bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chapter 12 Metallic mineral deposits
Authors: Crow M. J. , Van Leeuwen T. M. 
Published: December 2007

This account concentrates on the the primary metallic mineral deposits and occurrences in Sumatra, in particular the recent discoveries of gold, tin and base metals. The residual and placer deposits are given less emphasis, as no significant discoveries have been made in recent years.
The history of mineral exploration and discovery in Indonesia has been reviewed recently by van Leeuwen (1993, 1994), documenting the change in emphasis of mineral-based activities from western to eastern Indonesia since the World War II. These studies bring up-to-date the classic account by van Bemmelen (1949), written when the mineral deposits in western Indonesia, particularly those in Sumatra, were among the better known and prior to 1942, important contributors to the Indonesian economy.

The larger mineral deposits in southern Sumatra have been described briefly by Gafoer & Purbo-Hadiwidjoyo (1986), and are referred to in the regional descriptions of the mineral deposits of SE Asia by Hutchison & Taylor (1978) and Hutchison (1996). In wider-ranging reviews the geological setting of gold and base metal deposits in Indonesia have been discussed by Carlile & Mitchell (1994), while those of tin deposits in SE Asia are catalogued by Schwartz
et al.
(1995).

Sumatra has long been known as a source of gold, the name of the island being derived from the Sanscrit word
Svarnadvipa
, meaning 'Golden Island', dating from the importance of gold deposits to the rulers of the Hindu kingdoms that flourished in Sumatra from the seventh until the eleventh century. The estimated total production of precious
Chapter 13 Structure and structural history
Authors: Barber A. J. , Crow M. J. 
Published: December 2007

The present structure of Sumatra is dominated by the effects of the current subduction system in which the Indian Plate is being subducted northeastwards beneath the island at a rate of c. 7 cm a
1
. The structure of Sumatra was described by van Bemmelen (1949) and in terms of plate tectonics by Hamilton (1979). The main structural elements of Sumatra and its surrounding region are defined with respect to the Sumatran subduction system (Fig. 13.1).

(1) Forearc region, which includes the subduction trench, part of the Sunda Trench extending from Myanmar to eastern Indonesia, the developing accretionary complex, composed of ocean floor materials scraped off the Indian Plate, the forearc ridge which rises above sea level to form the forearc islands, and the forearc basins which lie between the ridge, and the volcanic arc on the mainland of Sumatra (Fig. 13.2).
(2) Barisan Mountains and the Sumatran Fault System. The Barisan Mountains are composed of an uplifted basement of Upper Palaeozoic and Mesozoic sedimentary and volcanic rocks, variously metamorphosed, deformed and intruded by granites, overlain by Cenozoic sediments and volcanics, including the products of the volcanoes related to the present subduction system, which form the currently active volcanic arc. The Sumatran Fault system is a complex of dextral strike-slip faults running the whole length of the island through the centre of the Barisan Mountains from NW to SE, with zones of compression and extension, forming areas of uplift and pull apart basins which form grabens along the line of the
Using production data and time domain seismic attributes for history matching
Authors: Fornel A. , Mezghani M. , Langlais V. 
Published: December 2007

Abstract
A fundamental goal of oil and gas reservoir characterization is to enhance the reliability of dynamic fluid flow simulation studies through better description of geological heterogeneity. Ideally, the geological model should be updated in real time with all available data (especially information derived from seismic, production, well test and core studies) to achieve significant optimization of field management. Such an update can lead to much improved understanding of the dynamic reservoir production forecasting. To this end we propose an integrated technique for improved geological modelling and reservoir characterization, which is based on a non-linear optimization loop for quantitative use of 4D seismic data in combination with production data.
Using physical properties to understand the porosity network geometry evolution in gradually altered granites in damage zones
Authors: Rosener M. , Géraud Y. 
Published: December 2007

Abstract
This study, based on petrophysics, is linked to the geothermal project developed at Soultz-sous-Forêts, in northeastern France. In such a context, understanding and modelling the thermo-hydro-mechanical and chemical processes implies a good knowledge of the porosity network geometry and its evolution during alteration. Various physical properties (permeability, specific surface and porosity) were measured on samples from the protolith and damage zones of fault zones in the geothermal reservoir exploited at Soultz-sous-Forêts. Measured porosity values vary from 0.2 to 10%, and using structural parameters (threshold values, specific surface and porosity distribution), three groups are identified. Each of them shows a specific pore shape distribution and the porosity increase within a given group is assumed to be associated with an increase of pore number rather than an enlargement or shape modification.
Numerical modelling of pressure solution deformation at axisymmetric asperities under normal load
Authors: Bernabé Y. , Evans B. 
Published: December 2007

Abstract
We developed a numerical model of compression of asperities by pressure solution (PS). The dissolution rate along the contact was determined by (1) computing the normal stress distribution from the present shape of the asperities, and (2) solving the diffusion equation inside the fluid-saturated solid–solid interface, including local dissolution source terms corresponding to the stress field previously determined. The change in shape of the asperities during an infinitesimal time interval can then be calculated and the entire procedure repeated as many times as desired. We simulated PS compaction of axisymmetric asperities with different sizes and shapes under various temperatures and loads, and using different values of the interface diffusion coefficient. Our results show that as the contact flattens and grows during PS, the initial elastic deformation is partially relaxed and the stress transferred from the contact centre to the edge. Transient stress release remains significant during an extended period and could strongly influence the interpretation of laboratory experiments. In our model, dissolution and interface diffusion are not sequentially combined as is usually assumed, making it impossible to identify a single rate-limiting process. The convergence rate of the asperities was approximately proportional to the mean effective stress at the contact, and depended in a complex way on the contact radius, but was not sensitive to the asperity size. We also estimated the conditions under which undercutting at the contact edge is triggered.
Weak elastic anisotropy in a cracked rock
Authors: Wong T.-F. , Zhu W. 
Published: December 2007

Abstract
The elastic properties of a cracked rock are transversely isotropic if its crack density distribution is axisymmetric. The three Thomsen parameters ε, δ and γ are used to characterize the seismic properties of a weakly anisotropic rock. In this study we calculated these anisotropy parameters in such a cracked rock under dry and saturated conditions. We derived analytic expressions for a dry rock based on an approximate model proposed by earlier workers, which shows elliptically anisotropic behaviour. Guided by microstructural observations we adopted a two-parameter axisymmetric distribution to characterize the crack density, which predicts that in a fluid-saturated rock the parameters δ and γ are related to ε in a nonlinear manner. All three parameters considered are sensitively dependent on the difference in the densities of cracks with normals parallel and perpendicular to the symmetry axis. Theoretical predictions of the model are compared with laboratory and field measurements of seismic anisotropy.
Overview of key experiments on repository characterization in the Mont Terri Rock Laboratory
Authors: Bossart P. 
Published: December 2007

Abstract
Repositories for radioactive waste are designed as disposal systems that perform a number of functions relevant to long-term safety and security, including (1) isolation of waste from the human environment, (2) long-term confinement and radioactive decay within the disposal system and (3) attenuation of radionuclide releases to the environment. The generic rock laboratory at Mont Terri plays an important role in the characterization of such repositories. The experimental results gained in this underground facility are used, together with information from natural analogues, deep drilling programmes and modelling, to assess the evolution and performance of a repository. A time scale for processes affecting repository performance is outlined. A transient phase in the first 10–20 ka is followed by an equilibrium phase. Key experiments cover processes observed over relevant time scales, feasibility experiments and experiments focusing on long-term process understanding. The last can only be partly investigated over realistic time scales in direct experiments because of the long time frame required. Key experiments are briefly outlined and key references are provided.
Velocity survey of an excavation damaged zone: influence of excavation and reloading
Authors: Damaj J. , Balland C. , Armand G. , Verdel T. , Amitrano D. , Homand F. 
Published: December 2007

Abstract

During gallery excavation, regardless of the method chosen, the surrounding rock is mechanically disturbed in the case of underground disposal of chemical or radioactive wastes, and such mechanical changes to the rock state can create preferential pathways for the release of material from the waste inside the excavation (e.g. chemical waste gases, brine or dissolved radionuclide) up to the biosphere. The mechanical characterization of this disturbed zone is thus essential in assessing the rock capacity necessary to form an impermeable geological rock barrier. The key to this effort lies in determining the nature, extent and change to this disturbed zone. A survey by ultrasonic wave analysis is particularly appropriate for these purposes, as it provides information on the zone left undisturbed by the boreholes. The main aim of this paper is to describe a recent
in situ
experiment (called EZ-A) conducted in Opalinus clay at the Mont Terri Rock Laboratory in Switzerland. This experimental campaign successfully studied the possibility of improving the properties of rocks forming the excavation damaged zone (EDZ). The experiments consisted of three stages: the first entailed locating the EDZ caused by the construction of gallery EZ-A at the Mont Terri laboratory; the second traced the evolution of the EDZ arising from a 20 cm thick and 150 cm deep slot excavation in the EZ-A gallery floor; and the third stage focused on the P-wave velocity evolution surrounding the slot during a pressure loading at the slot walls, which serves to characterize the EDZ evolution in the slot. These three stages were carried out using seismic tomography and then recording the wave propagations during the excavation and reloading stages. The measurement of velocity before and after slot excavation reloading, together with the survey during slot excavation, showed a decrease in P-wave velocity underneath the slot floor down to a 0.2 m depth. Reloading clearly improves P-wave propagation along the sidewall and slightly decreases it under the slot.
Temperature-induced evolution of the elastic and magnetic anisotropy in argillite samples from Bure underground research laboratory, eastern France
Authors: Robion P. , David C. , Colombier J. C. 
Published: December 2007

Abstract
The influence of temperature on magnetic and elastic properties of the Callovo-Oxfordian argillite formation, host of the French underground research laboratory for studying radioactive waste repository, has been investigated following two types of experiments. In the first experiment, rock samples were heated at 95 °C in an oven for 41 days, and in the second, heating–cooling cycles at increasing maximum temperatures were applied. Magnetic susceptibility and P-wave velocity measurements were conducted to investigate the effect of heating not only on the absolute values but also on the anisotropy. Whereas little variation was observed in the first experiment, the results of the heating–cooling cycles showed that different stages can be identified in the evolution of P-wave velocity and magnetic susceptibility with maximum temperature applied. At temperatures below 200 °C, the velocity increases sharply whereas the magnetic susceptibility remains unchanged: this is interpreted as being the result of mineralogical transformations, probably associated with dewatering of the clays. Above 200 °C, a large increase in susceptibility associated with a levelling off (or even a decreasing trend) of the velocity results from the competition between thermal cracking processes and another kind of mineralogical transformation affecting both properties. A magnetic mineralogical study showed that the main ferromagnetic mineral present is magnetite. An interesting result of the study is that in the temperature range investigated, the elastic properties are enhanced and the anisotropy is increased by raising the temperature, which has important consequences for the seismic monitoring of the storage site.
Investigation of the undrained poroelastic response of sandstones to confining pressure via laboratory experiment, numerical simulation and analytical calculation
Authors: Blöcher G. , Bruhn D. , Zimmermann G. , McDermott C. , Huenges E. 
Published: December 2007

Abstract

To describe the poroelastic behaviour of sandstones, two factors have to be considered: the grain structure and the pore volume included. Changes in these two factors through diagenetic processes, tectonic loading or other forces lead to different results. Often external stresses induce a compaction of the rock and, therefore, a reduction of pore volume and an increased fluid pressure. Under undrained conditions, the largest pore pressure response can be observed. Besides the Biot coefficient, the Skempton coefficient (
B
) is one of the most important variables of elastic rock deformation, as it describes the pore pressure change related to the acting stresses. This study shows three ways of determining the Skempton coefficient and gives evidence of its pressure dependence. First, the undrained poroelastic response of a Bentheimer sandstone sample to confining pressure change was measured. Second, a thin-section micrograph was transferred into a finite-element model, including a discretization of the grain structure and the pore space. Finally, the Skempton coefficient of a linear elastic hollow sphere was calculated to prove the laboratory experiment and the numerical simulation.
Compaction bands and the formation of slot-shaped breakouts in St. Peter sandstone
Authors: Haimson B. , Klaetsch A. 
Published: December 2007

Abstract

Drilling of vertical wellbores in sandstone often results in stress-induced failed zones called breakouts. In the laboratory, miniature drilling under simulated far-field crustal stress conditions above a certain threshold produces breakouts that can be studied to enhance our understanding of deformation and failure mechanisms in rock. We report on drilling experiments in St. Peter sandstone, an Ordovician aeolian rock consisting of well-rounded bimodal quartz grains held together by sutured contacts. Breakouts here are slot-shaped and oriented at right angles to the far-field maximum stress direction (σ
H
), resembling emptied compaction bands. We distinguish between two porosity ranges in this rock. In the high-porosity variety (16–22%), grains are bonded through narrow sutures. In the vicinity of the borehole at points aligned with the far-field least horizontal principal stress (σ
h
) direction, where the maximum compressive stress concentrates, grain sutures sever at relatively low stress levels, leading to intergranular cracking. Debonded intact grains repack and produce a reduced-porosity narrow compaction band. Loose grains in the band abutting the borehole wall are then flushed out, assisted by the circulating drilling fluid. This intensifies the stress concentration ahead of the breakout tip, advancing the compaction band and lengthening the slot-shaped breakout. The process continues sequentially. Grains in the lower-porosity sandstone (11–12%) are more substantially sutured over much larger surface areas. This makes the sutures nearly as strong as the grains themselves; hence, failure requires considerably higher stresses, sufficient to bring about intragranular cracking. Consequently, and in contrast to the high-porosity sandstone, breakouts here are preceded by compaction bands of shattered and crushed grains. Both types of compaction bands have been encountered in the field and in independent laboratory experiments.
Models for compaction band propagation
Authors: Rudnicki J. W. 
Published: December 2007

Abstract

A compaction band is modelled as a thin, ellipsoidal heterogeneity with an imposed inelastic compactive strain and different elastic moduli from the surrounding matrix. Previously published results are used to determine the stress state in the band. For a wide variation of properties, stress conditions, and inelastic strain, the stress state in the band for aspect ratios observed in the field, 10
−3
–10
−4
, is indistinguishable from the result in the zero aspect ratio limit. In this limit, the compressive stress immediately adjacent to the band tip is roughly 10–100 times the far-field stress for parameters representative of field conditions. This value is relatively insensitive to the elastic mismatch between the band and the surrounding material, and is primarily controlled by the ratio of the far-field stress to twice the shear modulus times the inelastic compactive strain. This ratio is inferred to be about 0.02–0.05 from published field results, but may be several times larger for laboratory specimens. The ratio of tip to far-field stress increases with decrease of band shear modulus and becomes unbounded if both the shear modulus and aspect ratio go to zero. A combined anti-crack–dislocation model, in which a compactive relative displacement 2
h
is specified in the centre of the band and uniform traction elsewhere, predicts that for growth at constant energy release rate
h
is proportional to

L

where
L
is the half-length of the band. For an energy release rate of 40 kJ m
−2
, inferred in an earlier study from field observations and comparable with compaction energies inferred from laboratory tests on circumferentially notched compression samples, the constant of proportionality is consistent with that inferred from laboratory observations and earlier field data.
The geodynamic evolution of the Alpine orogen in the Cyclades (Aegean Sea, Greece): insights from diverse origins and modes of emplacement of ultramafic rocks
Authors: Katzir Y. , Garfunkel Z. , Avigad D. , Matthews A. 
Published: December 2007

Abstract

The Alpine orogen in the Cyclades, wherein both high-pressure metamorphic rocks and ultramafic rocks co-occur, is a key area in studying the emplacement of mantle rocks into the crust. Within the Cyclades three distinct ultramafic associations occur: (1) HP–LT ophiolitic mélanges of the Cycladic Blueschist Unit (CBU) on Evia and Syros; (2) meta-peridotites associated with migmatized leucogneisses on Naxos, which represent the deepest exposed levels of the CBU; (3) a greenschist-facies metamorphosed dismembered ophiolite juxtaposed on top of the CBU by an extensional detachment on Tinos. Most of the Cycladic ultramafic rocks were serpentinized prior to Alpine metamorphism, suggesting denudation prior to reburial. The Naxos meta-peridotites preserve, however, relict mantle assemblage and mantle-like oxygen isotope ratios, and thus indicate direct emplacement from the mantle into an underthrust continent during collision and HP metamorphism (M
1
). Thus conditions for M
1
in the Naxos leucogneiss core are constrained by ultramafic assemblages to 550–650 °C and ≥14 kbar. Mafic blocks of the ophiolitic mélanges in the NW Cyclades span a wide range of chemical compositions indicating derivation from variable oceanic settings and sequential events of alteration and metasomatism. Given the comparable geochemical heterogeneity in the Syros and Evian mélange intervals, the garnet-bearing meta-basites of the Syros mélange record higher M
1
temperatures (450–500 °C) than the garnet-free epidote blueschists of the Evian mélanges (400–430 °C). It follows that going southeastwards from Evia progressively deeper (i.e. hotter) levels of the subducted plate are exposed. Correspondingly, temperatures of the M
2
overprint also increase from pumpellyite-bearing assemblages on southern Evia, through greenschists on Syros to upper-amphibolite, sillimanite-bearing gneisses on Naxos. The diverse
P
–
T
paths of the CBU form an array wherein the deeper a rock sequence is buried, the ‘hotter’ is its exhumation path. Such a pattern is predicted by thermal modelling of tectonically thickened crust unroofed by either erosion or uniform extension.
Structural evolution of Andros (Cyclades, Greece): a key to the behaviour of a (flat) detachment within an extending continental crust
Authors: Mehl C. , Jolivet L. , Lacombe O. , Labrousse L. , Rimmele G. 
Published: December 2007

Abstract
The continental crust extends in a brittle manner in its upper part and in more distributed (ductile) manner in its lower part. During exhumation of HP metamorphic rocks, brittle features superimpose on earlier ductile ones as a result of the progressive localization of deformation. The islands of Tinos and Andros are part of the numerous metamorphic core complexes exhumed in the Aegean domain. They illustrate two steps of a gradient of finite extension along a transect between Mt. Olympos and Naxos. This study confirms the main role of boudinage as an initial localizing factor at the brittle–ductile transition and emphasizes the continuum of strain from ductile to brittle during exhumation. Early low-angle semi-brittle shear planes superimpose onto precursory ductile shear bands, whereas steeply dipping late brittle planes develop by progressive steepening of structures or sliding across en echelon arrays of veins. The comparison between Tinos and Andros allows us to propose a complete dynamic section of the Aegean extending continental crust and emphasizes that the strain localization process depends on both its rheological stratification and its compositional heterogeneity.