Mass wasting events and their impact on the formation and preservation of submarine ore deposits

Mass wasting and landform modifying events have a profound impact on hydrothermal processes in terrestrial environments. Mass wasting events in submarine settings also modify hydrothermal systems and their associated mineralisation. We present evidence of a dynamic environment impacting on ore formation at the historically exploited Pb-Zn-(Ag) mineralisation of Triades, Milos island (Greece), formed in a submarine setting. Galena-sphalerite veins and barite-quartz gangue precipitated in the near subsurface or after exhalation of boiling hydrothermal fluids. Field evidence indicates that mineralisation was extensively reworked by debris flow events during formation. The mineral paragenetic sequence is consistent with a Pb-Zn-(Ag) massive sulphide system, and analogous to the early stages of a Kuroko-type deposit, but Triades lacks massive sulphide bodies. We suggest that mass wasting events literally truncated the developing mineral deposit as it formed on the seafloor, destroying massive sulphide bodies and limiting the development of the ore mineral assemblages. Mass wasting processes in volcanogenic massive sulphide systems are ore-destructive, with little opportunity for “telescoping”, unlike terrestrial equivalents. Shallow marine systems in terrains subject to mass wasting may have low preservation potential, or may be classified as epithermal-like vein systems rather than stockwork portions of massive sulphide deposits.