Annotated record of the detailed examination of Mn deposits from R/V "Jean Charcot" GEOMANCHE 76/2 stations

This report presents the preliminary results of the study of rocks and sediments obtained by dredging during four cruises of the R/V Jean Charcot and R/V Le Suroit during a cooperative program between CNEXO and CEPM (CH 58: April 1975; SU 01: December 1975; CH 66: February 1976; and CH 67: March 1976). Several dredges on the continental slope of the Goban Spur recovered "granitic" rocks on two morphological structures, Granite Cliff and "Menez Bihan" (Pautot et al., 1976), in water depths ranging from 3200 to 4200 meters. According to the radiometric age and petrology, the granodiorite appears to have a close affinity with similar igneous facies which have been described in Iberia (Capdevilla et al., 1973) and attributed to the Variscan intrusive episode which is also found in the nearby continental area (southwest Great Britain and Brittany, France). They often are coated by a centimeter-thick layer of ferromanganiferous deposits (Shaaf et al., 1977).

(Table 2, Page 270) Average chemical composition of manganese nodules and crust collected at different localities the Pacific Ocean

Considerable regional variations in the chemical composition of manganese nodules from a wide range of the Pacific Ocean have been observed. These variations can be more exactly expressed in terms of inter-element relationships. In particular, Cu-Mn and Cu-Ni associations reveal that Cu content in pelagic nodules increases rapidly in proportion to those of Mn or Ni. In nodules from continental borderland and hemipelagic areas, even if Mn or Ni contents increase, that of Cu increases only slightly. It is suggested that the considerable chemical differences within individual nodules and between nodules from the same site, at a limited pelagic area where there is no marked change in depositional conditions of nodules, are due to the role of hydrolyzable trace elements in the formation of nodules.