bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationships between thrust tectonics and sequence stratigraphy surfaces in foredeeps: model and examples from the Pyrenees (Cretaceous-Eocene, France, Spain)
Authors: Deramond Joachim , Souquet Pierre , Fondecave-Wallez Marie-José , Specht Martin
Published: April 2008

A new method of chronological and geometrical analysis is used for understanding the sedimentary and tectonic evolution of perisutural basins (foredeep and foreland basins). It may be applied to synorogenic basins whose infilling was controlled by sea-level fluctuations and where, as a result, the tectonic structures are well preserved. This method is based on the mapping of depositional sequence boundaries and maximum flooding surfaces defined by sequence stratigraphy. These planar markers are considered as synchronous and their numerical ages are determined by classical chronostratigraphic methods, by dating and by comparison with the eustatic global cycle chart.

The evolution of the studied perisutural basins is controlled by the propagation in space and time of a syn-depositional thrust-and-fold system including a fault-propagation anticline and two synclines (a foreland and a hinterland syncline) over and in front of a blind basal sole thrust. The propagation of this thrust-and-fold system toward the foreland is connected to unconformable depositional sequence sets, which indicate for each system a time span for thrusting of several eustatic cycles.

The evolution of a single thrust-and-fold system corresponds to a shortening accommodated by upward imbrication of second-order thrusts inside the anticline. Each of these thrusts is related, at least, to one depositional sequence lying unconformably on the external side of the fold and deformed by the successive development of the branch lines toward the hinterland. This tectono-sedimentary correlation indicates a time span sometimes as short as one eustatic cycle for each second-order thrust.

Thrusting and sea-level changes are not exactly synchronous, as the depositional sequence sets (which are tectonic in origin) do not systematically correlate with eustatic supercycles. The apparent time correlation between the two groups of independent phenomena is an artefact of the method which calibrates the tectonic evolution by comparison with eustatic fluctuations.

Applied to the South Central Pyrenees, the method has specified the structure of the Late Cretaceous foredeep basin and has revealed the successive stages of forward thrust-and-fold system migration (4 to 5 Ma for each one from 89 Ma) and of hindward second-order thrust migration (1 to 4 Ma for each one).

In the North Central Pyrenees as in the South Central Pyrenees, Late Cretaceous foredeeps are characterized by syntectonic turbidite deposits (from 89 Ma onward) and by a significant shortening due to a symmetrical and synchronous structural evolution. The Eocene foreland is a foreland syncline developed in the footwall of the North Pyrenean Thrust. This syncline is due to the occurrence of blind thrusts and it is infilled by fluvial deposits.
Luminescence dating of sand from the Kelso Dunes, California
Authors: Edwards Stephen R.
Published: April 2008

A relatively new luminescence dating technique, infra-red stimulated luminescence (IRSL), has been used to date dune sand from the Kelso Dunes, eastern Mojave Desert, California. This is the first time the technique has been applied to desert aeolian sands. The IRSL technique measures the time since sediment grains were last exposed to light, by sampling a highly light-sensitive signal which reduces rapidly to a negligible level when so exposed. The technique can be used to date very young samples. Of the ten samples dated, the surface sample gave an age of 40 ± 17 years, while subsurface samples gave high-precision middle and late Holocene dates. These results, obtained from the upper 8 m of the sand mass, indicate significant aeolian activity during the later part of the Holocene. Clustering of IRSL ages from the data so far available suggests that the aeolian activity may have been episodic.
Climbing and falling sand dunes in Finnish Lapland
Authors: Seppälä Matti
Published: April 2008

This paper presents the first description of climbing and falling sand dunes from Finnish Lapland. They are located on the slopes of a glaciated valley containing an esker. The largest climbing dune is 1800 m long and 2–5 m high. The slope of the fell dips 7 degrees on average. The material comprising the dune is typical aeolian sand with a median grain size about 0.23 mm but not very well sorted. The dunes were formed just after deglaciation under periglacial conditions.
Outcrop data-base for the geological characterization of fluvial reservoirs: an example from distal fluvial fan deposits in the Loranca Basin, Spain
Authors: Cuevas Gozalo M. C. , Martinius A. W.
Published: April 2008

Sedimentological data for stochastic modelling purposes consist both of qualitative and of ‘hard’ numerical data from reservoir-equivalent outcrops. Data requirements are defined prior to collection of the actual field data-base, and standard procedures for the collection and classification of these data are established. Required data are on individual sandbodies, such as genetic type, geometry, palaeoflow and size; and on the 2D and 3D sedimentary architecture (spatial distribution, interconnectedness).

Validity of the data-requirement definition, and feasibility of data acquisition for specific stochastic modelling purposes, were tested in reservoir-equivalent outcrops of distal fluvial fan deposits of Tertiary age in the Loranca Basin in central Spain. Several sandbody genetic types were recognized: meander-loop deposits, channel-fill deposits, crevasse-channel and crevasse-splay deposits and deltaic deposits. Statistical processing of the numerical outcrop data showed that meander-loop deposits are thicker, wider and present higher linearinterconnectedness values than channel-fill deposits.
Identification and significance of aeolian deposits within the dominantly fluvial Sherwood Sandstone Group of the East Irish Sea Basin UK
Authors: Cowan Greig
Published: April 2008

The Triassic Sherwood Sandstone Group sediments of the East Irish Sea Basin are over 4000 ft thick and comprise medium- to coarse-grained sandstones and rare thin mudstones. Facies models developed during production drilling on the South Morecambe Field show that deposition occurred in a braided fluvial setting with minor aeolian episodes. The major facies associations present are: (A) major channel fill; (B) ephemeral channel fill; (C) non-channelized sheetflood deposits; (D) and (E) non-reservoir fines (abandonment and playa respectively); (F) aeolian dune and sand-sheet. Volumetrically, the major channel (A) and sheetflood (C) facies dominate, and the alternation of these facies associations is correlatable across the field. The aeolian sandstones form units varying in thickness from a few grain diameters up to 3 m thick. The sand-sheet and dune deposits can be correlated over considerable distances and show pressure communication on RFT logs. Although the aeolian sandstones comprise only 5–10% of the reservoir they have very high porosities and permeabilities (up to 30% and 10 darcies) and make disproportionate contributions to flow into the wellbore. The depositional criteria used to differentiate between aeolian and fluvial deposition in the South Morecambe Field are pinstripe lamination, good sorting and lack of rounded clay clasts, but these criteria are not definitive. As a result of the dissolution of an early diagenetic cement, aeolian sandstones have very high porosities compared to fluvial sandstones. This high porosity is reflected in high sonic transit times and allows aeolian sandstones to be identified tentatively in uncored wells by use of sonic logs.
Modelling fluid flow through geologically realistic media
Authors: Lake L. W. , Malik M. A.
Published: April 2008

The most useful way to validate a predictive scheme is to compare its results against actual performance. While this approach has enjoyed some success, the interpretation of any reservoir process is complicated by many operational, reservoir and subjective issues. These issues mean that the process performance is rarely clear, and consequently the success of the prediction is always in doubt, no matter how closely the prediction agrees with performance. The work described in this paper adopts another means of validation: comparison of a highly detailed deterministic simulation against the results generated from conditional simulation (CS). Results show that, although it is highly flexible and generates realistic heterogeneity, CS must be tailored to the specific geological environment for best agreement with the deterministic simulation.
Preliminary Landsat lineament analysis of the northern Nanga Parbat-Haramosh Massif, northwest Himalaya
Authors: Cronin V. S. , Schurter G. J. , Sverdrup K. A.
Published: April 2008

Analysis of a mosaic of Landsat 2 MSS band 7 images covering the northern Nanga Parbat-Haramosh Massif (NPHM) has yielded approximately 540 lineaments, defined by sets of colinear drainage segments and aligned linear graytone boundaries. We recognized segments of the few well-mapped faults along the NPHM as lineaments. The paucity of field data concerning faults, joints, lithological fabric and contacts prevents us from interpreting most of the lineaments at this time. However, some of the prominent lineament trends probably mark the trace of previously unmapped active faults that accommodate the recent uplift of the NPHM. The origins of these lineaments must be established through structural geological field work.
Stratigraphy south of the Main Mantle Thrust, Lower Swat, Pakistan
Authors: Dipietro Joseph A. , Pogue Kevin R. , Lawrence Robert D. , Baig Mirza S. , Hussain Ahmad , Ahmad Irshad
Published: April 2008

The metamorphic sequence in Lower Swat is described and placed into the geological framework of Pakistan. The stratigraphic sequence consists of the Precambrian-Cambrian(?) Manglaur formation unconformably overlain by the Alpurai group which is subdivided into the Carboniferous or younger Marghazar formation, and the Triassic or younger Kashala, Saidu, and Nikanai Ghar formations. A third unit, the Jobra formation of unknown age, is present as discontinuous lenses unconformably below the Alpurai group. Type sections are indicated for each rock unit. Comparison with the stratigraphy in the Peshawar Basin indicates that the Lower Swat area existed as a highland with active normal faulting during and perhaps before deposition of the Marghazar formation. The Marghazar formation appears to be a rift facies that correlates with the Panjal Traps of western India. The Kashala and Nikanai Ghar formations represent a transition to a stable shelf environment. These units may correlate, in part, with the Zanskar Supergroup of western India. The Saidu formation may represent drowning of the shelf as it was pulled down and overridden by the Main Mantle Thrust suture melange. It may correlate with the Lamayuru Formation of western India. The Alpurai group thus records a depositional history from Late Paleozoic breakup of Gondwana, to development of a passive Mesozoic shelf, to drowning of the shelf at the onset of Himalayan orogeny.
Mechanisms of anabranch avulsion within gravel-bed braided rivers: observations from a scaled physical model
Authors: Leddy J. O. , Ashworth P. J. , Best J. L.
Published: April 2008

The physical modelling of gravel-bed braided rivers, using a 1:20 Froude scale model, permits analysis of the types and relative occurrence of different avulsion mechanisms. Anabranch avulsion within braided rivers involves three main mechanisms:
choking avulsion
caused by blockage of one channel by a sediment lobe,
constriction avulsion
produced by deflection, confinement and subsequent diversion of the flow by a barform and
apex avulsion
following erosion at the outside of sinuous thalwegs and confined meander bends. Each avulsion mechanism is described and analysis of the abundance of each type illustrates choking avulsion to be predominant without braided rivers. Three factors are found to control anabranch avulsions, namely flow discharge, sediment flux and floodplain topography. These are briefly discussed together with the implications of avulsion type for the alluvial architecture of gravelly braided alluvium.
Pleistocene Rhine gravel: deposits of a braided river system with dominant pool preservation
Authors: Siegenthaler Christoph , Huggenberger Peter
Published: April 2008

An example of a gravelly braided river deposit is described which exhibits a rather low structural diversity as compared to other ancient and modern braided river sediments. The presented model is based on a study of the Rhine gravel, formed in front of the Würm stage extension of the Rhine glacier (northern part of Switzerland). The observations in the Rhine gravel suggest that only processes which operate generally at a low topographic level of the braided river system generate a response in the geological record, i.e. (1) pool deposits produced at the junction of two channels (cross-bedded trough fills); (2) channel sediments which reflect thin bedload sheets deposited by moderate-magnitude flow stages with low suspension concentrations; (3) sheet flow deposits produced by extraordinary high-magnitude flow stages with high suspension concentrations, probably due to outbursts from glacial lakes.

Therefore, we postulate that in the Rhine gravel system only a limited number of braided river structures have a significant preservation potential: any deposit generated at an elevated geometric level, such as flood plain deposits or bars, are successively destroyed by channel formation and are replaced by channel deposits, which in turn may be reworked by pools which operate at the lowest geometric level. It is suggested that similar preservational hierarchies could eventually exist also in other braided river deposits.
The architecture of fluvial-deltaic sequences in the Upper Mesaverde Group (Upper Cretaceous), Book Cliffs, Utah
Authors: Miall Andrew D.
Published: April 2008

The Mesaverde Group is a clastic wedge that prograded eastward into the Western Interior Basin from the Sevier Orogen of central Utah during the Late Cretaceous. The Blackhawk Formation and the overlying Castlegate Sandstone represent tongues of fluvial-deltaic and shoreface strata that prograded far into the basin in response to pulses of tectonism.

The Desert Member of the Blackhawk Formation includes two fourth-order stratigraphic sequences and the Castlegate Sandstone represents the lower part of a third sequence. The upper two sequences begin with regional erosion surfaces, above which widespread fluvial blankets represent backfill deposits formed during periods of relative base-level rise. Transgressive and highstand deposits are poorly represented at the top of the Blackhawk Formation, having probably been removed by erosion prior to Castlegate sedimentation. The overriding tectonic control of this fluvial-deltaic wedge is demonstrated by regional changes in paleoslope and detrital sources. However, the sequence architecture indicates that this regional tectonism was modulated by short-term base-level changes, of tectonic or eustatic origin.

Architectural-element analysis of the fluvial units indicates deposition predominantly by large bars (macroforms) in braided river systems. The bars developed by lateral, oblique and downstream accretion. They combine laterally and vertically to form widespread sandstone sheets typically capped by thin mudstones and bounded by flat erosion surfaces. The sheets and their component bars thicken from an average of 4–6 m in the Price area to 6–9 m east of Green River, 140 km down palaeoslope, probably as a result of tributary amalgamation and consequent deepening of the river system. In the subsurface such sheets would define flow units for production purposes. However, they are not internally homogeneous, consisting of bar sandstones <400 m in lateral dimensions, and bar increments and small channels >120 m long and wide. Many of these heterogeneities are bounded by mudstone units, and contain dipping accretion surfaces which could act as baffles to lateral fluid movement.
The interaction and geometries of diapiric uprise centres along mid-ocean ridges — evidence from mantle fabric studies of ophiolite complexes
Authors: Bartholomew I. D.
Published: April 2008

Detailed structural mapping and thin-section fabric studies of oceanic upper mantle sections exposed within 3 ophiolite complexes have shown that in all of the ophiolites studied two co-existing high-temperature mantle fabric orientations can be identified. The fabrics are related both in time and space in that one fabric is ductile shear-folded by a later one to varying degrees. Olivine and orthopyroxene crystal slip-system and fabric orientation studies show that all the fabrics identified are high-temperature ‘primary’ asthenospheric flow fabrics and that simple shearing is the main flow process. The fabrics observed are at varying angles to the orientation of the Moho plane, with the slip directions varying both along strike with the Moho as well as vertically down from the Moho plane.

The identified flow fabrics are considered to be indicative of mantle flow directions ‘frozen’ into the mantle as it cooled from being ductile asthenosphere to lithosphere. Each fabric is interpreted as originating from a different localized mantle diapiric uprise centre. The centres interact with each other both in space and time, the observable ‘frozen’ fabrics indicating the closeness and ‘strength’ of individual diapirs relative to the position of the data measurement point.
Trace element models for mantle melting: application to volcanic arc petrogenesis
Authors: Pearce Julian A. , Parkinson Ian J.
Published: April 2008

Understanding mantle melting above subduction zones requires an evaluation of the behaviour of elements for which the mantle contribution greatly exceeds any subduction contribution. In this paper we present a compilation of partition coefficients for a suite of these elements (Nb, Zr, Y, Yb, Ca, Al, Ga, V, Sc, Fe, Mn, Co, Cr, Mg, Ni) for temperatures of 1200–1300°C, oxygen fugacities of QFM ± 1 and sub-alkaline compositions. These coefficients yield good-fit mantle depletion trends for abyssal, orogenic and trench-wall peridotites. Modelling of pooled melts from mantle melting columns, presented as FMM (fertile MORB mantle) normalized patterns, give signatures of the composition and degree of melting of the mantle wedge that are generally independent of the subduction component. In particular, patterns formed from melting of fertile mantle exhibit normalized element abundances in the order VHI > HI > MI (VHI = very highly incompatible, HI = highly incompatible and MI = moderately incompatible) at low degrees of melting, becoming VHI = HI = MI at high degrees of melting. With derivation from progressively depleted sources, the patterns for moderate degrees of melting change to VHI < HI = MI at moderate degrees of depletion and VHI < HI < MI at high degrees of depletion.

The details, but not the principles, can be varied by changing the shape of the melting column, the porosity of the mantle during melting, the potential temperature of the mantle, and the temperature and depth of initiation of melting. Bivariate plots of elements of contrasting compatibilities (Cr-Yb, Sc-Yb, Nb-Yb) can be contoured according to the degree of depletion or enrichment of the mantle and the degree of melting, with selected plots also emphasizing the role of garnet (Ti-Yb) and oxygen fugacity (V-Yb). Evaluation of data from present-day volcanic arcs suggests that: (1) intra-oceanic arcs with associated active backarc basins are derived principally from fertile MORB mantle that has lost up to about 3% melt in a previous melting event; (2) this depletion takes place in spinel lherzolite facies, supporting models that relate it to backarc basin melting events; (3) oceanic arcs with no associated backarc basins are derived principally from fertile MORB mantle, though enriched sources can be important locally; (4) intra-continental arcs are commonly derived from enriched mantle, probably because of the involvement of sub-continental lithosphere; (5) degrees of melting are probably high (in the order of 25–30%) in intra-oceanic arcs on thin crust, decreasing to 150r less in areas of thicker lithosphere; (6) some 10% melting can be explained by volatile addition to the mantle, the remainder by decompression.
The water inventory of the Earth: fluids and tectonics
Authors: Fyfe W.S.
Published: April 2008

As the human population continues to expand, to approach ten billion, there will be an increasing demand upon all Earth’s resources. Of particular importance will be resources related to energy, soil and water, all of which involve geofluids. Problems associated with waste disposal also involve systems for protecting near-surface water quality. There is an urgent need to quantify the fluid inventory and fluid dynamics of the near surface, while understanding volatiles and their deep recycling is fundamental to our understanding of the major dynamic processes of the Earth.
The nature of metamorphic fluids and significance for metal exploration
Authors: Phillips G. Neil , Williams Patrick J. , De Jong Geoffrey
Published: April 2008

Fluids are active at all levels in the crust during metamorphism. Devolatilization of many rock packages leads to the evolution of H
2
O, CO
2
and/or S as a fluid phase that is commonly of low salinity. The composition of the fluid phase released during devolatilization is controlled by the dominant mineral assemblage in the source region, and the evolution of such fluid is most dramatic where major changes in modal mineralogy occur; e.g. across metamorphic facies boundaries. Evidence for this loss of volatiles during metamorphism is provided by metamorphic assemblages that typically contain less volatile components as grade increases.

The metamorphism of mafic rock successions can yield a metamorphic fluid rich in H
2
O, CO
2
and S, and close in composition to fluids inferred in the formation of many gold-only deposits. The close affinity between gold and these fluids arises from the stability of the Au-S complexing.

Where evaporites are present in the succession, the fluids released during devolatilization can be quite saline. A further potential source of saline fluids in these environments is from crystallization of certain magmas. Saline fluids have a composition favourable for transporting gold
and
base metals, which is likely to explain the occurrence of gold as a co-product in many deposits where saline fluids are inferred.

The contrast between saline and low salinity fluids during metamorphism is not only reflected in ore metals, but also in the associated alteration and element mobility. Only a few elements are mobile in the low salinity fluids, and the alteration mineralogy is strongly influenced by the nature of the host rocks. Saline fluids readily transport many elements, and a similar alteration assemblage can be superimposed on many different precursors.
Origin of saline fluids in sedimentary basins
Authors: Hanor Jeffrey S.
Published: April 2008

Subsurface saline waters in sedimentary basins can be divided into three groups based on their anionic composition and salinity: (1) Waters with anions other than Cl dominant. These include Na-HCO
3
and Na-acetate waters. Most such waters have salinities of less than 10 000 mg 1
−1
; (2) Cl-dominated, halite-undersaturated waters having salinities between 10 000 and 250 000–300 000 mg l
−1
. These include Na-Cl waters and, at higher salinities, Na-Ca-Cl waters; (3) Cl-dominated, halite-saturated waters with salinities typically in excess of 300 000 mg 1
−1
. Ca and K become increasingly dominant and Na decreases with increasing salinity.

Subaerial evaporation of marine and continental waters and the subsurface dissolution of evaporites both have the potential for producing the range of salinities and dissolved chloride concentrations observed for most subsurface brines, but not their major cation compositions. The broad systematic increase in dissolved Na, K, Mg, Ca, and Sr and decrease in pH and alkalinity with increasing salinity support the hypothesis that the approach toward thermodynamic buffering by silicate-carbonate ± (halide) mineral assemblages is a first-order control on subsurface fluid compositions, even at temperatures well below 100°C. The chemical potential of chloride or, alternatively, the aqueous concentration of anionic charge, is a master variable which ranks in importance with such other variables as pressure and temperature in driving fluid-rock exchange and controlling bulk fluid compositions. This variable is in turn controlled largely by physical processes of fluid advection and dispersion.

Dissolved organic acid anions are associated primarily with low salinity waters, but dissolved metals, such as Cu, Pb, and Zn are preferentially found in brines having salinities in excess of 200 g 1
−1
. The high chloride concentration and low pH of these saline waters may enhance solubilization of metals through chloride complexing.
An integrated approach to the study of primary petroleum migration
Authors: Mann Ulrich
Published: April 2008

The precise mechanism of primary petroleum migration has been elusive despite intensive investigation and discussion. There is more than one mechanism, and the pathways and efficiencies of individual mechanisms vary from case history to case history due to the variable abundances of micropores, macropores and fractures in source rocks as well as different sources for the build-up of a pressure gradient. Primary migration probably proceeds as diffusion through source rock micropores via mesopores to macropores and fractures. From there, a petroleum bulk phase develops, and moves along the macropore and fracture system, possibly together with aqueous solutions.

In fact, many parameters influence petroleum transport out of a source rock, and all of them have seldom been checked by exploration geologists as most mature source rocks are inaccessible. In order to collect information about primary petroleum migration that is as complete as possible, an integrated approach consisting of sedimentology, petrophysics, organic geochemistry and numerical modelling should furnish geologically acceptable results: (i) by sedimentological methods, all potential primary migration pathways are identified, (ii) with the help of petrophysical methods, non-effective migration pathways are separated from effective pathways and excluded, (iii) organic geochemical results provide control and direct evidence for petroleum expulsion stage and efficiency, and (iv) numerical modelling finally quantifies all observed effects within the framework of the geological situation.
Reserve assessment of a stratified deposit with special reference to opencast coal mining in Great Britain
Authors: Nathanail C. P.
Published: April 2008

The assessment of reserves in a stratified deposit should define the areal extent of the mineral, the spatial variation of thickness and quality and the ratio of mineral to waste. The assessment of reserves at opencast coal mines in Great Britain also involves the estimation of the extent of areas where coal is absent or of reduced quality due to old mining activity, washout, alteration by igneous intrusions, lime burning and faulting. The most appropriate estimation technique will vary from site to site and, within an individual site, from seam to seam. Conventional non-spatial statistics can be used where the extent of areas of lost coal is not definable. Area-of-influence approaches such as Thiessen polygons are routinely used to estimate the spatial extent of old workings from point observations at boreholes. The use of indicator kriging may provide a refinement to this deterministic approach. Delaunay triangulations are used by popular mine design software for area and volume calculations. Kriging may also be used to model the variation of seam thickness and quality. Whatever method of estimation is used, poor quality input data will result in poor estimates. Metadata such as how, when and by whom information was collected should be used to decide whether or not a particular piece of information should be retained. Experience shows that each site must be treated as a unique entity with techniques and software being modified to suit the site circumstances. A black box ‘expert system’ approach would fail to identify site specific features and result in misleading estimates.
Phosphate rock: factors in economic and technical evaluation
Authors: Notholt A. J. G.
Published: April 2008

Phosphate rock in the mineral industry refers to the marketable, usually beneficiated, product. Geologically, however, the term embraces a very wide variety of rock types, of both sedimentary and igneous origin, as well as their weathering derivatives. Phosphate deposits thus form in markedly different geological environments and ore characteristics are so varied that a combination of nearly identical factors applicable to their evaluation seldom exists. In spite of this diversity, the phosphate component in most deposits is a member of the apatite group represented by the two end members: fluorapatite, the main mineral in crustal igneous rocks, and carbonate fluorapatite or francolite, by far the most important phosphate component of commercial sedimentary deposits. The identification of the correct apatite composition is important in assessing the quality of marketable phosphate concentrates.

Evaluation usually begins with a detailed mineralogical, petrographical, and chemical study of a representative sample of prospective phosphate ore to determine the principal constituents in the ore and their mode of occurrence. The data obtained establish the grade (P
2
O
5
content) of the rock and its chemical quality and, hence, the method and degree of beneficiation required to provide a commercially acceptable phosphate concentrate. Beneficiation technology is such that often the most difficult ore types (e.g. siliceous, dolomitic and Fe-Al-rich) can be upgraded satisfactorily, but the problems become more acute when impurities occur as substitutions in the apatite lattice. Quality rather than grade is often the deciding factor in determing the viability of a given deposit, in addition to other technical and economic factors.
Evaluation of grade estimation techniques
Authors: Bell T. M. , Whateley M. K. G.
Published: April 2008

A sample set was simulated from an exhaustive data set of silver values derived from blast holes of the 5220 bench. The sample set was used to estimate the ditribution of grade for the 5220 bench using a variety of estimating techniques. The estimating processes were controlled by the knowledge of the statistical and spatial distribution of the exhaustive data set. This approach was used to test the accuracy and precision of the different estimation techniques. The results from the simpler estimation methods (linear interpolation and triangulation) compared most closely to the blast hole samples. The more complex techniques (inverse distance and kriging), using weighting factors, were found to exaggerate the variance and smooth the interquartile range.
A review and evaluation of the costs of exploration, acquisition and development of copper and gold projects in Chile
Authors: Gorman Patrick
Published: April 2008

In recent years Chile has become the focus of activity for many multinational mineral resource companies. Undeniably they are attracted by the geological potential, business/investment rules and lifestyle, all of which are excellent by most standards.

In view of the continued interest in Chile a detailed profile of 36 gold and 27 copper projects and advanced prospects was prepared from a number of public sources of data. From this list a representative selection of about 10 projects was made and the costs associated with those projects were reviewed and evaluated. Based on the data a modest reserve containing 31 tonne (1 M oz) of gold might be discovered in Chile at a cost of US$ 225 kg
−1
Au (US$7 oz
−1
) or acquired for US$ 772 kg
−1
Au (US$24 oz
−1
) and then a mine constructed for US$ 1522 kg
−1
Au (US$ 47 oz
−1
). The total average cost taken from initial reconnaissance to start-up of the mine is equivalent to US$ 25 723 kg
−1
gold per year (800 oz
−1
Au per year). Historically a medium-sized copper deposit in Chile containing 1 M t of fine copper might have been discovered for US$ 6.5 t
−1
Cu (0.3 US cents lb
−1
) or acquired for US$ 10.3 t
−1
Cu (0.5 US cents lb
−1
) and then constructed for US$ 64 t
−1
Cu (2.9 US cents lb
−1
) Cu). The total cost to mine start-up is equivalent to US$ 3969 t
−1
Cu per year (US$ 1.80 lb
−1
Cu per year). The recent purchases by Emablos/Minorco of one-third of Collahuasi and Placer of 500f Zaldivar have increased the prices paid to acquire copper resources to US$ 60 and US$ 93 t
−1
Cu
in situ
(2.7 to 4.2 US cents lb
−1
) respectively. On the basis of the above figures, the cost of acquiring a gold project in Chile is typically equivalent to US$ 24 oz
−1
or 7.30f the price of gold at US$ 330 per ounce. Copper project acquisitions previously averaged the equivalent of 0.50f the price of copper at 95 US cents per lb, but this has reached 4.5% with the price paid for Zaldivar. These guideline values have been prepared to give explorationists, acquirers and developers useful empirical guidelines to help them to decide whether they have the budget to consider entry to Chile or whether to look elsewhere.
Volcanism associated with extension in an Oligocene—Miocene arc, southwestern Viti Levu, Fiji
Authors: Wharton M. R. , Hathway B. , Colley H.
Published: April 2008

The Wainimala Group rocks of southwestern Viti Levu, Fiji, represent part of an Oligocene-Miocene island arc. Some of the early volcanism in this arc took place on a substrate of Eocene-Oligocene frontal-arc crust. Mainly andesitic, transitional calcalkaline lavas were erupted from major subaerial volcanic edifices, while elsewhere tholeiitic magmas formed low-lying basaltic lava fields and small felsic volcanic centres on the seafloor. The intrusion of a dense bimodal basalt-dacite dyke swarm into the underlying frontal-arc crust indicates that significant crustal extension accompanied the eruption of the inter-edifice lavas.

Geochemical variations within the Wainimala volcanic suite are thought to have been generated through fractional crystallisation processes. While relatively slow ascent and mixing of magmas took place beneath the major edifices, efficient shallow-level fractionation and rapid ascent of magmas occurred in the areas between them. The contrasting styles of volcanism may reflect the interaction of ascending magmas with pre-existing heterogeneities in the frontal-arc substrate.
Neogene volcanoes of Chios, Greece: the relative importance of subduction and back-arc extension
Authors: Pe-Piper G. , Piper D. J. W. , Kotopouli C. N. , Panagos A. G.
Published: April 2008

The Aegean area has experienced both extension and subduction throughout the Neogene and Quaternary. Small volcanic centres with a wide range of rock types occupy a ‘back-arc’ position with respect to the subduction zone, but their geochemistry and chronological correlation with local basin subsidence indicates that their origin is primarily the result of extension. The position of voluminous andesite-dacite volcanism in the modern south Aegean arc relative to the seismically defined Benioff zone is similar to that of other active subduction zones, although the timing of vigorous volcanic activity correlates with periods of most rapid basin subsidence. The voluminous early Miocene intermediate igneous rocks of the northeast Aegean also appear closely related to subduction. Variations in subduction-related products through time are correlated with changes in the rate and direction of subduction inferred from regional tectonic data.

The island of Chios, in the eastern Aegean Sea, has several small, mid-Miocene (14–17 Ma) volcanic centres containing high-Mg calc-alkaline (adakitic) andesite, ne-normative basalt, and alkaline and calc-alkaline rhyolite. Both the ne-normative basalt and calc-alkaline andesite have Pb isotopic compositions similar to other Neogene volcanic rocks in the central Aegean region. The small size of the calc-alkaline centres (<10
−1
km
3
) distinguishes them from the nearby voluminous (1000 km
3
), 17–22 Ma, calc-alkaline to shoshonitic volcanic centres of Lesbos and Karaburum.

The minor volcanism on Chios occurred near the site of earlier voluminous arc volcanism. The rapid decrease in the rate of subduction in the mid-Miocene reduced both the production of slab-derived volatiles and silicic melts, as well as the volume of mantle wedge from which arc-type magma was extracted. At the same time, extension resulted in decompression of the lithosphere and the generation of small-volume partial melts. Volcanic products are not found near the major extensional centres: rather, they are associated with minor basin subsidence, which provided brittle pathways for magma flow.
A high-strain rift model for the southern Gulf of Suez (Egypt)
Authors: Bosworth William
Published: April 2008

Extensive exploratory and development drilling have documented the large extension produced during Miocene rifting in the southern Gulf of Suez. Basement fault blocks are commonly rotated > 40°, with maximum dips of 65°. Early fault planes along the rift axis now dip 23–35° NE, with later extension shifting to complex arrays of rider blocks. Multiple well penetrations show that some fault planes are gently listric between basement hanging wall and footwall cut-offs. Stratigraphic and structural relationships show that deformation shifted between several basin-bounding faults during a complex history of basin evolution and progressive sub-basin abandonment. One low-angle normal fault has been identified in outcrop and a detachment model can explain the Miocene structural development of the rift. Post-Miocene deformation and subsidence focused along the basin axis, with extension probably occurring on a new system of planar normal faults. Restoration and balancing of regional and local cross-sections indicate that the southern Gulf has been extended by 56–62%, and that total separation between Sinai and Africa was 34–36 km. Average regional β factor for the central basins of the rift is 1.9–2.0. These new extension estimates are in agreement with subsidence models and crustal thickness estimates for the Gulf, and help quantify plate reconstructions between Sinai, Africa and Arabia. They also indicate that the southern Gulf of Suez is one of the most highly extended, failed continental rifts preserved in the rock record. As such, it provides an important conceptual link between more numerous low-strain continental rifts and successful oceanic basins.
Stratigraphic response to basin formation: Jeanne d’Arc Basin, offshore Newfoundland
Authors: Driscoll Neal W. , Hogg John R.
Published: April 2008

Using seismic reflection and exploratory well data, the stratigraphic response of the Jeanne d’Arc Basin to early Cretaceous extension was examined. The Jeanne d’Arc Basin, located
c.
300 km east-southeast of St John’s, Newfoundland, is a large asymmetric half-graben, which trends north-northeast. The border faults delineating the western limit of the basin are eastward dipping. The structure and geometry of the border faults and transbasinal faults engendered by the early Cretaceous extension influenced the drainage and therefore, the sedimentation patterns in and around the Jeanne d’Arc Basin. In order to assess the stratigraphic response to basin formation and its spatial variation, it was necessary to establish a chronostratigraphic framework with which to examine the effects of the extensional deformation on the preserved stratigraphy. Time surfaces determined by sequence stratigraphy in conjunction with detailed palynology from wells have allowed correlation of time-equivalent coarse-grained proximal facies to the fine-grained distal facies within the Jeanne d’Arc Basin. Correlations among seismic reflection, sedimentological and biostratigraphic data reveal that the stratigraphic response to extensional basin formation varies spatially on both a local and regional scale. The local response was controlled by the small-scale basin architecture (i.e. border/transfer fault interaction) whereas the more regional response was governed by the pre-existing axial drainage networks that enter the basin along the southern basin-bounding transfer zone. The locally-derived sediments were allowed access to the basin near the transfer zones that segment the border faults possibly because of the diminished footwall uplift. These locally derived sandstone units correlate with prograding seismic reflectors that downlap onto the late Barremian rift-onset unconformity producing a wedge-shaped geometry. The wedge is thickest near the border fault and tapers basinward. Away from these locally-derived prograding wedges (i.e. fan delta deposits), the late Barremian rift-onset unconformity, defined from stratal patterns in seismic reflection data, correlates to a flooding surface within the basin depocentres where marine sandstones onlap on to restricted marine/lagoonal and non-marine subaerially-exposed shales. These shales are iron-stained and commonly contain abundant root structures, evidence for pedification, and sideritic concretions. The overlying marine sediments predominantly sourced from the southernmost transfer zone, infilled the basin longitudinally, are more regionally persistent, and onlap onto the locally-derived prograding wedge. Exploratory well data from the Jeanne d’Arc Basin suggest that the regionally derived sediments that infill the basin longitudinally are better hydrocarbon reservoirs than the locally-derived prograding wedges because of better sediment sorting and greater regional extent.
Neotectonics, drainage and sedimentation in central Greece: insights into coastal reservoir geometries in syn-rift sequences
Authors: Collier Richard E. Ll. , Gawthorpe Rob L.
Published: April 2008

The modern analogue of Greek environments was used to provide insights into the prediction of coastal syn-rift architectures. Sediment flux into rift basins reflects the drainage response to slope changes induced by normal faulting. The present day Greek drainage network reflects syn-rift modification of catchments draining the Alpine-Hellenide mountain chain. On a local scale, drainage around individual fault blocks commonly exploits transfer zones. Uplift and cannibalization of earlier sequences in the footwall of new normal faults also has a marked effect on sediment dispersal. Thus, consideration of catchment areas and their evolution offers an improved understanding of potential reservoir distribution and volumetrics within the stratigraphy of any given basin.

Quantitative data on modern fault displacements and on rates of climatically forced, sea- and lake-level changes allow the prediction of relative base-level change at different localities around a half-graben or graben. Maximum rates of tectonic subsidence exceed all but the most rapid rates of glacio-eustatic sea-level fall (such as have occurred in the late Pleistocene). These data indicate it is inappropriate to apply, without some modification, sequence stratigraphic models that have been developed from areas with relatively simple subsidence histories (e.g. post-rift megasequences on passive margins) to syn-rift successions. Spatial variation in subsidence/uplift rates around rift basins is clearly demonstrated in central Greece, where coastal half-grabens show the resulting spatial and temporal distribution of systems tracts and sequence boundaries, and stratal geometries developed on a parasequence and sequence scale. Broad patterns of sequence stacking in deltaic and paralic facies are shown to be predictable, despite the apparent complexity of syn-rift successions. The fundamental control upon differential subsidence is the displacement history on individual normal fault segments. Patterns of relative base-level change and predictable sequence architectures are therefore scaled to the length of the fault segment.
Newly developed techniques to determine proportions of undersized (friable) coal during prospective site investigations
Authors: Harris Ian H.
Published: April 2008

Site investigations to date have been unable to determine the presence of friable (undersized) coal within areas of extreme tectonic deformation. This is especially important in the northwest of the South Wales coalfield, where most of the coal extracted is for the smokeless fuel domestic market, which requires a consistent grade size. Coal in the proximity of the deformation zone is unlikely to be suitable for its intended market due to its small grain size.

The deformation process and fracture styles which contribute to the development of friable coal are discussed and a remote method utilizing the drilling parameters of speed of advance, thrust and torque is investigated to ascertain its suitability in determining the amount and position of friable coal within a prospective coal site. If areas and volumes of friable coal can be determined before the extraction stage of an opencast coal site, site boundaries can be amended so that they do not contain large volumes of the friable product.
Sedimentology and its applications within the UK opencast coal mining industry
Authors: Jones Neil S. , Guion Paul D. , Fulton Iain M.
Published: April 2008

The opencast coal industry seeks to identify and extract near-surface coal reserves. Within the UK Pennine Basin, most coal deposits suitable for opencast exploitation range from middle Westphalian A to lower Westphalian C in age. These deposits dominantly accumulated in an upper delta plain setting in which subsidence rates and depositional setting formed the primary controls on the initial distribution, thickness and quality of coal reserves. Hence an appreciation and analysis of the sedimentary setting and controls on sedimentation are important in the delineation of potential areas of thick, persistent coals.

The calculations of
in situ
coal reserves and coal to overburden ratios are important objectives during exploration for prospective opencast coal sites. Coal reserves are detrimentally affected by early, depositionally related factors such as as wash-outs, seam splits, channel bank collapse and compaction faults. The thickness and type of interseam sedimentary rock (overburden) is directly related to the original despositional environment and the nature of the overburden can change substantially across the working area of an opencast site, reflecting sedimentary facies variations. The various sedimentary facies have unique characteristics and adversely influence mining in a variety of ways, including highwall stability problems, seam gradient changes, groundwater problems, interseam interval variations and facies-specific discontinuities.

Many of these problems are related to the presence of palaeochannels. Palaeochannels occur at different scales and contain a variety of fills, and their identification is an important aspect of site exploration. Sedimentary facies mapping, incorporating facies analysis, the construction of isopach maps and palaeocurrent studies can play an important part in an opencast exploration programme. Facies maps have many applications which may be invaluable in site planning, including the delineation of areas of sedimentary disturbance, improved understanding of seam thickness and quality variations, and changes in the interseam strata.