MINIMUM DEPTHS OF SULFIDE-ORE DEPOSITION ON THE OCEAN FLOOR

Abstract

The paper discusses the shallowest possible sea depths at which copper-zinc sulfide mineralization is emplaced from hydrothermal solutions, given the possible effect of flashing of these solutions on ore genesis. Massive sulfide ores that are now being emplaced on the ocean floor and, perhaps, in overlying unconsolidated sediments are economically the most interesting. Therefore, it makes sense to search for mineralization along ocean margins at depths where the flashing effect on ore genesis would a priori be known to be slight, so there would exist the necessary, although not sufficient conditions for emplacement of massive rather than stockwork ores. Calculations of that 'critical' sea depth may be based on the curve of boiling point of seawater versus pressure. The present 'avalanche'-type emplacement of massive sulfide ores on the Pacific Ocean floor and the great importance of kinetic factors in it make this ore-forming process very different from laboratory experiments, so it is difficult to use experimental physicochemical data on ore genesis to estimate temperatures of sulfide deposition on the ocean floor. The intersection of the curve of boiling point versus pressure (or water depth) with the 270° isotherm gives the depth of flashing at about 550 m. Additional aspects of the subject are discussed.