The rocks at the center of the investigation are ultrapotassic lavas, an unusual family of magmas defined by their extraordinary enrichment in potassium relative to other elements. These rocks are rare on the modern Earth, but they are geochemical treasure troves because they form under very specific circumstances. In southern Tibet, ultrapotassic magmas were generated during the Cenozoic era, after the long-running subduction of oceanic crust beneath the region had ceased. When subduction ends, the lithospheric mantle, the rigid uppermost layer of the mantle beneath the continent, does not simply sit inert. Instead, it can be reactivated, particularly where it has been previously metasomatized, meaning it was chemically altered and enriched by fluids and melts released from the sinking slab. When this modified mantle partially melts, it produces the high-potassium, shoshonitic magmas that crystallize into ultrapotassic rocks.

Post-subduction magmas of this kind have attracted attention from economic geologists because they are sometimes spatially and temporally associated with porphyry copper deposits, the giant ore bodies that supply most of the world’s copper. Porphyry deposits form when copper-rich fluids exsolve from shallow magmas and precipitate metal sulfides in fractured rock above them. But the exact role that post-subduction ultrapotassic magmatism plays in the overall copper budget of the continental crust has remained ambiguous. Do these magmas add copper to the crust, or do they quietly remove it? The new research addresses this question using a combination of copper isotope measurements and geochemical modeling, providing a quantitative framework for how copper behaves as these magmas form and evolve.

Copper has two stable isotopes, copper-63 and copper-65, and the ratio between them, expressed in the standard delta notation as δ⁶⁵Cu, acts as a sensitive fingerprint of the chemical processes a rock has experienced. Because the two isotopes have slightly different masses, geological processes such as melting, crystallization, and fluid exsolution can fractionate them, preferentially concentrating the heavier isotope in some phases and the lighter one in others. Sulfide minerals, in particular, exert a strong control on copper’s behavior because copper is a chalcophile element, meaning it has a strong affinity for sulfur. Whenever sulfide liquid or sulfide crystals are present in a magma or its source, they tend to soak up copper, and they do so with measurable isotopic consequences.

The team’s analytical strategy hinged on a second geochemical tracer as well: the ratio of thorium to lanthanum, written Th/La. Thorium and lanthanum behave in broadly similar ways during mantle melting, but their ratio is sensitive to the presence of certain residual minerals and to the degree of melting in the source. By plotting copper contents and copper isotope compositions against Th/La across a suite of Cenozoic ultrapotassic rocks from southern Tibet, the researchers were able to distinguish two distinct stages in the life of these magmas. The variations in Th/La record a transition from the earliest stage, dominated by partial melting of the lithospheric mantle, to a later stage dominated by magmatic differentiation, in which crystals settle out of cooling magma and fluids escape from it.

During the first stage, the partial melting of the metasomatized lithospheric mantle, the key actor was sulfide retention in the source. As the mantle rock partially melted, not all of its sulfide minerals dissolved into the melt. Solid sulfide phases remained behind in the residual mantle, and because copper is so strongly chalcophile, those residual sulfides held on to the copper, preventing it from entering the melt. The result was a copper-depleted magma, and, crucially, a melt with a slightly heavier δ⁶⁵Cu signature than the source, because the isotopic fractionation between sulfide and melt left the light isotope preferentially in the retained sulfides. In other words, the mantle kept both the copper and its lighter isotopes, while the melts that rose into the crust carried away less copper than conventional models would predict.

This finding has profound implications for the continental copper budget. If ultrapotassic magmas generated by partial melting of sulfide-bearing lithospheric mantle are systematically copper-depleted, then the process of post-subduction mantle reactivation does not enrich the crust in copper; instead, it may contribute to the depletion of the continental crust. The copper that stays behind in the mantle source is effectively removed from the crustal inventory, sequestered in the deep lithosphere where it cannot form economic deposits. Over geological time, repeated episodes of this kind of magmatism could help explain why the continental crust contains so much less copper than the bulk silicate Earth would suggest. The missing copper, in this view, is not missing at all; it is stranded in sulfide-bearing mantle rocks that never gave it up.

The second stage of the story unfolds after the magmas have left their source and begun to cool and evolve in crustal magma chambers. Here, the control shifts from sulfide retention to fluid activity. As magmas crystallize, dissolved volatile components such as water and sulfur become concentrated in the remaining melt until they reach saturation and exsolve into a separate fluid phase. These exsolved fluids are efficient scavengers of copper, and the isotope data show that they preferentially remove the isotopically heavy copper, the copper-65-rich fraction. As a result, both the copper contents and the δ⁶⁵Cu values of the residual magmas decrease over time. The magmas become progressively poorer in copper and isotopically lighter as fluids bleed off the heavy copper, potentially carrying it toward shallow levels where, under the right circumstances, it could contribute to mineralization.

One of the most intriguing results of the study is that the copper isotopic evolution of these ultrapotassic magmas differs from that of the ore-bearing porphyries found in the same belt of southern Tibet. This isotopic divergence potentially reflects differences in the magma source or in the evolutionary history of the two magma types. Porphyry copper systems require a specific combination of ingredients: a copper-rich magma, abundant fluid exsolution, and favorable conditions for focusing those fluids into ore-forming sites. The ultrapotassic rocks, by contrast, record a history in which copper was lost to the mantle source before melting even began, and then further depleted by fluid scavenging during differentiation. The comparison suggests that not all post-subduction magmas are created equal, and that the isotopic signatures preserved in volcanic rocks can distinguish fertile from infertile magmatic systems.

Beyond its significance for understanding the deep copper cycle, the research arrives at a moment when copper has become a strategic commodity central to electrification, renewable energy infrastructure, and battery technology. Understanding the fundamental geochemical controls on copper’s distribution in the crust is not merely an academic exercise; it informs exploration models that guide the search for new deposits. By demonstrating that copper isotope ratios in common volcanic rocks can track the loss of copper to mantle sulfides and to exsolving fluids, the study adds a powerful new tool to the geochemist’s toolkit. The ultrapotassic rocks of southern Tibet, once considered geochemical curiosities, now serve as recorded witnesses to one of the great accounting problems in Earth science, showing in isotopic detail how the continental crust was quietly drained of its copper over millions of years, one sulfide grain and one fluid pulse at a time.

Subject of Research: Copper isotope evidence for crustal copper depletion recorded in post-subduction ultrapotassic rocks from southern Tibet

Article Title: Tracing missing copper: ultrapotassic rocks record isotopic evidence of crustal Cu depletion

Article References: Luo, C.-H., Liang, W., Wang, R., Nebel, O., & Zhao, Y. (2026). Tracing missing copper: ultrapotassic rocks record isotopic evidence of crustal Cu depletion. Nature Communications. https://doi.org/10.1038/s41467-026-78549-y

Image Credits: AI Generated

DOI: 10.1038/s41467-026-78549-y

Keywords: copper isotopes, ultrapotassic rocks, continental crust, lithospheric mantle, porphyry copper, southern Tibet, geochemistry, sulfide retention, magmatic differentiation, post-subduction magmatism, Th/La ratio, Nature Communications

The study, published as the inaugural article in the journal Space and Planetary Resources, was conducted by Kevin M. Cannon of Ethos Space Corp. and the Colorado School of Mines. Drawing on decades of laboratory analyses of nearly 400 martian meteorites and on in-situ measurements from the Spirit, Opportunity, Curiosity, Perseverance and Zhurong rovers, Cannon compiled the highest reported concentrations of 83 naturally occurring elements on Mars and compared them with the grades of ore deposits mined on Earth. The work arrives, he argues, at an inflection point between what may be the last large robotic science missions to Mars and the first serious steps toward commercialization and human landings.

A central theme of the analysis is that past discussions of planetary resources have often stumbled into logical errors that the terrestrial mining industry abandoned long ago. The most common is the presence-versus-absence fallacy: asking whether an element exists on Mars at all, when modern mass spectrometers can detect parts per trillion in virtually any material. What matters, Cannon stresses, is concentration, or grade, in a specific raw material at a specific location, because the energy and cost of extraction rise exponentially as grade falls. A gold mining company does not care how much gold is in Earth’s crust; it cares about the grade of a particular deposit. Similarly, the speciation of an element into separable ore minerals, such as zircon or monazite, versus lattice-bound substitutions in silicates, can make the difference between a practical resource and an impractical one.

The comparison baseline matters too. Average crustal composition is the wrong yardstick; martian concentrations must be measured against actual terrestrial ore bodies, which are enriched many orders of magnitude above bulk crust. When that comparison is made, the results span more than five orders of magnitude, with a median ratio of 27, meaning terrestrial ores are on average 27 times richer than the best-known martian materials. Six elements, including oxygen, sulfur, germanium, rubidium, argon and xenon, match or exceed the concentrations of the materials they are extracted from on Earth. Volatile elements such as sulfur, chlorine and bromine sit close to terrestrial ore grades, consistent with Mars having accreted from more volatile-rich building blocks. By contrast, the light metals lithium, beryllium and boron, the platinum group elements, the light rare earths, and the nuclear fuels thorium and uranium are orders of magnitude depleted in known martian samples.

Perhaps the most striking conclusions concern specific deposit types that rovers may have already brushed against. In Gale crater, ChemCam on the Curiosity rover detected copper enrichments throughout the stratigraphy of Mount Sharp, with the highest values in the Kimberley Formation. Detailed analysis suggests the copper occurs both in detrital grains of the potassic sandstones and adsorbed on manganese oxide coatings, pointing toward a porphyry copper or impact-hydrothermal deposit somewhere in the sediment source region. That would be a remarkable finding, because earlier theoretical work had specifically predicted that porphyry copper deposits should not exist on Mars, a prediction made before the discovery of evolved, potassic igneous lithologies and the full extent of ancient water-rock interaction on the planet.

At Jezero crater, the Perseverance rover has found strongly correlated nickel and copper enrichments in highly altered, aluminum-rich float rocks, with ore-grade values that support the long-standing prediction of Ni-Cu-PGE sulfide deposits associated with ultramafic volcanism. The region’s extensive olivine-rich unit, mapped from orbit and confirmed on the ground by an olivine cumulate outcrop on the crater floor, fits the terrestrial analog of large igneous provinces where such sulfide ores segregate from lava flows. Perseverance’s PIXL instrument has also detected lamellar bands of zirconium, titanium, chromium and phosphorus-bearing dense grains in deltaic sediments, evidence for heavy mineral lag deposits of the kind mined on Earth for ilmenite and zircon. Cannon notes that in all three cases the enriched materials were transported by water away from their sources, leaving only shadows of the original ore bodies, much as the California gold rush began in creek beds before prospectors traced the gold back to hard rock.

The quantitative picture is sharpened by extrapolation from element-element correlations in the meteorite collection. A single SuperCam point at Jezero reporting up to 2000 parts per million copper, if taken at face value, would predict roughly 2.2 parts per million ruthenium based on the meteorite correlation, exceeding typical terrestrial platinum-group ore grades even though the value falls below rover detection limits. Similarly, a PIXL spot measuring 1.4 weight percent zirconium, attributed to zircon or baddeleyite, implies about 362 parts per million hafnium, slightly above terrestrial ore values. These calculations suggest that ore-quality enrichments may already have been encountered on rover traverses, hidden below the sensitivity of onboard instruments, and that only a tiny fraction of the martian surface has been examined at all.

Mapping the indicators globally reveals a crucial geographic pattern. Olivine detections, potassium- and thorium-rich alkali terrains, aluminum clay exposures and fan-shaped sedimentary landforms, the best orbital proxies for sulfide, porphyry-like, leached and placer deposits respectively, cluster largely in equatorial regions such as Nili Fossae, Mawrth Vallis and eastern Valles Marineris. The mid-latitudes, where shallow ground ice is abundant, show a notable absence of these indicators, partly because younger lava flows, plains deposits and ice-dust mantles bury the ancient Noachian units where ores are most likely. This creates a potential tradeoff for settlement planning: if water is mined from ground ice, prospecting for metals may be pushed to marginal zones, but if water comes from hydrated minerals or other equatorial sources, the richest known mineral provinces become accessible. Atmospheric carbon dioxide and iron, available everywhere from regolith and iron meteorites, impose no such constraint.

Volumetrics remain a major uncertainty. The hematite-bearing unit at Meridiani Planum covers some 150,000 square kilometers, though its thickness is poorly known, while a native sulfur deposit recently discovered by Curiosity in Gediz Vallis has an estimated volume of 28,000 to 50,000 cubic meters. For the copper and nickel-copper signals at Gale and Jezero, the source deposits, if intact, likely exceed the transported materials in which they were detected, but elements like copper and nickel cannot yet be mapped from orbit. Cannon also flags unexplored geologic settings as prime targets for human fieldwork: evolved dacite terrains in Syrtis Major and the Eridania basin, impact-induced and magma-ice hydrothermal systems, speculative ancient seafloor deposits, and deeply leached aluminum clay stratigraphies like those at Mawrth Vallis, where extreme alteration hinted at by Jezero’s float rocks may have concentrated additional elements.

The bottom line is a sober but encouraging assessment. Mars falls between the Moon and Earth in its ore grades, as expected for a planet with intermediate geologic activity and water-rock interaction. Basic structural and industrial metals, including iron, aluminum, manganese, chromium, copper, zinc and titanium, show promising enrichments detectable with current orbital and geomorphologic data and should be prioritized for an initial settlement, while elements like lead, uranium and antimony are so depleted that substitution or import will likely remain necessary. As robotic exploration winds down and human missions approach, the study argues that the periodic table, not just the water cycle, must become the framework for choosing where on Mars to go and what to build when we get there.

Subject of Research: Assessment of non-volatile mineral and ore resources on Mars using meteorite and rover sample data

Article Title: Mineral resources of Mars based on decades of sample analysis

Article References: Cannon, K. M. (2025). Mineral resources of Mars based on decades of sample analysis. Space and Planetary Resources, 1(1), Article 1. https://doi.org/10.1007/s44461-025-00001-8

Image Credits: AI Generated

DOI: 10.1007/s44461-025-00001-8

Keywords: Mars, mineral resources, ore deposits, in-situ resource utilization, martian meteorites, Gale crater, Jezero crater, porphyry copper, Ni-Cu-PGE sulfides, heavy mineral sands, Perseverance rover, Curiosity rover