A bigger plant, more copper: what Sierra Gorda's fourth grinding line means

Located in the Antofagasta region of northern Chile, the conventional open pit copper mine is central to our copper growth plans.

On 1 July, the Sierra Gorda joint venture approved execution of the fourth grinding line project, which will increase the operation's processing capacity and support higher copper production from this long-life, high-margin operation.

The approval followed a feasibility study confirming the expansion could deliver attractive returns. As a brownfield project, the fourth grinding line will build on Sierra Gorda's existing plant and infrastructure, helping keep the capital cost of the additional capacity low.

What is a grinding line?

A key step in copper production is reducing mined ore to a size that allows copper-bearing minerals to be separated from the surrounding rock. This happens in the processing plant, where ore from the mine is crushed and ground to liberate the copper-bearing minerals.

Ore trucked from the pit passes through several stages of crushing before entering the grinding circuit, where a series of mills reduce the rock to a fine powder. At Sierra Gorda, this includes high pressure grinding rolls and ball mills that progressively reduce the ore size until the copper-bearing minerals can be separated from the surrounding waste rock.

The ground material then moves to flotation, where reagents are added and air is bubbled through the mixture. The copper minerals attach to the bubbles and rise to the surface, where they are skimmed off as a concentrate for export.

Sierra Gorda currently operates three grinding lines. This project will add a fourth, alongside expanded crushing and flotation capacity and supporting infrastructure, enabling the plant to process more ore each year. Processing capacity is expected to increase by approximately 25%, from around 48 Mtpa to around 60 Mtpa (100% basis).

Fourth grinding line proposed plant layout

The labelled and coloured equipment represents additional plant and infrastructure that will be installed as part of the fourth grinding line expansion.

What the fourth grinding line project can deliver

Following completion of the project, Sierra Gorda's annual average payable production is expected to reach around 250,000 tonnes of copper equivalent (100% basis), approximately 30% higher than current levels.

The larger plant is also expected to lower average operating unit costs by around 10%, as the fixed costs of running the operation are spread across more tonnes.

Growth capital expenditure on the project is expected to be about US$725 million (100% basis) between the 2027 and 2030 financial years. The project benefits from existing power and seawater infrastructure, which helps keep the capital intensity of the expansion low.

First production from the fourth line is targeted for the middle of FY30, with full production rates expected in FY31.

More to come at Catabela Northeast

The fourth grinding line is not the only source of upside at Sierra Gorda. The operation has existing opportunities to unlock further value through improved production efficiency, resource expansion and exploration.

One of the most promising opportunities is Catabela Northeast, a copper porphyry prospect next to the existing Catabela pit. An exploration drilling program of around 8,500 metres was completed in the first half of FY26, returning strong results.

Recent drilling at Catabela Northeast has defined an initial exploration target adjacent to the existing Catabela pit, demonstrating potential for resource growth and long-term value creation at Sierra Gorda.

That work allowed the team to define an initial Exploration Target ranging from 1.1 billion tonnes at 0.48% total copper to 2.9 billion tonnes at 0.45% total copper. It points to the potential to extend Sierra Gorda's life well beyond the current plan. Exploration and technical assessment will continue, with drilling expected to increase in the area of the identified anomaly. This work will help define the extent of the mineralisation, determine its grade and better understand the overall scale of the deposit.

For now, the focus is on safely delivering the fourth grinding line and bringing it into production from the middle of FY30. Beyond that, Catabela and Catabela Northeast highlight the longer-term growth potential that continues to emerge at Sierra Gorda.