mineral systems
A mineral system can run to completion and leave nothing behind. What survives to be found is decided long after the metal stopped moving, by oxidation, uplift, erosion, metamorphism and burial — and what is found today is never quite what formed.
About: Volcanogenic massive sulfide system · Nickel-cobalt laterite system
Volcanogenic massive sulfide deposits form at the sea floor, where sulfides oxidise rapidly. The survival of ancient examples has therefore been attributed to specific circumstances: anoxic or sulfidic bottom waters, a capping lava flow, or a chemical precipitate of silica or sulfate that seals the deposit off from oxidising water.[1,2]
Each of those is a separate event that had to happen after the system finished. None of them is caused by the system. A deposit that formed and was not capped is not a smaller deposit; it is no deposit.[1,2]
Nickel-cobalt laterites weather out of ultramafic rock, and ultramafic rock reaches the surface most often in accreted terranes and obducted ophiolite sheets — in other words, in tectonically active places. The USGS model records the consequence directly: laterites formed on accreted ophiolite are restricted by preservation potential in active regions, while those formed on cumulates in stable cratonic settings can be far more extensive, because without uplift the profile is not stripped and a single planation surface develops.[1]
Almost all known deposits lie within 26 degrees of the equator, which records where the climate could build a deep weathering profile. It does not record where such profiles were built and later removed, and it cannot.[1]
In magmatic nickel-copper systems the modification runs in both directions. Within the conduit, a later surge of magma remobilises, upgrades and redeposits sulfide already accumulated, while proto-ore injected into the footwall may be shielded from that upgrading entirely. After emplacement, cataclastic metamorphism may remobilise and disperse the sulfides; metamorphism may also raise the tenor of disseminated sulfide by destroying olivine and releasing its nickel; and the sulfides may simply be recrystallised.[1]
An observation of the present state is therefore the sum of formation and of everything that has happened since. Reading it backwards to a formation mechanism is an interpretation, and Lithoen labels it as one.[1,2]
Often said
“If a system worked, the deposit is there to be found.”
What the evidence supports
Sulfides on the sea floor oxidise rapidly, and the preservation of ancient deposits is attributed to separate mechanisms — anoxic bottom water, capping lavas, silica or sulfate caps — none of which the system itself produces.
Supporting records: formation-not-preservation · vms-preservation-mechanisms
Often said
“What is exposed at the surface is what formed.”
What the evidence supports
Later magma, metamorphism, weathering and erosion all overprint an original system. In magmatic nickel systems the same processes can concentrate metal in one place and disperse it in another.
Supporting records: ncp-modification-both-ways · lat-preservation
Bracketed references link to the structured entity records whose claims support each paragraph. Last updated 2026-09-07.