Only 3 of 6 Iron Ore Majors Replaced What They Mined in 9 Years

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The world’s six largest iron ore producers dug 11.1 billion tonnes of saleable reserves out of the ground between 2016 and 2025, and only three of them managed to put back as much as they took out.

That finding, published today by Wood Mackenzie in its “Iron Ore Reserve Depletion and Replacement Analysis” and first reported by Bloomberg, marks the point at which the industry’s reserve arithmetic became too stark to wave away as a cyclical wobble. Wood Mackenzie research director Mihir Vora captured the bind precisely: producers are “investing to sustain production, but having to work harder to stand still.” The data has crossed from analyst concern into documented structural trend.

Here is what the numbers reveal about which producers are running out of runway, which have found a way to stand still and actually move forward, and what the depletion pattern signals for iron ore supply over the next decade.

The reserve math that no longer adds up

Start with the ledger. Over nine years, the six largest producers pulled 11.1 billion tonnes of saleable, marketable reserves out of the ground. This is not a paper accounting adjustment or a downgrade of theoretical resources. It is ore physically extracted, shipped, and sold, gone from the reserve base for good.

Against that outflow, only three of the six replaced what they mined. The rest ran a deficit.

The clearest way to see the divergence is in the reserve replacement ratios Wood Mackenzie compiled across the peer group. They range from 28% at the low end to 159% at the high end. That spread tells you this is not a uniform industry affliction. It is a divergence story, and knowing which end of the range a producer sits on is exactly the signal that separates a durable asset base from one with a shortening runway.

A reserve replacement ratio is the long-term viability metric that quarterly earnings almost never surface. It measures tonnes added to reserves against tonnes mined. Anything below 100% means the asset base is shrinking with every cargo shipped, a structural headwind that accumulates quietly for years before it forces itself onto the balance sheet.

“Investing to sustain production, but having to work harder to stand still.” Mihir Vora, research director, Wood Mackenzie

Costs are the compounding factor sitting underneath all of this. Extraction costs for some of the majors have roughly doubled since 2016, and the capital required to add each new tonne of reserve now ranges widely across the group. The three headline pressures stack up as follows:

• Total depletion: 11.1 billion tonnes of saleable reserves removed, 2016-2025
• Replacement ratios: a spread of 28% to 159% across the six producers
• Capital intensity: US$2 to US$10 per tonne of new reserve added

The takeaway for an investor is that the sector is spending more to achieve less, and the gap between the disciplined and the exposed is widening rather than closing.

What is actually driving grade decline, and why the 2020s are different

The reserve deficit is not a story of management incompetence. It is largely a story of geology and timing, and understanding the mechanism matters because it determines how long the constraint will last.

The Pilbara mega-operations in Western Australia and the Carajás complex in Brazil were mostly built out between 2005 and 2015. A large cohort of giant pits is now hitting mid-life at roughly the same moment, around 15 to 20 years after construction. As these mines age, operators have to dig deeper and into lower-quality ore zones, which is why Wood Mackenzie records grade declines of as much as 1.6 percentage points for some producers since 2016.

The four mechanisms driving the squeeze work together:

Brownfield capital allocation has become the dominant industry response to rising greenfield permitting costs, but the data shows that directing spend toward sustaining existing output rather than new discovery accelerates effective grade depletion as impurity levels climb even when headline Fe percentages appear stable.

1. Mine maturation: the synchronised ageing of the world’s biggest pits, forcing extraction into deeper, lower-grade zones.
2. Brownfield capital bias: producers directing spend toward sustaining existing output rather than new high-grade discoveries, which accelerates effective grade depletion as impurity levels climb even when headline Fe percentages look stable.
3. Permitting and ESG constraints: longer lead times, heavier beneficiation requirements, and larger tailings volumes that raise the bar for any greenfield project and push capital back toward existing operations.
4. Decarbonisation quality demand: steelmakers pivoting toward premium feedstock, which pulls producers into selectively mining their best material.

The reason this matters to your read on the sector is duration. This is not a supply disruption that clears in a quarter. It is the predictable consequence of where dozens of the largest mines sit in their geological life cycles, and resolving the quantity problem does nothing to fix the quality problem.

How green steel ambitions are accelerating the quality squeeze

Direct reduced iron and hot briquetted iron processes, the lower-emission steelmaking routes central to decarbonisation, require feedstock above 67% Fe. The global average shipped grade in 2025 was roughly 62.6% Fe, according to Wood Mackenzie. Most existing seaborne supply simply falls short of the threshold without extra beneficiation.

Green iron production technology is reshaping feedstock economics because DRI and HBI processes require ore above 67% Fe, a threshold most existing seaborne supply cannot meet without significant beneficiation investment, creating a quality bifurcation that the depletion data compounds.

That gap creates a selective mining dynamic. Producers chasing premium DR-grade demand concentrate extraction on their highest-quality zones, which drains the best material fastest and leaves lower-grade ore as a growing share of what remains. Around 250 Mt of operating seaborne supply is projected to deplete between 2026 and 2035 on Wood Mackenzie estimates, and the quality of the ore left behind is deteriorating even as the tonnage shrinks. The industry is being pressed on volume and quality at the same time.

Three companies found a way through: what separates them

If three of the six replaced their reserves, the obvious question is how. Wood Mackenzie has not publicly named the successful trio, but two producers offer clearly documented illustrations of the strategies that work, and they took very different routes.

Vale’s Itabira complex in Brazil is the cleanest technology-led example. Through improved processing, geological modelling, and the reclassification of previously marginal lower-grade material, Vale expanded Itabira’s reserves from 759.7 Mt at 45.6% Fe to 1.1513 billion tonnes at 45.8% Fe, a roughly 52% increase achieved without a single new greenfield discovery. Its Northern System reserves rose a further 3%, from 5.3 Bt to 5.5 Bt in 2025.

A 52% reserve increase at Itabira, achieved through processing and geological modelling rather than new discovery.

Fortescue took the other road. Its durability rests on scale and cost: approximately 6.4 billion tonnes of total proven and probable reserves at end-FY2025, underpinned by systematic Pilbara exploration and supplemented by the Iron Bridge magnetite development, which delivers a 67.3% Fe product from 938 Mt of reserves. What makes the lower-margin ore worth mining is an industry-leading hematite C1 cost of US$17.99 per tonne, near the bottom of the global cost curve.

The common thread tells you what worked. Both invested in the ground before depletion pressure turned acute, one through geological conversion of marginal material, the other through beneficiation infrastructure and a cost base low enough to extract value from ore peers would leave behind. Neither path is easily copied by a producer whose grades are already falling and whose costs are already rising. With capital intensity ranging from US$2 to US$10 per tonne of new reserve, the producers who deferred that investment now face the steepest bill.

The structural supply gap and what it means for prices and investors

Move from diagnosis to consequence, and the depletion data starts to look less like a company problem and more like a supply-side floor forming under the entire market.

The scale of the gap is the headline. Industry assessments cited by Rio Tinto put the requirement at around 800 Mt of new supply over the next decade just to offset depletion, against roughly 300 Mt of replacement capacity committed. That leaves a shortfall of about 500 Mt before any demand growth is even counted.

The iron ore supply gap documented by Rio Tinto and Wood Mackenzie is not a demand-side story; it is a depletion-driven structural deficit that persists even in scenarios where Chinese steel output flatlines through the early 2030s.

The cost curve reinforces the point. S&P Global’s January 2026 outlook forecasts the weighted-average all-in sustaining cost on a CFR basis at $60.82 per dry metric tonne in 2026, up from $59.38 in 2025, while Wood Mackenzie put the average around US$59.8/t on its 2025 cost curve. Benchmark 62% Fe fines have traded in the mid-$90s to low-$100s per tonne through mid-2026, which leaves margins adequate but narrowing for the higher-cost operators. Industry cash margins peaked in 2021 and have since settled at roughly $50 to $60 per tonne.

For investors, three risks separate the winners from the exposed:

• Margin compression for high-cost producers if benchmark prices soften toward $80-$90/t while costs sit in the low-$60s.
• Quality bifurcation, with the spread between 62% Fe fines and 65% Fe-plus material likely to widen. 65% Fe fines were assessed at $115.70/t CFR China on 19 August 2026.
• DR-grade deficit risk before the mid-2030s, projected by IEEFA and AME Research, which rewards producers holding high-grade concentrate or pellet-feed portfolios.

What this tells you is that the analytical frame has shifted. The question is no longer whether iron ore demand holds up. It is whether supply volume and quality can keep pace, and on current evidence the answer is no, not without sustained capital the sector has yet to commit.

What the reserve data actually tells steelmakers and long-term investors

The Wood Mackenzie report gives you a map, not a verdict. The depletion is documented and the shortfall is quantified, but the outcome depends on decisions producers and markets are making right now.

Three variables will determine whether the tightness becomes prolonged price support or gets resolved by capital that has not yet appeared:

• Pace of capital deployment into replacement projects over the next three to five years.
• Speed of DR-grade demand growth as steelmaking decarbonisation accelerates.
• Benchmark price sustainability above the roughly $60/t average cost floor needed to justify high-capital-intensity reserve additions.

Draw the distinction clearly, because it is where the constraint bites hardest. A shortage of standard blast-furnace ore is unlikely in the near term. A high-grade DR-grade supply deficit is increasingly credible before the mid-2030s on current committed capacity. Those are two different markets, and the premium end faces the tighter squeeze.

That reframes the producer quality spectrum. Low-cost Tier-1 assets with large reserve bases and the ability to supply or upgrade to premium grades are structurally advantaged. Higher-cost, lower-grade operations face margin and reserve-duration risk at the same time, and with some producers having spent five times as much as peers to add equivalent reserve volumes, cost position now determines the economics of survival, not just the economics of growth.

If the 500 Mt shortfall is not closed by committed capital, the depletion constraint shifts from projection to price signal, and the low-cost, high-grade producers are the ones best placed when it does. Investors who understand the mechanics hold a genuine information advantage over those watching only the quarterly price tape.

For investors wanting a practical framework to apply the reserve replacement and cost-curve analysis covered here, our dedicated guide to evaluating iron ore stocks walks through the specific financial metrics and reserve disclosures that distinguish durable Tier-1 assets from higher-risk operations.

This article is for informational purposes only and should not be considered financial advice. Investors should conduct their own research and consult with financial professionals before making investment decisions. Past performance does not guarantee future results, and financial projections are subject to market conditions and various risk factors. Forward-looking statements regarding supply gaps and price outcomes are speculative and subject to change based on market developments and company performance.