Ferromanganese Oxide Research Articles

A radiochemically studied sediment core from the Philippine Sea Basin indicating no accumulation during the past few hundred thousand years.

A sediment core obtained from the northeastern Philippine Sea Basin was analyzed for 232Th, 230Th, 226Ra and 210Pb. Three sheets of Ferro-manganese oxide in a matrix of red clay were included in the 73 m core. Although the concentration of 232Th of land origin is normal as compared with that of the usual red clay or of the sediment obtained at the neighboring station, the concentration of radiogenic 230Th is extremely low and does not decrease with increasing depth. The radioactivity of rather soluble 226Ra at the station is not less than that of 230Th in the surface sediment, showing a tendency different from that observed in usual cores. Some enrichment in the comparatively short-lived 210Pb activity relative to 226Ra activity was found in the top sediment and in the first ferro-manganese sheet at the station. If the excess 210Pb in the ferro-manganese sheet is not due to contamination of the surface sediment, lead should migrate through the sheet. These facts suggest that the core has not been accumulating during the past few hundred thousand years or more.

Deep-sea phosphorite of tertiary age from Annan Seamount, eastern equatorial atlantic

Phosphatized bioclastic limestones of Early Tertiary age have been dredged from the crest of a seamount in the equatorial Atlantic near 9°N, 21°W. The samples were recovered from water depths of 700 to 970 m but clearly were deposited in a high-energy reefal environment, thus indicating significant Tertiary subsidence. The vertical movement is beleived to reflect reactivation of an old structural line, the Guinée Fracture Zone, which may have had important effects on the transfer of bottom waters of polar origin between the Sierra Leone and Gambia basins. Examination of foraminiferal limestone coating the shallow water material suggests that deep-water conditions were established on the seamount by Middle Miocene time. All phosphatized samples are covered with a layer of ferromanganese oxides which, from textural and faunal evidence, is Palaeocene or Eocene in age and of shallow water origin. Pervasive phosphatization of the bioclastic limestones appears to have been accomplished before the end of the Eocene while the crest of the seamount was near sea level, because Upper Eocene limestone of shallow water facies is unaffected by such radical diagenesis. Phosphatization probably was associated with vigorous upwelling near the seamount and has been taken to an unusually advanced stage, resulting in a phosphoritesof high economic grade. P 2O 5 contents are in the range of 37 to 41%. The purity of the phosphorites may be related to the intensity of upwelling during the Early Tertiary, but other factors such as the paucity of terrigenous detritus, frequent reworking of the sedimentary capping of the seamount, and a high primary porosity of the limestones may have been important in their information. The Early Tertiary period of phosphorite deposition on the seamount and in northwest Africa ended before the close of Eocene time in both areas, while shallow water conditions prevailed. It is argued that the cessation of phosphorite formation reflects major changes in the surface circulation of the Atlantic during the Eocene.

Thallium: a sensitive indicator of rock/seawater interaction and of sulfur saturation of silicate melts

Radiochemical neutron activation analysis for Tl in a number of young pillow basalts, hydrothermally altered basalts and associated hydrothermal and hydrogenous Mn crusts from the Mid-Atlantic Ridge and adjacent regions of the North Atlantic indicate that Tl is a sensitive indicator of both S saturation of silicate melts and of rock/seawater interactions. Rb-Cs-K-Tl trend lines for fresh MAR basalts (whose melts remained saturated with S during silicate fractionation) are distinctly different to Hawaiian basalts whose melts lost S during or prior to eruption, but were saturated with S at an earlier stage. Varying degrees of Tl enrichment are found in the hydrogenous Mn nodules (91,000 ppb), hydrothermal Mn crusts (2300–32,000 ppb), palagonitized glass (300–2700 ppb), hydrothermally altered basalts (1140–4560 ppb), and even slightly altered pillow interiors (11–45 ppb) relative to the fresh glasses (6–12 ppb). This enrichment has taken place due to incorporation of Tl into secondary silicate phases along with the alkalis and also due to co-precipitation of Tl with ferromanganese oxides and hydroxides. Thallium enrichment in the hydrothermal products is interpreted as being due to cooling and oxidation of hydrothermal fluids as these approached the sea floor. Haloes of Tl-enriched country rock may occur around sulfide deposits in which seawater has acted as the ore fluid.

Modern submarine hydrothermal mineralization: examples from Santorini and the Red Sea

Summary Submarine hydrothermal mineralization is known to occur on parts of the World Mid-Ocean Ridge System and in association with island arc volcanism. Two areas of submarine hydrothermal activity have been examined in detail — one in the Atlantis II Deep of the Red Sea and the other off the volcano of Santorini in the Cyclades Volcanic Arc, eastern Mediterranean. In each case hydrothermal solutions are mixing with sea water, resulting in the fractionation and precipitation of a variety of metal-bearing phases as the physico-chemical properties of the solution change. Sulphides occur locally as a minor component of the newly precipitated hydrothermal sediments off Santorini, which are principally composed of iron oxides. Iron precipitates close to the hydrothermal outlets and decreases in concentration away from the volcanic source. By contrast, manganese is low in the sediments richest in iron, but increases in concentration more than twenty-fold away from the hydrothermal outlets and iron-rich zone. The distribution of certain minor elements in the sediments follows that of Mn (e.g. Zn) and Fe (e.g. Mo), indicating that scavenging may be a control on their distribution. Early-formed precipitates from the Atlantis II Deep brines also include sulphides, principally of Cu, Zn and Fe. Subsequent precipitates include iron silicates, after which the remaining iron is oxidized and precipitated as ferric oxide and hydroxide. Finally, Mn 2+ is oxidized to Mn 4+ and can scavenge considerable quantities of trace metals out of solution on precipitation. Manganese precipitated in the waters over the Deep is probably redissolved on falling back into the brine. By contrast, manganese and those minor elements that escape from the Deep can precipitate up to 10 km from it, giving rise to well-developed geochemical dispersion haloes. The selective fractionation and precipitation of hydrothermally introduced metals on mixing with sea water in these two environments results in a geochemical zonation away from the metal source in each case. The principal fractionation, other than the early precipitation of metal sulphides, is between Fe and Mn, but some other metals also show distinctive concentration gradients. These observations may be of great potential value in geochemical exploration for submarine hydrothermal orebodies, as the extent of the dispersion of the most mobile elements can be many times the extent of the potential orebody itself. The significance of these observations in regard to metallogenesis on mid-ocean ridges in general has been discussed elsewhere. Metalliferous sediments found to date on the World Mid-Ocean Ridge System are of much lower grade than those in the Red Sea, but these may, in part, represent the analogues of the widely dispersed Fe and Mn oxides around the Atlantis II Deep. On this basis, Cronan concluded that higher-grade deposits, including metal-rich sulphides, might occur within the upper part of the oceanic crust and within the deep fracture zones that cut mid-ocean ridges in all the oceans. Furthermore, studies on the geochemical relationship between metalliferous sediments and ferromanganese oxides on mid-ocean ridges suggest that the two are genetically related in that they receive their metals from the same sources, but in different proportions and at different rates. Ancient volcanogenic orebodies sometimes show features similar to those described here, indicating that in the modern environment we may be observing a not uncommon volcanic ore-forming process in operation.

Comportement geochimique du Cuivre, du Nickel et du Cobalt a l'interface eau-sediment. Application a l'enrichissement en ces Elements dans les formations ferro-manganesiferes

We have studied the possibilities of chemical trapping of Copper, Nickel and Cobalt from sea water within ferromanganese oxides. A careful analysis of characteristic sediments together with interstitial water analysis leads us to point out that this trapping can be effected by a diagenetic process. Depending on the oxidoreduction state of the sediment, several models can explain the concentration mechanism. A thermodynamic calculation shows that only Cobalt can be oxidised to CoOOH as Manganese is oxidised. High concentrations of Copper, Nickel and Cobalt within Manganese nodules can be explained by this mechanism.

Environmental differentiation of morphology of ferromanganese oxide concretion in Shebandowan Lakes, Ontario1

Ferromanganese oxide concretions in Shebandowan Lakes show morphological differences depending on the environments of deposition. Six main morphological types have been defined, with subsidiary varieties. The best developed concretions occupy the shallowest most oxygenated portion of the lake. Changes in pH and Eh have resulted in the partial dissolution of some concretions in deeper water. The establishment of a relationship between concretion morphology and lake properties may aid in paleoenvironmental reconstructions in other lakes.

The geochemistry of basal sediments from the North Atlantic Ocean

Chemical analyses of North Atlantic D.S.D.P. (Deep Sea Drilling Project) sediments indicate that basal sediments generally contain higher concentrations of Fe, Mn, Mg, Pb, and Ni, and similar or lower concentrations of Ti, Al, Cr, Cu, Zn, and Li than the material overlying them. Partition studies on selected samples indicate that the enriched metals in the basal sediments are usually held in a fashion similar to that in basal sediments from the Pacific, other D.S.D.P. sediments, and modern North Atlantic ridge and non-ridge material. Although, on average, chemical differences between basal sediments of varying ages are apparent, normalization of the data indicates that the processes leading to metal enrichment on the crest of the Mid-Atlantic Ridge appear to have been approximately constant in intensity since Cretaceous times. In addition, the bulk composition of detrital sediments also appears to have been relatively constant over the same time period. Paleocene sediments from site 118 are, however, an exception to this rule, there apparently having been an increased detrital influx during this period. The bulk geochemistry, partitioning patterns, and mineralogy of sediments from D.S.D.P. 9A indicates that post-depositional migration of such elements as Mn, Ni, Cu, Zn, and Pb may have occurred. The basement encountered at the base of site 138 is thought to be a basaltic sill, but the overlying basal sediments are geochemically similar to other metalliferous basal sediments from the North Atlantic. These results, as well as those from site 114 where true oceanic basement was encountered, but where there was an estimated 7 m.y. hiatus between basaltic extrusion and basal sediment deposition, indicate that ridge-crest sediments are not necessarily deposited during active volcanism but can be formed after the volcanism has ceased. The predominant processes for metal enrichment in these deposits and those formed in association with other submarine volcanic features is a combination of shallow hydrothermal activity, submarine weathering of basalt, and the formation of ferromanganese oxides which can scavenge metals from seawater. In addition, it seems as though the formation of submarine metalliferous sediments is not restricted to active-ridge areas.

Desert varnish and marine ferromanganese oxide nodules: congeneric phenomena

BLACK, hydrated ferromanganese oxide (FMO) concretions of microscopic to macroscopic size and complex mineralogy cover ocean floors all over the world at depths of up to 8 km (ref. 1). These amorphous–crystalline nodules have a total Cu, Ni and Co content of 40 p.p.m. to 4% and vary greatly in trace element content, apparently because of varying growth rates caused by the different Eh and pH in their environments. Black, amorphous, hydrated desert varnish (DV) coatings, 10–100 µm thick, are extensively found in limited areas of the world's arid lands2,3 in both the subtropics and in non-sterile areas of the Antarctic dry valleys4. Marine FMO nodules are formed principally by biological fixation processes; the mode and rate of formation of DV, on the other hand, are not understood, but concern anthropologists in their efforts to date petroglyphs and other artefacts of ancient man5.

Duration of hydrothermal activity at an oceanic spreading center, Mid-Atlantic Ridge (lat 26°N)

Hydrothermal manganese oxide coats talus on the Mid-Atlantic Ridge at lat 26/sup 0/N until spreading moves the rock past the thermally and structurally active rift-valley wall. Hydrothermal activity is replaced by hydrogenous ferromanganese oxide precipitation on ocean crust older than 0.7 m.y. on the ridge-crest highlands.

Basal metalliferous sediments from the eastern Pacific

Analyses by atomic absorption spectrophotometry and spark-source mass spectrography of 25 basal metalliferous sediment units from widely spaced locations on the western flank of the East Pacific Rise show that the deposits are enriched relative to normal pelagic sediment in Fe, Mn, Ni, Cu, Pb, Zn, and many trace elements. The elements are partitioned differently between the various mineralogic constituents of the sediment, with Fe and Mn largely in separate phases and many of the remaining elements primarily associated with reducible ferromanganese oxide minerals but also with iron minerals and other phases. Most of the iron in the deposits is probably of volcanic origin, and much of the manganese and minor elements is derived from sea water. The bulk composition of the deposits varies with age; this is thought to be due to variations in the incidence of volcanic activity at the East Pacific Rise crest where the deposits were formed.

Manganese nodules and other ferromanganese oxide deposits from the Atlantic Ocean

Atlantic manganese nodules and encrustations are most abundant in areas of slow sedimentation beneath the carbonate compensation depth or where currents inhibit sediment accumulation. They principally contain the minerals todorokite and δMnO2, which are selectively concentrated into nodules and encrustations, respectively, and which show an environmental differentiation thought to be related to redox potentials. Excluding the continental margins, todorokite is most abundant in deepwater deposits. Mineralogical differences between nodules influence their chemical compositions, Ni and Cu being most abundant in samples rich in todorokite and Co in those rich in δMnO2. Chemically, the deposits differ from those in other major oceans principally in their higher Fe and lower Ni and Cu contents, which may be due to higher rates of supply of Fe to the deposits than those in the other oceans. Regional variations occur in the concentrations of several elements, Mn, Ni, and Cu being enriched in deepwater deposits from areas of slow sedimentation between the Mid-Atlantic Ridge and the continental margins and Co being enriched in some deposits from elevated localities. These variations are thought to be due to variation in the sources of the elements concerned and in the depositional environment.

Mechanism for nucleation and growth of manganese nodules

FERROMANGANESE oxide crusts and concretions cover vast areas of the sea floor1,2 and the relatively high concentrations of cobalt, nickel and copper in manganese nodules, together with the high population densities of polymetallic nodules on certain sea beds, such as the North Pacific Equatorial Belt3, mean that these marine sediments are potential ore deposits. A fact that is often overlooked, however, is that in many sedimentary environments most of the manganese and iron does not accumulate in the form of ferromanganese nodules, but instead is distributed throughout the sediment in the form of dispersed microscopic concretions4. A fundamental problem in accounting for the origin and distribution of polymetallic nodules is to explain the nucleation and growth of the host ferromanganese oxide phases. We demonstrate here that crystal-structure relationships between host manganese (IV) oxide and iron (III) oxide hydroxide phases control the authigenesis, mineralogy and metal enrichments of manganese nodules.

Geochemistry of Ferromanganese Oxide Concretions and Associated Deposits in Lake Ontario

Research Article| May 01, 1972 Geochemistry of Ferromanganese Oxide Concretions and Associated Deposits in Lake Ontario D. S CRONAN; D. S CRONAN Department of Geology, University of Ottawa, Ottawa, Ontario, Canada Search for other works by this author on: GSW Google Scholar R. L THOMAS R. L THOMAS Canada Centre for Inland Waters, Burlington, Ontario, Canada Search for other works by this author on: GSW Google Scholar GSA Bulletin (1972) 83 (5): 1493–1502. https://doi.org/10.1130/0016-7606(1972)83[1493:GOFOCA]2.0.CO;2 Article history received: 14 Jun 1971 rev-recd: 16 Nov 1971 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation D. S CRONAN, R. L THOMAS; Geochemistry of Ferromanganese Oxide Concretions and Associated Deposits in Lake Ontario. GSA Bulletin 1972;; 83 (5): 1493–1502. doi: https://doi.org/10.1130/0016-7606(1972)83[1493:GOFOCA]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract A large deposit of ferromanganese oxide coated sands and scattered manganese nodules occurs in the northern portion of Lake Ontario. The Mn and Fe contents of the concretions are similar to those in concretions from other environments, while their Ni, Cu, and Co contents are lower than in deep-sea nodules, but higher than in most previously described lacustrine concretions. Pb and Zn are high in the coatings and exceed the concentrations found in many previously analyzed Mn deposits. Within the deposit, Mn, Ni, Co, and Zn contents are correlated, and they vary inversely with Fe. Mn, Fe, Ni, Cu, and Pb are present in the interstitial waters of the sediments underlying the deposit in higher concentrations than in the overlying lake waters, thus providing a potential source of metals for concretion formation.The origin and compositional variations in the deposit possibly can be explained in terms of the fractionation and precipitation of Fe and Mn as a result of redox variations in the lake sediments. Eh increases from south to north across the deposit in such a way that iron may be selectively oxidized and precipitated in the south and manganese, in the north. The upward diffusion of Mn, Fe, and associated elements from the underlying sediments probably provides the principal source of the metals in the south of the deposit, while metal-enriched bottom waters are probably the principal source in the north. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Ferromanganese concretions in Lake Ontario

A large deposit of ferromanganese oxide concretions has been found in the northern portion of Lake Ontario. The concretions occur mainly in the form of coatings on sand grains but manganese nodules are present at several localities. Mineralogically, the ferromanganese oxide phases are amorphous, and their Fe and Mn contents are similar to those in concretions from other environments. However, their Ni, Co, and Cu contents are significantly higher than those reported in previously described North American lacustrine ferromanganese concretions, and this may, in part, be a reflection of their probable low rates of accumulation.

Connection of a mass-analyzer to a sealed electronic vacuum device

Todorokite is considered to form from vernadite in nature and commonly concentrates nickel. However, this mineralogical transformation has never been imaged nor explained mechanistically, and its effect on the uptake of nickel has never been quantified at the molecular-level. We have characterized these reactions at the macroscopic, microscopic, nanoscopic and atomic scales in a marine manganese concretion by combining transmission electron microscopy, electron and X-ray microprobe analysis, powder and micro X-ray diffraction, and Mn and Ni K-edge EXAFS spectroscopy. The concretion was collected during the Ticoflux II expedition near the Nicoya Peninsula, Costa Rica, and is representative of Mn deposits in hemipelagic sediments. It consists of 5 to 25 μm aggregates, shaped like sea-urchins, with a core of 7Å-vernadite (1.0 wt% Ni), a rim of 10Å-vernadite (3.8 wt% Ni), and an outermost region of todorokite fibers (1.9 wt% Ni) that extend outwards. The crystallites of 7Å-vernadite are single- to bi-layered, with hexagonal layer symmetry (a = b = 2.83 Å), and an average structural formula of Mg0.1612+Ca0.0102+K0.016+[Mn0.9024+Vac0.083Ni0.0152+]O2·nH2O. The crystallites of 10Å-vernadite contain 10 to 20 layers semi-coherently stacked in the ab plane and uniformly separated in the [0 0 1] direction by ∼9 Å due to the intercalation of hydrated Mg2+ cations. The average structural formula of 10Å-vernadite is Mg0.1872+Ca0.0162+K0.013+[Mn0.8644+Vac0.074Ni0.0622+]O2·nH2O if the layers contain vacancy sites, or alternately Mg0.2022+Ca0.0182+K0.014+[Mn0.6134+Mn0.3203+Ni0.0672+]O2·nH2O, if they contain Mn3+. The average formula of todorokite is Mg0.1782+Ca0.0132+K0.019+[Mn0.6124+Mn0.3563+Ni0.0322+]O2·nH2O.A genetic model is proposed based on combining these new data with previously published results. The thermodynamically unstable 7Å-vernadite transforms via dissolution-recrystallization to semi-ordered Mg-rich 10Å-vernadite. Nickel is released from dissolved biogenic silica or reduced organic matter, and taken up mainly in the Mn layer of 10Å-vernadite. Interlayer magnesium serves as a template to the further topotactic transformation of 10Å-vernadite to todorokite. The dimension of the todorokite tunnels in the [0 0 1] direction is uniform and determined by the size of the hydrated Mg2+ ion (8.6 Å). The tunnel dimension in the [1 0 0] direction depends on the density of Mg2+ in the interlayer and the superstructure of the phyllomanganate layer. If the parent phyllomanganate contains high amounts of Mg2+ (i.e., high layer charge), or Mn3+ and Mn4+ cations ordered following the Mn3+–Mn4+–Mn4+ sequence as in synthetic triclinic birnessite, then the tunnel dimension is ideally 3 × 3 octahedral chain widths in both crystallographic directions. Otherwise, the tunnel dimension is incoherent in the [1 0 0] direction (i.e., T(3,n) tunnel structure), as has been observed in all natural todorokites. Natural todorokite is defective because the precursor natural phyllomanganates either have a layer charge deficit below 0.33e per octahedral site, or rarely are triclinic birnessite. The abundance of Mg in seawater and its key role in converting phyllomanganate to tectomanganate with T(3,n) tunnel structure explain why todorokite is common in marine ferromanganese oxides, and seldom present in terrestrial environments. The topotactic phase transformation described here is the only known route to todorokite crystallization. This implies that all natural todorokites may be authigenic because they are formed in situ from a phyllomanganate precursor.

AUTHIGENIC CEMENTATION OF SCORIACEOUS DEEP‐SEA SEDIMENTS WEST OF THE SOCIETY RIDGE, SOUTH PACIFIC1

SUMMARYHarmotome‐rich scorias and indurated tuffaceous mudstones occur in sediments west of the Society Ridge, South Pacific. Diagenetic alteration of mafic palagonite produces the following authigenic minerals: harmotome, phillipsite, goethite, limonite and montmorillonite. A major mode of induration of pyroclastic‐rich marine sediments is the devitrification of mafic palagonite producing the following diagenetic cementing minerals: phillipsite, harmotome, limonite, and to some extent, manganese and ferromanganese oxides.

Damping of oscillations of the magnetic system of BPV-2 current meters: Artemenko N. P., 1963. (In Russian). Trud[formula omitted] arkt. nauchno-issled. Inst., No. 254: 40–42 (Abstracted in: Soviet-Bloc Res., Geophys., Astron. Space. 94: 95)

Phosphatized bioclastic limestones of Early Tertiary age have been dredged from the crest of a seamount in the equatorial Atlantic near 9°N, 21°W. The samples were recovered from water depths of 700 to 970 m but clearly were deposited in a high-energy reefal environment, thus indicating significant Tertiary subsidence. The vertical movement is beleived to reflect reactivation of an old structural line, the Guinée Fracture Zone, which may have had important effects on the transfer of bottom waters of polar origin between the Sierra Leone and Gambia basins. Examination of foraminiferal limestone coating the shallow water material suggests that deep-water conditions were established on the seamount by Middle Miocene time. All phosphatized samples are covered with a layer of ferromanganese oxides which, from textural and faunal evidence, is Palaeocene or Eocene in age and of shallow water origin.Pervasive phosphatization of the bioclastic limestones appears to have been accomplished before the end of the Eocene while the crest of the seamount was near sea level, because Upper Eocene limestone of shallow water facies is unaffected by such radical diagenesis. Phosphatization probably was associated with vigorous upwelling near the seamount and has been taken to an unusually advanced stage, resulting in a phosphoritesof high economic grade. P2O5 contents are in the range of 37 to 41%. The purity of the phosphorites may be related to the intensity of upwelling during the Early Tertiary, but other factors such as the paucity of terrigenous detritus, frequent reworking of the sedimentary capping of the seamount, and a high primary porosity of the limestones may have been important in their information. The Early Tertiary period of phosphorite deposition on the seamount and in northwest Africa ended before the close of Eocene time in both areas, while shallow water conditions prevailed. It is argued that the cessation of phosphorite formation reflects major changes in the surface circulation of the Atlantic during the Eocene.

The origin of manganese nodules on the ocean floor

Manganese oxide minerals occur on the ocean floor as concretions, crusts, and as fine disseminations in sediments. Nodules studied have palagonitic cores, which, themselves, contain segregations of ferro-manganese oxides. Association of nodules with phillipsite and montmorillonitic clay, regarded as alteration products of palagonite, suggests a genetic relation of nodules to basic submarine volcanism. Acid solutions produced by mingling of sea water and basic magma may leach out and concentrate manganese. Sea water, continually entering the system, may cause neutralization and oxidation resulting in precipitation of manganese oxides. Minor elements concentrated with manganese may also be of volcanic origin.

Petrology of submarine volcanics and sediments in the vicinity of the Mendocino Fracture Zone

Pyroxene-rich basalts, glassy basalts, olivine basalts and paloganite tuff breccias of various sizes were dredged from the top and in the vicinity of the Mendocino Fracture Zone. Some of these rocks have encrustations of ferromanganese oxide minerals. In addition, manganese nodules of different sizes were recovered which contain a nucleus of palagonite tuff.Several sediment cores collected to the north and south of the Mendocino Fracture Zone contain mostly medium yellowish brown clay, commonly known as red clay. Study of the cores revealed two areally restricted bio-lithologic units: (1) Radiolaria-Foraminifera-rich silty clay, and (2) Radiolaria-rich silty clay. The above units grade down into Foraminifera-rich silty clay and silty clay barren of Radiolaria respectively. Red clay is characteristically confined to Radiolaria-rich silty clay, silty clay barren of Radiolaria and contains abundant ferromanganese micronodules. Greater concentrations of ferromanganese micronodules occur below the sediment surface and are associated with palagonite grains. The sediments to the north of the Mendocino Fracture Zone are rich in zircon, rutile? and zeolites.The petrography and petrology of the dredged basalts, manganese nodules and sediments are discussed. It is suggested that the sediments, especially in the Radiolaria-rich clay, are dominantly volcanic in origin and locally derived. It is concluded that manganese nodules and red clay containing manganese micronodules (manganese grains) are genetically associated with palagonite complexes formed by submarine volcanism which was related to the development of the Mendocino Fracture Zone.

Origin of Oceanic Manganese Minerals

A criterion is suggested for discrimination between ferromanganese oxide minerals, deposited after the introduction of manganese and associated elements in sea water solution at submarine vulcanism, and minerals which are slowly formed from dilute solution, largely of continental origin. The simlultaneous injection of thorium into the ocean by submarine vulcanism is indicated, and its differentiation from continental thorium introduced into the ocean by runoff is discussed.