Amulsar 2019 Feasibility Study Crushes 10 Mtpa to 19 mm for a Heap Leach on a 120 m Valley-Fill Pad With CIC and AARL Gold Recovery

Lydian's 2019 feasibility study for the Amulsar gold project in Armenia keeps the 2017 flowsheet, with most major equipment already installed. The one addition is a third secondary crusher. A 5.3 km downhill overland conveyor generates about 3 MW.

The Feasibility Study Technical Report, Amulsar Project, Armenia, was prepared by JDS Energy & Mining for Lydian International Ltd., with an effective date of September 16, 2019 and a report date of October 15, 2019. Its recovery methods are taken from the 2017 Amulsar NI 43-101 by Samuels Engineering. No new metallurgical testwork had been done since then, and the flowsheet was unchanged except for a third secondary crusher and ancillary equipment. The mine plan had changed, lowering average life-of-mine throughput to 10.0 Mtpa from 10.4 Mtpa in 2017. The plant receives about 27,400 t/d of run-of-mine ore, crushes it in two stages, and heap leaches it. Gold is recovered in a carbon-in-column (CIC) and adsorption-desorption-recovery (ADR) plant as doré. LOM gold grade is 0.74 g/t at a recovery of 87.5%.

Critical Data

Overview

Run-of-mine ore is crushed in a primary jaw crusher. Triple-deck screens and three secondary cone crushers produce the final product. An overland conveyor carries it to a crushed ore stockpile and truck loadout bin. Pebble lime is added, and contract trucks haul the ore to the heap leach pad, where it is stacked in 8 m lifts and irrigated with dilute cyanide. Pregnant solution drains to a process pond and is pumped through five carbon columns. Loaded carbon is acid washed, stripped by the AARL method, regenerated in a kiln and returned. Gold is electrowon and refined to doré.

Key Process Stages

Primary crushing and screening. Trucks tip into a 600 t live dump hopper or onto a 540,000 t ROM stockpile, with a rock breaker for oversize. An apron feeder and vibrating grizzly feed the jaw crusher. A 1,600 t crushed ore bin feeds three triple-deck multi-slope screens. Undersize at P85 18 mm goes to the overland conveyor, and oversize goes to the secondary crushers. A crushed ore sampler handles metallurgical accounting.

Overland conveying and loadout. The conveyor descends 700 m over 5.3 km. Its regenerative drives return about 3 MW, roughly what the crushing circuit uses. Three pan feeders under a 5,000 t live stockpile reclaim onto the loadout conveyor, where a screw feeder adds pebble lime from a 200 t silo. A 100 t loadout bin holds three truck loads.

Stacking. A local contractor hauls ore in 30 t trucks, and the Phase 1 pad needs an estimated 13 trucks. A dozer maintains the tip head and rips the surface before irrigation.

Heap leach facility. The pad sits in a valley at Site 28. It has a composite liner of LLDPE geomembrane (1.5 mm where the heap is 60 m or less, 2 mm elsewhere) over a compacted low-permeability soil liner or geosynthetic clay liner. A drain pipe network lies in a 0.6 m granular layer. The heap is stacked in five stages over 12 years at 10.0 Mtpa.

Carbon adsorption. Pregnant solution flows by gravity through five stepped, flared columns that keep carbon bed expansion at about 70% over a range of flow rates. Carbon is advanced counter-current by recessed impeller pump, and fresh or reactivated coconut carbon is added to column 5.

Acid wash, elution and reactivation. Loaded carbon is washed with dilute nitric acid for one to two hours and neutralized with 2 to 5% NaOH. Strip solution of 3% NaCN and 2% NaOH at 115°C soaks the carbon for about 30 minutes. Six bed volumes of water at about 115°C then produce the pregnant eluate. Carbon is reactivated in a rotary kiln at 550 to 700°C under steam. Fresh carbon is attrited for 20 to 30 minutes before use, which generates 3 to 5% fines.

Additional Interesting Data and Summary

A stock-proof mesh fence surrounds the leach pad to keep wildlife out and to deter unauthorized access. In-line samplers on the pregnant feed and the barren solution track adsorption performance. Pre-development site grades at the pad range from 4 to 6% in the valley bottoms to 55% on the upper sides. Fill placed at the toe of the Phase 1 pad creates a bench with a 1% downhill gradient for heap stability.

In summary, the 2019 Amulsar feasibility study is a two-stage crushing and valley-fill heap leach operation at 10 Mtpa. Ore reaches the pad by a power-generating overland conveyor, and gold is recovered in a conventional CIC, AARL and electrowinning plant.

Key Processes

• Jaw crushing, screening and secondary cone crushing to P94 19 mm
• Regenerative overland conveying
• Lime addition and truck stacking on a lined valley-fill pad
• Cyanide heap leaching with drip and sprinkler irrigation
• Carbon-in-column adsorption
• Nitric acid wash, AARL elution and kiln reactivation
• Electrowinning and smelting to doré

Source: Feasibility Study Technical Report, Amulsar Project, Armenia, prepared by JDS Energy & Mining Inc. for Lydian International Ltd., effective date September 16, 2019.