The Cangrejos Gold-Copper Project is located in southwestern Ecuador. (Credit: Uncle Kick-Kick/ Wikipedia)
The project is estimated to contain probable reserves of 659Mt grading 0.55 grams per tonne (g/t) of gold, 0.10% copper, and 0.69g/t of silver. (Credit: James St. John/ Wikipedia)
The Cangrejos project has two open pit mines known as Cangrejos (eastern pit) and Gran Bestia (western pit) located adjacent to each other. (Credit: Sue/ Flickr)

The Cangrejos Gold-Copper Project in southwestern Ecuador is being developed by its 100% owner Lumina Gold, a Canadian precious and base metals exploration and development company.

The Preliminary Economic Assessment (PEA) of the Cangrejos project was completed in 2020.

In April 2023, Lumina Gold received positive results from the Preliminary Feasibility Study (PFS) for Cangrejos Project. According to the company, the mineral resource expansion made Cangrejos the 26th largest primary gold asset in the world by contained gold in mineral resources.

Initial capital costs for the development of the project are estimated to be $925m, which includes working capital and excludes refundable value added tax (VAT).

Cangrejos is expected to produce 371 thousand ounces gold (koz) of gold and 41 million lbs (Mlbs) of copper annually. The 26-year mine life will have a life of mine (LOM) revenue mix of 79% gold, 20% copper and 1% silver.

Location and Site details

The Cangrejos project is located in the Andean foothills of El Oro province of Ecuador. The site is around 223km from Guayaquil and 30km southeast of the provincial capital of Machala.

According to the PFS published in 2023, the property consists of six mining concessions covering a total area of 5,682 hectares (ha).

All the concessions are held by Odin Mining del Ecuador, a 100% owned subsidiary of Lumina Gold. Additionally, Odin owns or controls around 1,729.97ha area.

The property can be accessed via paved and 8km of gravel roads.

Geology and Mineralisation at Cangrejos

The Cangrejos Project lies in the El Oro Metamorphic Belt Zone of the Cordillera Real. The elevation at the location ranges from approximately 100 metres above sea level (masl) to 1,370masl.

It is underlain by Miocene dacite porphyry intrusions that intrude the El Oro metamorphic complex. The breccia zones located near the contacts of these Miocene intrusions are associated with a gold-copper soil anomaly.

The Cangrejos Zone is a northeasterly trending zone of porphyry-style, gold-copper-silver-molybdenum mineralisation. It stretches around 1,500m in a northeasterly direction with a width ranging from 70m to 600m.

The zone has been defined to a depth of at least 600m and remains open to expansion on all sides except to the southwest.

Mineralisation primarily consists of finely disseminated chalcopyrite, pyrite and minor bornite, molybdenite and pyrrhotite. The host rocks feature patchy secondary biotite (potassic) alteration and a late-stage, calcic-sodic alteration.

Cangrejos Reserves

The gold-copper project is estimated to contain probable reserves of 659Mt grading 0.55 grams per tonne (g/t) of gold, 0.10% copper, and 0.69g/t of silver for contained metal totalling 11.56Moz gold (Au), 1,420Mlbs copper (Cu), and 14.38Moz silver (Ag).

The total indicated mineral resources for Cangrejos are estimated to be 1079.9Mt grading 0.48 g/t Au, 0.09% Cu, 0.7 g/tAg, and 17.8 ppm Mo for contained metals totals of 16.8 Moz Au, 2,166 Mlbs Cu, 24.3 Moz Ag, and 42.4 Mlbs Mo.

Inferred mineral resources stand at 296.3Mt grading 0.39 g/t Au, 0.07% Cu, 0.7 g/t Ag, and 11.7 ppm Mo for contained metal totals of 3.7Moz Au, 483Mlbs Cu, 7.0Moz Ag, and 7.6Mlbs Mo.

Mining and Ore Processing

The Cangrejos project features two open pit mines known as Cangrejos (eastern pit) and Gran Bestia (western pit) situated adjacent to each other.

Both pits are planned to be mined using conventional hard rock open pit mining methods. The terrain at both pit areas is expected to be steep with evergreen montane secondary forest, saprolite, and saprock overlying the area.

The project will use three categories of mining equipment for operations. This will include a primary production fleet (shovels and 220-tonne trucks), a narrow mining fleet (FEL and 91-tonne trucks) and a pioneering fleet (excavators and 38-tonne articulated trucks).

Run-of-mine (ROM) material will be hauled from the mine by truck for stockpiling, or it will be directly dumped into the primary crusher. The primary crushed material will be transported by an apron feeder and short conveyor to the overland conveyor system for delivery to the process plant site.

With the process plant to undergo a staged expansion, the mine will deliver 30 kilo tonnes per day (kt/d) of ore to the plant from mid-Year 1 through Year 3. The production will increase in Year 4 to deliver 60kt/d of ore from Years 5 to 6 and again in Year 7 to delivers 80kt/d of ore from Year 8 to the end of mine life (25 ½ years).

The selected flowsheet for the process plant design includes a three-stage crushing circuit where the crushed product is sent to the ball mill grinding circuit in a closed circuit with a cyclone cluster. The cyclone overflow material is transferred to sequential copper flotation.

The final concentrate is thickened and filtered before it is shipped or sold to the market.

The tailings from the rougher flotation are transferred to the sand flotation circuit, while the tailings from the cleaner scavenger flotation stage and the concentrate from the sand flotation stage are leached using a hybrid Carbon-in-Leach (CIL) circuit.

The gold doré is produced after electrowinning and smelting.

The tailings from the sand flotation stage and the detoxified tailings from the CIL circuit are thickened and filtered, and then dumped in the dry-stack tailings facility (DSTF) on site.

Cangrejos Project Infrastructure

The Cangrejos project will have three areas of operation separated by 13.5km of road. The open pits, waste rock storage facility (WRSF) and truck shop will be southeast of the process plant, which will be located between the open pits and the dry-stack tailing facility (DSTF).

The filtered tailings facility will be towards the northwest of the process plant. The main access road connects the site to a public road.

A single 230kV incoming line will supply power to a 230kV/25kV outdoor on-site substation. Subsequently, power will be distributed across the site using 25kV overhead lines.

The project is expected to meet its water requirements from meteoric contact water sources procured from the pits, the WRSF, and contact water and filter press reclaim water from the DSTF.

Contracts and Agreements

The PFS was prepared by Ausenco Engineering Canada.

Independent Mining Consultants (IMC), Wyllie & Norrish Rock Engineers, N D King Consulting, SIM Geological, Robert Michel Enterprises and Global Resource Engineering were also contracted by Lumina to help in preparing the report.

In 2019, MTB Enterprises was engaged to update the 2018 PEA and PEA.

CH Plenge & CIA conducted metallurgical testing programmes from 2014 to 2020.

In May 2023, Lumina Gold entered into a precious metals purchase agreement with Wheaton Precious Metals International. Under the agreement, Lumina will receive $48m pre-construction funding and $252m of construction funding for 6.6% of the payable gold produced from the Cangrejos project.