bluuebunny/crossref_metadata_2025_split huggingface dataset:
A syn-rift to post-rift transition sequence in the Main Porcupine Basin, offshore western Ireland
Authors: Moore John G. 
Published: April 2008

Abstract
The evolution of the Main Porcupine Basin can be divided into pre-rift, syn-rift and post-rift stages. The syn-rift/post-rift transition represents a gradual change from extensive fault activity through localized faulting and passive infill to sporadic faulting during post-rift times. This Transition Sequence is present in localized areas (sub-basins). It infills the remnant syn-rift topography after which the post-rift stage begins. Sub-basins developed during the syn-rift stage have a general N-S to NE-SW orientation and range in size from approximately 30 km × 20 km to approximately 12 km × 8 km. Their shapes range from symmetrical fault-bounded depocentres to half-graben. The sub-basins have several internal unconformities which merge into a single composite erosion surface at the margins. Areas in which the Transition Sequence is developed usually have an element of fault control, especially during the early stages. Clastic fans are identified prograding from fault scarps. Later passive onlap during a rising sea-level progressively infills the subbasins. The age of the Transition Sequence is problematical, but borehole data suggests that it spans uppermost Kimmeridgian/Tithonian to end-Berriasian times. The sub-basins appear to be broadly coincident with small Permo-Triassic basins. This may point to a deep-seated fault control on the location of the Transition Sequence sub-basins. Comparable syn- to post-rift Transition Sequences are also present in the Orphan and Jeanne d’Arc Basins, offshore Eastern Canada, and possibly in other North Atlantic rift basins also.
Basement tectonics and their relationship to Mesozoic megasequences in the Celtic Seas and Bristol Channel area
Authors: Ruffell A. H. , Coward M. P. 
Published: April 2008

Abstract
A synthesis of new and pre-existing data on the deep geological structure of the Celtic Sea and Bristol Channel basins shows similarities to published models of deep structure from the onshore Wessex Basin to the east. A series of Variscan thrust planes, reactivated in the Mesozoic as normal faults, underlie the study area. Beneath the Bristol Channel, one such southward-dipping thrust may be equated with the ‘Variscan Front’. This structure is offset by NW-SE orientated transcurrent faults, structures thought to be active from the late Palaeozoic to the present-day. Mesozoic stratigraphic successions from the North Celtic Sea Basin and South Celtic Sea; Bristol Channel, and northern Wessex Basins suggest uplift and erosion of the latter areas in the late Jurassic. This is contrasted with increased subsidence at the same time in the North Celtic Sea. This uplift may have been facilitated by reactivation of the ‘Variscan Front’ thrust as a thrust in the east of the area, and by similar thrusts beneath the Pembrokeshire Ridge to the west. This reactivation and uplift during North Atlantic opening is suggested to have controlled the preservation of Upper Jurassic-Lower Cretaceous sedimentary megasequences.
Application of mineral deposit models in exploration: a case study of sediment-hosted gold deposits, Great Basin, Western United States
Authors: Adams Samuel S. , Putnam Borden R. 
Published: April 2008

Abstract
This paper emphasizes the development of mineral deposit models for exploration using as a case study the sediment-hosted, structure-controlled, disseminated gold deposits in the Great Basin of the Western United States. More than 60 deposits have been found in this area since the discovery of the Carlin deposit in 1962. Most deposits were discovered by direct prospecting and sampling of outcropping silicified zones (jasperoids). Similar poorly exposed and unexposed deposits remain to be discovered, but future exploration will require improved models that indirectly predict locations of these deposits.
Many of these sediment-hosted gold deposits occur within silicified and structurally complex zones in calcareous rocks below regional east-directed thrusts. Geological characteristics that have been successfully employed in exploration include: erosional windows (fensters) through the thrusts; silty to arenaceous calcareous host rocks below the thrusts; silicified zones; anticlines and domes of the lower plate calcareous sediments; alignment of deposits along linear trends; and geochemical anomalies (Au, Ag, As, Sb, Tl, etc.). Although the use of these criteria will discover new deposits, exploration now requires additional criteria that are reliably, but not so directly, associated with the deposits. Identification of these criteria will require the development of genetic models that tie more regional geological characteristics to ore formation and localization.
Development of successful mineral deposit models first requires a working definition of the sediment-hosted gold deposit class and its geological characteristics. The characteristics of each deposit included in this class are then documented and validated. Next, the geological processes most likely responsible for the shared characteristics are identified. Finally, the most reliable, informative and accessible criteria, reflective of each ore-forming process, are selected. From these criteria are chosen the most efficient and effective geological features for continued exploration.
Processes currently suggested to be important in the formation of sediment-hosted gold deposits include: regional wrench fault tectonics; plutonism; hydrothermal fluid flow driven by intrusions and/or thrusting; fluid flow along regional unconformities; gold precipitation following carbonate dissolution, or fluid mixing; and dissolution of synsedimentary gold from the allochthonous western assemblage sediments and reprecipitation of that gold in the deposits. A general approach for identifying additional possible processes, testing alternative processes and finally selecting exploration criteria is presented.
Mineralogy in the evaluation of ore deposits
Authors: Kingston G. A. 
Published: April 2008

Abstract
Mineralogical characterization of an ore deposit is an essential on-going activity in a continuum of evaluation exercises and decisions which operate from the very first recognition of mineralization to the cessation of mining and beyond. The main input of the mineralogist to ore evaluation is through the provision of a detailed qualitative and quantitative mineralogical representation of an ore that is specifically targeted to the needs of the process engineer in determining metallurgical recovery, especially during the exploration and pre-production stage. This process mineralogical input is often related to fine-tuning in mining and processing resulting from unexpected variations in the mineralogy of the ore to the mill. Mineralogical characteristics of platinum ore, refractory gold ores, and complex Cu-Zn-Pb ores are used to illustrate aspects of process mineralogical input at various stages in the life cycle of a mine. It is concluded that it is difficult for the mineralogist to become established as an essential and ongoing participant of exploration and mine evaluation exercises. It is thus important that both process engineers and geologists are given a better training in process mineralogy than is presently the case. Most mineralogical training and research in geology departments is exclusive of industrial applications.
Geophysical logs and the search for opencast coal reserves
Authors: MacCallum R. 
Published: April 2008

Abstract
The application of down-hole wireline logging techniques in the exploration for, and evaluation of, opencast coal reserves is described. The paper concentrates on the nuclear geophysical suite, in particular gamma and gamma-gamma logging which, to date, provide the most accurate geophysical means of identifying coal seams and estimating their thickness. The use of such logs in the identification of partings in coal seams, abandoned underground workings, sandstones, marine bands, ironstones and water levels is also described. The way in which such logs can be used in the correlation of individual coal seams is demonstrated, together with their use in the interpretation of geological structures in complex structural terrains. The advantages gained by the geophysical logging of boreholes far outweigh the increased costs incurred during exploration.
Sampling, grade control and ore reserve estimation at Renco gold mine, Zimbabwe: past, present and future
Authors: Armitage M. G. , Robinson I. E. 
Published: April 2008

Abstract
Modern gold mining activity at Renco Mine in southern Zimbabwe started in 1936. Since then a series of different companies have held the option to mine. The current owners, Rio Tinto Zimbabwe, took it over in 1973.
Accurate grade control and ore reserve estimation has in the past been hampered by the complex geology. However, improved geological understanding since 1986 has led to changes in the sampling techniques, which in turn have brought about improvements in both grade and tonnage factors.
For ore reserve evaluation, blocks of reef are defined by raises and reef drives. For each block the average grades and reef widths, calculated from the sampling of the peripheral developments, are used to estimate tonnages and grades.
Since 1987, a geostatistical software package has been used to generate kriged plans of gold grade and reef thickness. It is now planned to incorporate the results of more recent geological research into this software package in the hope of further improving the accuracy of the orebody evaluation and production data.
Computerized grade control in complex porphyry copper deposits
Authors: Franklin P. J. 
Published: April 2008

Abstract
Grade distribution within porphyry copper deposits can sometimes be erratic in nature. Conventional, manual grade control techniques for open pit mining have proved to be inadequate for accurately predicting mining head grades and for delineating ore and waste contacts.
This paper describes a highly interactive computerized grade control system that uses a combination of geostatistical modelling and graphical techniques to perform the daily grade control operations. The software is used to improve the reliability of grade predictions and to perform reconciliation of mined materials with planned materials.
The paper is illustrated with examples from operating copper open pits located in western Canada.
Reconciliation studies and reserve estimation
Authors: Sides Edmund J. 
Published: April 2008

Abstract
Reconciliation studies involve the comparison of different sets of data, and the analysis of differences between them in terms of accuracy and precision. Such studies are important during reserve estimation as a means of validating input data and modelling techniques used, as well as providing a means of checking the accuracy and precision of the resultant models. Examples of such studies from work done at the Neves-Corvo copper-tin mine in southern Portugal are given. It is argued that reconciliation studies should form an integral part of any reserve estimation, as a means of controlling the quality of the estimation procedures used.
Geostatistical ore reserve estimation: a case study in a disseminated nickel deposit
Authors: Dowd P. A. 
Published: April 2008

Abstract
This paper describes the geostatistical evaluation of a disseminated nickel orebody which contains remnants of high grade vein mineralization. The problems of dealing with high grade outliers are discussed together with the difficulties of modelling the semivariograms. Methods for the validation of the variogram models are presented prior to their use in a geometrically and geologically controlled kriging procedure to estimate recoverable blocked ore reserves.
The application of geostatistically controlled elliptical weighting techniques at Boulby potash mine, Cleveland
Authors: Annels A. E. , Ingram S. 
Published: April 2008

Abstract
Statistical studies of a portion of the Boulby potash seam revealed that distinct subareas are present in which stationarity could be shown to exist and which are characterized by statistically distinct populations of seam thickness and % KCl. Semivariogram modelling in these sub-areas allowed the definition of the axes of anisotropism in each case and hence the dimensions and orientation of the search ellipses for ore reserve purposes. Inverse distance weighting was then applied to evaluate individual ore blocks and the efficiency of the method tested by cross-validation of actual borehole values. Considering the problems induced by the sampling method applied (low angle deflection of in-seam drill holes), the results were generally satisfactory and form the basis for a more detailed comparative study of inverse distance and kriging techniques at Boulby.
Organic carbon removal in the sea: the continental connection
Authors: Ittekkot V. , Haake B. , Bartsch M. , Nair R. R. , Ramaswamy V. 
Published: April 2008

Abstract
Time series sediment traps have been deployed since May 1986 in the Arabian Sea and since October 1987 in the Bay of Bengal. The results of one and a half years from the western, central, and eastern Arabian Sea and of one year from the northern Bay of Bengal show that particle flux patterns are related to the strong monsoon winds and heavy rains. Particle flux maxima in the Arabian Sea are mainly related to wind-induced deeper mixing and nutrient enrichment of surface waters during the SW and NE monsoons. Extremely high particle fluxes with high biogenic opal contents during the SW monsoon at the western location show that it is reached by nutrient-rich water from the near-shore upwelling centres. In the northern Bay of Bengal, particle flux maxima coincide with the period of maximum discharge of the Ganges and Brahmaputra rivers during which river plumes enriched in nutrients are advected into offshore areas. Additionally, the winds and river plumes supply enormous amounts of mineral matter during the periods of high productivity and high particle fluxes. The interaction between marine-biogenic material with eolian and fluviatile mineral particles plays a key role in sedimentation. The incorporation of mineral matter into biologically formed aggregates ensures their rapid sedimentation and thus enhances the removal of biologically fixed atmospheric carbon dioxide to the deep sea.
Water depth and diagenetic constraints on the use of barium as a palaeoproductivity indicator
Authors: Von Breymann Marta T. , Emeis Kay-Christian , Suess Erwin 
Published: April 2008

Abstract
Sediments underneath the high productivity areas of the coastal upwelling and equatorial divergence zones in the Pacific and Indian oceans are enriched in barium, and on this basis the barium content of the sediments has long been suggested as a potential palaeoproductivity indicator. Analyses of sediments from the Peru margin corroborate the pattern of enhanced barium accumulation in areas of high primary productivity in the deep ocean, but also show that this pattern cannot be extended to shallow-water deposits. Sediments from the Peru shelf lack any barium enrichment, whereas this element is significantly enriched in slope and basinal deposits in water columns deeper than 2000 m. This depth effect is further illustrated at Site 682 located in the rapidly subsiding Lima Basin. The Quaternary sequence deposited at water depths >3000 m is enriched in organic carbon, opal and biogenic barium. The Miocene sediments, although deposited under highly productive waters associated with a coastal upwelling centre, do not show an enrichment in the barium record corresponding to the very high organic carbon and opal levels; a pattern that is consistent with deposition in shallow basins.
In addition to the effect of water depth on the barium distribution, overprinting of primary signals can be observed in sediments from upwelling areas undergoing strong anoxic diagenesis. Microcrystalline barite is partly dissolved in intervals depleted in interstitial sulphate as shown for sediments from the Peru margin. Dissolution of barite in sulphate depleted intervals of deep water sections leads to high barium concentrations near the termination of the sulphate reducing zone, where downward sulphate and upward barium diffusion foster local barite precipitation in diagenetic fronts.
The barium distribution in sedimentary oxic and suboxic environments at deep water depositional sites has a high potential as a palaeoproductivity indicator; however, barium accumulation as a proxy for ocean fertility should be used with caution in areas of varying water depths and in anoxic diagenetic environments where sulphate depletion undersaturates the interstitial waters with respect to barite.
The Benguela Current and associated upwelling on the southwest African Margin: a synthesis of the Neogene-Quaternary sedimentary record at DSDP sites 362 and 532
Authors: Diester-Haass Liselotte , Meyers Philip A. , Rothe Peter 
Published: April 2008

Abstract
Sediments cored at DSDP Sites 362 and 532 on the Walvis Ridge provide a Neogene-Quaternary history of the development of the upwelling system on the southwest African margin. Upwelling occurs principally on the landward side of the Benguela Current. The upwelling centres have shifted northward since the Middle Miocene as the current has intensified and has flowed farther to the north. Changes in productivity are recorded in the types, proportions and preservation of foraminifera, radiolaria, diatoms, organic matter, and clay minerals in the sedimentary record. Prior to the Late Miocene (10 Ma), the Benguela Current did not reach the Walvis Ridge, and enhanced productivity is not evident in the sediments at this location. Between 10 to 5.2 Ma, upwelling was recorded in the DSDP sites in glacial periods, indicating that the Benguela Current intensified during glacial periods and transported evidence of upwelling to Sites 362/532 from near-coastal areas. During interglacial periods the current was not as strong and did not reach the Walvis Ridge, turning instead to the west within the Cape Basin. Strengthening of the current continued such that by the Pliocene and Quarternary the upwelling signal is contained in interglacial sediments. Sediments deposited in these more recent glacial times contain a weak or absent upwelling signal because glacial intensification shifts the Benguela Current system northward to reach the Angola Basin before it turns westward away from its coast-parallel direction.
Techniques and applications of petrophysical correlation in submarine fan environments, early Tertiary sequence, North Sea
Authors: Hatton I. R. , Reeder M. , Newman M. St. J. , Roberts D. 
Published: April 2008

Abstract
Accurate stratigraphic delineations and correlations are key factors in exploration and development of early Tertiary reservoirs of the North Sea. In the submarine fan environment, application of biostratigraphic data can be complicated by stacking of sand sequences. A sand indicator is derived from a wireline log computation. The sand intervals are then edited out to generate a log profile of the background sedimentary sequence. Additional refinement is obtained by use of cross plot analysis to define petrophysical attributes of selected stratigraphic units. An example is described where such analysis has been applied to the Balder Formation where a ‘tuff profile’ has been established. Further examples illustrate how the methods serve to extrapolate detailed biostratigraphic data of wells into adjacent wells with limited or no data.
Evaluating thinly laminated reservoirs using logs with different vertical resolution
Authors: Ruhovets N. , Rau R. , Samuel M. , Smith H. , Smith M. 
Published: April 2008

Abstract
Reservoirs with thin laminations can be more accurately evaluated by using logging tools with inherently better vertical resolution, by employing enhanced vertical resolution input processing methods, and by incorporating interpretation models that properly handle log inputs with different vertical resolutions and reconstruct all outputs with high vertical resolution. The paper discusses a specific high-resolution interpretation model and provides comparative analyses of how model outputs are affected by the vertical resolution of its input logs and by the reservoir type. Three field examples are provided. Increases in predicted hydrocarbons were noted in two of these examples when the input log resolution was increased. In these two examples, the observed increases were confined to a number of isolated thin beds. In the third field example, significant decreases in predicted hydrocarbons were observed when high-resolution input data were used; the reservoir in this case appears to illustrate thin sand-shale laminae extended over a 27 metre interval.
Borehole breakouts and stress analysis in the Timor Sea
Authors: Hillis R. R. , Williams A. F. 
Published: April 2008

Abstract

Boreholes drilled in the search for oil in the Vulcan Sub-basin (Timor Sea, Northwest Shelf, Australia) commonly exhibit an elliptical cross section believed to be the result of wellbore failure known as borehole breakout. The azimuths of the long axes of breakouts identified in 13 wells in the Vulcan Sub-basin show a reasonably consistent 130–170°N trend implying that maximum horizontal compressive stress (
SH
max
) is oriented 040–080°N.

This NE-ENE
SH
max
orientation in the Vulcan Sub-basin does not coincide with the direction of absolute plate velocity, nor is it consistent with compression transmitted from the nearby Australia/Banda Arc collision zone. However, it is in agreement with theoretical models of stress distribution based on the plate-driving forces throughout the Indo-Australian plate.

The breakout analyses, in conjunction with structural interpretations, suggest that the instabilities observed in vertical wells will be exacerbated by orienting horizontal wells 040–080°N, and that drilling in the 130–170°N direction may enhance both stability and production rates.
An integrated interpretation of fracture apertures computed from electrical borehole scans and reflected Stoneley waves
Authors: Hornby Brian E. , Luthi Stefan M. 
Published: April 2008

Abstract
Fractures crossing the borehole are probed using electrical currents generated by Formation MicroScanner* pads and Stoneley waves generated by an acoustic source. New techniques have been developed to invert these measurements for estimates of equivalent fracture aperture, a crucial parameter controlling the fluid flow in fractured reservoirs. The objective of this paper is twofold: first, to compare aperture estimates in a variety of rock types; and second to exploit the different physical measurements in order to improve our understanding of the fracture system. Single fractures in controlled borehole experiments are used to cross-validate the two techniques, and good comparisons were found in the aperature range from 10 μm to several millimetres. Core data, acoustic borehole televiewer images, and in one case results using the Dual Laterolog* measurement serve as supporting evidence. Three case studies are presented: one from crystalline rocks, another from a chalk and shale sequence, and a third one from a fractured dolomite reservoir. In these case studies we found that a combined analysis of the two methods yields valuable additional information concerning fracture extent, fracture connectivity and borehole effects such as fracture enlargement and borehole rugosity.