Solubilities of galena in sodium chloride brines at temperatures near 100 degrees C are such that rather acid conditions are required to transport ore quantities of lead if the required reduced sulfur is transported in the same solution. If either calcite or dolomite is stable in the brine, this degree of acidity is ruled out, and if chalcopyrite is stable, the brine must be not only quite acid but highly reduced. Formation waters probably do not attain this degree of acidity, so to transport ore quantities of lead their reduced sulfur content must be very low, and must therefore be supplied at the site of deposition, causing precipitation. Mississippi Valley-type orebodies represent sites where metals from basinal brines and sulfide from limestones got together for considerable lengths of time, and the migration of H 2 S through the limestone to the site is at least as important as the flow of metal-bearing brine through the basin.

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