bluuebunny/crossref_metadata_2025 huggingface dataset:
Sedimentology and gravel bar morphology in an Archaean braided river sequence: the Witpan Conglomerate Member (Witwatersrand Supergroup) in the Welkom Goldfield, South Africa
Authors: Karpeta W. P.
Published: April 2008

The Witpan conglomerate member is the lower, thicker, more channelized of the two auriferous conglomerates that comprise the Archaean ‘A’ Reefs (Aandenk Formation, Central Rand Group, Witwatersrand Supergroup) mined in the southern part of the Welkom Goldfield, Republic of South Africa. It is interpreted as the deposit of a degrading, gravelly, braided river system with well developed topographical differentiation. Three morphological elements have been identified in the Witpan Conglomerate member, namely Major Channels, Minor Channels and Terrace areas which are comparable to Levels 1, 2 and 3 of the modern Donjek River. Nine facies are present in the Witpan Conglomerate member combined into eight facies assemblages which show differing three dimensional architecture and relationship to channels. The four conglomeratic bar facies assemblages (FA1 to FA4) are interpreted as longitudinal, diagonal, transverse and side bars respectively and are combined to form compound bars. The three quartzitic channel fill facies assemblages (FA5 to FA7) represent active, slough and abandoned channel fills. The eighth facies assemblage (FA8) forms the interchannel terrace areas.

The distribution of gold mineralization in the Witpan Conglomerate member is related to sedimentological factors including the presence of massive gravels, the accessibility of these gravels to flood water and the formation of areas of confined, convergent flow. Hence the bar facies assemblages are the richest followed by channel fill facies assemblages with the interchannel facies assemblage having generally low gold concentrations. Of the bars, diagonal bars are the most favourable for gold mineralization followed by longitudinal bars then side bars with transverse bars being the lowest.
Debris provenance mapping in braided drainage using remote sensing
Authors: Copley Victoria R. , Moore John McM.
Published: April 2008

The NERC Geoscience community airborne remote sensing test site near Carboneras in southeast Spain is dissected by several flash flood drainage channels. These contain a variety of clastic debris types related to diverse source rocks in the catchment basins. As part of a larger study of source rock, regolith and drainage debris relationships, the spectral reflectance characteristics of debris types in braided flash flood channels have been used to map debris dispersion with remotely sensed imagery. The study is based upon 11 channel 7.5 m pixel Airborne Thematic Mapper (ATM) imagery acquired by NERC in May 1989. The objective of the research was to achieve optimum discrimination of channel debris types and to study the integration of distinctive source rock/regolith spectral signatures caused by progressive downstream mixing during transport.

Image processing enhances small spectral variations to improve discrimination of debris types. Imagery was masked to display only channel bed pixels and maximise spectral discrimination within drainage channels. Several enhancement techniques, including principal components and hue-saturation-intensity transformations, and decorrelation and contrast stretches, were then used to emphasise spectral differences among the debris assemblages in the channel beds. One of the most successful products is a selective principal components colour composite image. The image data are presented as a debris lithology distribution map.
Trace element geochemical effects of imperfect crystal-liquid separation
Authors: O’Hara M. J.
Published: April 2008

The strongly contrasted effects of melting or crystallization under perfect equilibrium conditions; of perfect fractional partial melting; and of perfect fractional crystallization upon the relative concentrations of the highly incompatible and highly compatible elements are well known and are surveyed briefly at the start. A major role for either of the two latter processes in the genesis of natural basaltic magmas and peridotitic residues is apparently excluded provided that the liquids or crystals are removed in infinitesimally small batches, the crystals and melts are perfectly separated and there is no flux of source material or residue in or out of the greater system during the process (either liquid or crystals must be removed from the immediate, or lesser, system if it is undergoing perfect fractional melting or perfect fractional crystallization).

The consequences of small departures from (i) infinitesimal size of the batches of liquid or crystals removed, (ii) perfect separation of the crystal and liquid phases, or (iii) perfect closure of the greater system to fluxes of the source material and the residue are explored. These departures can very substantially reduce the differences between the trace element concentrations generated in the products and those expected in a perfect equilibrium process.

These effects are illustrated here by means of 3D plots of the logarithm of relative concentration in the liquid phase as a function of the logarithm of the distribution coefficient and the logarithm of the mass fraction of liquid involved in each process. There are also significant complementary effects on the compositions of the residues or precipitates from these processes which are not illustrated in this paper, although the necessary equations and some worked examples are provided. With the values of parameters chosen in these examples, the fluxing of liquid or solid through a ‘box’ in which fractional crystallization or fractional melting is taking place proves to be by far the most important factor in modifying the results towards those of the equilibrium processes.

Although much trace element behaviour in basalts can be quite successfully modelled using the perfect equilibrium melting relationships, it is unsafe to exclude on these grounds a major role for physical processes of fractional melting and fractional crystallization in the genesis of these magmas or to conclude that equilibrium partial melting is the principal physical process involved in their genesis.
Development of concepts concerning the Troodos ophiolite and adjacent units in Cyprus
Authors: Robertson Alastair , Xenophontos Costas
Published: April 2008

The foundations for study of the Troodos ophiolite and adjacent units in Cyprus were laid down by systematic mapping by the Cyprus Geological Survey Department (1952–1970). Prior to the late 1950s, Cyprus geology was interpreted in classic geosynclinal terms. The first, integrated description of the Troodos was given by Gass & Masson Smith in 1963. Publication of the Vine & Matthew’s (1963) sea-floor spreading hypothesis was followed by Ian Gass’s key interpretation in 1968 of the Troodos as oceanic lithosphere formed by sea-floor spreading. During the early 1970s, the dominant view of the Troodos was of a mid-ocean ridge, formed by spreading at a narrow, linear spreading zone, fed by a single, axial magma chamber. However, early geochemical studies suggested that genesis could have taken place above a subduction zone. During the 1980s, drilling related to the International Cyprus Crustal Study Project stimulated much new field work. By 1990 a popular view of the Troodos was that it had formed above a northward-dipping subduction zone during the earlier stages of convergence within an oceanic basin, similar in some respects to the origin of SW Pacific forearcs. Others favoured an origin as a marginal basin formed by spreading above a southward-dipping subduction zone, either in the vicinity of Cyprus, or located in central Turkey. In whatever scenario, it is generally accepted that the spreading fabric was unstable and was fed by small, multiple magma chambers. The extension outpaced magma supply and this favoured extensional detachment faulting, mainly near the base of the sheeted dykes. The Troodos lithosphere was also bounded by an oceanic fracture zone to the present south. Studies of the Late Cretaceous-Recent sediment cover have documented deep-sea sedimentation and later uplift, related to Africa-Eurasia convergence. In W Cyprus, the adjacent Mamonia Complex was pieced together as a Mesozoic passive margin bordering a small ocean basin, although whether this was a Red Sea-type basin, or a backarc marginal basin is still debated. The Mamonia lavas and sediments were juxtaposed with the Troodos ophiolite by processes, variously interpreted as subduction/accretion, oceanic transform faulting, strike-slip, collision and/or palaeorotation of a Troodos microplate. The Kyrenia Range in N Cyprus also includes remnants of Mesozoic passive margin; it was emplaced in stages apparently by a combination of strike-slip and thrusting. On a regional scale, the Troodos ophiolite preserves part of one of a number of inferred small oceanic basins within the Mesozoic Tethyan area of the Eastern Mediterranean.
Structure and tectonic evolution of the Southern Troodos Transform Fault Zone, Cyprus
Authors: MacLeod C. J. , Murton B. J.
Published: April 2008

A major strike-slip fault zone, at least 5 km in width, trends E-W along the southern margin of the Troodos ophiolite. It is an ocean-floor feature, overlain by undeformed pelagic sediments, and is orientated perpendicular to the mean strike of the sheeted dyke complex of the main ophiolite massif. It has long been recognized as probably the foremost example of a fossil transform fault within an ophiolite.

We present here detailed description of the structure and tectonic evolution of this so-called ‘Southern Troodos Transform Fault Zone’ (STTFZ), based upon 1:5000 scale mapping of the whole of the southern margin of the Troodos ophiolite. The styles of strike-slip deformation at all levels of the oceanic crust and upper mantle, and the variations in deformation style with time, are documented and the role of vertical-axis rotations within and adjacent to the transform zone is discussed. Evidence for the kinematics of deformation is reviewed; previous studies have been unable to agree even on such fundamentals as the sense of slip of the STTFZ. In an attempt to resolve the controversy we have made a systematic re-examination of the evidence for the direction of motion along the transform, supplemented by new field observations where necessary. We conclude that, although there is incontrovertible evidence for both sinistral
and
dextral shear along the STTFZ whilst it was in an oceanic environment, the overwhelming indications are for dextral slip. We show that sinistral indicators are restricted to a few small mylonite shears that are probably related to local geometrical complexities associated with the intrusion of gabbroic plutons into the transform; there is no need to invoke wholesale reversal of slip sense along the STTFZ as a whole.
Petrogenesis of ophiolitic chromitite
Authors: Roberts Stephen , Neary Christopher
Published: April 2008

Chromite deposits comprise an integral part of the mantle sequences observed within many ophiolite complexes; in particular, those where a harzburgite is the dominant mantle sequence lithology. The chromite segregations are invariably contained within a dunite envelope and show a wide variety of ore textures, some of which are directly analogous to those observed within major layered intrusions. The majority of chromite segregations contain chromite and olivine of variable modal proportions although in certain instances a wide variety of interstitial silicates may be preserved including plagioclase, orthopyroxene, clinopyroxene and amphibole. Evidence of deformation linked to increasingly lower temperatures is invariably present which can be linked either to high temperature ‘flow fabrics’ away from the spreading axis, the obduction of the ophiolite or post-obduction regional deformation events.

Analysis of chromite grains from a variety of ophiolitic chromite segregations shows them to be chrome-spinels with variable Cr* values (Cr/(Cr+Al)), typically between 0.4 and 0.85, with Mg* values (Mg/(Mg+Fe
2+
)) between (0.5 and 0.8) and invariably restricted Fe
3+
contents. By way of a simple contrast to major layered intrusions the ophiolitic chromite segregations tend to range to lower Cr* values and show higher and more restricted Mg* ratios. The variation of the Cr* ratio from chromite segregations within an individual ophiolite can be related to the position of the segregation within the mantle sequence. The more aluminous deposits being located towards the petrological moho, whereas the more chrome-rich horizons tend to occur deeper within the sequence, in particular toward the harzburgite lherzolite transition.

A model is described which considers the chromite deposits to represent the early fractionates of ascending magmas within highly depleted mantle, likely to have developed above subduction zones, or at fast spreading centres. Transport of the mantle away from the spreading zone results in deformation of the chromite deposits within a falling P-T regime involving both ridge-axis and post-obduction deformation.
An overview of the PGE concentrations in the Shetland ophiolite complex
Authors: Prichard H. M. , Lord R. A.
Published: April 2008

Extremely anomalous platinum-group element (PGE) concentrations are known at one site, Cliff, in the Shetland ophiolite complex. Systematic PGE analysis of all the mafic and ultramafic igneous and alteration lithologies in the ophiolite has revealed many lower grade anomalous PGE occurrences throughout the cumulate ultramafic sequence and their distribution is described here. More sites with PGE enrichments as anomalous as those at Cliff have not been found.

At Cliff the anomalous values of over 60 ppm Pt + Pd are restricted to a chromite-rich sulphide-bearing dunite forming a small part of a 200 m dunite lens in mantle harzburgite close to the basal thrust of the ophiolite. Lower values of up to 6.4 ppm Pt + Pd occur in chromite-poor, sulphide-rich dunites also within this dunite lens. The only other chromite-rich dunite lens in the Cliff area also has detected Pt and Pd but with low Pt + Pd values of 200 ppb. In contrast, harzburgites, metasediments underlying the basal thrust, serpentinites from the basal thrust and internal faults are all barren of Pt and Pd (detection limit = 20 ppb). In the Cliff area, therefore, detected PGE values are restricted to magmatic chromite-rich dunite lenses. PGE analyses of drill core from beneath the disused chromite quarries at Cliff are low (227 ppb Pt + Pd) indicating that the extremely anomalous PGE values are very restricted. This supports the idea that PGE, concentrated magmatically within the dunite lens at Cliff, may have been remobilized locally to produce extremely anomalous PGE values in an alteration zone only a few metres in diameter.

Elsewhere in the ophiolite, anomalous Pt + Pd values of up to 4 ppm occur in chromite-rich, sulphide-bearing dunite within the dunite unit, which stratigraphically overlies the harzburgite. Pt + Pd concentrations of up to 1 ppm are present in the pyroxenites and wehrlites of the upper part of the ultramafic sequences. High-level wehrlites and pyroxenites within the gabbro unit, representing late ultramafic differentiates, contain lower levels of PGE of up to 310 ppb Pt + Pd. The gabbros all have less than 20 ppb Pt and Pd. This distribution indicates that the PGE concentrations occur in specific primary magmatic lithologies and pathfinder analysis shows that they are associated with Ni, Cu, Au and Cr. PGE have not been found above detection limits in fault zones away from primary PGE mineralization sites and it is concluded that PGE are not significantly hydrothermally reconcentrated. At Cliff, remobilization may have occurred over short distances of only a few metres at most.
Geochemical and thermal fluxes, high-temperature venting and diffuse flow from mid-ocean ridge hydrothermal systems: the TAG hydrothermal field, Mid-Atlantic Ridge 26°N
Authors: Elderfield H. , Mills R. A. , Rudnicki M. D.
Published: April 2008

Submarine hydrothermal activity provides a source of many elements to sea water at rates of a similar order to those of input by rivers. Estimates of hydrothermal fluxes from geophysical models which attribute only about 200f the advection to the axial region are up to an order of magnitude lower than those based upon geochemical budgets (from
3
He, Mg and
87
Sr/
86
Sr). Evidence for ridge-flank and on-axis low-temperature hydrothermalism is reviewed. Diffuse flow appears to account for about ¾ to

3/4 to 6/7
of the total heat flux of 500–900 MW for the TAG vent field, but is poorly characterized chemically. Processes in hydrothermal plumes moderate the primary hydrothermal fluxes of trace elements to the oceans. Recent studies of the plume above the TAG hydrothermal field are discussed. Oxyanions and particle-reactive trace metals are co-precipitated with iron oxyhydroxides that form during mixing in the buoyant plume. Particle-reactive metals are further scavenged during lateral transport of the plume whereas chalcophile elements are removed from the plume. The overall effect of plume reactions is that hydrothermal activity acts as an oceanic sink for several trace elements.
Orogenic uplift and collapse, crustal thickness, fabrics and metamorphic phase changes: the role of eclogites
Authors: Dewey J. F. , Ryan P. D. , Andersen T. B.
Published: April 2008

Coesite-bearing eclogites in several deep crustal metamorphic assemblages now exposed in extensionally-collapsed orogens indicate the tectonic denudation of more than 90 km of crustal rocks and pre-collapsed crustal thicknesses of at least 120 km. For mountain ranges and orogenic plateaux up to 5 km in elevation and average crustal densities of about 2.8, crustal thickness cannot exceed about 80 km unless pre-shortening crustal/lithosphere thickness ratios were less than 0.135 or some way can be found to preferentially thicken the lithospheric mantle. This problem can be avoided and very thick orogenic crusts built up if granulite facies rocks transform to denser eclogite facies during shortening, where the petrographic Moho is continuously depressed below a density/seismic velocity Moho buffered at about 70 km and mountains at about 3 km. Advective thinning of the lithosphere combined with the resultant heating and eclogite to sillimanite-granulite/amphibolite transformation causes surface uplift of about 2 km, a rapid change in isostatic compensation level, and a switch from a shortening to an extensional/collapse regime. We have developed a simple numerical model based upon field observations in southwestern Norway in which coherent regional-scale transformation of lower crustal rocks to eclogite facies during lithospheric shortening is followed by heating, transformation of eclogite to amphibolite and granulite, extension, and crustal thinning by coaxial then non-coaxial mechanisms. The model also explains strong lower crustal layering (eclogite and other lenses in horizontally-extended amphibolites), regionally horizontal gneissic fabrics, rapid return from orogenic to ‘normal’ crustal thickness with minor erosion, the lateral and vertical juxtaposition of low-grade and high-grade rocks and rapid marine transgression shortly after orogeny.
Amphibolite dehydration-melting: sorting out the solidus
Authors: Wyllie Peter J. , Wolf Michael B.
Published: April 2008

Amphibolite melts under vapour-absent conditions by dehydration-melting, during which H
2
O released from hornblende is transferred directly into H
2
O-undersaturated silicate liquid. Five independent 1991 studies on amphibolite dehydration-melting differ from each other and from earlier conceptual treatments. Five solidi between 7 and 10 kb vary from 975°C to 740°C. Two solidi above 10 kb are near-vertical, near 975°C and 850°C. Some differences are due to different amphibolite compositions and mineralogy. We use the results of earlier experiments involving garnet, supported by our own new results, to construct a closed-system phase diagram for a simple, fully-hydrated amphibolite (hornblende + plagioclase) showing the solidus and the melting interval for (hornblende + garnet + other minerals + liquid). The amphibolite vapour-absent solidus is defined by the beginnings of two multivariant reactions: (1) a near-vertical curve (large positive dP/dT) where the formation of augite dominates; and (2) a near-horizontal curve at higher pressures where the formation of garnet dominates. The solidus curve bends back (estimated near 900°C, 9 kb) with slope changing to low positive dP/dT. The new phase diagram expands the field for liquid generation with garnet-amphibolite residues to much lower temperatures and pressures than the other recent experimental results, increasing the range from which small amounts of hydrous granitoid melts may be segregated by compaction. The reversed, near-horizontal slope of the solidus near 10 kb has interesting petrological consequences.
The Proterozoic Gardar rift zone, south Greenland: comparisons with the East African Rift System
Authors: Macdonald Ray , Upton Brian G. J.
Published: April 2008

The late Tertiary to Recent Kenya rift valley and the deeply dissected, Proterozoic, Gardar province of south Greenland are both parts of continental rift systems thousands of kilometres long. Both were generated within stabilized orogenic belts skirting cratonic forelands, in regions in which repeated reactivation of earlier structures has occurred. Both may represent failed attempts at continental separation.

Mafic magmatism in Kenya has ranged from strongly silica-undersaturated, melanephelinitic types through basanites to mildly alkaline and transitional basalts. Gardar activity was dominated by mildly alkaline and transitional basalts; basanites and nephelinites are rare or absent, the most undersaturated representatives being ultramafic lamprophyres. Very primitive (possibly primary) magmas are scarce in both rifts. Trace element chemistry suggests that the majority of the mafic rocks have lithospheric signatures, and that asthenospheric magmas had no direct access to the crust. The primary magmas were generated as small-degree melts in mantle sources which had experienced earlier depletion events and which were subsequently metasomatized. An important, mantle-derived feature of the Gardar basalts is their strongly aluminous nature, which appears to have generated an abundance of anorthositic bodies in the crust; this feature is not shown in the Kenya rift. Considerable amounts of underplating are inferred to characterize both rifts, limiting crustal thinning in regions of lithospheric extension.

Both rift zones have extensive axial dyke swarms, which are particularly focused on central complexes/caldera volcanoes. Kenya apparently lacks, however, the massive dykes, up to several hundred metres wide, of the Gardar province.
Alkali basalts from Shuqra, Yemen: magmas generated in the crust-mantle transition zone?
Authors: Cox K. G. , Charnley N. , Gill R. C. O. , Parish K. A.
Published: April 2008

The alkali basalts from Shuqra, Yemen, contain a megacryst suite consisting of olivine, aluminous diopside, kaersutite, pleonaste, plagioclase, and apatite. Deformational kink bands in the olivines, and the existence of multi-phase inclusions (e.g. olivine + pleonaste, aluminous diopside + pleonaste, kaersutite + pleonaste, aluminous diposide + plagioclase) suggest that the megacrysts are derived from disaggregated plutonic rocks. Whole-rock compositional variation cannot have been generated by the fractionation of the phenocrysts present (olivine, augite, labradorite), but is readily explicable as a mixing line between alkali basalt melt and restite, represented by the megacryst suite. It is suggested that the source rock was a deep-crustal, or uppermost mantle, hydrous, and very alkalic, picritic, gabbroic, or syenogabbroic intrusion, which was remelted, perhaps by the injection of further picritic magma. Although the Shuqra rocks themselves do not appear to contain mantle xenoliths, the proposed mechanism of magma generation, if operating on an interleaved crust/mantle transition zone, could provide a general explanation for the occurrence of occasional alkali basalt flows which are extremely rich in spinel lherzolite inclusions.
Coal and coal-bearing strata as oil-prone source rocks: an overview
Authors: Fleet Andrew J. , Scott Andrew C.
Published: April 2008

Despite many advances in our knowledge over the last decade, understanding of why some coals and coal-bearing strata are oil prone, and our ability to predict such sequences ahead of drilling in petroleum exploration, is relatively poor. Here we review the current status of the knowledge, highlighting contributions made in this volume. Oil-prone coals are hydrogen rich. Those which are generally acknowledged to have given rise to significant oil accumulations occur either as low latitude Tertiary deposits or within late Jurassic-Palaeogene sequences of the Australian region. Oils derived solely from coals and other terrigenous kerogens can be recognized using geochemical criteria. Recognition of oil-prone coals and associated mudrocks visually or geochemically, however, is problematical. What controls the expulsion of petroleum in the liquid phase from coal-bearing sequences is probably the critical factor. Our knowledge of the botanical, depositional and diagenetic controls which determine the formation of oil-prone coaly sequences, and hence our ability to predict their presence, is currently empirical and lacks understanding of the inputs and processes involved.
Geochemical characteristics of oils derived predominantly from terrigenous source materials
Authors: Philp R. P.
Published: April 2008

It is well established that there are many major accumulations of crude oils that are derived predominantly from higher plant source materials. All of these oils have a number of geochemical characteristics in common. These features include
n
-alkane distributions, presence of a variety of sesqui-, di-, tri-, tetra-, and pentacyclic terpanes and isoprenoids. Variations in the distribution of these compounds reflect variations in the nature of the source materials and the original depositional environment. The purpose of this paper is to review these characteristic features so that they can be used to determine whether or not new oil samples are derived predominantly from higher plant source materials. The geochemical approach has been used successfully in the past to characterize samples derived from hypersaline and carbonate environments.
Chemical heterogeneity among adjacent coal microlithotypes — implications for oil generation and primary migration from humic coal
Authors: Stout Scott A.
Published: April 2008

Laser radiation focused onto a coal polished perpendicular to bedding has been used to thermally extract and pyrolyse the organic matter from three adjacent microlithotypes in a Tertiary, autochthonous, hydrogen-rich, sub-bituminous (early catagenesis/bituminization stage) humic coal from Indonesia. The distribution of hydrocarbons released during laser irradiation are shown to vary on a millimetre scale between adjacent humotelinite-, liptodetrinite-, and resinite-dominated microlithotypes. This variability is not due to varying thermal maturity but rather to (1) the inherent chemical variability of the macerals comprising each microlithotype; and/or (2) the presence of migrated, or non-indigenous, bitumen/oil. Hydrocarbon yields from each microlithotype suggest that primary migration between microlithotypes has occurred. Specifically, long chain
n
-alkanes and isoprenoids, which were most likely generated in the cutinite-derived liptodetrinite-dominated microlithotype (liptoclarite), are much more abundant in the overlying liptinite-free, humotelinite-dominated microlithotype (telite) and in the underlying resinite-dominated microlithotype (resinoclarite). These observations suggest that while the type of macerals plays an important role in the generation of oil within coals, it is the physical association between macerals (i.e. the microlithotypes present) which significantly influences the primary migration of oil within, and expulsion of oil from, coal seams. Thus since coals are extremely variable, both chemically and physically, generalizations suggesting all liptinite-rich humic coals can act as oil source rocks may be misleading. Liptinite-rich humic coals with high concentrations of finely-admixed liptinite and huminite macerals (e.g. liptodetrinite in a humodetrinite and mineral matrix, as would occur in microlithotypes with a detrital origin) may permit both oil generation
and
expulsion. Characteristics of the telite suggest, due to their high absorptive capacities and (micro)-porosity throughout most of bituminization/catagenesis, coals which contain an abundance of massive huminite macerals (e.g. humotelinite or gelinite) may tend to trap hydrocarbons generated from nearby or encased liptinites within their networks. Such macerals (the precursors to desmocollinites in bituminous coals) may become relatively hydrogen rich and often fluoresce under uv light and may not expel hydrocarbons until they are subsequently cracked to gas.
Coal-bearing strata as source rocks — a global overview
Authors: Macgregor Duncan S.
Published: April 2008

Compilation of a global source rock database has shown that coal-bearing sequences are significant oil generators only in very specific and relatively uncommon geological settings. Coals and associated carbonaceous shales are thought to be the primary oil-prone source facies in Australasia and an important secondary source facies in Southeast Asia. In other regions of the world, there is, however, no evidence that they have expelled major quantities of oil. In terms of their contribution to the worldrss petroleum reserves, coal measures are the origin of relatively minor proportions of oil, but of significant amounts of gas. Coal sequences that are believed to have expelled significant amounts of liquid hydrocarbons seem to be restricted to two palaeoclimatic and palaeobotanical ‘fairways’.

1.

Tertiary angiosperm assemblages within 20° of the palaeo-equator.

2.

Late Jurassic-Eocene gymnosperm assemblages formed on the Australian and associated plates.

The reasons for this are not well understood. Multidisciplinary research work is recommended to compare these oil-prone coals with the much greater volumes of apparently gas-prone coals deposited outside these regions.
Fluid flow and heat transfer in sedimentary basins
Authors: Jessop Alan M. , Majorowicz Jacek A.
Published: April 2008

One of the major assumptions underlying the science of geothermics over the last 100 years has been that heat is transported through the Earth’s crust only by conduction, except in the immediate vicinity of active volcanoes. In old shields this assumption may be justifiable, but in sedimentary basins the ability of water to move through permeable aquifers provides a means of heat transport that may under certain conditions be as effective as conduction.

The thermal history of a basin depends on its tectonic origin and the circumstances of its development. The dissipation of excess heat associated with basin formation and the transfer of the continuous heat supply from the basement depend on the thermal properties of the strata and their water content. In some basins widespread contrasts of heat flow are observed, both laterally and vertically, suggesting forced convection by water migration. In basins where part of the surface is above sea-level a hydrological drive may be inferred from the topographic surface. In sub-sea basins this drive is not available in the same form. Nevertheless, patterns of heat-flow variation have been observed for which some form of water flow seems to be the most probable explanation.

A complete quantitative description of the present thermal state has not yet been developed for any basin. Some two-dimensional numerical models have been developed, but, since flow directions may vary between aquifers, three-dimensional models must be the ultimate objective. There is scope to extend such models to the geological past by using palaeotemperature indicators such as vitrinite reflectance and fission-track measurements. So far we have been able to establish only an understanding of the principles and processes that control the thermal state of basins, so that detailed description of small parts or two-dimensional models may be developed.
Earthquakes, strain-cycling and the mobilization of fluids
Authors: Muir Wood R.
Published: April 2008

Employing empirical observations of the hydrological changes that follow major earthquakes, it becomes possible to predict subsurface fluid flows that accompany tectonic activity. Coseismic hydrological changes are found to be critically dependent on the style of fault displacement. Normal faults involve post-seismic compressional elastic rebound and displace large volumes of fluid from the crust: rainfall equivalent discharges have been found to exceed 100 mm close to the fault and remain above 10 mm at distances greater than 50 km; the total volume of water released in two M7 normal fault earthquakes in western USA was 0.3–0.5 km
3
. In contrast, reverse fault earthquakes involve extensional elastic rebound that increases crustal porosity, drawing fluids into the crust. The magnitude and distribution fo the water-discharge for normal fault earthquakes has been compared with deformation models calibrated from seismic and geodetic information, and found to correlate with the crustal volume strain down to a depth of up to 5 km.

These results suggest that fluid-filled cracks are ubiquitous throughout the brittle continental crust, and that these cracks open and close through the earthquake cycle. By repeatedly drawing fluids into microcracks distributed throughout a very large volume of rock, strain-cycling can achieve very significant chemical fractionation. Different classes of tectonics impose particular configurations of fractures and according to the origin of fluid recharge, lead to a range of different types and styles of mineralization. Seismic strain-cycling can also produce primary and secondary oil migration within a single causative mechanism.
Fluid flow in actively deforming sediments: ‘dynamic permeability’ in accretionary prisms
Authors: Stephenson E.L. , Maltman A.J. , Knipe R.J.
Published: April 2008

Recent investigations into active accretionary prisms have emphasized both the importance of the deformation/fluid-flow interplay in governing fundamental aspects of prisms and the need for quantitative data on the processes. Even the basic parameter of permeability is little known in this and other geological settings where the sediments are undergoing active deformation. New experimental data are presented which show that permeability during accumulating strain, here called thedynamic permeability, is not a static value but is highly variable. Moreover, microstructural analysis and precise determination of permeant volume reveal that this dynamic permeability is not solely the varying capacity of the deforming medium to transmit fluid, a quantity here called theDarcyan permeability, but includes a contribution to the amount of permeant from the medium itself. In the laboratory experiments this additional contribution, called thedynamic component, arises from pore-volume fluctuations associated with microstructural changes, but in nature there may be further mechanical and chemical effects. Applying conventional methods of permeability determination to an actively deforming sediment will necessarily include this dynamic component in the measurement, a consideration relevant to a variety of geological and engineering situations.
Origin and nature of trace element species in crude oils, bitumens and kerogens: implications for correlation and other geochemical studies
Authors: Filby Royston H.
Published: April 2008

Crude oils and bitumens contain trace elements whose abundances range from less than a part per billion (ppb) to more than several thousand parts per million (ppm). Nickel and vanadium are usually the most abundant metals with values ranging up to 200 ppm Ni and 2000 ppm V. Abundances of other trace elements are generally less than 100 ppm. Nickel and vanadium occur in oils and source-rock bitumens as metalloporphyrins and non-porphyrin species. The nickel and vanadium porphyrins are predominantly DPEP or etio complexes of Ni
2+
or VO
2+
although smaller amounts of benzo and other complex porphyrins are found. The metalloporphyrins are formed during early diagenesis of source rocks and the relative abundances of nickel and vanadium are related to the depositional environment. The origin of the non-porphyrin nickel and vanadium complexes and the complexes of other trace elements in crude oils may be primary or secondary. Primary processes include release of metal complexes from kerogen during categenesis and formation of metal-organic complexes by mineral-kerogen reactions during catagenesis. Secondary processes such as interaction of oils with mineral matter or formation waters during migration, maturation or biodegradation may also affect the concentrations of some elements in crude oils, e.g. Hg.
Organic matter alteration and fluid migration in hydrothermal systems
Authors: Simoneit Bernd R.T.
Published: April 2008

Hydrothermal systems associated with oceanic spreading centres are now recognized as relatively common phenomena, and the organic chemistry occurring there is geologically rapid and novel. Especially in the marine hydrothermal systems at water depths >1.5 km, this chemistry proceeds at high temperatures (up to >400° C) and high pressures (>150 bar) in an aqueous open flow medium. Continental systems may also be of interest, as for example failed or dormant rifts and regions around piercement volcanoes. Organic matter alteration to petroleum hydrocarbons by reductive reactions occurs in hydrothermal systems over a wide temperature window (
c.
60 to >400° C), under high pressure, and in a brief geological period of time (years to hundreds of years). Thus, the products are considered to be in a metastable equilibrium state during their brief formation and residence times at high temperatures. These conditions are conducive to organic chemistry which yields concurrent products by reduction (due to mineral buffering), oxidation (high thermal stress) and synthesis. Therefore, this brief time interval coupled with the wide range of hydrothermal petroleum compositions indicates that organic matter maturation and petroleum generation, expulsion and migration occur as an overlapping continuous process during hydrothermal activity. The behavior of organic matter (CH
4
-C

40
+

) in near to supercritical water, in many cases with associated high concentrations of CO
2
and methane, needs to be further characterized in order to understand the implications of this novel phenomenon in geological and geochemical processes.
What is a mineral resource?
Authors: Riddler G. P.
Published: April 2008

Mineral resource evaluation is one of a whole spectrum of quantitative methods which have been used since biblical times for the purpose of improving the process required to aid problem-solving and to increase the quality of strategic management decisions at all levels. Such evaluation leads to the classification of mineral resources. It is important to have a clear knowledge of how mineral resources are classified and what the classification nomenclature actually means to ensure decisions are based on a sound understanding of criteria applied.

As interest for investment in mineral resource development spreads into Eastern Europe and the former Soviet Union, the need for some form of harmonization in terminology, nomenclature, criteria, as well as the approach to the classification process for the definition of mineral resources has again been highlighted.

The approach to quantitative studies is discussed, and guidelines are given that may improve mineral reserve and resource estimates so that implementation failure of mining projects can be avoided.

Approaches to the classification of mineral resources are reviewed along with the uses made of such mineral resource information.

The argument is put for a standard approach to mineral resource classification and consistency of international nomenclature with a discussion of some of the related problems. Principles are established which may suggest a way forward illustrated by a recent major resource assessment project.
Classification of mineral reserves in the former Comecon countries
Authors: Jakubiak Z. , Smakowski T.
Published: April 2008

Classification of reserves in the former Comecon countries is based on two reference axes: the abscissa represents the degree of reserve identification and the ordinate shows the possibility of economic utilization. Accordingly, reserves are classified as documented and prospective and as economic and uneconomic.

Documented reserves are divided into categories A, B, C
1
and C
2
. The first two of these categories relate only to developed and blocked reserves, with category A being in practical terms restricted to reserves under advanced exploitation, often at a stage nearing exhaustion. Category C
1
comprises reserves which have been identified and examined to such an extent as to enable a positive definition of their suitability for exploitation; these reserves are often in early production phases. Category C
2
relates to reserves which have been identified and documented at a preliminary stage only. Terminology of prospective reserves differs from country to country. In the former USSR and in the majority of other countries that adopted this classification, prospective reserves are divided into categories P
1
, P
2
and P
3
. However, in the classification used in Poland, on which this paper is based, prospective reserves are divided into prognostic reserves in categories D
1
, D
2
and D
3
and theoretical reserves in category E, categories D
1
and D
2
being equivalent to categories P
1
and P
2
respectively and combined categories D
3
and E roughly equivalent to category P
3
. Included in category D
1
are reserves either in areas adjoining documented reserves classified in category C
2
or reserves that occur at depths considered to be uneconomic. Assigned to category D
2
are reserves inferred from surface showings and indirect indications and quantified on the basis of statistical analysis of reserves known in similar mineralized structures in the proximity, whilst category D
3
includes reserves inferred from indirect indications alone. Finally, theoretical reserves E are deducted only from regional structural, lithological, metallogenic and other considerations.

Reserves in categories D
2
and above are divided along the ordinate into economic and uneconomic on the basis of the so-called criteria of balance defined by authorities in charge of the project(s). In centrally-planned economies the selection of these criteria generally reflected prevailing economic policies and priorities rather than profit considerations. Another set of criteria called the criteria of workability is then applied to economic reserves to define mineable reserves and these are called industrial reserves.

Put in the context of the IMM definitions, categories A and B are equivalent to measured mineral resources, categories C
1
and C
2
are broadly comparable to indicated mineral resources, whilst prospective reserves straddle the fields covered by indicated resources and mineral potential. Industrial reserves are comparable to the mineral reserve category as defined by the IMM definitions.
Fault interpretation from coal exploration borehole data using SURPAC2 software
Authors: Gribble P. D.
Published: April 2008

The use of isopach or contour plans for geological surfaces as the basis for fault interpretation of coal data, even when a dense drilling pattern has been applied, is often unsatisfactory. These plans tend to ‘smooth’ or underemphasize the effects of faulting, making assessment of the likely fault pattern difficult.

Within the
surpac2
Software system a series of modelling tools is available to assist with this interpretation process. An appropriately oriented grid is overlain on a digital terrain model (DTM) of the geological surface in question to regularize the data. The dip between data points is calculated, and a model of dip change created using the DTM method. A new contour model, which highlights trends in dip change, is produced, clearly showing likely fault traces and throw. This model may be sectioned to illustrate more graphically the disturbed and undisturbed areas. The fault model is then used as the basis for interpretation, to be compared with other models of the geology, and known local and regional faulting trends. Use of the macro facilities within
surpac2
allows a series of surfaces to be rapidly analysed to build up a picture of likely fault continuity and pattern within the succession.

Once the fault pattern is established, it can then be used elsewhere in
surpac2
for further modelling and evaluation. Application can be simple, such as the formation of boundaries of faulted areas for estimation of mineable coal resource. More complex modelling can be achieved by interaction between geological surfaces and the fault surfaces defined by the interpretation process. A complete model of the faults and their impingement on the coal and associated layers is formed, for further use within the
surpac2
design tools.
Optimal open pit design: sensitivity to estimated block values
Authors: Dowd P. A.
Published: April 2008

This paper discusses two important, and often overlooked, aspects of optimum open pit design: the information and support effects. Pit designs are ultimately based on estimated block grades and, as such, their optimality can only ever be approximate; as the errors of estimation of the block grades increase the pit design will deviate more and more from true optimality. Estimation errors depend on the amount of data available (information effect) and on the size of the block to be estimated (support effect). There is a lower limit to the block size used in grade and revenue block models for pit design and this lower limit is determined by the drilling grid. The use of blocks which are significantly smaller than the drilling grid will produce block models which will yield erroneous pit designs. Geostatistical simulation is used to quantify these effects for a particular case and to demonstrate the most effective way of dealing with small selective mining units at the planning stage.
Dilution in underground bulk mining: implications for production management
Authors: Scoble M. J. , Moss A.
Published: April 2008

The minimization of dilution represents a major opportunity for quality improvement in Canadian underground metal mining. The characteristics of the principal forms of dilution, planned and unplanned, are reviewed. These are controlled by quality factors relating to exploration, mine design and stoping practice. The scope for quality improvement and the need for technology development is analysed in the context of underground bulk mining. The design principles for a production management system which tightly monitors and controls dilution are proposed. This revolves around the reconciliation of accurate and timely data on ore reserves, stope fragmentation, cavity morphology, rockmass integrity, and production statistics. Particular priority will require to be placed on continued sensor development for measurement of cavity geometry, borehole deviation, grade and tonnage. This is intended to exploit a rapidly evolving underground communications technology and forms part of a rationale for future computer integrated mining.
The optimal design of quarries
Authors: Dowd P. A.
Published: April 2008

This paper describes the various general approaches to the optimal design of pits and quarries. Three types of deposit and corresponding numerical models can be distinguished and in each case a particular method of optimization can be used. In the most general case computer methods must be used to construct optimal pit/quarry outlines on the basis of a regular, three-dimensional revenue/grade block model. The paper includes a Fortran algorithm for a simple implementation of the Lerchs-Grossmann method for optimal pit/quarry design.