Description and chemical composition of ferromanganese encrustations and deposits in the Atlantic Ocean from R/V Atlantis II cruises 20, 42, 60, 85; R/V Chain cruise 35; R/V Knorr cruise 61 and RRS Shackleton cruise 75/1 stations

Chemical and mineralogical compositions of ferromanganese oxide coatings on rocks dredged from the New England Seamounts, the Sierra Leone Rise and the Mid-Atlantic Ridge near the Equator have been determined in an investigation of regional differences in Atlantic ferromanganese deposits. Most encrustations are clearly of hydrogenous origin, consisting mainly of todorokite and delta MnO2, but several recovered from the equatorial fracture zones may be hydrothermal accumulations. Differences in the chemistry of the water column and in growth rates of the ferromanganese coatings may be important in producing this regional contrast in composition. Fine-scale changes in element abundances within the encrustations indicate that the nature of the substrate has little influence on compositional variations.

Geochemical composition of a representative collection of manganese nodules and slabs collected in the Western Pacific

Chemical analyses were performed on seveteen manganese nodules collected from the Pacific Ocean floor. The results were discussed compared with the previous data on the manganese nodules. Minerals were found to be todorokite, delta-MnO2 and other silicates, montmorillonite, illite, phillipsite and alpha-SiO2. Average composition shows that copper is concentrated on the deep sea nodules more than the shallow ones, and that the todorokite rich nodules contain more copper and nickel than the delta-MnO2 rich ones.

Description and chemical composition of manganese nodules collected in the Pacific Ocean

Chemical and X-ray analyses were performed on the fifteen manganese nodules collected from the Pacific Ocean floor. The results were discussed compared with the previous data on the manganese nodules. Minerals were found to be todorokite, delta-MnO2 and other silicates, montmorillonite, illite, phillipsite and alpha-Si02. Average composition shows that copper is concentrated on the deep sea nodules more than the shallow ones, and that the todorokite rich nodules contain more copper and nickel than the delta-MnO2 rich ones. The analyses of fresh water iron-manganese precipitates by bacterial activity suggest that biological process is one of the important factors on the genesis of the sedimentary iron-manganese deposits, in¬cluding the manganese nodule.

Geochemistry of a manganese nodule from the WALDA (R/V Jean Charcot) expedition

During the 1971 WALDA expedition of the R/V Jean Charcot in the Equatorial and South Atlantic, manganese nodules were recovered at Station 24 - DS 17 at the base of the continental platform off the coast of Angola. They were analysed at the Laboratoire de Géochimie des Eaux, Université Paris VII Denis Diderot.

Chemical composition and description of a ferromanganese crust, sample 89D, obtained during R/V Capricorne cruise ARCANTE 1

A manganese oxide encrustation (2.5 kg) was dredged, in an island arc setting, downslope of Bertrand bank, a seamount culminating at 70-m depth and located NNE of Grande-Terre, Guadeloupe, and SE of Antigua, West Indies. A thorough texturai analysis indicated a rhythmic precipitation and growth polarity as well as mineralogical ( 10 A tektomanganate) and geochemical (low concentrations of Ni, Cu, Co, Zn, Pb and REE) criteria, point to a submarine hydrothermal origin for most of the sample. The crust was coated with a fine ferromanganese oxide cortex deposited iii a "normal" oceanic environment; it also included micritic fillings, a main pyroclastic zone near the top of the crust, and a Mg-Al sulphate deposit. Planktonic foraminifera coeval with the precipitation of the manganese oxide indicate an age of ca. 3 m. y. (upper Pliocene); i.e., more than 20 m. y. after the cessation of the volcanic activity of the Lesser Antilles outer arc that was responsible for the buildup of the Bertrand seamount. Furthermore, the genesis of the crust is not linked to the activity of the contemporaneous inner arc (Miocene to Present), particularly of its nearmost segment (Basse Terre, Guadeloupe-Montserrat) located about 50 km to the West. The authors suggest that the manganese oxide is the result of convective circulation of sea water through a faulted system occurring in an area of intense seismic activity. The remobilization of chemical elements (Mn, S, etc.) within the seamount volcanic core bas probably affected a substratum that was still hydrothermally altered during the previous volcanic activity of the outer arc. The authors insist on the interest in using texturai analysis for Fe/Mn oxide investigations.

Description and chemical composition of manganese nodules collected during Hakuho Maru Cruise KH-72-2, Oct-Dec, 1972 in the Southwest Japan Arc and Ryukyu Arc areas

The cores and dredges described in this report were taken on the KH-72-2 Expedition in October-December, 1972 by the Ocean Research Institute, University of Tokyo from the R/V Hakuho Maru. A total of 21 cores and dredge sites have been recovered.

Annotated record and chemical composition of Mn deposits from R/V Mahi Cruise Abyssal Hills 69 stations

A University of Hawaii oceanographic cruise, Abyssal Hills 69, with the R/V Mahi, was carried out to study the association of manganese nodules with an abyssal hill. Manganese nodules from three dredge hauls on an abyssal hill located at 36°W and 157°W exhibited differences in morphology and composition between stations only three miles apart. The morphology of the nodules suggests that nodules from a single site have similar morphologies because they began growth at the same time, probably because of a volcanic event. Differences in morphology between stations indicate a local supply of elements. Atomic absorption analysis for manganese, iron, cobalt, nickel, and copper revealed that nodules nearest to a probable fault line and source of volcanism have a, lower manganese to iron ratio than nodules farther removed. This finding supports the theory that volcanism contributes to the formation of some nodules. Additional evidence showing association with volcanism consists of volcanic nuclei in nodules, crusts formed on layers of volcanic ash, and basalt encrusted to various degrees. The variation in cobalt, nickel, and copper contents Gt the nodules from a single dredge is two-to threefold, but iron content is more uniiorm. Four of the six cores from the area increased in manganese concentration with depth, suggesting that diffusion is concentrating manganese in the upper zone of the sediments or in nodules. The author concludes that volcanism is contributing to the formation of nodules by supplying nuclei and transition elements, but is not necessary for the formation of manganese nodules.

Description, geochemistry and growth rate of buried nodules from the Central Indian Basin

Buried nodules from siliceous sediments in the central Indian Basin are morphologically variable and mineralogically consist of d-MnO2 and incipient todorokite. Compositionally they are weakly diagenetic. The sediment coarse fractions (>63 µm) at different depths show variable abundances of micronodules, volcanic glass shards and biodebris. Dissolution of biodebris increases and abundance of micronodules decreases with increasing depth. Enrichment in Mn, Fe, Cu, Ni, Co, together with a decrease in organic carbon in the sediment column, may result from diagenetic metal remobilization. Diagenetically remobilized trace metals might have been utilized for the growth of micronodules over the buried nodules.

Chemical composition of manganese micronodules from expedition VA-05/1 in the Pacific Ocean

A radioisotope energy-dispersive X-ray (EDX) system has been used on board the German research vessel "Valdivia" during an exploration expedition in the northern equatorial Pacific in 1973. The instrumentation used consisted of an X-ray detection system incorporating a 30 mm2 effective-area Si (Li) detector with a measured energy resolution of 195 eV for Mn K alpha X-rays, standard nuclear electronics, a 1024-channel analyser and a data read-out unit. The X-ray spectra in the manganese-nodule samples were excited by a 30-mCi 238Pu source. The six elements Mn, Fe, Co, Ni, Cu and Zn were analysed on board. Precision values for the analyses were less than 3% for Mn, Fe, Ni, Cu and Zn and about 5% for Co. A total amount of 350 analyses was carried out during a one-month cruise. Average contents of 190 analysed whole manganese-nodule samples from all the sampling sites of the covered area were 23.3% Mn, 6.7% Fe, 0.23% Co, 1.16% Ni, 0.94% Cu and 0.10% Zn. The average content of the base metals expressed as the sum of the Co, Ni, Cu and Zn contents was 2.48%. A linear relationship between Mn and Ni in all analysed samples, including whole manganese-nodule samples, zones of manganese nodules and manganese crusts, was observed. The Mn/Ni ratio calculated by regression analysis was 23.0. Zonal variations of the chemical contents of the six elements in the manganese nodules were found. A size classification of the manganese nodules has been suggested. Geochemical correlations of Cu and Ni versus Mn/Fe in the investigated samples are given.

Annotated record and chemical analysis of manganese nodules from R/V Moana Wave Cruise Mn-74-01 and Mn-74-02 stations

Cruise Mn-74-02 of the R/V MOANA WAVE was the second part of the field work of the NSF/IDOE Inter-University Ferromanganese Research Program in 1974, and we gratefully acknowledge the support of the office for the International Decade of Ocean Exploration and the Office of Oceanographic Facilities and Support. This program was designed to investigate the origin, growth, and distribution of copper/nickel-rich manganese nodules in the Pacific Ocean. The field effort was designed to satisfy sample requirements of the fifteen principal investigators, while increasing general knowledge of the copper/nickel-rich nodule deposits of the equatorial Pacific. This report is the second of a series of cruise reports designed to assist sample requests for documented nodules, sediment, and water samples so that laboratory results can be realistically compared and related to the environment of nodule growth. Nodule samples and bathymetric and navigational data are archived at the Hawaii Institute of Geophysics, University of Hawaii. Bulk chemical analyses of nodules and reduction of survey data were carried out at Hawaii. Sediment cores were stored at the University of Hawaii and at Scripps Institution of Oceanography. The SIO analytical facility provided stratigraphic data on sediment chemistry.

Zircon U-Pb and Hf-O analysis of porphyries from the Duolong porphyry Cu-Au deposit in the Bangongco copper belt, central Tibet

The Duolong porphyry Cu-Au deposit (5.4 Mt at 0.72% Cu, 41 t at 0.23 g/t Au), which is related to the granodiorite porphyry and the quartz-diorite porphyry from the Bangongco copper belt in central Tibet, formed in a continental arc setting. Here, we present the zircon U-Pb ages, geochemical whole-rock, Sr-Nd whole-rock and zircon in-situ Hf-O isotopic data for the Duolong porphyries. Secondary ion mass spectrometry (SIMS) zircon U-Pb analyses for six samples yielded consistent ages of ~118 Ma, indicating a Cretaceous formation age. The Duolong porphyries (SiO2 of 58.81-68.81 wt.%, K2O of 2.90-5.17 wt.%) belong to the high-K calc-alkaline series. They show light rare earth element (LREE)-enriched distribution patterns with (La/Yb)N = 6.1-11.7, enrichment in large ion lithophile elements (e.g., Cs, Rb, and Ba) and depletion of high field strength elements (e.g., Nb), with negative Ti anomalies. All zircons from the Duolong porphyries share relatively similar Hf-O isotopic compositions (d18O=5.88-7.27 per mil; eHf(t)=3.6-7.3), indicating that they crystallized from a series of cogenetic melts with various degrees of fractional crystallization. This, along with the general absence of older inherited zircons, rules out significant crustal contamination during zircon growth. The zircons are mostly enriched in d18O relative to mantle values, indicating the involvement of an 18O-enriched crustal source in the generation of the Duolong porphyries. Together with the presence of syn-mineralization basaltic andesite, the mixing between silicic melts derived from the lower crust and evolved H2O-rich mafic melts derived from the metsomatizied mantle wedge, followed by subsequent fractional crystallization (FC) and minor crustal contamination in the shallow crust, could well explain the petrogenesis of the Duolong porphyries. Significantly, the hybrid melts possibly inherited the arc magma characteristics of abundant F, Cl, Cu, and Au elements and high oxidation state, which contributed to the formation of the Duolong porphyry Cu-Au deposit.