Review of the Kuroko deposits

Abstract

Kuroko deposits have been traditionally defined by volcanogenic, strata-bound， massive sulfide and sulfate deposits in submarine environment. Recently, it is suggested to include the following term in the definition: relating to bi-modal volcanism in back-arc tectonic setting. The deposits are essentially composed of zonal massive sulfide layers underlain by massive gypsum and disseminated or stockwork sulfides in the footwall unit. On the other hand, varieties exist in forms of deposits such as single unit stratiform ore, stockwork sulfide without significant massive sulfides and dominance of sulfate minerals, and so on. In the present paper, the following geological aspects related to Kuroko deposits are reviewed; geologic setting in the Hokuroku district as a representative Kuroko cluster, tectonic background and magmatic process relating to the Kuroko deposits based on previous studies. The primary ore textures are also discussed followed by discussion of deep marine environments during ore formations based on recently accumulated knowledges. Lastly, several exploration methods, which have been accumulated in a mining company for a long time, are introduced including low magnetic susceptibility, low Na₂O anomalies in the footwall rocks, and alteration mineral zoning around ore deposits.