bluuebunny/crossref_metadata_2025 huggingface dataset:
Deformation and submarine landsliding caused by seamount subduction beneath the Costa Rica continental margin — new insights from high-resolution sidescan sonar data
Authors: Hühnerbach V. , Masson D. G. , Bohrmann G. , Bull J. M. , Weinrebe W.
Published: April 2008

Subduction of seamounts at destructive sedimented plate margins results in spectacular deformation of the overriding plate. High-resolution sidescan sonar imagery from the Costa Rica margin show the tracks of five individual seamounts, of which four are described in this paper. These were subducted at various times during the last 690 ka and each represents a different stage in the subduction process. Each subducted seamount leaves a parallel-sided depression in its wake, that can be traced for up to 55 km landward of the deformation front. This wake is created by deformation and uplift of the continental slope as the seamount passes beneath it, followed by collapse due to landsliding as support for the uplifted area is withdrawn. Areas of uplift above seamounts are characterized by complex normal and strike-slip fault patterns. Collapse of the uplift along the trailing edge of the seamount creates a zone of slope failure (landsliding) that migrates upslope (or landward) with the seamount. Landslide processes are dominated by debris flow, but also include sliding of coherent blocks and debris avalanche. Erosion occurs by repeated landslides, which produce a series of overlapping debris flows. Downslope sediment transport typically extends over limited distances, resulting in partial ‘backfilling’ of the scar as its headwall moves up slope. The amount of margin material disrupted by seamount subduction is four to five times the volume of the subducting seamount, of which about three quarters seems to be recycled downslope, backfilling the scar, and nearly one quarter is subducted with the seamount.
Seismic and aseismic weakening effects in transtension: field and microstructural observations on the mechanics and architecture of a large fault zone in SE Tibet
Authors: Edwards M. A. , Ratschbacher L.
Published: April 2008

Fault-zone surveying and microstructural analyses focus on a transtensionally strained section of a >100 km-long, 5–15 km-wide, active, sinistral strike-slip W-E fault — the Damxung-Jiali Shear Zone (DJSZ). Deformation fabric superposition, palaeostress and neotectonic measurements reveal a progressive dominance of the transtension coaxial component. Vertical flattening and broadening of the DJSZ results in a 10–20 km-wide pull-apart depression with reciprocal emergence of flanking highlands that expose abandoned fault-zone domains that are hundreds of metres by tens of km in size. Polylithological fault rocks preserve a suite of frictional and viscous deformation to
c.
350 °C. Amongst the fault strands, intensity and distribution of grain size reduction from comminution, widespread solution transfer, intragranular plasticity and recrystallization is heterogeneous. A regular pattern of pseudotachylite-coated surfaces short-cutting strong volcanic mylonite domains between weak creeping calcite domains indicates seismic with aseismic strain, and is interpreted as velocity-weakening evidence. Re-brecciation of solution-transfer accommodation-assisted S-C-cataclasite domains document switches from frictional to viscous strain and back again. The co-location of brittle and plastic constituent behaviour for varied fault lithologies plus our interpretations on deformation temperatures suggests major overlap for the frictional and viscous depth ranges. This indicates a very broad and strongly velocity- and fluid-dependent ‘brittle-ductile’ transition.
Electrical conductivity images of active and fossil fault zones
Authors: Ritter O. , Hoffmann-Rothe A. , Bedrosian P. A. , Weckmann U. , Haak V.
Published: April 2008

We compare recent magnetotelluric investigations of four large fault systems: (i) the actively deforming, ocean-continent interplate San Andreas Fault (SAF); (ii) the actively deforming, continent-continent interplate Dead Sea Transform (DST); (iii) the currently inactive, trench-linked intraplate West Fault (WF) in northern Chile; and (iv) the Waterberg Fault/Omaruru Lineament (WF/OL) in Namibia, a fossilized intraplate shear zone formed during early Proterozoic continental collision. These fault zones show both similarities and marked differences in their electrical subsurface structure. The central segment of the SAF is characterized by a zone of high conductivity extending to a depth of several kilometres and attributed to fluids within a highly fractured damage zone. The WF exhibits a less pronounced but similar fault-zone conductor (FZC) that can be explained by meteoric waters entering the fault zone. The DST appears different as it shows a distinct lack of a FZC and seems to act primarily as an impermeable barrier to cross-fault fluid transport. Differences in the electrical structure of these faults within the upper crust may be linked to the degree of deformation localization within the fault zone. At the DST, with no observable fault-zone conductor, strain may have been localized for a considerable time span along a narrow, metre-scale damage zone with a sustained strength difference between the shear plane and the surrounding host rock. In the case of the SAF, a positive correlation of conductance and fault activity is observed, with more active fault segments associated with wider, deeper and more conductive fault-zone anomalies. Fault-zone conductors, however, do not uniquely identify specific architectural or hydrological units of a fault. A more comprehensive whole-fault picture for the brittle crust can be developed in combination with seismicity and structural information. Giving a window into lower-crustal shear zones, the fossil WF/OL in Namibia is imaged as a subvertical, 14 km-deep, 10 km-wide zone of high and anisotropic conductivity. The present level of exhumation suggests that the WF/OL penetrated the entire crust as a relatively narrow shear zone. Contrary to the fluid-driven conductivity anomalies of active faults, the anomaly here is attributed to graphitic enrichment along former shear planes. Once created, graphite is stable over very long time spans and thus fault/shear zones may remain conductive long after activity ceases.
High-temperature and pressure seismic properties of a lower crustal prograde shear zone from the Kohistan Arc, Pakistan
Authors: Burlini L. , Arbaret L. , Zeilinger G. , Burg J.-P.
Published: April 2008

Anastomosing shear zones exposed in the lower crust of the Kohistan palaeoisland arc in Pakistan have parageneses indicating increasing pressure during deformation. Therefore, they represent a rare example of strain localization during crustal thickening. We investigated the seismic properties of a sheared gabbro with constant bulk chemistry across one of these shear zones. The compressional wave velocity was measured at confining pressures of up to 0.5 GPa and temperatures of up to 600 °C. The density, the average V
p
(compressional P-wave velocity) and the acoustic impedance at room temperature increase from the undeformed protolith through the strain gradient to the intensely sheared mylonite. The seismic anisotropy is largest for the strain gradient.

The
V
p
dependence of the velocities on temperature is much higher in the mylonite than in the protolith. The acoustic impedance contrast between protolith and mylonite is high enough to generate seismic reflections at low temperatures, but not at high temperatures. This suggests that the seismic reflectivity may also depend on the temperature. Consequently, ductile shear zones can be detected in reflection profiles of crusts with low geothermal gradients, and may be transparent in crusts with high geothermal gradients.
Damage and recovery of calcite rocks deformed in the cataclastic regime
Authors: Schubnel A. , Fortin J. , Burlini L. , Guéguen Y.
Published: April 2008

Compressional and shear wave velocities have been measured during the experimental deformation of Carrara marble and Solnhofen limestone in the cataclastic regime, both in dry and wet conditions at room temperature. Measurements were performed under hydrostatic conditions (up to 260 MPa confining pressure and 10 MPa pore pressure) during triaxial loading (at the constant strain rate of 10
−5
s
−1
) as well as during differential stress relaxation. During a full cycle, our results show that the seismic velocities first increase as effective mean stress increases. However, when the stress onset of cataclastic deformation was reached, elastic velocities showed rapid decrease due to stress-induced damage in the rock. During stress relaxation tests we observed an increase of elastic velocities with time, which suggested a fast ‘recovery’ of the microstructure. A substantial and rapid drop in the velocities occurred when reloading, suggesting that the previous ‘recovery’ was only transient. Subsequent relaxation tests showed other marked increases in velocities. These experimental results suggests that during the deformation of low-porosity calcite-rich rocks, dilatant (crack opening and frictional sliding) and compaction micro-mechanism (pore closure) compete. Evolutions of elastic properties (mainly sensitive to crack density) and macroscopic volumetric strain (more sensitive to porosity) are therefore not systematically correlated and depend on the strain rate, the solid stress conditions and the pore pressure.
The effect of grain size and melt distributions on the rheology of partially molten olivine aggregates
Authors: Bruhn David , Kohlstedt David L. , Lee Kyong-Ho
Published: April 2008

Grain size distribution affects the distribution of melt in partially molten rocks, as melt is partitioned into the finer grained regions. As the creep strength of partially molten rocks depends on melt fraction, grain size distribution affects rheology in two ways: in the diffusion-creep regime the strength of the rock decreases with decreasing grain size; and by affecting the melt distribution, grain size distribution affects rock strength in the dislocation and the diffusion-creep regimes. To investigate this effect on partially molten dunites, we deformed synthetic aggregates of olivine + mid-ocean ridge basalt (MORB) with varying grain size distributions and melt fractions. We found that samples with bimodal grain size distributions did not obey the flow law derived for samples with a uniform grain size distribution. In the samples with bimodal grain size distributions the finer grained parts are enriched in melt, reducing the relative melt fraction in the coarser grained parts. The stress exponent is close to 1 for lower stresses for samples with non-uniform grain size distributions, while it is close to 3 for samples with a uniform grain size distribution. Electron backscatter diffraction (EBSD) analysis shows crystallographic preferred orientation (CPO) well developed in all samples. Microstructural investigation shows that partitioning of the liquid out of the coarser grained part of the aggregate into the finer grained part leads to a localization of the strain into the weaker, finer grained and melt-enriched part. By treating the two parts as mechanically different phases that deform at a uniform stress, we are able to approximate the rheological behaviour of the aggregates with bimodal grain size distribution.
Creep constitutive laws for rocks with evolving structure
Authors: Evans Brian
Published: April 2008

Zones of localized strain are common geological features at all spatial scales, are persistent in time and have important implications for rock strength. Technical advances now allow mechanical tests to be carried out to high strain, and, thus, there is both need and the opportunity to formulate constitutive laws for rocks as their structure (i.e. fabric, texture and mineralogy) changes. This paper reviews some attempts to describe quantitatively the mechanical behaviour of calcite rocks deformed to large strains. To include the effect of evolving structure on strength, three or more interlinked laws are needed: an evolution equation describing the rate of change for each structural variable; a kinetic equation relating mechanical and thermodynamic loading and the structural variables to the rate of strain; and a kinematic equation involving a time integral of inelastic strain rate. Structure variables may be explicitly identified or implicitly determined without identification. Appropriate explicit state variables might include aspects of the dislocation microstructure or the grain size, as are common in studies of plasticity in metals. But because natural tectonic situations are more complex, a much broader class of state variables will be needed. Among these additional variables might be crystal lattice preferred orientation, progress variables for metamorphic reactions, solid-solution chemistry, porosity and pore fluid fugacity.
Geochemical variations and element transfer during shear-zone development and related episyenites at middle crust depths: insights from the Mont Blanc granite (French — Italian Alps)
Authors: Rossi M. , Rolland Y. , Vidal O. , Cox S. F.
Published: April 2008

This paper highlights the relationships between the formation of shear zones, associated quartz-rich veins and their quartz-depleted alteration haloes (‘episyenites’) that have formed in the Mont Blanc Massif during the Alpine orogeny. The shear zones are steeply dipping and formed late (18–13 Ma) during collisional orogeny, at mid-crustal depths (5 ± 1 kbar, 400 ± 50 °C) during uplift of the Mont Blanc Massif. Between the shear zones, nearly undeformed granite contains widely dispersed, subhorizontal veins with a quartz-dominant quartz + albite + chlorite + adularia assemblage. They do not intersect the shear zones and are surrounded by quartz-depleted alteration haloes up to several metres wide. The compositions of the shear zones and the vein-alteration haloes (episyenites) show substantial departures from the bulk composition of the host rock. Shear zones are characterized by greenschist facies assemblages (epidote-, chlorite- or K-white-micabearing assemblages). Each shear zone type is featured by a specific chemical change: depletions in K
2
O, and enrichments in Fe
2
O
3
and CaO (epidote-); with depletions in CaO, Na
2
O, K
2
O and slight SiO
2
enrichments (white mica-chlorite-); with depletions in SiO
2
, CaO, Na
2
O, K
2
O and enrichments in MgO (phlogopite-chlorite shear zones). Episyenites are characterized by chemically induced porosity enhancement due to dissolution of magmatic quartz and biotite, with subsequent partial infilling of pore spaces by quartz, chlorite, albite and adularia. The vein arrays have accommodated minor vertical stretching in the Mont Blanc Massif, probably at the same time as the adjacent shear zones were accommodating more substantial vertical stretching in the massif. Coupled quartz dissolution in the wallrock alteration haloes and quartz precipitation in veins could be interpreted to reflect local mass transfer between wallrock and veins during essentially closed-system behaviour in the relatively underformed granite domains between shear zones. In contrast, shear zones probably develop in opened systems due to their kilometric length.
Terrane processes at the margins of Gondwana: introduction
Authors: Vaughan Alan P. M. , Leat Philip T. , Pankhurst Robert J.
Published: April 2008

The process of terrane accretion is vital to the understanding of the formation of continental crust. Accretionary orogens affect over half of the globe and have a distinctively different evolution to Wilson-type orogens. It is increasingly evident that accretionary orogenesis has played a significant role in the formation of the continents. The Pacific-margin of Gondwana preserves a major orogenic belt, termed here the ‘Australides’, which was an active site of terrane accretion from Neoproterozoic to Late Mesozoic times, and comparable in scale to the Rockies from Mexico to Alaska, or the Variscan-Appalachian orogeny. The New Zealand sector of this orogenic belt was one of the birthplaces of terrane theory and the Australide orogeny overall continues to be an important testing ground for terrane studies. This volume summarizes the history and principles of terrane theory and presents 16 new works that review and synthesize the current state of knowledge for the Gondwana margin, from Australia through New Zealand and Antarctica to South America, examining the evolution of the whole Gondwana margin through time.
Kinematic history of western Marie Byrd Land, West Antarctica: direct evidence from Cretaceous mafic dykes
Authors: Siddoway Christine S. , Sass Louis C. , Esser Richard P.
Published: April 2008

Intracontinental deformation occurred in West Antarctica during the final stages of plate convergence along the Cretaceous Gondwana margin. In western Marie Byrd Land, 115 Ma to 95 Ma A-type granitoids and mafic dykes record a change in plate kinematics. The magmatism typically is viewed as a record of extension leading to orthogonal break-up between New Zealand and Marie Byrd Land by
c.
67 Ma. This paper presents new kinmatic and
40
Ar/
39
Ar age data for a mafic dyke array in the Ford Ranges, a region >1000 km
2
dominated by plutonic and metamorphic bedrock. The mean dyke trend of N16W corresponds to a maximum finite strain axis orientated N74E, highly oblique to the N58E-trending margin and to on-land crustal structures defined from airborne geophysics.
40
Ar/
39
Ar emplacement ages for most dykes fall between 114 Ma and 97 Ma, coeval with emplacement of a gneiss dome at 101-96 Ma and with development of mylonitic shear zones at 100–95 Ma in coastal western Marie Byrd Land. The oblique orientation of maximum finite strain with respect to large faults, geophysical lineaments and the rifted margin of western Marie Byrd Land is consistent with transcurrent tectonics along this segment of the Gondwana margin at
c.
100 Ma.
Terrane and basement discrimination in northern Britain using sulphur isotopes and mineralogy of ore deposits
Authors: Lowry D. , Boyce A. J. , Fallick A. E. , Stephens W. E. , Grassineau N. V.
Published: April 2008

This study of four well characterized and adjacent terranes in Northern Britain outlines the sulphur isotope variations, assesses the overall importance of crustal and mantle sulphur, and presents a model that can be applied to terrane distinction throughout the North Atlantic Caledonides. The characteristics of metal components within the mineralization provide additional information that can be related to the nature of underlying basement and events from the onset of sedimentation to the cessation of mineralization within stratigraphically linked packages of rock.

The δ
34
S data show that the dominant crustal units in each terrane, whether upper crustal sediments or cratonic basement, provide the main alternative sulphur source to the mantle and act also as the main contaminant of subcrustal melts. The δ
34
S values of granitoid-related mineralization are either within the subcrustal melt-range of −3‰ to +3‰ or deviate toward the values of major crustal units in the terrane, i.e. toward
34
S depletion in the Southern Uplands and toward
34
S enrichment in the Lakesman and Grampian terranes. More complex mineralization in the Northern Highland terrane is linked to the presence of thick North Atlantic craton beneath upper crustal metasediments. Across the region the vein systems beyond the influence of magmatic components represent homogenized sulphur, metals and fluids from local upper crustal units. The sulphur isotope data and style of mineralization for the British terranes are compared with terranes of similar age along strike in Eastern Canada revealing notable correlations.
A reassessment of the tectonic zonation of the Uralides: implications for metallogeny
Authors: Herrington R. J. , Puchkov V. N. , Yakubchuk A. S.
Published: April 2008

A review of the structural zonation of the ‘oceanic’ Urals shows that only its westernmost Sakamara, Tagil and Magnitogorsk zones reveal the presence of thrust structures, whereas in the East Uralian megazone and Trans-Uralian zone, the classic zonation rather reflects late- or post-collisional granitic welding and strike-slip displacement of the orogen for 100–300 km. This sinistral strike-slip displacement is responsible for the lens-shapes structure of the individual zones in the Urals.

Metallogenically, these orogen-parallel faults and the eastern boundary of the East European craton control the distribution of the orogenic Au deposits. Restoration of the individual zones into their pre-strike-slip fault positions suggests that the Urals contains only two magmatic arcs, one in the west and one in the east. The western Tagil-Magnitogorsk immature arc hosts a variety of chromite, Alaska-type PGE and major VMS deposits. The eastern Valerianovka arc effectively stitches together the Kazakh-Tien Shan structures and is host to important copper-gold and giant iron(-copper) skarn deposits.

The geodynamic evolution of the Urals can be observed with the generation of the immature Tagil-Magnitogorsk magmatic arc in the Late Ordovician. Metallogenic zoning of the VMS deposits supports the petrological data that the arc developed due to eastward subduction inside the oceanic back-arc basin that existed in the rear of the Kazakhstan-Tien Shan arcs. In the late Palaeozoic, these arcs collided with each other and were together thrust onto the East European craton. Syncollisional granitoid intrusions welded the magmatic arcs, which were soon displaced into presently observed fragments along the post-collisional orogen-parallel strike-slip faults.
The terrestrial record of stable sulphur isotopes: a review of the implications for evolution of Earth’s sulphur cycle
Authors: Farquhar James , Wing Boswell A.
Published: April 2008

The observation of anomalous (non mass-dependent) sulphur isotope compositions in Archaean and early Proterozoic rocks but not in rocks younger than approximately 2 Ga has been interpreted to reflect fundamental change in the terrestrial sulphur cycle, in atmospheric chemistry, and in atmospheric oxygen content. Similar non mass-dependent sulphur isotope compositions in present-day samples (atmospheric aerosols and ice-core horizons containing remnants of stratosphere-piercing volcanic eruptions) are interpreted to carry information about modern atmospheric chemistry and transport. The interpretation of these observations hinges on our understanding of the processes that produce non mass-dependent sulphur isotope compositions, the processes that transport and transfer the isotopic signals throughout the sulphur cycle, and the processes that act to preserve or erase these isotopic signals once they are established. The growing dataset and hypotheses related to non mass-dependent sulphur are evaluated, emphasizing that which remains to be learned about the evolution of the record, the compositions of key reservoirs, and the transfer of the signal from the atmosphere to the surface and ultimately to the deep Earth.
Reactive iron enrichment in sediments deposited beneath euxinic bottom waters: constraints on supply by shelf recycling
Authors: Raiswell R. , Anderson T. F.
Published: April 2008

Modern and ancient euxinic sediments are often enriched in iron that is highly reactive towards dissolved sulphide, compared to continental margin and deep-sea sediments. It is proposed that iron enrichment results from the mobilization of dissolved iron from anoxic porewaters into overlying seawater, followed by transport into deep-basin environments, precipitation as iron sulphides, and deposition into sediments. A diagenetic model shows that diffusive iron fluxes are controlled mainly by porewater dissolved iron concentrations, the thickness of the surface oxygenated layer of sediment and to a lesser extent by pH and temperature. Under typical diagenetic conditions (pH < 8, porewater Fe
2+
= 10
−6
g cm
−3
) iron can diffuse from the porewaters in continental margin sediments to the oxygenated overlying seawater at fluxes of 100–1000 μg cm
−2
a
−1
. The addition of reactive iron to deep-basin sediments is determined by the magnitude of this diffusive flux, the export efficiency (ɛ) of recycled iron from the shelf, the ratio of source area (
S
) to basin sink area (
B
) and the trapping of reactive iron in the deep basin. Values of ɛ are poorly constrained but modern enclosed or semi-enclosed sedimentary basins show a wide variation in
S/B
ratios (0.25–13) where the shelf source area is defined as sediments at less than 200 m water depth. Diffusive fluxes in the range 100–1000 μg cm
−2
a
−1
are able to produce the observed reactive iron enrichments in the Black Sea, the Cariaco Basin and the Gotland Deep for values of ɛ ×
S/B
from 0.1–5. Transported reactive iron can be trapped physically and/or chemically in deep basins. Physical trapping is controlled by basin geometry and chemical capture by the presence of euxinic bottom water. The
S/B
ratios in modern basins may not be representative of those in ancient euxinic/semi-euxinic sediments but preliminary data suggest that ɛ ×
S/B
in ancient euxinic sediments has a similar range as in modern euxinic sediments.
The formation of economic porphyry copper (-gold) deposits: constraints from microanalysis of fluid and melt inclusions
Authors: Heinrich C. A. , Halter W. , Landtwing M. R. , Pettke T.
Published: April 2008

This paper summarizes our current understanding of the formation of porphyrystyle Cu ± Au ± Mo deposits, in the light of data obtained by direct analysis of the ore metals in individual fluid and melt inclusions using laser-ablation ICP mass spectrometry. An integrated study of the evolution of the calcalkaline Farallón Negro Volcanic Complex hosting the Bajo de la Alumbrera porphyry Cu-Au deposit (Argentina), and supplementary fluid-chemical data from Bingham (Utah) and other examples, permit a quantitative re-assessment of the fundamental processes controlling the key economic parameters of porhyry-style ore deposits. Deposit size (total metal content) is optimized by exsolution of a relatively dense (>0.3 g cm
−3
) single-phase fluid or a two-phase brine + vapour mixture from a moderately large hydrous pluton, possibly with an intermediate step involving the scavenging of the ore-forming elements in a magmatic sulphide melt. Emplacement mechanism, magma-chamber dynamics and possibly an additional source of sulphur are probably more decisive for the formation of a large deposit than sheer pluton volume and elevated Cu contents in the melts. Primary bulk ore grade is determined by temperature-controlled precipitation of ore minerals, which is optimized where a large magmatic fluid flux is cooled through 420–320 °C over a restricted vertical flow distance. Bulk metal ratios of the deposits, exemplified by the economically important Au/Cu ratio in the ore, are primarily controlled by the magmatic source defining the composition of the fluids before they reach the deposit site, although selective precipitation may contribute to metal zoning within orebodies.
Quantitative determination of hydraulic properties of fractured rock using seismic techniques
Authors: Liu Enru , Chapman Mark , Hudson John A. , Tod Simon R. , Maultzsch Sonja , Li Xiang-Yangi
Published: April 2008

There have been significant advances over the last ten years in the use of the seismic anisotropy concept to characterize subsurface fracture systems. Measurements of seismic anisotropy are now used to deduce quantitative information about the fracture orientation and the spatial distribution of fracture intensity. Analysis of the data is based upon various equivalent medium theories that describe the elastic response of a rock containing cracks or fractures in the long wavelength limit. Conventional models assume scale/frequency independence and hence cannot distinguish between micro-cracks and macrofractures. The latter, however, control the fluid flow in many oil/gas reservoirs, as the fracture size and spacing (hence fracture storability) are essential parameters for reservoir engineers. Recently, a new equivalent medium theory for modelling of wave propagation in media with multi-scale fractures has been presented. The model predicts velocity dispersion and attenuation due to a squirt-flow mechanism at two different scales: the grain scale (micro-cracks and equant matrix porosity) and formation-scale fractures. Application of this model to field data shows that fracture density and fracture size can be inverted successfully from the frequency dependence of the time delay between split shear waves. The derived fracture length matches independent observations from borehole data. This paper presents the results of the latest development in the seismic characterization of natural fractures, with an emphasis on the quantitative determination of fracture sizes.
Precise numerical modelling of physical transport in strongly heterogeneous porous media
Authors: Xie Zhongqiang , Mackay Rae , Cliffe K. Andrew
Published: April 2008

A library comprised of precise numerical simulation results for two-dimensional flow and advective transport through statistically-equivalent, structured, porous media is being created to investigate upscaling procedures for contaminant dispersal and physical transport at large space and long time-scales. Several technical challenges were overcome to achieve high precision in the velocity fields and particle paths. A Cholesky Decomposition method for efficient media generation has been extended to generate ‘artefact’-free, areally-extensive random fields of hydraulic conductivity variation. An efficient mixed finite-element method, capable of handling periodic boundary conditions was used to compute the flow distributions through the generated media. The method permits exact solution of particle trajectories. Comparison of particle migration patterns with available analytical solutions confirms persistent non-Fickian behaviour of particle migration at large space and times-scales, as well as confirming the accuracy of the simulations. Boundary effects on particle trajectories are found to be significant and cannot be removed totally from the steady-state flow fields. Periodicity, both parallel and perpendicular to the flow direction, results in particle trajectories that are almost periodic and so are inappropriate for transport studies of realistic media. A compromise solution has been adopted whereby only the domain boundaries parallel to the flow are periodic.
Fabric development and the smectite to illite transition in Upper Cretaceous mudstones from the North Sea: an image Analysis Approach
Authors: Worden R. H. , Charpentier D. , Fisher Q. J. , Aplin A. C.
Published: April 2008

In this study, Upper Cretaceous Shetland Group mudstone cuttings from a range of depths in the Northern North Sea, have been studied using X-ray diffraction, mercury porosimetry and electron microscopy. Millimetre to micrometre mudstone textures have been quantified using image analysis of backscattered electron microscope images. Relatively shallow samples (1615 m) have isotropic mudstone fabric (no alignment of clay minerals), are dominated by smectite and have porosity values of approximately 35%. In contrast, more deeply buried samples (3300 m) have developed an anisotropic fabric (distinct alignment of clay minerals), are dominated by illite and have porosity values of approximately 22%. The change in mineralogy is due to smectite replacement by illite, which occurs simultaneously with porosity-loss and fabric development during progressive burial. Image analysis of differentially buried mudstones has proved to be a rapid, flexible and quantitative method for characterizing mudstone textures. The coincidence of mineralogical evolution with textural development and compaction implies that the transformation of smectite to illite occurs by dissolution and precipitation and that chemically facilitated compaction may contribute to porosity loss.
The μ2M project on quantifying the effects of biofilm growth on hydraulic properties of natural porous media and on sorption equilibria: an overview
Authors: Brydie J. R. , Wogelius R. A. , Merrifield C. M. , Boult S. , Gilbert P. , Allison D. , Vaughan D. J.
Published: April 2008

The physical and chemical effects of bacterial biofilm formation upon hydraulic conductivity, mineral-solution interactions and the formation of biogenic mineral precipitates have been studied over a wide range of scales, from microscopic to macroscopic. Several novel pieces of equipment have been designed, constructed and commissioned in order to measure the physical effects of biofilms upon fluid flow through fractures and porous media, the overall effects of biofilm formation upon mineral surface reactivity, and the imaging and identification of mineral precipitates formed due to the presence of biofilm and bacterial cell surface polymers on a quartz surface. This paper presents an overview of key experimental methods and selected results; further experimental information is being published elsewhere.

Biofilm formation with quartz sand in artificial groundwater resulted in a two orders of magnitude reduction in hydraulic conductivity under bench-scale constant head conditions. However, under quasi-environmental conditions within macroscopic centrifuge experiments, a reduction of 21% was measured, revealing differences in measurements and, hence, the value of the macroscopic experimental work in scaling from micro to macro.
In-situ
microscopic evaluation of biofilms within simulated quartz rock fractures and in porous media reveal only a small percentage of the biomass to be in direct contact with the mineral surface, allowing mineral chemistry to be predominantly controlled by mineral surface reactivity, rather than by a diffusion-limited mineral-biofilm-solution interface. This is true even when a mineral surface is apparently completely covered by biofilm. The alteration of mineral surface drastically increases the kinetics of surface-coordinated trace metal precipitate formation by providing nucleation sites upon extracellular biopolymers and cell wall polymers. Over geological time-scales, these processes, particularly the formation of thermodynamically stable pore-blocking mineral precipitates, are envisaged to markedly change the flow paths, flow rates and interaction of migrating geofluids (water, petroleum, ore-forming solutions) with minerals and rocks.
Overview of the NERC ‘Understanding the Micro to Macro Behaviour of Rock-Fluid Systems’
Authors: Shaw R. P.
Published: April 2008

The NERC μ2M Programme funded 17 projects over a period of six years. A brief outline of the programme and of all the component projects is provided here.
Enhancing the contribution of mining to sustainable development
Authors: Hobbs Jonathan C. A.
Published: April 2008

This paper reviews recent developments aimed at improving the mining sector’s contribution to sustainable development. Mineral endowments are regarded by many development and environmental non-governmental organizations (NGOs), as a ‘curse’ and counterproductive to long-term growth and poverty reduction goals, even antithetical to sustainable development in developing countries. This paper argues that, in spite of some empirical evidence in some countries, this is not an inevitable general rule and that the mining sector offers numerous possibilities for catalysing sustainable development and attainment of the millennium development goals. This is, however, conditional upon adequate governance and social and environmental safeguards being in place. The heterogeneity of the mining sector is considered and concern is expressed for the undermanagement of the growing, albeit not new, phenomenon of artisanal and small-scale mining in developing countries. Without better management of this sector any attempts to improve the contribution of mining to sustainable development will be severely limited.
Sustainable river mining of aggregates in developing countries
Authors: Harrison D. J. , Fidgett S. , Scott P. W. , MacFarlane M. , Mitchell P. , Eyre J. M. , Weeks J. M.
Published: April 2008

Throughout the developing world, river sand and gravel is widely exploited as aggregate for construction. Sediment is often mined directly from the river channel and makes an important contribution to the national demand for aggregates. However, instream mining, if not carefully controlled, can cause significant damage to the river and its associated biota, and to the adjacent land, as well as creating conflict with other users of the river. The economic and environmental geology of river sand and gravel mining in developing countries is poorly known and there is little knowledge available to inform existing regulatory strategies. Research work on selected river systems in Jamaica and Costa Rica has generated a considerable amount of new information on resources and sediment budgets, on market and supply options, on the physical, biological and social impacts of extraction, and on best-practice legislative and mineral planning issues. A methodology has been developed for effective control of instream sand and gravel mining operations including a Code of Practice, which regulators can use for examining and reconciling the conflicting claims of sand and gravel extraction and the environment.
Sustainable mineral development: case study from Kenya
Authors: Davies T. C. , Osano O.
Published: April 2008

The last two to three decades have witnessed a rapid growth in the mining industry in Kenya. The suite of minerals includes metals such as gold, silver, copper, zinc and titanium, and industrial minerals ranging from talc and gypsum to dolomite and gemstones. Methods of exploitation, processing and beneficiation of these mineral resources can have diverse effects on the country’s socio-economic position, its varied ecosystems and general environment. The Mining Act (Cap 306) of 1940, which has been the principal Act for regulating minerals use and mining, lacks clear provisions on environmental management. This paper discusses mining guidelines set forth in a new regulatory framework known as the Environmental Management and Coordination Act of 2000, and evaluates their effectiveness and applicability by examining the proposed titanium mining project in the Kwale district. Through a major mining project, the Environmental Impact Assessment exposed the difficulties often encountered in implementing regulatory controls in all new mining ventures in Kenya, both large- and small-scale. It is submitted that the challenge of sustainability should be a major concern of the mineral industry to demonstrate not only profitability but also benefits to society and preservation of environmental integrity.
Artisanal and small-scale mining in Africa: the poor relation
Authors: D’Souza K. P. C. J.
Published: April 2008

The artisanal and small-scale mining (ASM) sector in sub-Saharan Africa is a sector usually associated with conflict minerals, fatal diseases, smuggling, criminal activity and civil war. Throughout Africa the ASM sector is unfortunately viewed in a negative and distorted manner with little appreciation or understanding for the realities and hardship of miners, their families and communities. However, the sector is burdened and plagued with issues ranging from child labour, gender inequality, the spread of HIV/AIDS, environmental devastation, poor health and safety, migrant workers, lack of capital and fair markets, and conflict with the private large-scale mining sector. The paper discusses the many over-lapping and complex drivers, challenges, constraints and issues that characterize the sector and considers the potential solutions through the adoption of appropriate best practice, hopefully leading to sustainable livelihoods in the ASM sector and overall poverty alleviation. Key issues, such as institutional capacity, governance, assistance schemes, legislation, miners’ organizations, gender mainstreaming, child labour, health and safety, environmental protection, mineral trading and marketing, adding value, finance and credit, and the co-existence with the large-scale mining sector are all detailed. The paper also highlights ideas of what individual countries can do to help formalize and provide assistance to this vulnerable sector. Some of what is discussed concurs with the findings of the Mining, Minerals and Sustainable Development (MMSD) Project, the multi-donor Communities & Small-Scale Mining (CASM) initiative, the UN Economic Commission for Africa (UNECA) and UN Department for Economic and Social Affairs (UNDESA) — Yaoundé Seminar on ASM in Africa, and most recently the African Mining Partnership (AMP). The bulk of this paper, however, has come from the experience gained by the author while managing and working on numerous projects commissioned by the UK’s Department for International Development (DFID), the World Bank, United Nations, various African Governments, private mining companies and NGOs in over 20 African countries.
The Gold Ridge Mine, Guadalcanal, Solomon Islands’ first gold mine: a case study in stakeholder consultation
Authors: Tolia Donn H. , Petterson M. G.
Published: April 2008

The Pacific small island state of Solomon Islands gained independence from Britain in 1978. Solomon Islands has a population of around 400 000 mainly Melanesian people distributed across six moderately sized islands and hundreds of smaller islands. The traditional economy has been based on hunter-gatherer and small-scale farming activities, with the bulk of the population residing in self-sufficient rainforest and coastal villages. Melanesians have a particularly strong cultural attachment to land, which is considered to be within the custodianship of the community at large. Individual land ownership in the Western economic sense is largely unknown. Melanesian society and culture is strong and complex. Colonial and post-independence Solomon Islands has had to face the challenges of a transition from a traditional society to a partially urbanized society and a rapidly increasing population and changing economic drivers and dynamics. Mining and mineral development is one area of economic activity that holds the promise of generating hard currency quickly to develop the country, but that needs to be achieved in a sustainable manner. Gold Ridge is situated in Central Guadalcanal, some 22 km southeast of the country’s capital town, Honiara. Gold Ridge hosts around 1.4 million ounces of epithermal volcanic-hosted gold. Ross Mining NL began the construction of Solomon Islands’ first gold mine in 1997 and operated a highly successful gold mine between 1997 and 2000, when ethnic tensions (unrelated to the mine) closed the operations. This paper documents the painstaking negotiations and planning that took place from 1993 and particularly from 1995 – 1996 which paved the way forward for the development of a gold mine within a fragile tropical rainforest environment among traditional Melanesian people who had little prior knowledge of modern mining activities.
Construction raw materials in Timor Leste and sustainable development
Authors: Carvalho Jorge F. , Lisboa José V.
Published: April 2008

Timor Leste is the newest and one of the poorer nations in the world. One of its main challenges that could lead to poverty reduction is the reconstruction and maintenance of the infrastructures that were almost completely destroyed after its independence referendum. To achieve this, there is an imperative need for construction raw materials in a country where the extractive industry is scarce and artisanal. Available geological studies deal with the island’s geology and tectonic evolution or its oil and gas potentialities. Very few broach other geological resources. A general study of the country’s territory demonstrates that Timor Leste possesses large resources in clays, limestones and sand and gravel, which can support small- to large-scale raw material extractive industries. Some selected areas have been the target of more detailed study: Venilale and Aileu, with resources for structural ceramics and whiteware respectively, and Beheda, where a crinoid-rich limestone crops out, with potential for usage as ornamental stone. These resources are suitable for non-sophisticated small-scale mining operations that should be able to accomplish environmental and social liabilities. No public policy exists for the management of these mineral resources, which is essential for the sustainable development of Timor Leste.
Capacity building of developing country public sector institutions in the natural resource sector
Authors: Stephenson M. H. , Penn I. E.
Published: April 2008

The natural resources of developing countries, particularly in a post-conflict situation, are the key to creating wealth, getting people back to work, and to improving security. However, public sector institutions like geological surveys, and government departments such as mines, energy and water ministries often need help in their vision to promote and sustainably develop their natural capital, as well as to protect the lives and livelihoods of people affected by development. Some have few physical resources, and a poorly trained and motivated workforce; others may be housed in buildings that have borne the brunt of prolonged fighting and a long period of neglect. In many developing countries, such institutions have a rather inward-facing colonial-style civil service culture that lacks the ability to liaise and engage with modern multinational investors. Unfortunately, donor organizations that seek to build the capacities of institutions do not build sufficient ‘project ownership’ and fail to incorporate into their plans the culture of the organization, or fail to integrate parts of multidisciplinary projects. Development projects supported are often perceived to reflect donor agendas rather than the needs of the recipient institution. Using experience in a number of developing country and post-conflict contexts, a methodology to plan and integrate capacity building has been developed, to help employees and management, and donor organizations, deal with these difficulties. Through training tuned to business need, institutions will develop appropriate IT and communication skills, while at the same time developing corporate understanding of the private sector, which is needed to interact successfully with it. Stakeholder analysis gauges the organization’s strengths and weaknesses and ensures coordination of aid, which takes account of the local social, political and business context. The methodology will also establish a system allowing regular cyclical business/training review, so that the institutions can adapt to further change.
Sustainable development and minerals: measuring mining’s contribution to society
Authors: Shields D. J. , Šolar S. V.
Published: April 2008

Traditional development theory focuses on two goals, income growth and poverty alleviation, and many mineral-rich developing countries have depended on resource exploitation to achieve those goals. In reality, mineral-driven economies have often experienced less growth than mineral-deficient economies. Conversely, the potential positive contributions of mineral development are often overlooked in countries with limited mineral endowment. Such under- or over-emphasis on the minerals sector can be lessened by addressing mineral development within the context of sustainable development. Each country identifies sustainability goals, with respect to social equity, environmental health, and economic growth that are appropriate to its circumstances. The contribution of mineral resources to the achievement of those goals will be similarly context dependent. In this paper we discuss the concept of sustainable mineral resource management. We then describe how indicators of sustainability can be used to measure the contribution of the minerals sector to a country’s economic development and track progress toward its overall sustainability goals. We present an example of sustainable mineral management policy and related mineral indicators from a country with a transitional economy and limited mineral resources.