TSX-V-listed Oroco Resources has published the results of a revised preliminary economic assessment (PEA) and updated mineral resource estimate for the North zone and South zone of its Santo Tomas Porphyry copper project in Sinaloa state, Mexico.

Highlights of the revised PEA include a net present value of $2.64-billion pre-tax and $1.48-billion post-tax.

The PEA is based on a staged openpit mine and processing plant achieving 60 000 t/d production in year one and expanding to 120 000 t/d in year eight over a 22.6-year life-of-mine (LoM).

Production is preceded by two years of construction and one concurrent year of prestripping.

The revised PEA also estimates an internal rate of return of 30.3% pre-tax and 22.2% post-tax.

Total LoM payable copper production is 4.77-million pounds.

The PEA shows a pre-tax payback period of 2.9 years and a post-tax payback of 3.8 years from first concentrate production.

Initial capital costs are estimated at $1.1-billion and sustaining and expansion capital costs at $1.73-billion.

The PEA indicates an average copper equivalent grade of 0.51% over the first seven years of production.

Total mineralised material mined is 83-million tonnes.

“When we completed the initial PEA in December 2023, it was clear there was additional value to be unlocked at Santo Tomas. Upon careful analysis, a staged approach to the mine expansion and a focus on exploiting the higher-grade near-surface material in the early years of mining has unlocked a considerable increase in value,” says CEO Richard Lock.

“We have established a plan that invokes a very efficient use of capital and establishes a rapid post-tax payback of 3.8 years. The plan starts with the use of smaller equipment to provide rapid entry to the mineralised material and maintains a higher-grade feed profile to delay the requirement of an expansion until year eight.

“Copper equivalent production in the first seven years is forecast at 1.34-billion pounds at a mill feed average grade of 0.51% copper equivalent,” he says.

Lock avers that this work establishes Santo Tomas as “one of the most capital efficient large-scale, low-cost copper projects in the world”.