mineral systems
No magma, no heat source, no volcano. Warm salty water moving through limestone deposits lead and zinc at temperatures a domestic oven would exceed — and this system supplies the clearest evidence in the corpus that a geological control is not a geological prediction.
About: Mississippi Valley-type system
Mississippi Valley-type systems form where basinal brines carrying metals and sulfur from crustal sources deposit sulfides in carbonate rocks, mainly by replacing the carbonate and to a lesser extent by filling open space. The alteration is dolomitisation, dissolution of the host, and brecciation.[1,2,3]
The conditions are modest by ore-forming standards: brines of about 10 to 30 weight percent salts, depositing at typically 75 to about 200 degrees Celsius. There is no igneous driver anywhere in the chain, which is the reason Lithoen records this system alongside the magmatic ones. Concentrating a metal does not require heat, magma, or depth.[1,2,3]
Deposition is mainly by fluid mixing, and also by change in pH, change in temperature, and redox reactions of sulfate. Several mechanisms operate, and which one dominates varies.[1]
The controls on where this happens are faults and fractures, dissolution collapse breccias, and lithological transitions. The model treats them as factors in fluid transmissivity: features that focus flow and create opportunities for deposition to occur.[1,2]
And then the model says the thing that ought to be printed at the top of every prospectivity map. Each ore-controlling feature typically has an unmineralised counterpart in each district — which suggests that the coincidence of several controls must have been important in localising ore.[1]
This is not caution imported by Lithoen. It is a Tier A source, describing districts it knows in detail, recording that the features it has just named as the most important controls also occur, barren, in the same rocks nearby. A structure earns the name pathway by having focused flow, and that has to be shown.[1,2]
More than 80 percent of these deposits are hosted in Phanerozoic rocks. Many formed in Devonian to Permian time, during the intense tectonic events of the assembly of Pangaea, and the second most important period was Cretaceous to Tertiary.[1]
A distribution in time of known deposits records two things at once: when systems operated, and what has survived and been found since. The two cannot be separated from the distribution alone.[1,2]
Often said
“Ore deposits require heat, magma or great depth.”
What the evidence supports
Mississippi Valley-type systems have no igneous driver, deposit between about 75 and 200 degrees Celsius from basinal brine, and supply a substantial part of the world’s lead and zinc.
Supporting records: mvt-source · mvt-fluid-temperature · mvt-definition
Often said
“Finding the right structure in the right rocks locates mineralisation.”
What the evidence supports
Each ore-controlling feature typically has an unmineralised counterpart in the same district. The coincidence of several controls, not the presence of one, is what appears to have localised ore.
Supporting records: one-control-not-enough
Bracketed references link to the structured entity records whose claims support each paragraph. Last updated 2026-09-07.