The La Libertad processing plant is a conventional agitated cyanide leaching and carbon-in-pulp operation with a design capacity of approximately 2.25 Mtpa and historical gold recoveries of 87.1% to 95.5%.
Report context
The La Libertad Complex technical report, dated March 30, 2021, describes a processing plant that treats ore from open pit and underground mines combined with reclaimed material from historical heap leach operations. Historical heap leaching occurred from 1994 to 1996 and from 2001 to 2007. The plant is owned by Calibre Mining Corp. and is located in the Chontales Department, Nicaragua.
Processing route
Comminution
The plant uses single-stage crushing with two jaw crushers capable of processing approximately 400 tonnes per hour (tph) and 200 tph respectively. One crusher is utilized for run-of-mine (ROM) ore and the other for reclaimed material from the leach pads. Crushed ore is stockpiled before feeding a two-stage grinding circuit.
The grinding circuit is a conventional semi-autogenous grinding (SAG) circuit followed by ball milling and pebble crushing (SABC). It consists of one SAG mill followed by two ball mills operating in parallel, with an integrated pebble crushing circuit. The SAG mill is 20 ft x 9 ft and each ball mill is 13 ft x 20 ft, each with a 1,680 kW motor. The target grind size is P70 75 µm.
Leaching and carbon adsorption
Pre-leach thickening raises the slurry density to 45% solids. Leaching is carried out in 11 agitated leach tanks (four of 1,500 m³ and seven of 570 m³) with oxygen addition, providing a total residence time of 32 hours. Carbon adsorption is performed in six carbon-in-pulp (CIP) tanks of 550 m³ each.
Carbon elution and gold recovery
Loaded carbon is stripped using a pressure Zadra stripping process in either of two carbon stripping columns. The combined stripping capacity supports two campaigns, or 12 tonnes per day of carbon. Stripped carbon is returned to the adsorption circuit after regeneration in a gas-fired kiln.
Gold is recovered from the pregnant elution solution by electrowinning. The precipitate is smelted in a liquefied petroleum gas (LPG) fired furnace to produce doré bars typically containing up to 55% silver, depending on the ore source. Doré is sent to the United States for refining.
Tailings management
Tailings are pumped to the lined La Esperanza tailings storage facility (TSF). As of the report date, the La Esperanza TSF reportedly had remaining capacity for tailings disposal until August 2021. Studies had been conducted for disposal of tailings to one of the spent open pits, providing approximately 3.5 years of capacity. A new La Libertad TSF was permitted with construction starting in March 2021, to be operational by August 2021.
Tailings return water is used as process water. Cyanide destruction is deemed not necessary due to the low levels of cyanide in the water.
Feed sources and blending
The plant processes a combination of feed from open pit and underground mines and reclaimed spent heap leach material. Reclamation and re-treatment of the historical heap leach material currently makes up approximately two thirds of the plant feed. There are reportedly approximately 3.0 Mt of material remaining. Reclamation allows both recovery of residual gold and disposal of waste material in a lined TSF.
Ore from the Pavón deposit will be blended with other feed sources. Metallurgical test work has been performed on samples for the Pavón Norte deposit. Pavón Norte and Pavón Central are hosted by the same geological structures and are expected to have similar metallurgical performance.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Plant design capacity | 2.25 Mtpa | Design |
| Crushing capacity (primary jaw crusher, ROM ore) | 400 tph | Design |
| Crushing capacity (secondary jaw crusher, reclaimed material) | 200 tph | Design |
| Target grind size | P70 75 µm | Design |
| Pre-leach thickening density | 45% solids | Design |
| Number of leach tanks | 11 (4 x 1,500 m³ + 7 x 570 m³) | Design |
| Total leach residence time | 32 hours | Design |
| Number of CIP tanks | 6 x 550 m³ | Design |
| SAG mill dimensions | 20 ft x 9 ft | Design |
| Ball mill dimensions | 13 ft x 20 ft | Design |
| Mill motor power (each) | 1,680 kW | Design |
| Carbon stripping capacity | 12 tpd | Design |
| Doré silver content | up to 55% | Design |
| Gold recovery (historical, 2010–2020) | 87.1%–95.5% | Actual operating data |
| Gold recovery (current reported range) | 92%–95% | Actual operating data |
| Gold recovery (last seven months of 2020) | 92.3% average | Actual operating data |
| Monthly mill throughput (2020, last seven months) | 126,000 t average | Actual operating data |
| Average processing operating cost (2020) | US$16.26/t | Actual operating data |
| Process operating cost range (2020) | US$11.29–$16.25/t | Actual operating data |
| Process maintenance cost range (2020) | US$2.91–$4.48/t | Actual operating data |
| Total process cost range (2020) | US$12.05–$20.10/t | Actual operating data |
| Reclaimed material as proportion of feed | approximately two thirds | Actual operating data |
| Remaining historical heap leach material | approximately 3.0 Mt | Actual operating data |
| Gold recovery, test work (Pavón Norte) | not specified in Section 17 | Test work |
Project website: https://miningdataonline.com/property/1558/La-Libertad-Complex.aspx
Project website: https://www.equinoxgold.com/our-mines/libertad-gold-mine/
Technical qualifications
The report states that energy, water, and process material specific consumptions are not anticipated to change materially over the remainder of the life of mine (LOM). The report also notes that the spent heap leach material was historically deposited between the location of the current La Libertad processing plant and the current La Esperanza TSF on an unlined disposal site. The La Esperanza TSF remaining capacity for tailings disposal was reported as sufficient only until August 2021, making the new La Libertad TSF critical for continued operations.
—
*Source:* La Libertad Complex, NI 43-101 Technical Report, Section 17.0 Recovery Methods, March 30, 2021. Calibre Mining Corp., SLR Project No: 233.03320.R0000.
