bluuebunny/crossref_metadata_2025 huggingface dataset:
Reconstructing the erosion history of glaciated passive margins: applications of
in situ
produced cosmogenic nuclide techniques
Authors: Stroeven Arjen P. , Fabel Derek , Harbor Jon , Hättestrand Clas , Kleman Johan
Published: April 2008

Offshore sediment accumulations provide an intriguing record of the net sediment output resulting from geomorphological evolution of the circum-Atlantic continental margin since the commencement of Neogene glaciation. However, the onshore record of the timing, pattern and amount of bedrock erosion that produced these sediments is comparatively poorly constrained and understood, although there are good general models of glaciation history. The geomorphology of circum-Atlantic continental margin mountains, as assessed from remote sensing data and field observations, includes palimpsest landforms and landscapes that reflect a complex pattern of spatial and temporal variations in the impact of glacial, fluvial and periglacial processes. Perhaps most surprising is that, despite having been repeatedly overridden by large ice sheets, parts of the landscape appear to be relict, with nonglacial morphology. This has important implications both for glaciological conditions under ice sheets, and for sediment source areas and erosion rates. Conventional dating and analysis have provided an excellent way to begin unravelling the timing and pattern of erosion, landform development, and possible landform preservation under ice. However, testing hypotheses developed from current models, and addressing critical unresolved questions, requires additional approaches. The use of
in situ
cosmogenic nuclide production in bedrock is a new approach for investigating landscape evolution in mountainous areas. With careful interpretation of geomorphological settings, cosmogenic nuclides can be used to determine apparent surface exposure age and landscape preservation, and constrain erosion depths and duration of burial by ice. Here we provide a framework for the interpretation of cosmogenic nuclide concentrations in bedrock surfaces of landscapes affected by glacial, fluvial and periglacial processes, illustrated with examples from the northern Swedish mountains. This demonstrates potential uses of cosmogenic nuclide techniques, and provides a foundation for attempts to improve geomorphologically based reconstructions of relict landscapes, to reconstruct and analyse the dynamics of landscape change in glacial times, and to define the consequences of different process regimes in terms of erosion patterns, sediment transport, and the supply of sediments that are deposited offshore.
The thermotectonic development of southern Sweden during Mesozoic and Cenozoic time
Authors: Cederbom Charlotte
Published: April 2008

Late Carboniferous-Early Mesozoic exhumation of southern Sweden has previously been traced using apatite fission-track thermochronology. In addition, the morphotectonic development of the region has been studied using geomorphology. The aim of this study is to attain further knowledge of the Mesozoic and Cenozoic thermotectonic development of southern Sweden by integrating results from these methods.

Well-dated re-exposed palaeosurfaces and sedimentary records in the surrounding areas were used as constraints in the modelling of apatite fission-track data from the Precambrian basement. The obtained modelled thermal histories suggest that southern Sweden can be divided into three main tectonic areas associated with different cooling histories. In Triassic and Jurassic time, low to moderate exhumation in the central part was accompanied by more rapid exhumation in the SE and NW. Additionally, individual block movements may have occurred in the NW. It has also been possible to estimate the heating effect of renewed Cretaceous-Paleogene burial to 20–35°C on the west and SE coasts.

Final Cenozoic unroofing of the basement is indicated by the modelled thermal histories. Areas around the southern tip of Lake Vättern together with the SE coast experienced the most pronounced exhumation compared with the surrounding parts.
Cenozoic uplift and denudation of southern Norway: insights from the North Sea Basin
Authors: Huuse Mads
Published: April 2008

The Cenozoic evolution of the North Sea Basin is described, drawing on subsurface data and a series of palaeogeographical maps compiled from a variety of published studies, mainly emphasizing the development of the eastern part of the basin. A model that accounts for the sedimentation history of the North Sea Basin and the topography (including maximum and mean surface elevation) of southern Norway is proposed. The model involves regional plume-related uplift of an initial low-elevation peneplain in early Paleogene time followed by repeated episodes of climatic deterioration and eustatic fall, most notably at the Eocene-Oligocene transition, in late Mid-Miocene time, and eventually culminating with the development of full glacial conditions in southern Norway in Plio-Pleistocene time. These episodes correspond to periods of accelerated sediment supply from southern Norway that reflect increased rates of incision (dissection) of the source area. It is argued that the present-day elevation of > 2 km of mountain peaks in southern Norway adjacent to deep valleys and fjords could have been caused by isostatic uplift in response to dissection of a high-elevation peneplain. Hence it may not be necessary to invoke late Cenozoic tectonic uplift events to explain the present-day topography of southern Norway.
Tectonic impact on sedimentary processes during Cenozoic evolution of the northern North Sea and surrounding areas
Authors: Faleide Jan Inge , Kyrkjebø Rune , Kjennerud Tomas , Gabrielsen Roy H. , Jordt Henrik , Fanavoll Stein , Bjerke Morten D.
Published: April 2008

This paper focuses on the Cenozoic evolution of the northern North Sea and surrounding areas, with emphasis on sediment distribution, composition and provenance, as well as on timing, amplitude and wavelength of differential vertical movements. Quantitative information about palaeo-water depth and tectonic vertical movements has been integrated with a seismic stratigraphic framework to better constrain the Cenozoic evolution. The data and modelling results support a probable tectonic control on sediment supply and on the formation of regional unconformities. The sedimentary architecture and breaks are related to tectonic uplift of surrounding clastic source areas, thus the offshore sedimentary record provides the best age constraints on Cenozoic exhumation of the adjacent onshore areas. Tectonic subsidence accelerated in Paleocene time throughout the basin, with uplifted areas to the east and west sourcing prograding wedges, which resulted in large depocentres close to the basin margins. Subsidence rates outpaced sedimentation rates along the basin axis, and water depths in excess of 600 m are indicated. In Eocene times progradation from the East Shetland Platform was dominant and major depocentres were constructed in the Viking Graben area, with deep water along the basin axis. At the Eocene-Oligocene transition, southern Norway and the eastern basin flank became uplifted. The uplift, in combination with prograding units from both the east and west, gave rise to a shallow threshold in the northern North Sea, separating deeper waters to the south and north. The uplift and shallowing continued into Miocene time when a widespread hiatus formed in the northern North Sea, as indicated by biostratigraphic data. The Pliocene basin configuration was dominated by outbuilding of thick clastic wedges from the east and south. Considerable late Cenozoic uplift of the eastern basin flank is documented by the strong angular relationship and tilting of the complete Tertiary package below the Pleistocene unconformity. Cenozoic exhumation is documented on both sides of the North Sea, but the timing is not well constrained. Two major uplift phases in early Paleogene and late Neogene times are related to rifting, magmatism and break-up in the NE Atlantic and isostatic response to glacial erosion, respectively. Additional uplift events may be related to mantle processes and the episodic behaviour of the Iceland plume.
Sonic velocity analysis of the Tertiary denudation of the Irish Sea basin
Authors: Ware Philip D. , Turner Jonathan P.
Published: April 2008

Interaction between uplift related to the Cretaceous—Paleocene opening of the North Atlantic, Neogene shortening (basin inversion) and Pleistocene glacio-isostasy is illustrated by the complex denudation pattern of Britain; such denudation is greatest over the submergent East Irish Sea basin, some 500 km from the Atlantic margin. This paper reports on analysis of sedimentary porosities using sonic velocity logs from 42 wells in the East Irish Sea basin. We present a new map showing the variation in exhumation magnitude at the uppermost Mesozoic unconformity (i.e. thickness of denuded Mesozoic and Cenozoic sedimentary rocks), today buried beneath a thin veneer of Pleistocene sediment. It indicates that exhumation is mostly < 1500 m (632–2132 m; mean standard deviation 407 m), less than denudation results obtained from vitrinite reflectance and apatite fission-track data. The map also reveals substantial variation in exhumation over short distances, often between adjacent wells sited on opposing walls of individual faults. This is interpreted in terms of the influence of Neogene basin inversion on the exhumation of the EISB. The role of late Tertiary tectonics in western UK exhumation is therefore discussed.
Genesis and age of the Erlend Volcano, NE Atlantic Margin
Authors: Jolley David W. , Bell Brian R.
Published: April 2008

The Palaeogene Erlend Volcano subcrops in the Faroe-Shetland Basin on the NE Atlantic Margin and was first recognized on the basis of its pronounced positive gravity and magnetic anomalies. Three hydrocarbon exploration wells (209/3-1; 209/4-1A; 209/9-1) have penetrated thick sequences of subaerial facies basaltic lavas and subaqueous volcanic breccias (the ‘Basaltic Suite’), overlying Palaeogene (Thanetian) and Cretaceous (Maastrichtian and Campanian) sedimentary rocks interbedded with medium to fine-grained silicic igneous rocks (the ‘Acidic Suite’). Detailed palynological and petrological analysis indicates that the basaltic rocks were contemporaneous with the Faroes Lower Lava Formation at
c.
56.6-55 Ma, and were erupted into environments ranging between dry land and brackish to freshwater lagoons at the margin of a marine channel separating the Erlend Volcano from the Brendan’s Volcano to the north. The subjacent Acidic Suite is interpreted as a series of sills emplaced approximately contemporaneously with the volcanic rocks on the basis of their diachronous relationship with interbedded sedimentary rocks, together with high Thermal Alteration Index values of
in situ
fossils.
Rates of volcanic deposition, facies changes and movements in a dynamic basin: the Nuussuaq Basin, West Greenland, around the C27n-C26r transition
Authors: Pedersen Asger K. , Larsen Lotte M. , Riisager Peter , Dueholm Keld S.
Published: April 2008

The initial stages of Palaeogene volcanism in the Nuussuaq Basin in West Greenland were characterized by eruption of basaltic and picritic magmas through sediments of Cretaceous to early Paleocene age into a marine or lowlying coastal environment. Recent magnetostratigraphic work has recognized the C27n-C26r transition (estimated duration less than 10 ka and here assumed to be 5 ka) as a
c.
170 m thick zone within a succession of thin picritic lava flows. Multimodel photogrammetry combined with chemical and lithological analysis of the volcanic rocks has allowed detailed 3D analysis of the facies variation within this narrow time window. Subaerial lavas flowed eastwards over a more than 40 km wide front. On northern Disko they covered an existing lava plateau and buried a subaerial landscape of dipping Cretaceous sandstones, while on Nuussuaq they flowed into an up to 700 m deep marine embayment and formed prograding hyaloclastite fans passing into fine-clastic mass flows. With a progradation rate of 0.5–1 m a
−1
the palaeogeography of the basin changed considerably during the short time interval. In addition to substantial basin subsidence, the volcanic facies changes have also preserved a record of synvolcanic differential movement of extensional fault blocks. The following parameters are estimated for the volcanism within the Nuussuaq Basin during the C27n-C26r transition: Production rate
c.
0.042 km
3
a
−1
, productivity
c.
1.2 × 10
−3
km
3
a
−1
km
−1
(rift), volcanic aggradation
c.
33 m ka
−1
, subsidence
c.
25 m ka
−1
. If the volcanism evolved continuously at this high aggradation rate, all of the Vaigat Formation could have erupted in 70 ka. However, the complex geological record indicates a much longer total duration, and the volcanism must have had an intermittent character.
The properties, morphology and distribution of igneous sills: modelling, borehole data and 3D seismic from the Faroe-Shetland area
Authors: Smallwood John R. , Maresh Jenny
Published: April 2008

An extensive suite of igneous sills, collectively known as the Faroe-Shetland Sill Complex, has been intruded into the Cretaceous and Tertiary sedimentary section of the Faroe-Shetland Channel area. These sills have been imaged offshore by three-dimensional (3D) reflection seismic surveys and penetrated by several exploration boreholes. Data from wireline log measurements in these boreholes allow us to characterize the physical properties of the sills and their thermal aureoles. The borehole data has been compiled to produce new empirical relationships between sonic velocity and density, and between compressional and shear sonic velocities within the sills. These relationships are used to assist in calculation of synthetic seismic traces for sills intruded into sedimentary section, in order to calibrate the seismic response of the sills as observed in field data. This paper describes how the seismic amplitude response of the sills can be used to predict sill thickness where there is some nearby well control, and use this technique to estimate the volume of one well-imaged sill penetrated by Well 205/10-2b. Since the sills have a high impedance contrast with their host rocks, they return strong seismic reflections. 3D seismic survey data allow mapping of the morphology of the sills with a high level of confidence, although in some instances disruption of the downgoing seismic wavefield causes the seismic imaging of deeper sills and other structures to be very poor. Examples of sub-circular and dish-shapes sills, and also semi-conical and sheet-like intrusions, which are highly discordant are shown. The introduction of intrusive rocks can play an important role in the subsequent development of the sedimentary system. An example is shown in which differential compaction or soft sediment deformation around and above the sills appears to have controlled deposition of a reservoir quality sand body. The positioning of the sills within sedimentary basins is discussed, by constructing a simple model in which pressure support of magma from a crustal magma chamber provides the hydrostatic head of magma required for intrusion at shallow levels. This model is made semi-quantitative using a simple equation relating rock densities to intrusion depth, calibrated to observations from the Faroe-Shetland area. The model predicts that sills can be intruded at shallower levels in the sedimentary section above basement highs, which agrees with observations detailed in this paper.
The monitoring and modelling of mine water recovery in UK coalfields
Authors: Whitworth Keith R.
Published: April 2008

This paper draws together the information that has been obtained on mine water recovery since the large-scale closure of coal mines in the 1980s and 1990s. The data show that, following cessation of pumping, mine water recovery follows an exponential curve similar to the recovery of an aquifer following a pumping test. Several previously unpublished examples of mine water recovery data from around the UK are included in the paper and there is a detailed assessment of mine water recovery in the East Fife Coalfield in Scotland. The reasons for this type of mine water recovery are discussed and examples are given of the use of the data for both the interpretation and modelling of mine water recovery. In coal mining areas where no water-level recovery data are available, methods for the prediction of mine water inflow and recovery modelling are proposed and the problems associated with mine water recovery modelling are discussed.

The paper concludes that modelling of mine water recovery, based on mine water inflow and estimated void space, can be used to give reasonably accurate predictions of recovery times and flows, but that water level monitoring is essential for precise predictions.

The control of mine water during the period when coal mining was a nationalized industry was generally based on a safety first principle. This meant that when doubt existed about underground connections between modern mines and old abandoned areas of workings, mine water pumping always continued in the old areas. The result of this policy was a general lack of experience of mine water recovery and continuing doubt about underground connections.

The large-scale closure of mines in the 1980s and 1990s mean that in many cases whole coalfields were abandoned and that the pumping of mine water either completely stopped or was greatly reduced. Estimations of mine water recovery made by British Coal at the time of these closures were generally based on a water inflow related to the volume of water pumped from a mine and a residual void-space calculation. The void-space was calculated using roadway dimensions for supported excavations and a figure of 10% of the original extractions thickness for unsupported (total extraction) workings (National Coal Board 1972). Using this principle it was assumed that mine water recovery would proceed as a series of steps, with very little recovery when water was ‘filling’ a large void, followed by a period of more brisk recovery until the next large void was reached.

The monitoring of mine water recovery by IMC Consulting Engineers on behalf of the Coal Authority (the government agency set up to look after the non-privatized areas of coal mining) has shown that, at least at large scales, mine water recovery follows precise exponential curves that appear to be independent of the distribution of mining voids. These curves are very similar to the recovery curves observed following an aquifer pumping test.
Effects of longwall mining in the Selby Coalfield on the piezometry and aquifer properties of the overlying Sherwood Sandstone
Authors: Dumpleton Stephen
Published: April 2008

In the UK, the first longwall faces at Wistow Mine in the Selby Coalfield, with only 80 m depth of cover to the base of the Permian, experienced several inrushes of groundwater derived from the overlying Lower Magnesian Limestone, causing serious disruption to coal production. Subsequent decrease in panel width coupled with increased depth of cover to the Permian reduced the incidence of water problems. However, there has never been any quantitative investigation to determine the effects of mining on the hydraulic properties of the stratigraphically higher Permo-Triassic age Sherwood Sandstone, a major aquifer of regional importance.

This opportunistic study fills that gap. Precautionary observation boreholes had been drilled above and around the margins of two proposed longwall panels prior to working the 2.5-m thick Barnsley seam at a depth of 550–600 m. Data loggers permitted continuous monitoring of the Sherwood Sandstone and Drift piezometric levels over a 2-year period. Widespread drawdown and recovery effects due to intermittent groundwater abstraction from a nearby factory were observed. Standard aquifer pumping test analyses of the hydrographs allowed transmissivity and storativity to be determined before, during and after mining. The results showed apparently permanent post-mining transmissivity increases of up to 149% around the margins of the panels, and up to 234% directly over the first panel. Post-mining storativity remained mostly unchanged. However, the greatest effects were noted during the closest approach by the second longwall panel, which also caused some additional subsidence over the first panel, when peak transmissivity increases of 1979% and storativity increases of 625% occurred. Anomalous, intra-cycle, recovery-drawdown events were also observed during this phase and interpreted as indicating rapid mining-induced dilation and compression of fractures within the aquifer fabric.

The results are consistent with similar investigations carried out at relatively shallow depths (<220 m) in USA coalfields. However, the Selby study shows that mining at much greater depths still has a significant impact on shallow aquifers, with implications for enhanced aquifer recharge, abstraction well yield and possible increased contaminant transport rates.
Depressurization of the north wall at the Escondida Copper Mine, Chile
Authors: McKelvey Patrick , Beale Geoff , Taylor Adam , Mansell Simon , Mira Benjamin , Valdivia Cristian , Hitchcock Warren
Published: April 2008

Concurrent dewatering and slope depressurization operations have been underway at the Escondida open pit since 1996. A hydrogeological investigation has been undertaken as part of the depressurization operation on the north wall. It has shown that there are two distinct hydrogeological units in the slope, the altered and unaltered Escondida Porphyry. The hydrothermally altered Escondida Porphyry is clay rich and has relatively high matrix permeability. The underlying silicified, or unaltered porphyry, has very low matrix permeability and groundwater flow is in steeply dipping NW-trending fracture systems. Pore pressures in the silicified porphyry are higher than the altered material.

A system of horizontal drains and vertical wells has been in operation to reduce pore pressures in the altered porphyry. To investigate effective drainage measures for the silicified porphyry, a groundwater model of the slope was constructed. This analysis showed that a drainage tunnel with horizontal drains was the most effective method of draining significant areas of the slope to the required pore pressure targets.
Hydrogeological framework for assessing the possible environmental impacts of large-scale gold mines
Authors: Kuma J. S. , Younger P. L. , Bowell R. J.
Published: April 2008

Hydrogeological information is crucial to the development of a sound environmental impact assessment (EIA) for a proposed mine, as well as the management of potential environmental impacts during and after exploitation. However, the determination of hydrogeological parameters is not customarily included in mineral exploration surveys, with the result that many EIAs end up being rather light in hydrogeological content. Examples from the Tarkwa gold mining district of Ghana illustrate this point. Consequences of such an inadequate hydrogeological understanding are potentially serious, ranging from an inability to predict future problems in water quality after the cessation of mining, to a lack of understanding of hydrogeological controls on slope stability, which is arguably manifest in the catastrophic spill of cyanide-rich processing effluents from a breached tailings dam at Wassa West, near Tarkwa, on 16 October 2001. To redress this deficiency, we propose that a hydrogeological database be assembled during the mineral exploration phase, according to a specified protocol (‘check-list’). Using these data, a rational conceptual hydrogeological model for the mine site and its surrounding area can be developed, providing the basis for a thorough consideration of groundwater aspects within the statutory Environmental Impact Assessment, which is (as in most other countries) required by Ghanaian government statute before a mining lease is approved. The resources required to set-up such a database are small compared to the benefits.
Predicting mineral weathering rates at field scale for mine water risk assessment
Authors: Banwart Steven A. , Evans Katherine A. , Croxford Stephanie
Published: April 2008

A general challenge to the environmental management of mine sites is the relatively high costs of site investigation and the associated development of conceptual site models and parameterization of reactive transport models. A particular problem is the inability to predict at field scale the rates of processes that give rise to long-term dissolved contamination due to active sulphide mineral weathering. Mineral weathering rates determined from laboratory and field observations generally do not agree, often exhibiting a discrepancy of two-three orders of magnitude.

Recent work on mine waste deposits has demonstrated that this discrepancy can be explained by considering a small number of bulk physical and chemical properties of mine rock at field sites. The apparent decrease in mass-normalized rates between bench-scale batch reactors and pilot-scale column reactors is predicted by accounting for differences in temperature, where lower temperatures in the column reactors reduced reaction rates due to activation energy effects. The columns also contain a significantly greater mass fraction of larger particles that have lower specific surface area and, thus, exhibit lower weathering rates.

The further apparent decrease in rates between the column reactors and field scale is predicted by additionally accounting for the spatial variability of sulphide-bearing rock at the site, which gives rise to only localized weathering. Localized zones of sulphide weathering are also associated with locally active weathering of silicate minerals due to lower pH. Hydrological factors are also important due to preferential flow within the field site, whereby a fraction of dissolved weathering products are retained within immobile water and do not reach the effluent stream, where ion mass flows resulting from weathering reactions are determined. These results suggest that application of compiled laboratory data to prediction of weathering rates at mine sites may be feasible. This is potentially valuable for application to Tier 1 risk assessment of mine sites, where reliable prediction of weathering rates from tabulated laboratory data would provide significant information to support the generally sparse datasets that are available, particularly for orphan mine sites.
The importance of pyritic roof strata in aquatic pollutant release from abandoned mines in a major, oolitic, berthierine-chamosite-siderite iron ore field, Cleveland, UK
Authors: Younger Paul L.
Published: April 2008

The Cleveland Ironstone Field (NE England) is a major sedimentary iron orefield in which the principal ore minerals are iron silicates (berthierine, chamosite) and carbonates (siderite). The siderite in this area is known to be rich in Mg and Mn in solid solution with Fe. Although this ore assemblage would not normally be expected to give rise to acid mine drainage phenomena, a number of discrete ferruginous mine water discharges (totalling some 6.5 million litres (Ml) day
−1
) have been identified flowing from abandoned underground mine workings and old spoil heaps in the ore field. Some of these discharges are extremely acidic (pH ≥ 3.3), with total Fe reaching 1220 mg l
−1
. At the point of first emergence to the surface, most of the discharges are so highly charged with dissolved CO
2
that they effervesce. Upon degassing, one of the discharges precipitates a ferroan calcite deposit, which is most unusual as a mine water discharge precipitate. All the other discharges precipitate more usual ferrihydrite and goethite ‘ochres’. The geochemistry of these waters supports the view that oxidation of pyrite in the roof strata initiates dissolution of siderite in the old workings, releasing CO
2
, Fe and Mg to solution. This chain of reactions results in these waters having SO
2−
4
as their major anion (from pyrite weathering) with Mg as the major cation (except where Fe exceeds Mg in concentration). Two of the near-coastal discharges have Na as the major cation, and elevated Cl concentrations, suggesting a sea-water component. However, SO
4
/Cl ratios suggest that sea water can account for no more than 20% of these waters. Most of the Cleveland mine waters have significant environmental impacts, ranging from ecological damage to receiving water courses to flooding problems caused by the clogging of surface sewers with mine water precipitates. A range of remedial measures are proposed.
Arsenic removal by oxidizing bacteria in a heavily arsenic-contaminated acid mine drainage system (Carnoulès, France)
Authors: Leblanc Marc , Casiot Corinne , Elbaz-Poulichet Françoise , Personné Christian
Published: April 2008

In the Carnoulès Pb-Zn mining site (Gard, France), abandoned 40 years ago, acidic waters (pH 3) with an extremely high As content (80–350 mgl
−1
) emerge from the base of a tailings stock containing As-rich pyrite (2–4% As). From the acidic spring, the oxidation — reduction potential (Eh) and O
2
parameters strongly increase within a few metres and a Fe-As-rich (up to 22% As) material precipitates and covers the bed of the acidic creek. Consequently, there is a sharp decrease in arsenic concentration of the acidic waters downflow (<10 mgl
−1
As) and of the Fe-rich precipitates (down to 2% As). Seasonal variations in dissolved arsenic concentrations of the spring waters are important. Furthermore, the Fe-As-rich stream sediments that were stored, during drought periods, are reworked and transported downflow during rainy periods. The annual fluxes of total arsenic comprise between 2 and 6 t; the lifetime of the As-releasing system is that of several centuries.

Fe and As speciation measurements have been carried out. Fe(II) and As(III) dominate all along the acidic stream. Fe(III) is rapidly precipitated. The removal of total dissolved arsenic mostly corresponds to a decrease in dissolved As(III) and results in the formation of As-rich ferric precipitates. A further decrease in arsenic concentration in water can be attributed to adsorption mechanisms on ferric hydroxides.

In the Fe-As-rich products, the most common bacteria are long rod-shaped phenotypes of the genus
Thiobacillus ferooxidans
. Laboratory experiments have been carried out to investigate the potential catalytic role of these acidophilic oxidizing bacteria on the removal of arsenic: in the biotic systems, 60–80% As were removed in a few days against 5% for abiotic systems.
Fingerprinting mine water in the eastern sector of the South Wales Coalfield
Authors: Brown M. M. E. , Jones A. L. , Leighfield K. G. , Cox S. J.
Published: April 2008

Coal has been mined in the South Wales Coalfield for centuries. Substantial dewatering operations have attended these activities, particularly with the advent of steam and electric pumps that facilitated deeper mining operations. However, underground coal mining in South Wales has been in decline since 1913. The closure of the last deep mine in the eastern part of the coalfield in 1992 entailed a cessation of pumping over a large geographical area, with a resultant recovery of the groundwater. A consequence of this recovery is that emissions of mine water are occurring at the surface.

Surface water emissions of known provenance from the Upper Coal Measures were sampled in 2000 and characterized in terms of their major ion composition. Also, known emissions of mine water within the catchments of the Rivers Ebbw, Ebbw Fach, Rhymney and Taff Bargoed were sampled, and the major ion data plotted on trilinear Piper diagrams. The results indicate that two distinctive hydrochemical facies could be identified from these plots. By combining knowledge of the underground mine workings and lithology, and by comparison with the Upper Coal Measures ‘fingerprint’, it is possible to divide the mine water emissions into those sourced from the Upper and Middle and Lower Coal Measures, and at times to infer a degree of mixing between the two.

The conclusion is that in the eastern valleys of the South Wales Coalfield, the Upper Coal Measures water has a calcium-sulphate facies and the Middle and Lower Coal Measures water has a sodium-sulphate to sodium-bicarbonate facies. This information can be added to the available knowledge to aid in assessing the nature and the progress of groundwater recovery within the coalfield.

This paper refers to preliminary work that has been carried out in the South Wales Coalfield to attempt to ‘fingerprint’ mine water emissions to identify their underground source. This, in turn, provides valuable information on the hydrogeological regime and, coupled with the geological and mining setting, may further assist in identifying underground flow paths. This information helps to fill in some of the ‘knowledge gaps’ and provide a tool for use in the prediction of future surface mine water emissions and in the formulation of treatment-mitigation strategies. The current work uses observations and interpretations of the hydrochemistry of the coal Measures to develop a robust and simple to use method of characterizing and classifying mine water emissions within the South Wales Coalfield. It is anticipated that a similar interpretive process could be applied to mine water emissions in other coalfields, although it should be stressed that this cannot be considered as a ‘stand alone’ process and that the initial characterization of the mine water needs to be carried out with reference to the geological and mining setting for any particular area under consideration.
Alkaline mine drainage from metal sulphide and coal mines: examples from Svalbard and Siberia
Authors: Banks David , Parnachev Valery P. , Frengstad Bjørn , Holden Wayne , Vedernikov Anatoly A. , Karnachuk Olga V.
Published: April 2008

Not all water from coal or metal mines is acidic. Circum-neutral or alkaline mine drainage may be due to: (i) a low content of sulphide minerals; (ii) the presence of monosulphides rather than pyrite or marcasite; (iii) a large pyrite grain-size limiting oxidation rate; (iv) neutralization of acid by carbonate or basic silicate minerals; (v) engineering factors (introduction of lime dust for explosion prevention; cement or rock flour during construction works); (vi) neutralization of acid by naturally highly alkaline groundwaters; (vii) circulating water not coming into effective contact with sulphide minerals; and (viii) oxygen not coming into direct contact with sulphide minerals or influent water being highly reducing.
Assessment, prediction and management of long-term post-closure water quality: a case study — Hlobane Colliery, South Africa
Authors: Hattingh R. P. , Pulles W. , Krantz R. , Pretorius C. , Swart S.
Published: April 2008

Hlobane Colliery, located in the Vryheid Coalfields of South Africa, is to close down its operations after more than a century of mining activities. This paper presents a review of the assessments that were undertaken in order to determine the long-term water quality risks after mine closure and evaluate the effects of various water management actions thereon. An integrated assessment approach was adopted that incorporated hydrological, hydrogeological, mineralogical and geochemical assessment, and modelling techniques to predict the volumes and qualities of water discharging from various points on the mine for the base case situation where no water management options were implemented. Various water management options were identified that are primarily aimed at preventing the contamination of clean water, and the effects of these strategies were predicted and compared with the base case situation in order to provide a rational basis for the selection of the most appropriate strategies.
Formation and evolution of Archaean cratons: insights from southern Africa
Authors: James D. E. , Fouch M. J.
Published: April 2008

Archaean cratons are the stable remnants of Earth’s early continental lithosphere, and their structure, composition and survival over geological time make them unique features of the Earth’s surface. The Kaapvaal Project of southern Africa was organized around a broadly diverse scientific collaboration to investigate fundamental questions of craton formation and mantle differentiation in the early Earth. The principal aim of the project was to characterize the physical and chemical nature of the crust and mantle of the cratons of southern Africa in geological detail, and to use the 3D seismic and geochemical images of crustal and mantle heterogeneity to reconstruct the assembly history of the cratons. Seismic results confirm that the structure of crust and tectospheric mantle of the cratons differs significantly from that of post-Archaean terranes. Three-dimensional body-wave tomographic images reveal that high-velocity mantle roots extend to depths of at least 200 km, and locally to depths of 250–300 km beneath cratonic terranes. No low-velocity channel has been identified beneath the cratonic root. The Kaapvaal Craton was modified approximately 2.05 Ga by the Bushveld magmatic event, and the mantle beneath the Bushveld Province is characterized by relatively low seismic velocities. The crust beneath undisturbed Archaean craton is relatively thin (
c.
35–40 km), unlayered and characterized by a strong velocity contrast across a sharp Moho, whereas post-Archaean terranes and Archaean regions disrupted by large-scale Proterozoic magmatic or tectonic events are characterized by thicker crust, complex Moho structure and higher seismic velocities in the lower crust. A review of Re-Os depletion model age determinations confirms that the mantle root beneath the cratons is Archaean in age. The data show also that there is no apparent age progression with depth in the mantle keel, indicating that its thickness has not increased over geological time. Both laboratory experiments and geochemical results from eclogite xenoliths suggest that subduction processes played a central role in the formation of Archaean crust, the melt depletion of Archaean mantle and the assembly of early continental lithosphere. Co-ordinated geochronological studies of crustal and mantle xenoliths have revealed that both crust and mantle have experienced a multi-stage history. The lower crust in particular retains a comprehensive record of the tectonothermal evolution of the lithosphere. Analysis of lower-crustal xenoliths has shown that much of the deep craton experienced a dynamic and proteracted history of tectonothermal activity that is temporally associated with events seen in the surface record. Cratonization thus occurred not as a discrete event, but in stages, with final stabilization postdating crustal formation.
The development of lithospheric keels beneath the earliest continents: time constraints using PGE and Re-Os isotope systematics
Authors: Pearson D. G. , Irvine G. J. , Carlson R. W. , Kopylova M. G. , Ionov D. A.
Published: April 2008

Continued studies of xenolith suites found in kimberlites on and around the Kaapvaal Craton, together with those from newly discovered localities on other cratons, are providing new insights into the generation and evolution of the Earth’s oldest continents. Comparison of modal abundance data with melt depletion models, together with trace element and isotope systematics in Kaapvaal low-temperature peridotites, suggest that much or all of the diopside and garnet in these rocks may have formed significantly after initial melt depletion. The Re-Os isotope system has been instrumental in providing an improved understanding of the timing of the formation of cratonic lithospheric keels. New studies that focus on carefully selected whole-rock peridotites and use combined platinum group element (PGE) and Re-Os isotope analysis provide better constraints on the significance of Re-Os model ages. The large database of Re-Os isotope analyses for peridotites for the Kaapvaal Craton indicate formation of significant amounts of lithospheric mantle in Neoarchaean time, associated with voluminous mafic magmatism. Formation of lithospheric mantle in Neoarchean time (3.0–2.5 Ga) follows the cessation of major crustal differentiation events at
c
. 3.1 Ga and marks the onset of craton stabilization. Some lithospheric mantle was produced in Palaeo- to Mesoarchaean time (3.8–3.0 Ga) in southern Africa, which preserved ancient crustal fragments. Large-scale preservation of Archaean continental masses was effective only after the formation of substantial, buoyant, rigid, deep lithospheric keels and their stabilization in Neoarchean time. Formation of lithospheric mantle beneath the surrounding Proterozoic crustal regions occurred in Mesoproterozoic time, with lower degrees of mantle melting than associated with the cratonic peridotites. This circum-cratonic mantle is of similar age to the oldest overlying crust and has been coupled to the margins of the craton since its formation. Major magmatic events, some coincident with the formation of circumcratonic mantle, added new lithosphere to the Kaapvaal mantle root but failed to destroy it. The mechanically strong, buoyant lithospheric keels beneath cratons protect their crust from subduction and recycling over 3 Ga time periods.
Seismic evidence for a mantle source for mid-Proterozoic anorthosites and implications for models of crustal growth
Authors: Musacchio Gemma , Mooney Walter D.
Published: April 2008

Voluminous anorthosite intrusions are common in mid-Proterozoic crust. Historically, two end-member models have been proposed for the origin of these anorthosites. In the first model anorthosites derive from fractionation of a mantle source leaving a residue of metagabbro in the lower crust; in the second model anorthosites are the product of partial melting of the lower crust with residual pyroxene and high-grade minerals (i.e. a pyroxenitic and/or metapelitic lower crust). Although a general consensus has developed that the first model provides the best fit to petrological and geochemical constraints, the sparse evidence for mafic and ultramafic counterparts to the anorthosites leaves the issue still unresolved. We use the absolute P-wave velocity and the ratio between P- and S-wave velocities (
V
P
/
V
S
) to infer the composition of the lower crust beneath the Marcy Anorthosite (New York State, USA). Seismic refraction data reveal a lower crust 20 km thick, where
V
P
and V
P
/V
S
range from top to bottom between 7.0 km s
−1
and 7.2 ± 0.1 and 1.84 km s
−1
and 1.81 ± 0.02, respectively. Laboratory measurements on rock samples indicate that these seismic properties are typical of plagioclase-rich rocks. Magmatic underplating of basaltic melts is a mechanism to form plagioclase-rich bulk composition for the Grenville crust. At the bottom of the lower crust, increase of P-wave velocity, slight decrease of
V
P
/
V
S
ratios and the presence of a low-reflective seismic Moho are additional observations supporting crustmantle interactions related to magmatic underplating. High P-wave velocity (8.6 km s
−1
) in the upper mantle may indicate that the ultramafic portion (e.g. pyroxenites) of the underplated magma has become eclogite. High average P-wave velocity (6.7 km s
−1
) and
V
P
/
V
S
(1.81), and the exceptional abundance of anorthosites-norites-troctolites among the rocks exposed at the surface, indicate that the Grenville Proterozoic crust may have a unique plagioclase-rich bulk composition. We suggest magmatic underplating, occurring either over a wide time span or with separate syn- and post-collisional magmatic pulses, as being a major crust-forming mechanism operating in mid-Proterozoic time.
Neoarchaean tectonic evolution of the Zimbabwe Craton
Authors: Jelsma Hielke A. , Dirks Paul H. G. M.
Published: April 2008

An overview is presented of the field relations, age data and geochemical characteristics of the Neoarchaean granites and greenstones of the Zimbabwe Craton, southern Africa. A major tectono-magmatic event at
c.
2.7 Ga produced two distinct greenstone successions. One succession is reminiscent of rift- or back-arc environments and is associated with an old continental fragment. A second succession is indicative of arc magmatism and is associated with juvenile crust. Both were affected by a major accretionary event that, in an apparent sense, swept across the craton between 2.68 and 2.60 Ga. During this 80 Ma time period, concomitant late volcanism, regional deformation, the development of syntectonic sedimentary successions in foreland-type basins, and late syntectonic plutonism took place in selected shear-zone-bounded tectonic domains over limited periods of time (<10–20 Ma). Deformation led to isostatically stable, 30–40 km thick continental crust, without significant exhumation of high-pressure rocks, suggesting that lithospheric shortening was accommodated independently in a rheologically strong upper and weak lower crust. Deformation was followed by pan-cratonic crustal melting and strike-slip shear motions, and led to stabilization of the crust at 2575 Ma, heralded by the emplacement of the Great Dyke.
Carbon dioxide cycling through the mantle and implications for the climate of ancient Earth
Authors: Zahnle Kevin , Sleep Norman H.
Published: April 2008

The continental cycle of silicate weathering and metamorphism dynamically buffers atmospheric CO
2
and climate. Feedback is provided by the temperature dependence of silicate weathering. Here we argue that hydrothermal alteration of oceanic basalts also dynamically buffers CO
2
. The oceanic cycle is linked to the mantle via subduction of carbonatized basalts and degassing of CO
2
at the mid-ocean ridges. Feedback is provided by the dependence of carbonatization on the amount of dissolved carbonate in sea water. Unlike the continental cycle, the oceanic cycle has no thermostat. Hence surface temperatures can become very low if CO
2
is the only greenhouse gas apart from water. Currently the continental cycle is more important, but early in Earth’s history the oceanic cycle was probably dominant. We argue that CO
2
greenhouses thick enough to defeat the faint early Sun are implausible and that, if no other greenhouse gases are invoked, very cold climates are expected for much of Proterozoic and Archaean time. We echo current fashion and favour biogenic methane as the chief supplement to CO
2
. Fast weathering and probable subduction of abundant impact ejecta would have reduced CO
2
levels still further in Hadean time. Despite its name, the Hadean Eon might have been the coldest era in the history of the Earth.
Global modelling of continent formation and destruction through geological time and implications for CO
2
drawdown in the Archaean Eon
Authors: Kramers Jan D.
Published: April 2008

The possible drawdown of a massive CO
2
atmosphere in early Earth history is discussed using two working hypotheses: first, that this removal of CO
2
from the atmosphere occurred mainly via silicate weathering; second, that crust-to-mantle recycling rates found from forward modelling of crust-mantle history can be used to estimate rates of this ancient silicate weathering. Previous U-Th-Pb and Sm-Nd forward modelling efforts are reviewed, from which it was concluded that an insignificant amount of continental crust existed at 4.4 Ga, i.e. so-called ‘no-growth models’ for the continental crust appear untenable. New modelling carried out is based on a crustal growth curve starting with zero mass at 4.2 Ga and reaching 75% of the present crust mass by 2 Ga. It concerns variations in crust-to-mantle recycling rates through geological time. Best fits to isotope data are obtained if it is assumed that erosion rates (mass removal per unit surface) were approximately constant from early Archaean time to the present. From the results it can be estimated that drawdown of a massive CO
2
atmosphere by silicate weathering could have been completed by the end of Archaean time at the earliest, and about 1.5 Ga ago at the latest.