A Billion-Year Revelation in Iron Ore Genesis – Rewriting the Hamersley Legacy - Is There A Hidden Source of Iron Ore Waiting To Be Discovered?
- Noel Ong
- Jun 22
- 7 min read
Updated: Jun 22
A recent technical paper has shown that the Pilbara Iron Ore Region may be misunderstood, and there may be other sources of high-grade iron ore. The Pibara iron ore heaven may be the tip of the iceberg. Could there be a new region hosting billions of tonnes of high-grade iron ore waiting to be discovered?
What If We’ve Been Wrong About the Hamersley Iron All Along?
As an exploration geologist, the Hamersley iron story has always fascinated me. For decades, we’ve treated the timeline of iron ore formation in the Pilbara’s Hamersley Province as almost gospel. We referenced phosphate dating and clast-bearing conglomerates as reliable benchmarks. But what happens when new geochronological tools rip apart that foundation?
The recent study by Courtney-Davies et al. (2024) has done just that. It shifts the age of the world’s largest hydrothermal ore systems forward by up to a billion years. As someone who has spent decades working on the presumption that the mechanics of mineralisation and structural deformation are the key to understanding mineral exploration, this revelation strikes like a geophysical anomaly demanding immediate follow-up, or does it?
I was drawn to this article from a post that was more interested in clickbait than making a valid intellectual discussion. However, unbeknownst to the author, I am interested in the article, and it had relevance for me.
Let’s unpack the so-called groundbreaking findings and why this isn’t just a win for academia, but a turning point for exploration investment strategies across Australia and beyond.
Setting the Scene: Pilbara’s Geological Backbone
The Hamersley Province is iron ore’s cathedral. Nestled within the Pilbara Craton, it boasts the Brockman and Marra Mamba Iron Formations, host to tier-one iron ore assets like Mt. Tom Price, Mt. Whaleback, and Paraburdoo (Figure 1).
Figure 1: Geologic map of the Pilbara Craton and sample locations (source: PNAS)
Traditionally, the mineralisation was linked to early Paleoproterozoic processes (~2.2 to 2.0 Ga), anchored by the appearance of hematite clasts in conglomerates and phosphate mineral dates. These methods were logical but indirect. And therein lies the problem.
Traditionally, the mineralisation was linked to early Paleoproterozoic processes (~2.2 to 2.0 Ga), anchored by the appearance of hematite clasts in conglomerates and phosphate mineral dates. These methods were logical but indirect. And therein lies the problem.
The Technology Disruption: Iron Oxide U–Pb Dating
Until recently, hematite geochronology wasn’t a viable method. But advances in U–Pb LA–ICP–MS techniques have allowed direct dating of iron oxides (Figure 2). This is a game-changer for the academics, but for the insiders and those exploring it, I am not sure of the relevance.
Figure 2: Tera-Wasserburg diagrams showing hematite U–Pb dates from Pilbara deposits (source: PNAS)
Courtney-Davies et al. analysed 235 hematite spot samples from seven different deposits. The verdict? All high-grade, microplaty hematite deposits formed not in the Paleoproterozoic but between 1.4 and 1.1 Ga, during the Mesoproterozoic, well after the so-called Great Oxidation Event.
According to the implementation of the paper, this finding isn’t trivial. It fundamentally reorients our understanding of tectonic and hydrothermal events tied to ore formation. It also puts the Hamersley deposits squarely within the geological timeline of the Rodinia supercontinent assembly.
Two Distinct Events, One Enormous Iron Province
The study confirms two distinct ore-forming phases:
~2.2 to 2.0 Ga – Represented by eroded ore clasts and likely related to the breakup of Vaalbara and the Bushveld superplume.
~1.4 to 1.1 Ga – The main event, producing the lion’s share of microplaty hematite deposits, coinciding with the formation of Rodinia.
What’s striking is the absence of tectonic fabric in these microplaty ores, suggesting their formation postdates all major orogenic events in the region.
Implications for Exploration and Discovery
Here’s where it gets exciting for explorers and investors.
By associating iron mineralisation with supercontinent cycles (Figure 3), we gain a predictive exploration model. If tectonic amalgamation triggers fluid migration and ore deposition, we should focus our search around other cratonic suture zones that saw similar Mesoproterozoic activity.
Figure 3: Global correlation of iron ore formation periods and supercontinent cycles (source: PNAS)
This also means re-evaluating previously overlooked Mesoproterozoic basins and structures across the Yilgarn, Gawler, and even offshore terrains.
Dissecting the Mt. Tom Price Data
The most robust data comes from Mt. Tom Price:
SE Prongs: 1377 ± 49 Ma
S Ridge Deep: 1398 ± 55 Ma
Combined: 1387 ± 30 Ma
These samples all fall neatly into the Mesoproterozoic, with high uranium concentrations and consistent linearity on age plots. By contrast, phosphate minerals like xenotime tell a chaotic story, recording ages from 2.2 Ga to as young as 0.85 Ga.
Why the discrepancy? It boils down to elemental mobility. Phosphate is easily reset by meteoric water and later hydrothermal events, whereas hematite retains its isotopic integrity unless subjected to very high temperatures (>550°C).
Why This Matters: A New Iron Ore Formation Model
The findings point to a multistage process:
Initial Deposition of BIF (~2.6–2.45 Ga)
Minor Early Hydrothermal Upgrading (~2.2–2.0 Ga)
Major Hematite Formation (~1.4–1.1 Ga)
This sequence aligns with a broader understanding of mineral systems as products of episodic fluid movement, fault reactivation, and tectonic stress, all modulated by plate dynamics (Figure 4).
Figure 4: Conceptual model showing fault reactivation and fluid movement during Rodinia assembly (source: PNAS)
For mineral explorers, this is a clear directive: stop chasing ghosts from the GOE (Great Oxidation Event) and start drilling where the plates came together.
The Bigger Picture: From Pilbara to Planetary Context
This isn’t just about Australia. The study also aligns iron ore formation in the Pilbara with similar-aged deposits in Brazil, South Africa, and North America. It suggests that Mesoproterozoic mineralisation was a global phenomenon tied to deep Earth processes.
Samso Concluding Comments
Reading through this paper as an exploration geologist who has not worked intimately in the iron ore industry is exciting. It is exciting from the angle that I am gaining great insights into the potential that there may be other areas that have the potential to host high-grade iron ore. In geological terms, the identification of an area for a commodity is primarily based on historical information, either from previous explorers or historical understanding of the geological conditions that are favourable to mineralisation.
Typically, with time, the newer understanding of geology and the formation of metal deposits are shedding some new insights into mineral exploration. These new insights have come in the form of new methods highlighting potential mineralisation, such as new geophysical or chemical techniques or interpretation, but rarely due to a new understanding of the genesis of ore.
I feel that if the conclusion of this paper can be put to the test, as in finding areas where you are looking at the formation. The genesis of high-grade haematite during the hydrothermal event, rather than the eventual deposition of the haematite, as in the BIF, a new source of haematite can be discovered.
One has to remember that the deposition of hematite ends up in the Banded Iron Formation (BIF) and the Channel Iron Deposits (CID). The genesis of the haematite is another proposition. The flip side of this comment is that the BIF and the CID (the weathered and eroded BIF) may be where it concentrates and makes the "deposit" economically viable.
The answer to that statement is best left to those who know a lot more about the whole iron ore business than me. I do like the concept, and I am sure those who know more and have greater wisdom will have the answer.
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References
Courtney-Davies, L. et al. (2024). A billion-year shift in the formation of Earth’s largest ore deposits. PNAS, 121(31), e2405741121. https://doi.org/10.1073/pnas.2405741121
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