A new model for Kuroko-type deposits of Japan

Abstract

From the Archean to the present, Kuroko-type massive sulfide deposits have been formed repeatedly on the sea floor in various island arcs. Discoveries of sea-floor hydrothermal deposits in the Okinawa Trough and in the Izu-Bonin arc of the northwestern Pacific Ocean have shed new light on the genesis of their fossil analogs. We are able now to assess the proposed models of the generation of Kuroko deposits by combining information on present-day and ancient deposits. Several lines of evidence suggest that acidic magma emplaced at a high level in the Earth's crust is inevitable as the source of metals and sulfur in the Kuroko deposits. However, metals like lead could be supplied partially from the wall rock as a result of leaching by downward-circulating seawater.