Robe River: A Stake Since 1965Narrow moat

Mitsui & Co. (8031) — moat facet

Mitsui has owned a third of Robe River for sixty years and pays its share to keep it producing.

Mitsui joined the Robe River iron ore venture in Australia in February 19651. It now owns 33.0%, with Rio Tinto at 53% as operator and Nippon Steel at 14%2, and its share of production in the latest year was 20.8 million tonnes3.

Robe River ownership (%)53%Rio Tinto (operator)33%Mitsui14%Nippon SteelMitsui release on West Angelas, October 2025
A third of a Rio Tinto mine, held since 1965.

A minority stake in a mine someone else operates is a particular kind of asset. Mitsui pays its share of the capital and receives its share of the ore and the profit; it does not decide how the mine is run. In October 2025 the partners approved a sustaining investment at West Angelas, one of Robe River's operations, of A$998 million, of which Mitsui's share is A$329 million, to keep capacity at 35 million tonnes a year4.

That kind of spending is the cost of keeping a sixty-year-old position. It is also the reason the position is valuable: the infrastructure, the ports and the approvals are already in place, and new mines in the Pilbara take years to build.

West Angelas has a capacity of 35 million tonnes a year5, of which Mitsui's third corresponds to roughly 12 million tonnes. The sustaining investment keeps that volume rather than adding to it, which is typical of a mature venture: the capital goes into replacing depleted pits with new ones nearby. Robe River is the oldest of Mitsui's iron ore interests and, at a third, its largest share among the producing ventures, against 7% in the BHP venture6.

The measure is Mitsui's share of Robe River's production. Holding it near 20.8 million tonnes7 while the sustaining projects are built would show the investment doing its job.

Moat trajectory: Holding steady

Production is held by sustaining investment rather than expansion.

The number that tests this moat
Reported
Robe River equity production, latest year
20.8 million tonnes (33.0% share)

The oldest of the iron ore stakes; a falling share of production would show the sustaining spend falling short.

Source: Mitsui & Co. results presentation, May 2026 ↗
⚠ Threats to the moat
⚠ THREAT 01
Paying for Mines It Does Not Control
Mitsui pays a third of the bill at Robe River and decides none of the mine plan.
References
  1. ReportedMitsui joined the Robe River iron ore venture in Australia in February 1965.
    Mitsui & Co., Annual Securities Report for the year to March 2026 (English) - company history, employees, share price history, total shareholder return, equity production, the revenue of the Singapore trading subsidiary, competition and the Arctic LNG 2 guarantees. — FY to March 2026 · publ. 12 August 2026 · source ↗
  2. ReportedIt now owns 33.0%, with Rio Tinto at 53% as operator and Nippon Steel at 14%, and its share of production in the latest year was 20.8 million tonnes.
    Mitsui & Co. release, 7 October 2025 - sustaining investment at Robe River's West Angelas, with the interests of Rio Tinto, Mitsui and Nippon Steel. — October 2025 · publ. 7 October 2025 · source ↗
  3. ReportedIt now owns 33.0%, with Rio Tinto at 53% as operator and Nippon Steel at 14%, and its share of production in the latest year was 20.8 million tonnes.
    Mitsui & Co., results presentation for the year to March 2026 - producing assets with partners and stakes, LNG projects, affiliates and power contracts. — FY to March 2026 · publ. 1 May 2026 · source ↗
  4. ReportedIn October 2025 the partners approved a sustaining investment at West Angelas, one of Robe River's operations, of A$998 million, of which Mitsui's share is A$329 million, to keep capacity at 35 million tonnes a year.
    Mitsui & Co. release, 7 October 2025 - sustaining investment at Robe River's West Angelas, with the interests of Rio Tinto, Mitsui and Nippon Steel. — October 2025 · publ. 7 October 2025 · source ↗
  5. ReportedWest Angelas has a capacity of 35 million tonnes a year, of which Mitsui's third corresponds to roughly 12 million tonnes.
    Mitsui & Co. release, 7 October 2025 - sustaining investment at Robe River's West Angelas, with the interests of Rio Tinto, Mitsui and Nippon Steel. — October 2025 · publ. 7 October 2025 · source ↗
  6. ReportedRobe River is the oldest of Mitsui's iron ore interests and, at a third, its largest share among the producing ventures, against 7% in the BHP venture.
    Mitsui & Co., results presentation for the year to March 2026 - producing assets with partners and stakes, LNG projects, affiliates and power contracts. — FY to March 2026 · publ. 1 May 2026 · source ↗
  7. ReportedHolding it near 20.8 million tonnes while the sustaining projects are built would show the investment doing its job.
    Mitsui & Co., results presentation for the year to March 2026 - producing assets with partners and stakes, LNG projects, affiliates and power contracts. — FY to March 2026 · publ. 1 May 2026 · source ↗
Sources
Generated September 24, 2026