Cenozoic record of continental mineral deposit on Broken and Ninetyeast Ridges, Indian Ocean

The mineral component of pelagic sediments recovered from the Indian Ocean provides both a history of eolian deposition related to climatic changes in southern Africa and a record of terrigenous input related to sediment delivery from the Himalayas. A composite Cenozoic dust flux record from four sites in the central Indian Ocean is used to define the evolution of the Kalahari and Namib desert source regions. The overall record of dust input is one of very low flux for much of the Cenozoic indicating a long history of climate stability and regional hyperaridity. The most significant reduction in dust flux occurred near the Paleocene/Eocene boundary and is interpreted as a shift from semiarid climates during the Paleocene to more arid conditions in the early Eocene. Further aridification is recorded as stepwise reductions in the input of dust material which occur from about 35 to 40 Ma, 27 to 32 Ma, and 13 to 15 Ma and correlate to significant enrichments in benthic foraminifer delta18O values. The mineral flux in sediments from the northern Indian Ocean, site 758, records changes in the terrigenous input apparently related to the erosion of the Himalayas and indicates a rapid late Cenozoic uplift history. Three major pulses of increased terrigeneous sediment flux are inferred from the depositional record. The initial increase began at about 9.5 Ma and continued for roughly 1.0 million years. A second pulse with approximately the same magnitude occurred from about 7.0 to 5.6 Ma. The largest pulse of enhanced terrigenous influx occurred during the Pliocene from about 3.9 to 2.0 Ma when average flux values were severalfold greater than at any other time in the Cenozoic.

(Table 3) Carbon and oxygen isotopic data of carbonates from Core SLR 37-1, HYC 25-1 and an aragonite crust from station DR 35-1

An area of massive barite precipitations was studied at a tectonic horst in 1500 m water depth in the Derugin Basin, Sea of Okhotsk. Seafloor observations and dredge samples showed irregular, block- to column-shaped barite build-ups up to 10 m high which were scattered over the seafloor along an observation track 3.5 km long. High methane concentrations in the water column show that methane expulsion and probably carbonate precipitation is a recently active process. Small fields of chemoautotrophic clams (Calyptogena sp., Acharax sp.) at the seafloor provide additional evidence for active fluid venting. The white to yellow barites show a very porous and often layered internal fabric, and are typically covered by dark-brown Mn-rich sediment; electron microprobe spectroscopy measurements of barite sub-samples show a Ba substitution of up to 10.5 mol% of Sr. Rare idiomorphic pyrite crystals (1%) in the barite fabric imply the presence of H2S. This was confirmed by clusters of living chemoautotrophic tube worms (1 mm in diameter) found in pores and channels within the barite. Microscopic examination showed that micritic aragonite and Mg-calcite aggregates or crusts are common authigenic precipitations within the barite fabric. Equivalent micritic carbonates and barite carbonate cemented worm tubes were recovered from sediment cores taken in the vicinity of the barite build-up area. Negative ?13C values of these carbonates (>?43.5? PDB) indicate methane as major carbon source; ?18O values between 4.04 and 5.88? PDB correspond to formation temperatures, which are certainly below 5°C. One core also contained shells of Calyptogena sp. at different core depths with 14C-ages ranging from 20 680 to >49 080 yr. Pore water analyses revealed that fluids also contain high amounts of Ba; they also show decreasing SO42- concentrations and a parallel increase of H2S with depth. Additionally, S and O isotope data of barite sulfate (?34S: 21.0-38.6? CDT; ?18O: 9.0-17.6? SMOW) strongly point to biological sulfate reduction processes. The isotope ranges of both S and O can be exclusively explained as the result of a mixture of residual sulfate after a biological sulfate reduction and isotopic fractionation with 'normal' seawater sulfate. While massive barite deposits are commonly assumed to be of hydrothermal origin, the assemblage of cheomautotrophic clams, methane-derived carbonates, and non-thermally equilibrated barite sulfate strongly implies that these barites have formed at ambient bottom water temperatures and form the features of a Giant Cold Seep setting that has been active for at least 49 000 yr.

Table 2 Analytical data of the samples by the "Dipole CHIM" at the Yingezhuang gold deposit

CHIM method involves extracting metal ions of electromobile forms in either anodes or cathodes, facilitated by a man-made electric field. This paper presents two newly developed CHIM alternatives that are electrified by a low voltage dipole. The firstly improved technique enables cationic ions to be extracted in a single cathode, whereas the secondly improved technique allows both anionic and cationic species to be extracted simultaneously in an anode and in a cathode. Compared with the traditional CHIM methods, the innovative techniques developed in this paper are characterized by simple instrumentation, low cost and easy operation in field, and in particular enables simultaneous extraction of anionic and cationic species of elements, from which more information can be derived with higher extraction efficiency. Field tests at several well-known mine areas in China confirm the effectiveness and efficiency of the new techniques in exploring for deeply buried ore bodies.

(Table 2, page 1177) Composition of manganese deposit samples from Cuba

Todorokite is a very abundant manganese oxide mineral in many deposits in Cuba and has been noted from other localities. Six new analyses are givenl they lead to the approximate formula (Na, Ca, K, Mn+2)(Mn+4, Mn+2, Mg)6O12.3H2O. Electron diffraction data show the mineral to be orthorhombic, or monoclinic with beta near 90°. The x-ray powder pattern is indexed on a cell with a=0.75A, b=2.849A, c=9.59A, beta=90°. A differential thermal analysis curve is given.