Mississippi Valley-type ore deposits provide most of the lead and a large part of the zinc presently mined in the world. They are stratabound epigenetic precipitates largely in dolostone host rocks that occur on the flanks of deeply subsiding sedimentary basins or between two sedimentary basins along an axis of reduced subsidence. They were commonly emplaced at or close to the platform-to-basin facies front, well removed from igneous or metamorphic influences. Sulfides commonly infill interstitial or intramoldic porosity in collapse breccias, and are formed by the intrastratal solution of evaporites and/or carbonates either by downward-percolating meteoric waters or by upward-escaping basinal fluids. In a few places, karstic caverns were precursors to ore precipitation; m re commonly, lower grade deposits occur in intergranular or intercrystalline space. The strong force of crystallization of sulfide minerals may cause local pressure solution encroachment on the carbonate host rock, but the vast bulk of any deposit is void-filling and, therefore, the average porosity (% voids) determines the likely grades.

The mineralogy is simple: galena and/or sphalerite, marcasite and/or pyrite, accompanied by only a white sparry dolomite, in places calcite and/or quartz gangue.

The host rocks have many of the attributes of a carbonate rock petroleum reservoir of recognizable anticlinal or stratigraphic trap type. Residues of hydrocarbons and former evaporites are common characteristics.

The metals probably migrated considerable distances as soluble chloride complexes in low-temperature, high-salinity brines and precipitated where these brines encountered host-rock brines with abundant reduced sulfur. Lead and sulfur isotopic and trace-element compositions of the ores and host rocks are complex and the brines strongly resemble petroleum-associated basinal fluids, but, so far, geochemical criteria have failed to impose a consensus on metal(s) source(s). Some Mississippi Valley-type deposits appear to be little younger than their host rocks; others may lag by long periods of time.

Genetic models lead to consequent exploration thinking that mimics many aspects of oil finding.

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