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ABSTRACT: High Temperature Polymetallic Sulfide Deposits in Back Arc Environment: Lau Basin SW Pacific

Y. Fouquet, U. Von Stackelberg, P. Herzig

During the French-German diving cruise Nautilau, black smokers were observed for the first time in a back-arc environment. Twenty-two dives have been completed to investigate the southern Lau basin. The objectives were to understand the genesis of sulfide ores, the volcanic and tectonic activity in a back arc close to an island arc. The four diving sites in a water depth of about 2000 m are located between 21°25^primeS and 22°40^primeS. Three types of hydrothermal deposits were discovered during the cruise:

1. Low temperature (40°) deposits that are related to discharge through highly vesicular andesite and dacite. They are characterized by extensive deposits of Fe-Mn oxides underlaid by sulfides.

2. Medium- to high-temerature barite/sulfides mineralization was observed in many places along the ridge. The most important field, a few hundred meters in diameter and 20 m high, consists of barite chimneys and massive barite boulders mixed with massive sulfides.

3. Very high temperature black and white smokers were discovered at the central Valu Fa Ridge. The chemistry of the fluid and the plume is described elsewhere. The temperature measured at the vents (342°C) and the general anomalies of the bottom seawater (up to 25°C) indicate that the area is one of the most active known in the oceans at the present time. A complete cross section was sampled through a massive sulfide deposit including the stockwork.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990