San Francisco-based Marathon Fusion says it has produced stable gold from mercury with fusion neutrons at a rate ten times CERN’s 2025 record, raising questions about lab-made precious metals and future fusion economics for global markets.

A San Francisco startup has revived one of humanity’s oldest dreams by claiming it has turned mercury into real, stable gold through nuclear processes linked to fusion energy research. Marathon Fusion announced that experiments conducted the previous month achieved high-rate production of gold-197 from mercury, exceeding a benchmark set by CERN by a factor of ten. The claim, which has not been independently verified and does not disclose the quantity of gold produced, has sparked widespread discussion about the intersection of nuclear science, clean energy and commodity markets.

The announcement comes at a time when lab-grown diamonds have already disrupted the jewellery trade. Gold, however, presents a fundamentally different challenge because it requires changing one chemical element into another rather than rearranging atoms of the same element. The development highlights how advanced nuclear technologies could one day generate valuable by-products alongside electricity.

How the Transmutation Process Works

Gold has 79 protons in its nucleus; mercury has 80. Marathon Fusion’s approach relies on nuclear transmutation driven by high-energy neutrons. In a deuterium-tritium fusion reaction, fast neutrons with energies around 14 MeV strike mercury-198, a stable and relatively abundant isotope. The reaction knocks out a neutron, converting the mercury-198 into radioactive mercury-197. Mercury-197 then decays by electron capture, with a half-life of roughly 64 hours, into stable gold-197 – the only non-radioactive form of gold found in nature.

This is distinct from earlier particle-accelerator experiments. CERN’s ALICE detector at the Large Hadron Collider produced gold nuclei from lead-ion collisions, but the amounts were minuscule – about 29 picograms over several years of operation – and the nuclei existed only fleetingly. Marathon Fusion says its neutron-based method achieved a higher production rate, and it has shared gamma-ray spectra consistent with the presence of mercury-197 and gold-197. The company has also reported producing medical isotopes such as copper-64 and copper-67 from zinc under similar irradiation conditions.

A 2025 preprint paper by the team outlined how the process could be integrated into the breeding blanket of a future fusion power plant. Neutrons that would otherwise be used primarily to breed tritium fuel could simultaneously transmute mercury, potentially yielding more than two tonnes of gold per gigawatt of thermal power each year without compromising electricity output or fuel production.

From Laboratory Demonstration to Industrial Scale

The gap between a laboratory demonstration and commercial supply remains substantial. Marathon Fusion has not released figures on the absolute mass of gold produced, the enrichment level of the mercury feedstock, recovery efficiency or overall costs. Its current experimental systems operate at power levels orders of magnitude below those of a commercial fusion plant. Scaling the process would require large quantities of isotopically enriched mercury-198, sophisticated handling of radioactive intermediate products, and fusion reactors that do not yet exist at industrial scale.

Freshly produced gold would also contain radioactive impurities. To meet stringent safety standards – comparable to the radioactivity of everyday items such as bananas – the material would need to be stored for many years, with some analyses suggesting periods approaching 17 to 18 years, before it could enter general commerce. These practical constraints mean that any contribution to global gold supply lies well in the future.

Global mined gold production stands at several thousand tonnes annually. Even optimistic projections from Marathon Fusion’s modelling suggest that a fleet of gigawatt-scale fusion plants would be required to generate volumes large enough to influence prices meaningfully. Enrichment of mercury-198 itself is currently expensive, further limiting near-term economic viability.

Implications for Gold Markets and the Energy Transition

The prospect of laboratory gold inevitably invites comparison with lab-grown diamonds, which have reduced prices for natural stones in certain segments of the jewellery market. Yet the parallel is imperfect. Diamond synthesis replicates natural growth conditions using carbon; gold production requires changing nuclear identity and managing radioactivity. Market analysts note that gold’s value rests on scarcity, industrial demand, monetary history and cultural significance. Significant additional supply would need to be both large and low-cost to exert sustained downward pressure on prices.

For the fusion industry, the more immediate opportunity may lie elsewhere. Medical isotopes for cancer imaging and therapy command high value and face supply constraints. By designing blankets that generate these isotopes alongside tritium and gold, fusion plants could improve their overall economics long before they deliver grid-scale electricity. Marathon Fusion, founded in 2023 and backed by investors including entities linked to Breakthrough Energy and mining interests, positions its work as dual-purpose: advancing fusion fuel cycles while creating high-value co-products.

International observers tracking the clean-energy transition will recognise the broader pattern. Advanced nuclear technologies increasingly seek multiple revenue streams – electricity, heat, hydrogen, isotopes and potentially precious metals – to offset high capital costs. Whether gold becomes a meaningful by-product depends on progress in fusion itself, which remains years or decades from commercial deployment in most roadmaps.

Scientific Caution and Verification Needs

Independent experts have emphasised the need for full data disclosure and peer review. Extraordinary claims require rigorous validation of yields, purity, neutron spectra and background subtraction. Until such evidence is public and confirmed, the demonstration remains an intriguing but unconfirmed step. Historical attempts at artificial gold production, from alchemical furnaces to early nuclear experiments, produced either vanishingly small quantities or radioactive material unsuitable for ordinary use. Marathon Fusion’s work sits in this long tradition while leveraging modern fusion neutron sources.

The company continues to develop related technologies, including isotope separation with plasma centrifuges, and is constructing a higher-power experimental reactor in San Francisco. These engineering efforts may prove more consequential in the near term than the gold claim itself.

Unexpected Intersections

Marathon Fusion’s announcement illustrates the unexpected intersections that can emerge from fundamental research. Nuclear fusion is pursued primarily for abundant low-carbon energy. The possibility that the same neutrons could transmute base metals into gold adds a layer of economic intrigue, yet the practical barriers – scale, cost, radioactivity and the unfinished task of commercial fusion – remain formidable.

Whether the process ever supplies meaningful quantities of gold will depend on breakthroughs still to come in fusion engineering and materials science. In the meantime, the claim serves as a reminder that the boundary between energy research and materials science continues to blur, with potential consequences for industries far beyond power generation. Global gold markets, jewellery demand in Asia, investment flows into fusion startups and the long-term economics of clean energy all form part of the larger picture that this development invites the world to examine carefully.