Brazil Highlights: Boa Esperanca Copper Project

Brazil is better known for its iron ore deposits but it is also rich in base metals such as copper and gold. The Boa Esperanca copper project, located in Para, Brazil. is a perfect example. 

The project was originally owned by Codelco but was sold to Mineracao Caraíba (MCSA) in 2007. The present owner Ero Copper acquired an 85% interest in the project from MCSA in December 2016 with an additional 14.5% stake in June 2017.

Ero Copper originally completed a feasibility study in June 2017 but recently released the results of an optimized feasibility study in September 2021. The updated feasibility study doubled life-of-mine copper production and increased the mine life to 12 years from nine. 

Highlights from the Updated Feasibility Study –

• Total life of mine production is now estimated at 326,000 tonnes, up from 163,000 tonnes previously.
• Capital costs for the 4 million t/y open pit operation is USD$294 million, with sustaining capital of $196 million.
• The new study improves the after-tax payback period to 1.4 years from 3.6. It also features a lower life-of-mine head grade of 0.83% compared with 0.95%. 
• Cash costs per lb. of copper are expected to be $1.36 per lb. Over the first five years of mine life, when production is expected to be 35,000 tonnes per year (compared with the life of mine average of 27,000 tonnes), cash costs will be only $1.12 per lb.
• The company also sees additional exploration potential at the project. In the near-term, it’s targeting the Gap zone, a target area within the pit shell that has seem limited drilling.

Geology

• The Boa Esperanca copper deposit lies within an isolated hill with mineralisation hosted in a series of brecciated zones comprising quartz, magnetite, and the Neoarchean biotite granite.
• The deposit is a variant of a IOCG deposit type due to the absence of pervasive hydrothermal alterations in the host rock and the absence of gold.

Mining Method

• The Boa Esperanca will be a conventional open pit with with a stripping ratio of 3.73:1 (waste to ore).
• The mine will use relatively small equipment consisting of 4m3 hydraulic excavators and 35t trucks will be employed to extract and haul ore to the primary crusher or the run-of-the-mine (ROM) stockpiles. Waste rocks will be hauled to dump sites.
• The ROM ore will undergo three-stage crushing followed by screening, jigging, and ball mill grinding. Further, it will pass through rougher and cleaner flotation to produce copper concentrate, which will be thickened, dewatered, and filtered before shipping.
• Due to Brazilian mining conditions, specialised mine haulage equipment will be substituted for highway trucks using rock beds in the 40t range. This improves project economics due to reduced labour costs, maintenance, selective mining, capital intensity and import duties.

Infrastructure

• Facilities will include a tailings storage facility, waste rock dumps, workshops, and storage areas for fuel and explosives.
• The project is estimated to require up to 9.1MW of electricity, which will be supplied through a 138kV power transmission line from the regional grid.
• The primary logistic challenges facing the Project are: Long distance to port; Limited accessibility to the railroad, owned by a private company with a track record of poor third-party service levels; Limited port infrastructure; and, Chronic congestion at ports near the Project.

Next Steps

• Ero has started detailing engineering for the project and early construction works could start in the first half of 2022 with board approval. It will continoue to grow near term resources by targeting the gap zone. 

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