P'amous area

Deep-sea hydrothermal deposits were observed. mapped and sampled in situ with the submersible "Cyana" in the Famous area of the Mid-Atlantic Ridge. Two neighbouring fields, each covering an area of about 600 m2, are associated with low. E-W trending sediment-covered ridges that lie at a depth of about 2 700 m close to the axis of Transform Fault "A". In each field the deposits are thicker (up to about 1 m) close to the small. fissure-like vents through which they were evidently delivered. Despite their heterogeneous composition. their mineralogical and chemical variations have an orderly pattern. The principal constituents are a green clay-rich material and Fe-Mn oxides in the form of black concretions. The relative abundances of these products Vary with distance from the source-vent. The green clay-rich material, abundant near the vent. consists of hydromica. smectite and an amorphous Fe-Si compound. Further away. the Fe-Mn concretions, made up of rancieite and todorokite. are the dominant components. r The hydrothermal deposits from Transform Fault "A" have a consistently low Ni (20- 270 ppm), Cu (26-275 ppm), Co ( < 91 ppm) and Zn (5-126 ppm) content which sets them apart from known deep-sea metalliferous sediments, manganese nodules and Fe-Mn coatings of ocean floor basalts. The 6e-~n coatings of basaltic rocks from Transform Fau1t-A" have a lower Si/Al ratio (z 1 .6)and a narrower range in their FeIMn ratio (2-3) than the hydrothermal deposits (AI/Si =4-153 and Fe/Mn =O. 3-35).