(Table 1, page 220), Spot chemical analyses of a section of nodule 5133.7

Microscopic and electron probe examination of some manganese nodules show that they consist of segregations of manganese-iron oxides in an interstitial material almost free of manganese but rich in iron and silicates. The segregations are widely spaced in the volcanic cores of the nodules but become more abundant towards their outer crusts where they form the centres of linked polygons of interstitial materials. Most of the minor elements are concentrated in the segregations compared to the interstitial materials. It is suggested that the structures observed result partly from solution and reprecipitation of elements in the original volcanic cores of the nodules and partly from the replacement and coating of these cores by manganese-iron oxides precipitated from sea water.

(Table 1, page 129) Chemical composition of ferromanganese coating on glacial erratics from Lydonia Canyon

Ferromanganese coatings have been found on glacial erratics in Lydonia Canyon, off the United States northeastern coast. The coatings, which are about 17 µm thick, consist of an outer manganese-rich layer which covers the top of the erratic, a middle transitional layer, and an internal iron-rich layer that encircles the entire surface of the erratic. Chemical analyses of the coatings, when compared with similar data on abyssal marine ferromanganese deposits, reveal comparable Mn/Fe ratios, higher P and Ti concentrations, and an order of magnitude less of Co, Ni, Cu, and most other metals. A comparison of the Lydonia Canyon coatings with desert varnishes reveals obvious chemical, mineralogical, and morphological differences.

Geochemistry of nodules from a young seamount

Manganese nodules made of radiating rods of well crystallized birnessite were sampled at 8 degree 481.2'N, 103 degree 53.8W, 1875 m below sea level by a dredge that also collected hyaloclastite and basaltic talus. The nodule field is on the floor of a caldera within a young tholeiitic seamount and was discovered and photographed during a deep-two survey. It is interpreted as a brecciated hydrothermal deposit, crystallized from an amorphous manganese oxide precipitate that formed when seawater-based hydrothermal fluids mixed with oxidized seawater. The nodules and surrounding igneous rocks have subsequently been encrusted with hydrogenous ferromanganese oxides.

Description and composition iron-manganese concretions from the Pacific

One the most interesting features of ocean sedimentation is the manganese formations on the surface of the ocean floor in some areas. These are especially widespread in the Pacific Ocean as concretions, grains, and crusts on rock fragments and bedrock outcrops. Iron-manganese concretions are the most abundant as they completely cover about 10% of the bottom of the Pacific Ocean where there are ore concentrations. The concretions occupy from 20-50% of the bottom and up to 80-90% on separate submarine rises. Such concretions are found in different types of bottom deposits, from abyssal red clays to terrigenous muds, but they occur most widely in red clays and quite often in carbonate muds. Their shape and their dimensions are very diverse and change from place to place, from station to station, varying from 0.5-20 cm. They may be oval, globular, reniform, or slaggy and often they are fiat or isometric concretions of an indefinite shape. The concretions generally have nuclei of pumice, basalt fragments, clayey and tuffaceous material, sharks' teeth, whale ossicles, and fossil sponges. Most concretions have concentric layers, combined with dendritic ramifications of iron and manganese oxides.

The geochemistry, mineralogy, and petrology of basalts at DSDP Leg 59 Holes

Legs 59 and 60 of the International Phase of Oceanic Drilling (IPOD) were designed to study the nature and history of volcanism of the active Mariana arc, its currently spreading inter-arc basin (the Mariana Trough), and the series of inactive basins and intervening ridges that lie to the west. The older basins and ridges were drilled during Leg 59 as the first part of a transect of single-bit holes drilled in each major basin and ridge. The eastern part of the transect - the technically active region - was drilled during Leg 60. The evolution of island-arc volcanos and magma genesis associated with lithospheric subduction remain some of the most complex petrologic problems confronting us. Many types of source material (mantle, oceanic crust, continental crust) and an unusually wide range of possible physical conditions at the time of magma genesis must be identified even before the roles of partial melting and subsequent magma fractionation, mixing, and contamination can be assessed.