Hydrodynamic Constraints on the Formation of Kuroko Deposits

Abstract

Simple calculations are presented to illustrate the kinds of constraints hydrodynamic considerations can place on genetic hypotheses. It is tentatively shown that the rhyolite plugs commonly associated with Kuroko deposits are too small to be the cause of Kuroko mineralization. A larger intrusive heat (or magmatic fluid) source at depth is needed. Convective velocities in rocks of reasonable permeability are so much smaller than minimum ocean bottom current velocities that it is very unlikely Kuroko mineralization could have been precip-itated from solutions above the sea-sediment (or rock) interface. Hydrothermal solutions would be swept away as soon as they left the protective sediment or rock cover. Finally hydrothermal convection may be expected to promote ore slumping if the permeability of the precipitated ore is low. The "slumped" nature of some Kuroko ores may thus find a natural genetic explanation.