(Table 1) Chemical element contents in ferromanganese encrustations from the Sierra Leone Rise

A detailed study of chemical and mineral compositions of ferromanganese encrustations indicated that their variability dependent on composition of host substrate and on geological and oceanological processes.

(Table 2) Layer-by-layer chemical composition of barite crusts from the Atlantis II Deep of the Red Sea rift zone

Results of studies of hydrothermal sulfide-sulfate rocks occurring in the Atlantis II Deep of the Red Sea are reported in the paper.

Mineral and chemical compositions of sedimentary and volcano-sedimentary rocks drilled in DSDP Legs 43 and 44

Sedimentary cover on the bottom of the Northwest Atlantic Ocean is underlain by Late Jurassic - Cretaceous tholeiite-basalt formation. It consists of come sedimentary formations with different lithologic features and age. Their composition, stratigraphic position and, distribution are described on materials of deep-sea drilling. Mineralogical and geochemical studies of DSDP Leg 43 and Leg 44 holes lead to new ideas about composition and genesis of some sediment types of and their associations. High metal contents in the chalk formation of black clays on the Bermuda Rise probably result from exhalations. Connection of red-colored and speckled deposits with hiatuses in sedimentation is shown. Main stages of geological history of the North American Basin are reflected in accumulation of the followed formations: ancient carbonate formation (Late Jurassic - Early Cretaceous), formation of black clays rich in organic matter (Cretaceous), formation of speckled clays (Late Cretaceous), siliceous-clayey turbidite formation (Eocene), hemipelagic and pelagic clayey formation (Neogene), and terrigenous turbidite formation (Pleistocene).

Mineralogical composition, copper and d18O at DSDP Site 59-448

Alteration in a submarine remnant volcanic arc should leave an important record of (1) the mineralogy of sea water-volcanic arc rock interaction; (2) the chemistry of solid reaction products; (3) the isotopic characteristics of such reactions (Muehlenbachs and Clayton, 1972; Spooner, Beckinsale, et al , 1977; Spooner, Chapman, et al., 1977); (4) the metallogenesis within such a sequence (Mitchell and Bell, 1973); and (5) the geothermal gradient during the alteration. The volcaniclastic breccias, tuffs, and igneous units of Sites 448 (993 m) and 451 (930.5 m) on the Palau-Kyushu and West Mariana ridges, respectively, are particularly suited for such studies because the thick sequences have remained submarine throughout their history, seemingly unaffected by magmatic or hydrothermal events after cessation of volcanic activity. Also, shipboard observations indicated a change in alteration products with depth. At both sites the igneous units and volcaniclastic rocks were altered to brownish clays and zeolites near the top of the volcanic sequence; to bright blue green clays and zeolites at moderate depths; and to very dark, nearly opaque, forest green clays and zeolites at still greater depths. Native copper occurs both as disseminated pockets in the volcaniclastic breccias and vesicular basalts and as veins in the breccias; native copper is restricted to stratigraphic levels characterized by the absence of sulfides or oxides of copper and iron. Although some native copper is found in vesicles of basalts and may be orthomagmatic, most of it is clearly secondary. Near dikes and sills, higher sulfur fugacity conditions caused the precipitation of iron and copper sulfides with an absence of native copper (Garrels and Christ, 1965). The occurrence of native copper may be an initial stage of Cu metallogenesis that forms porphyry coppers in island arcs (Mitchell and Bell, 1973). This study will address primarily the possibility that hydrothermal sea water interaction with volcanic arc rocks has created the mineralogical and isotopic zonation in Leg 59 cores. Hydrothermal activity can be expected in a rapidly growing island arc and is probably the result of a high geothermal gradient prevalent during arc magmatic activity. The chemical character of the alteration is further discussed by Hajash (1981).

Composition of dissolved, particulate and sinking material in hydrothermal plumes above the TAG and Broken Spur hydrothermal fields

The paper reports data on distribution of dissolved (Mn, Zn, Cu, Pb, and Cd) and particulate (Fe, Mn, Zn, Cu, Pb, Ni, and Co) species of metals in hydrothermal plumes above the active TAG and Broken Spur hydrothermal fields (26° N and 29° N in the MAR rift valley, respectively). Sediment trap data on fluxes of hydrothermal sedimentary material in the areas indicate that (i) the predominant Zn source for metalliferous sediments at the TAG field is material precipitating from the neutrally buoyant plume, and (ii) the predominant source of Fe and Co is re-deposited ore material coming from the area of extensive settling of sulfides.

Chemical composition of bottom sediments and interstitial waters from DSDP Sites 252, 285, 315, 317, 336, and 386

Six Deep Sea Drilling Project (DSDP) Sites (252, 285, 315, 317, 336, 386) were examined for the chemical composition of the dissolved salts in interstitial waters, the oxygen isotopic composition of the interstitial waters, and the major ion composition of the bulk solid sediments. An examination of the concentration-depth profiles of dissolved calcium, magnesium, potassium, and H218O in conjunction with oxygen isotope mass balance calculations confirms the hypothesis that in DSDP pelagic drill sites concentration gradients in Ca. Mg. K, and H218O are largely due to alteration reactions occurring in the basalts of Layer 2 and to alteration reactions involving volcanic matter dispersed in the sediment column. Oxygen isotope mass balance calculations require substantial alteration of Layer 2 (up to 25% of the upper 1000 m). but only minor exchange of Ca, Mg, and K occurs with the overlying ocean. This implies that alteration reactions in Layer 2 are almost isochemical.