Hydrothermal input in recent sediments proximal to the Eastern Lau Spreading Centre, Lau Basin, SW Pacific

The partition geochemistry and recent Mn accumulation rates have been studi ed in 14 sediment cores collected adjacent to the Eastern Lau Spreading Cen tre (ELSC) in the Lau Basin, SW Pacific. The sediments are oxic in nature, formed of ash with abundant nannofossil ooze and hydrothermal Mn oxides dis persed within the calcareous sediments. These oxides represent distal plume fallout derived mainly from the hydrothermal fields along the ELSC and pos sibly from the nearby Central Lau Spreading Centre (CLSC). Nickel, Mo, Pb a nd, to a lesser extent, Co and V are associated with the Mn-oxide phase, po ssibly scavenged by Mn precipitates. Only low proportions of Fe, Zn and Cu are found in the oxide phase, these elements being mainly associated with t he detrital/altered-detrital sediment phases. Some peaks in the Mn distribu tion downcore appear to correlate among the cores studied, indicating commo n pulses of hydrothermal plume fallout, The similar Fe/Mn oxide ratios (1.4 -1.9) in surficial sediments proximal to the Eastern and Central Lau Spread ing Centres, suggest similar plume fallout compositions in these two areas. Mean Mn accumulation rates average 26 mg cm(-2) ka(-1). The hydrothermal s edimentation near the ELSC is probably related to a fully developed hydroth ermal plumbing at the spreading centre and thus the ELSC has a good potenti al for hosting massive sulphide deposits, although a lower hydrothermal inp ut at its northernmost tip may indicate a drop in magmatic activity and min eral potential in the oldest section of this spreading ridge.