, filtered, dried, mixed with fluxes, and smelted in a diesel-fired furnace. The report notes that if significant mercury levels are identified in the ore during subsequent studies, provision for appropriate mercury handling facilities may be necessary.
Manpower and consumables
A total of 95 employees are budgeted for the process facilities at an estimated cost of US$2.0 million per year, including a 30% burden, equivalent to US$1.29 per tonne of material processed.
Total process plant operating cost (excluding labor) is estimated at US$5.73 per tonne, comprising consumable costs of US$2.30/t, operating and maintenance supplies of US$1.68/t, wear parts of US$1.06/t, and power of US$0.59/t. Total power consumption is estimated at 4.57 kWh/t.
Key reported parameters
| Parameter | Units | Design / Proposed | Testwork / Historical |
|---|---|---|---|
| Crushing circuit capacity | t/h | 260 | , |
| Operating availability | % | 70 | , |
| Stacking rate | t/d | 4,300 | , |
| Annual throughput | Mt/y | 1.55 | , |
| Primary crusher: jaw crusher | inches | 30 x 42 | , |
| Primary crusher CSS | inches | 4 | , |
| Secondary screen: top deck | inches | 1.5 | , |
| Secondary screen: bottom deck | inches | 3/8 | , |
| Secondary cone crusher CSS | inches | 3/4 | , |
| Final crushed product size | inches | -3/8 | , |
| Cement addition | kg/t | 2 | , |
| Leach cycle time | days | 60 | , |
| Primary leach application rate | L/h/m² | 10 | , |
| Secondary leach application rate | L/h/m² | 5 | , |
| Area under irrigation | m² | 55,000 | , |
| NaCN concentration | g/L | 300 | , |
| Gold extraction | % | 70 | , |
| Silver extraction | % | 23 | , |
| Cyanide consumption | kg/t | 0.3 | Based on closed-cycle column testwork and commercial operations |
| Lime consumption | kg/t | 1.0 | Based on column test results |
| Cement consumption | kg/t | 2.0 | Maximum without detrimentally effecting gold extraction |
| Pregnant solution pond capacity | m³ | 20,182 | , |
| Barren solution pond capacity | m³ | 15,353 | , |
| Emergency pond capacity | m³ | 27,667 | , |
| CIC columns: number | , | 5 | , |
| CIC column diameter | ft | 12 | , |
| Carbon capacity per column | t | 2 | , |
| Strip solution temperature | °F | 150 | , |
| Strip batch cycle time | hours | 16 | , |
| Electrowinning rich electrolyte Au | g/m³ | 100 | , |
| Electrowinning lean electrolyte Au | g/m³ | 1.3 | , |
| Total power consumption | kWh/t | 4.57 | , |
| Process plant operating cost (excl. labor) | US$/t | 5.73 | , |
| Manpower | employees | 95 | , |
| Annual labor cost (incl. burden) | US$ | 2,002,650 | , |
Technical qualifications
The report identifies that cyanide consumption of 0.3 kg/t is based on closed-cycle column testwork conducted at Metcon and adjusted based on experience with commercial operations, noting that cyanide consumption in commercial operations is typically much less than reported during column testing. Lime consumption of 1 kg/t is based on column test results. Cement consumption of 2 kg/t was determined as the maximum amount that could be added without detrimentally effecting gold extraction.
The report notes uncertainty regarding the heap leaching strategy for Taunus pit material due to expected high fines content, stating that additional studies will be required to assess whether conventional multi-lift or on/off heap leaching is appropriate and to maintain adequate percolation rates. The report also notes that if significant mercury levels are identified in subsequent studies, provision for appropriate mercury handling facilities may be necessary.
All design criteria and equipment selections presented are for the proposed process facilities only and do not represent historical operating data or current project status.
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*Source: Trinidad/Taunus Project , 2012 Technical Report, NI 43-101 PEA, SRK Consulting (U.S.), Inc., June 1, 2012. Sections 15 Recovery Methods, 15.1 Processing Methods, 15.2 Process Design Criteria and Major Equipment Selection, 15.3 Manpower Schedule, 15.4 Consumable Requirements.*
