bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mineralogy and geochemistry of Archaean greenstone belt-hosted Mn formations and deposits of the Dharwar Craton: Redox potential of proto-oceans
Authors: Manikyamba C. , Naqvi S.M. 
Published: September 2007

AbstractLate Archaean greenstone belts of the Dharwar supergroup are uniquely characterized by a marker horizon that consists of Fe + Mn formations, carbonates (± stromatolites), and phyllites (± organic matter). Microfossils are found in cherts associated with stromatolites and banded Fe-Mn carbonate. Manganese-bearing arenites-argillites-carbonates have a varied mineralogy that is reflected by variations in chemical composition. Trace elements characteristic of felsic and volcanic rocks such as Zr, Hf, Rb, Sr, U, Th, Ni, Cr, Co, V, and Sc are low or high depending on the amount and type of clastic debris deposited with the chemical precipitates. REE also are influenced by the clastic fluvial and hydrothermal fluxes. Banded Fe + Mn carbonate-chert rocks (BMF) contain lower amounts of REE compared to samples containing ripidolite, which have higher Al2O3, ΣREE, Zr and Hf contents. Both positive and negative Eu, La and Ce anomalies are observed which reflect variable mixing of hydrothermal solutions with ambient ocean water and divergent clastic material. The data indicate that FeO, MnO and SiO2were added to the Archaean proto-ocean by hydrothermal solutes produced along a spreading ridge axis. The redox potential of these proto-oceans was very low near the ridge axis, but increased towards the shelf, due to higher organic productivity and photosynthesis reflected by the presence of stromatolites, organic matter, and microbiota. Precipitation of stable Mn oxides at the margin of the greenstone belts is probably the consequence of the high redox potential.
Manganese ores of the Ghoriajhor-Monmunda area, Sundergarh District, Orissa, India: geochemical evidence for a mixed Mn source
Authors: Nicholson Keith , Nayak V. K. , Nanda J. K. 
Published: September 2007

Abstract

The Proterozoic sedimentary manganese ores of the Gangpur Series, Orissa, India are of gonditic type and are variable in size, depth and grade of ore. The host sediments were deposited in a shallow shelf environment, as reflected in the variable clastic input into the sequence. Braunite and hollandite are the principal ore minerals, with bixbyite, rare jacobsite and rare vredenburgite. Manganese minerals in the gondites are spessartine and rhodite, together with quartz and aluminosilicates. Supergene weathering and enrichment of the ore horizon and gondite produced secondary ores composed of cryptomelane and pyrolusite. The geochemistry of the deposits shows Mn/Fe≈4, low trace element concentrations and arsenic enrichments that exceed 3000 mg kg
−1
. These are interpreted as indicating a mixed hydrogenetic-hydrothermal source for the manganese oxides of the original precurser (pre-metamorphism) sediments. Regional metamorphism to amphibolite grade transformed this variable oxide-clastic sequence into manganese ores, sharply interbedded with gondites.
Iron and manganese oxide mineralization in the Pacific
Authors: Hein James R. , Koschinsky Andrea , Halbach Peter , Manheim Frank T. , Bau Michael , Kang Jung-Keuk , Lubick Naomi 
Published: September 2007

Abstract
Iron, manganese, and iron-manganese deposits occur in nearly all geomorphologic and tectonic environments in the ocean basins and form by one or more of four processes: (1) hydrogenetic precipitation from cold ambient seawater, (2) precipitation from hydrothermal fluids, (3) precipitation from sediment pore waters that have been modified from bottom water compositions by diagenetic reactions in the sediment column and (4) replacement of rocks and sediment. Iron and manganese deposits occur in five forms: nodules, crusts, cements, mounds and sediment-hosted stratabound layers. Seafloor oxides show a wide range of compositions from nearly pure iron to nearly pure manganese end members. Fe/Mn ratios vary from about 24 000 (up to 58% elemental Fe) for hydrothermal seamount ironstones to about 0.001 (up to 52% Mn) for hydrothermal stratabound manganese oxides from active volcanic arcs. Hydrogenetic Fe-Mn crusts that occur on most seamounts in the ocean basins have a mean Fe/Mn ratio of 0.7 for open-ocean seamount crusts and 1.2 for continental margin seamount crusts. Fe-Mn nodules of potential economic interest from the Clarion-Clipperton Zone have a mean Fe/Mn ratio of 0.3, whereas the mean ratio for nodules from elsewhere in the Pacific is about 0.7. Crusts are enriched in Co, Ni and Pt and nodules in Cu and Ni, and both have significant concentrations of Pb, Zn, Ba, Mo, V and other elements. In contrast, hydrothermal deposits commonly contain only minor trace metal contents, although there are many exceptions, for example, with Ni contents up to 0.66%, Cr to 1.2%, and Zn to 1.4%. Chondrite-normalized REE patterns generally show a positive Ce anomaly and abundant ΣREEs for hydrogenetic and mixed hydrogenetic-diagenetic deposits, whereas the Ce anomaly is negative for hydrothermal deposits and ΣREE contents are low. However, the Ce anomaly in crusts may vary from strongly positive in East Pacific crusts to slightly negative in West Pacific crusts, which may reflect the redox conditions of seawater. The concentration of elements in hydrogenetic Fe-Mn crusts depends on a wide variety of water column and crust surface characteristics, whereas concentration of elements in hydrothermal oxide deposits depends of the intensity of leaching, rock types leached, and precipitation of sulphides at depth in the hydrothermal system.
Some controls on the geochemical variability of manganese nodules with particular reference to the tropical South Pacific
Authors: Cronan D. S. 
Published: September 2007

Abstract
Superimposed on traditional controls on manganese nodule compositional variability, such as metal source and nodule mineralogy, are additional controls related to biological productivity, water depth, the depth of the calcite compensation depth (CCD) and the nature of the associated sediments. Fluxes of Mn, Ni, and Cu to the nodules increase in equatorial regions of high biological productivity but high values of these metals in south equatorial Pacific nodules appear to occur only within about 200 m of the CCD. This is thought to result from the concentration of labile organic matter there, the decay of which fuels the diagenetic reactions leading to Mn, Ni, and Cu enrichment in the nodules. However, this process appears to be at its most intense on the flanks of the South Pacific equatorial high productivity zone. Under the most highly productive waters, Mn, Ni, and Cu rich nodules do not occur at any depth nor are nodules abundant there. This is thought to be due to the presence of biogenic silica, the concentration of which is not depth dependent, as the main diluent of the labile organic material at depths near and below the CCD under the most highly productive waters.
Geochemical constraints on the hydrothermal origin of ferromanganese encrustations from the Rodriguez Triple Junction, Indian Ocean
Authors: Nagender Nath B. , Plüger W. L. , Roelandts I. 
Published: September 2007

Abstract
Ferromanganese crusts recovered from a spreading ridge north of the Rodriguez Triple Junction in the Indian Ocean were studied for their mineral and geochemical compositions. The crusts are highly porous, have maximum thickness of 2 cm, and occur on basaltic substrates. The composition of the crusts resembles that of hydrothermal ferromanganese crusts from other oceanic spreading centres. Compared to hydrogenous ferromanganese crusts and nodules, the hydrothermal crusts exhibit very low Mn/Fe ratios, lower transitional metal contents, low ΣREE contents and negaive Ce anomalies, which are all characteristics of hydrothermal origin. Geochemical discriminant plots of crust data show similarities to data for metalliferous sediment and hydrothermal deposits recovered from other areas. Shale-normalized REE patterns indicate that the hydrothermal contribution to the crusts is between 60 and 92%. Crusts have rarely been reported to occur at Indian Ocean spreading centers, and those described here are consistent with the earlier findings on water column temperature and chemical anomalies indicative of hydrothermal activity in the region.

Some aspects of the crusts, such as
δ
-MnO
2
mineralogy and middle REE enrichment, are not typical of hydrothermal Fe-Mn oxides. Microprobe studies show that some layers within the crusts have Mn/Fe ratios close to unity, suggesting a significant input from normal seawater.

Growth rates, estimated from an algorithm based on Mn, Fe and Co contents, are orders of magnitude faster than rates determined for hydrogenous Fe-Mn oxides. The outer layers and some internal layers of the crust had relatively faster growth rates indicating that the crusts precipitated from distinct hydrothermal episodes.
Deception Island (Antarctica): a new target for exploration of Fe-Mn mineralization?
Authors: Rey J. , Somoza L. , Martínez-Frías J. , Benito R. , Martín-Alfageme S. 
Published: September 2007

Abstract
This work correlates the submarine volcanic and hydrothermal structures detected through seismic profiles on Deception Island (DI) with geochemical distribution patterns of the volcanic sediments which make up the seafloor of the island. A comparison of subaerial and submarine volcanic events is also carried out and three groups of submerged seismo-depositional units are defined. A model is proposed according to which the highest contents of Fe-Mn-Zn are related to volcanic cones, mounds and vents formed in relation with extensional normal low-angle faults. The As-Ba anomalies, active fumaroles and hot-springs are associated to later tensional faults.
Terrestrial hot-spring Co-rich Mn mineralization in the Pliocene-Quaternary Calatrava Region (central Spain)
Authors: Crespo A. , Lunar R. 
Published: September 2007

Abstract
Central Spain hosts a series of high-Co (up to 1.7% Co) Mn mineralizations displaying a variety of morphologies: spring aprons and feeders, pisolitic beds, wad beds and tufa-like replacements of plants and plant debris. The Mn mineralogy consist of cryptomelane, lithiophorite, birnessite and todorokite. The spring apron deposits formed in close proximity to Pliocene volcanic rocks (alkaline basaltic lava flows and pyroclastics) belonging to the so-called Calatrava Volcanic Field. The spring aprons are found along or near to normal faults bounding small basins and topographic highs. Mn tufa-like deposits are found near to the spring sources, while both pisolitic and wad beds are clearly distal facies occuring well within the Pliocene basins. The two latter are interbedded with clastic lacustrine and fluvial sediments. Collectively, these deposits contain a complex suite of Mn-(Co) mineralization ranging from proximal, hot-spring-type Mn facies, grading into more distant sedimentary, stratabound mineralization. Volcanism, basin formation and Mn deposition took place within a failed rift environment which triggered hydrothermal activity and Mn-(Co) deposition as proximal (near to the volcanic axes) and distal (of sedimentary affinities, within the basins) facies.
Formation of solid phases of manganese in oxygenated aquatic environments
Authors: Gramm-Osipov Lev M. 
Published: September 2007

Abstract

The article describes a thermodynamic analysis of the formation process of solid manganese phases in oxygenated aquatic environment. The first step of this process is the formation of the compound MnOOH. In the second step the latter in a disproportionation reaction is transformed into a complicated oxohydroxide [(MnO
2
)

2
n
−3

(MnOOH)

4−2
n

] with O/Mn ranging from 1.700 to 1.999. As an example of using results of thermodynamic analyses the behaviour Mn system in the ocean is described. It is shown that Mn
3
O
4
and MnOOH respectively control concentrations and distribution of the manganese in the upper (150–600 m) and lower oceanic water column.
P-T-X relationships during metamorphism of manganese-rich sediments: Current status and future studies
Authors: Dasgupta Somnath 
Published: September 2007

Abstract
This paper aims at reviewing the mineralogy, mineral chemistry and petrology of metamorphosed manganese-rich sediments from occurrences described since 1988. It presents a summary of new experimental data and evaluates the merits and shortcomings of the petrogenetic grids so far proposed for Mn-rich metamorphic rocks. The paper focuses on the inadequacies of experimental data on Mn-rich systems and discusses the problems associated with further quantification of the petrogenetic grids. Finally, a few suggestions for future research on Mn-rich systems are put forward.
Zincian rancieite from the Kato Nevrokopi manganese deposits, Macedonia, northern Greece
Authors: Nimfopoulos M. K. , Michailidis K. M. , Christofides G. 
Published: September 2007

Abstract

At the 25th km main Mn-mine of Kato Nevrokopi, Macedonia, northern Greece, rancieite forms flaky to laminated aggregates encrusting vugs, and replacing pyrolusite and todorokite in massive deposits of the Falakron marbles. It has an unusually high ZnO (1.53–3.07 wt%) content and therefore it was named ‘zincian rancieite’. The average (18 spots) chemical composition of rancieite by EPMA is (wt%): MnO
2
62.01, CaO 6.83, ZnO 2.54, Al
2
O
3
1.18, MgO 0.63 plus minor oxides (Fe
2
O
3
, K
2
O & SiO
2
), total of 73.98. Assuming H
2
O-content as 26.02 (100 − 73.98) wt%, these data reflect the following empirical formula: (Ca
0.67
Zn
0.17
Al
0.12
Mg
0.09
Fe
0.02
3
K
0.02
Si
0.02
)Mn
3.90
4
O
9
7.9H
2
O. A high H
2
O-content is also evidenced by the XRD pattern, which together with optical microscopy and SEM, indicates a poor structural order. Rancieite formation at Kato Nevrokopi belongs to the last stage of mineral genesis, which took place at ambient P, low T (around 25°C) by percolating oxygen bearing, Ca-Zn rich, meteoric water through the host marble.
A non-contacting resistivity imaging method for characterizing whole round core while in its liner
Authors: Jackson P. D. , Gunn D. G. , Flint R. C. , Beamish D. , Meldrum P. I. , Lovell M. A. , Harvey P. K. , Peyton A. 
Published: September 2007

Abstract
Recent laboratory experimentation has shown that non-contacting whole-core resistivity imaging, with azimuthal discrimination, is feasible. It has shown the need for very sensitive coil pairs in order to provide resistivity measurements at the desired resolution. Independent high-resolution ‘galvanic’ resistivity estimations show the ‘non-contacting’ measurements to be directly proportional to the resistivity of core samples. The response of the technique to a variety of synthetic ‘structures’ is presented. A whole-core image of a dipping layer is used to demonstrate the three dimensional response of the technique and to show that the resolution of the measurements is of the order of 10 mm.
Experiments are described which show that the technique is capable of investigating to different depths within the whole round core. The results agree with theoretical predictions and indicate that the technique has the potential to assess invasion near the surface of the core.
The technique is intrinsically safe and has the potential to be packaged in a form that would be suitable for whole-core imaging at the well site, or laboratory, without taking core from their liners. Thus it is possible to acquire information crucial for core selection, in addition to acquiring resistivity data at a resolution not too far removed from that of the downhole imaging tools.
Network analogues of wettability at the pore scale
Authors: McDougall S. R. , Dixit A. B. , Sorbie K. S. 
Published: September 2007

Abstract
This paper examines the macroscopic consequences of wettability variations at the pore scale. Important theoretical issues relating to distributed contact angles are examined and a process simulator capable of simulating the full flooding cycle characteristic of laboratory wettability tests is described. Simulations predict that final waterflood recoveries from weakly water wet (or even weakly oil wet) systems can often exceed those from strongly water-wet systems (even though initial imbibition rates may lead to the opposite conclusion). The underlying pore level physics has been explored by defining a capillarity surface, which incorporates the combined effects of both contact angle and pore dimension during the imbibition process. Finally, a regime-based framework has been developed which may go some way towards reconciling apparently contradictory wettability experiments.
Pore-structure visualization in microdioritic enclaves
Authors: Pugliese S. , Petford N. 
Published: September 2007

Abstract

We present a simple methodology for estimating key petrophysical characteristics of partially molten (igneous) porous media using microgranular (microdiritic) enclaves from the Ross of Mull granite, Scotland, as examples. A number of enclaves have been infiltrated by granitic melt while still partially molten, with the infiltration (porosity) network now preserved as frozen-in granitic melt. By serial sectioning through individual enclaves, we show that the preserved infiltration channel network is interconnected in three dimensions. Using image analysis techniques, we have estirnated the porosity (
φ
) of individual enclave sections and obtained the variation in porosity with depth. Simple representation of the pore-channel network on a branch and node chart allows useful petrophysical characteristics including the connectivity, genus and tortuosity of the network to be estimated. Computer-enhanced reconstructions of the pore network in three dimensions are shown that provide a powerful way of visualizing complex geometries in porous media.
Pore-size data in petrophysics: a perspective on the measurement of pore geometry
Authors: Basan Paul B. , Lowden Ben D. , Whattler Peter R. , Attard John J. 
Published: September 2007

Abstract
Mercury injection capillary pressure (MICP), backscattered electron images (BSEI) and nuclear magnetic resonance (NMR) provide pore-geometry parameters useful for understanding variations in rock properties. MICP pore size is an area-equivalent diameter of the throats connecting the pore system. The MICP distribution contains a point (the turning point) that reveals where mercury first encounters the permeable network. This point identifies both critical pore size and connected porosity. BSEI measure pore area and diameter. Both parameters are unrelated to any specific morphological element. NMR pore size is a derivative of the pore-surface:volume ratio. Like BSEI, NMR pore size is unrelated to morphological elements. Like MICP, NMR provides a pore-size distribution that represents the entire sample volume.
All three techniques provide a data distribution suitable for cross-correlation. Matching distributions determines the character of the permeable pore system. NMR and MICP distributions compare through the entire time and pressure spectra, matching best in the central part of the distributions. The match suggests pore-throats merge with the pore channels in the permeable part of the system. BSEI distributions match only with the low-pressure, slow-time parts of the other distributions. However, image porosity has a stronger correlation with permeability than any of the other parameters, suggesting that the BSEI distribution is near the turning point.
Measurements of the relationship between Sonic wave velocities and tensile strength in Anisotropic rock
Authors: Apuani T. , King M. S. , Butenuth C. , De Freitas M. H. 
Published: September 2007

Abstract
This work investigates relationships between the mechanical behaviour under tension of a building stone widely used in Italy and the compressional and shear-wave velocities within the stone. The stone investigated is the Antigorio orthogneiss, which is characterized by an orthotropic petrographical anisotropy.

This rock was sampled in three orthogonal directions two of which lie in the plane of schistosity, the first parallel and the second perpendicular to the elongated structures in that plane, with the third sampling direction oriented normal to the plane of schistosity. In these directions rock cylinders were cored co-axially to provide hollow cylinders of 14cm outer diameter together with their inner solid cores of approximatly 5 cm diameter. These inner cores were used for ultrasonic wave velocity measurements (
V
p
and polarized
V
5
) oriented at 90° to the core axis, and conducted at intervals around their circumference so as to obtain wave velocities through the gneiss in different orientations. The hollow cylinders were cut into hoops and tested by the hoop tension test to provide measurements of tensile strength in the same directions as those in which wave velocities had been measured. Thus nondestructive velocity tests and destructive tensile tests were conducted in the same orientations. The paper describes the results so obtained using dry samples.
Prediction of petrophysical properties from seismic quality factor measurements
Authors: McCann C. , Sothcott J. , Assefa S. B. 
Published: September 2007

Abstract

Over the past eight years the Geophysics Group of the Postgraduate Research Institute for Sedimentology has developed equipment for accurately measuring the seismic properties of centimetre-size samples of sedimentary rocks at ultrasonic frequencies (0.5–1 MHz) and under simulated
in situ
conditions. Relationships between the ultrasonic properties and the mineralogical/petrophysical properties of a wide range of rock types have been investigated. The results indicate that the attenuation of seismic waves at high frequencies is dominated by the ‘imperfections’ in the rock, defined in a broad way. For instance, at low pressures the attenuation depends on the volume concentration of microcracks; at high confining pressures the attenuation depends on the distribution of porosity between the macro inter-particle porosity and the micro intra-clay or intra-particle porosity. For some rocks, analysis of these relationships leads to the ability to predict petrophysical properties, including the permeability, from the seismic data. Techniques for up-scaling the relationships to the wavelengths of field seismic surveys are discussed.
Estimation of aspect-ratio changes with pressure from seismic velocities
Authors: Sun Y. F. , Goldberg D. 
Published: September 2007

Abstract

Seismic velocities are modeled as a function of rock mineralogy, porosity, fracture density, aspect ratio and fluid saturation. We compare the model with seismic velocity measurements made by Nur and Simmons in 1969 and predict quantitative aspect ratio changes as a function of differential pressure. The velocity change with pressure is initially caused by the deformation and collapse of pre-existing cracks and pores followed by the initiation of new cracks. For low porosity Casco granite (0.25% pore and 0.45% crack), we estimate that crack aspect ratio increases from 5.9
e
−3
to 0.01, then decreases to 5.0
e
−5
for a pressure increase from 0 to 300 MPa. Most pre-existing cracks and pores close at differential pressures < 40MPa, a lower pressure than predicted with standard approximations. These model results can be used to determine
in situ
porosity, fluid content, and pore pressure from seismic data by inversion and for reservoir monitoring from drilling and core data.