mineral systems
The only system here whose engine is the weather. Rainwater removes magnesium and silicon from ultramafic rock over millions of years and leaves nickel behind — and the same uplift that exposes the rock destroys the profile that concentrates it.
About: Nickel-cobalt laterite system
Nickel-cobalt laterites are supergene deposits formed by pervasive chemical and mechanical weathering of ultramafic rocks. The model describes laterite as a profile in tropically weathered regolith in which the most soluble elements are removed and the least soluble progressively redistributed, through a series of more to less weathered protoliths, to form a concentrated deposit.[1,2]
The nickel is not brought in. Unweathered ultramafic rock already holds 0.2 to 0.4 percent nickel inside olivine and serpentine, with less in accessory pyroxene and chromite. The system does not add nickel; it removes everything else.[1,2]
The water responsible is circulating rain water and water within the water table. It travels the path of least resistance, guided by the crystal structure of the protolith and by inherited structure — the fabric the rock already had.[1]
Nickel re-precipitates on saturation, deposited with hydrated alteration minerals rather than staying in the solution that carries the magnesium and silicon away. Deposition here is a change in solubility at ambient temperature, not a change in a hot fluid.[1]
Almost all known deposits lie within 26 degrees of the equator, with a few exceptions such as Riddle in Oregon and deposits in the Urals, Greece and the Balkans.[1]
Preservation then works against the setting. Laterites formed on accreted ophiolite sequences are restricted by preservation potential in tectonically active regions, while those formed by weathering of cumulates in stable cratonic environments can be far more laterally extensive, because without uplift the profile is not mechanically stripped and a single planation surface develops.[1]
So the rock has to reach the surface, the climate has to be right for long enough, and then nothing much may happen for a very long time. The third condition is the one most easily forgotten.[1,2]
Often said
“Laterite deposits form where nickel-rich fluids were concentrated.”
What the evidence supports
The nickel is inherited from the protolith at 0.2 to 0.4 percent and stays put; magnesium and silicon are removed by percolating rainwater, and the nickel is left behind and re-precipitated into hydrated alteration minerals.
Supporting records: lat-source · lat-protolith-nickel · lat-deposition
Bracketed references link to the structured entity records whose claims support each paragraph. Last updated 2026-09-07.