Hydrothermal Alteration Around the TA 26 Seamounts of the Tofua Volcanic Arc in Lau Basin, Tonga

We have researched the distribution and characteristics of seafloor hydrothermal deposits for the development of economic mineral deposits in the Lau Basin, Tonga since 2009.In this study, we interpreted hydrothermal alteration around TA 26 seamounts of the Tofua volcanic arc using X-ray diffraction analysis for bulk sample and preferred-oriented specimen of clay fraction.We used 2 core samples and several surface samples.Plagioclase and quartz are dominant mineral in the basement rock, whereas kaolin mineral and smectite are superior in marine surface sediments.Especially sulfate and sulfide minerals such as gypsum, barite, sphalerite, and pyrite are predominant in the vent sediments.When we compare the mineral composition between basement rock and sea surface sediments, argillic alteration zone composed of kaolin mineral and smectite could be produced by hydrothermal fluids.Based on the downcore variation of mineral assemblages, most portion of MC08H-06 core could be interpreted as argillic alteration zone composed of kaolin mineral and smectite except top 2 cm area.