Search

Major element and selected trace element compositions pf acid-leachable (5M HCl) and clay-size (

Major uranium (U) deposits worldwide are exploited by acid leaching, known as 'in-situ recovery' (ISR). ISR involves the injection of an acid fluid into ore-bearing aquifers and the pumping of the resulting metal-containing solution through cation exchange columns for the recovery of dissolved U. Rehabilitation of ISR-impacted aquifers could be achieved through natural attenuation, or via biostimulation of autochthonous heterotrophic microorganisms due to the associated acid neutralization and trace metal immobilization. In this study, we analyzed the capacity of pristine aquifer sediments impacted by diluted ISR fluids to buffer pH and immobilize U. The experimental setup consisted of glass columns, filled with sediment from a U ore-bearing aquifer, through which diluted ISR fluids were flowed continuously. The ISR solution was obtained from ISR mining operations at the Muyunkum and Tortkuduk deposits in Kazakhstan. Following this initial phase, columns were biostimulated with a mix of molasses, yeast extract and glycerol to stimulate the growth of autochthonous heterotrophic communities. Experimental results showed that this amendment efficiently promoted the activity of acid-tolerant bacterial guilds, with pH values rising from 4.8 to 6.5 - 7.0 at the outlet of the stimulated columns. The reduction of sulfate, nitrate, and metals as well as dissimilatory nitrate reduction to ammonia induced the rise in pH values, in agreement with geochemical modeling results. Biostimulation efficiently promoted the complete immobilization of U, with the accumulation of up to 3,343 ppm in the first few centimeters of the columns. Synchrotron analysis and SEM-EDS revealed that up to 60% of the injected hexavalent U was immobilized as tetravalent non-crystalline U onto bacterial cell surfaces. 16S rRNA amplicon analysis and qPCR data suggested a predominant role played for members of the Phylum Firmicutes (from the genera Clostridium, Pelosinus, and Desulfosporosinus) in biological U reduction and immobilization.

Based on an extensive seismic and multibeam dataset, 1-5 km wide giant polygons were identified at the bottom of the Grenada basin, covering a total area of ~55000 km². They represent the top part of an active underlying polygonal fault system due to the volumetric contraction of clay- and smectite-rich sediments during burial. To date, this is the widest area of outcropping polygonal faults ever found on Earth. The seabed polygons are bounded by rectilinear ~1000-1500 m wide and ~10-60 m deep furrows, depending on the ESSOAr | https://doi.org/10.1002/essoar.10506638.1 | CC_BY_NC_4.0 | First posted online: Thu, 1 Apr 2021 00:40:54 | This content has not been peer reviewed location in the basin. They are relatively regular in the north Grenada Basin, whereas they are getting longer and more elongated in the south Grenada Basin. The polygonal faults consist in a set of discrete normal faults affecting a 700 to 1200 m thick interval, initiated in the shallow sub-surface at the transition between Early to Middle Pliocene and then having propagated both upward and downward during sedimentation. The centre43 to-centre method has been applied to determine the local ellipse of strains, providing a major orientation for extension needed for polygons to initiate. In the north, the minor axes are oriented N40°, indicating a general NE-SW extension of the upper part of the sedimentary cover consistent with the forearc/backarc regional extension. In the south Grenada Basin, minor axes are progressively turning towards the south, pointing out the actual maximum subsidence point. This implies that seabed polygonal faults could thus be indicative of the present-day (or recent) strain state within the upper sedimentary column.

IE TCD MS 4027 is a ‘Journal of a tour through part of Ireland begun Aug 26th continued from October 1 1787’ by Daniel Augustus Beaufort, 1739-1821, vicar of Collon. Extent: 90 folios. The second of three volumes: see also IE TCD MS 4026 and 4028.

IE TCD MS 7941, a diary of Daniel Augustus Beaufort, Rector of Collon, Co. Louth, 14 August 1781-19 November 1786. Diary IV. 198 folios; blank folios not imaged.

IE TCD MS 4032 is a collection of copies of letters written to William Lewes [Louis] Beaufort (1771-1849) from his parents Daniel Augustus Beaufort (1739-1821) and Mary Beaufort. On thr front cover is written: ‘Letters from my father and mother’. Letters date from 28 November 1793 to 3 November 1802. Extent: 33 folios.

IE TCD MS 4024 is a travel journal kept by Daniel Augustus Beaufort during the years 1764 to 1766.It includes: a journal of a tour in the Low Countries, 17 June-4 November 1764;a journal of a tour in the North of Ireland, 15 August-1 September 1765; a journal of a tour in England and Wales 25 May-10 June 1766;a journal of a tour in Waterford, England and Wales 9 August -16 September 1779; it proceeds from Mountrath (Queen's County), via Kilkenny, Knocktopher, Mullinavat, Waterford, Curraghmore 9-15 August; and via Passage, Tramore, Portmore, Passage, Duncannon, Milford Haven (31 August 1779). Folios 27-30 (from 27 May – 1 June 1766) describe the journey through Wales. The places DAB visited in Wales, written exactly as they appear in the diary, are Conway, Denbigh Sh[ire], Abergely, Flint Shire, St Asaph, and then on to Holywell, Cheshire. DAB writes short descriptions of the towns and of the people he encounters. Folios 58-68 (from 31 August to 16 September 1779) also contain entries of time spent in Wales. Places mentioned are Conway, Pembrokeshire, Milford Haven, Tenby, Caermarthen, Narbarth, Camrose, Brechnock, Llether, St Davids and Trefigin. Fols 41-68 have a mileage count and there is a sketch of Carrickfergus on fols 69-70.Extent: i, 71 fols.

IE TCD MS 4028 is a ‘Journal of a tour through part of Ireland begun Aug 26th continued from Novr 4th 1787’ by Daniel Augustus Beaufort, 1739-1821, vicar of Collon. Extent: 86 folios.The third of three volumes: see also IE TCD MS 4026 and 4027.

IE TCD MS 4026 is a ‘Journal of a tour through part of Ireland begun August 26th 1787’ by Daniel Augustus Beaufort, 1739-1821, vicar of Collon. Extent: 90 folios.The first of three volumes: see also IE TCD MS 4027 and 4028.

IE TCD MS 4030 is a journal of a tour of Ireland begun on 3 July 1788 and ended on September 17th 1788 by Daniel Augustus Beaufort, 1739-1821, vicar of Collon. This volume includes entries for 14 August-17 September 1788. Extent: 94 folios. The second of two volumes: see also IE TCD MS 4029. Note: MS 4030 due to the foliation 63 does not exist. There is no missing folio, it continues on to fol. 64 after fol. 62. Some text from TCD MSS 4029 and 4030 is published in Gerard J Lyne, 'Rev Samuel Beaufort's tour of Kerry 1788' in Journal of the Kerry Archaeological and Historical Society, 18 (1985) and some of this is due to be republished in Cornelius Kelly and Penny Durrell, The grand tour of Kerry (Cailleach Books, 2001).Cornelius Kelly, The grand tour of Galway (Cailleach Books, 2002) uses extracts from 17 September 1787, 20 Sept, 4 October 1787, and from this MS 2 August 1788. County Clare passages are published in Brian Ó Dálaigh, The stranger's gaze: travels in County Clare 1534-1950 (Ennis: Clasp Press, 1998), pp 127-134.

International audience; The first geothermal well of Illkirch located South of Strasbourg (France), GIL-1, has been drilled to 3.8 km deep in a granitic basement. Drill cuttings and geophysical logs from basement were investigated in terms of hydrothermal alteration and natural fractures respectively. Petrographic observations of the 250 cuttings samples between 2900 and 3800 m MD were conducted on-site during the drilling with binocular loupe and enabled to identify the hydrothermal alteration grades in the open-hole granitic section of the well. From binocular examination, secondary minerals like drusy quartz, carbonates and anhydrite were spatially correlated to the occurrences of natural fractures. In the granitic section corresponding to propylitic alteration, phyllosilicates include primary biotite, muscovite and secondary chlorite. Then, 48 cuttings samples were analyzed by X-ray diffraction (XRD) to identify the secondary clay mineralogy corresponding to poorly crystallized illite (PCI) and illite-rich illite-smectite mixed layers (I/S ML) which generally takes place within fractured zones (FZs). Mud logging and geophysical logs acquired in the granitic section of GIL-1 well have been used for characterizing fracture location (calcimetry, temperature log) and fracture orientation (electrical image logs). The granitic section of the well is characterized by a dense network of natural fractures. From 2900 to 3300 m MD, about 220 electrical conductive fractures have been observed on the image logs. From temperature logs, three main permeable zones have been identified and correlated with the occurrences of natural conductive fractures. From 2900 to 3200 m MD, the clay signature is mainly governed by the occurrences of PCI and I/S ML which are correlated to permeable FZs. In the deepest part of the granitic section, secondary chlorite and possible secondary well crystallized illite (WCI) have been observed. In parallel, an innovative shortwave infrared (SWIR) spectroscopy method was developed for characterization of clay minerals in those fractured reservoirs. It was first applied to the granitic section of the Soultz and Rittershoffen geothermal wells (Alsace, France). This time-saving method allows the quantification of illitic hydrothermal alteration and indirectly the recognition of permeable FZs. In perspective, SWIR data acquired in GIL-1 will also be analyzed in order to confirm the applicability of this routine and cheap method for deep geothermal well in the Upper Rhine Graben (URG). 1. INTRODUCTION Since more than 30 years, a geothermal rush was observed in the Upper Rhine Graben (URG). The pioneer project of Soultz-sous-Forêts investigated the naturally fractured granitic reservoir within four geothermal deep wells (5 km). The nearby Rittershoffen project took then advantage of the lessons learned from Soultz by drilling two deep geothermal wells (3km) in the granitic basement targeting the multiscale network of fractures. Two more geothermal projects are under drilling operations in the Strasbourg area, in Vendenheim and in Illkirch. This contribution focuses on the preliminary geological results (petrography, secondary mineralogy, natural fractures) collected in the granitic section of the Illkirch GIL-1 well drilled to 3.8 km. The mid-Carboniferous granitic basement of the URG has been affected by several extensional and compressional tectonic phases which developed a multi-scale fracture network (Schumacher, 2002; Villemin and Bergerat, 1987). In deep geothermal projects, the target is to cross these natural fracture zones (FZs) which are today the seat of hydrothermal circulations and act as the main pathways for the natural brine through wide convection cells (Baillieux et al., 2013; Dezayes and Lerouge, 2019; Schellschmidt and Clauser, 1996). At the top of the highly fractured granitic basement, several temperature anomalies localized along the main faults are the expression of the fluid circulation in the FZs (Figure 1). In these complex FZs, specific mineralogical assemblages are evidences of paleo or present hydrothermal circulations. Clay minerals like illite, chlorite and tosudite are very sensitive to the fluid/rock (F/R) ratio, to the pH and to the temperature and are systematically precipitated in FZs (Ledésert et al., 2010). But the occurrence of other secondary minerals like drusy quartz, carbonates, barite, and anhydrite is also associated to fracture infillings (Smith et al., 1998; Traineau et al., 1992). Hence, this study will investigate the alteration mineralogy in the granitic section of the deviated GIL-1 well drilled between 2.9 and 3.8 km. Alteration mineralogy from about 250 cuttings will be derived from petrographic observation with binocular loupe and with X-ray diffraction (XRD). These petrographic results will be linked to the FZs occurrences on the electrical image logs. The goal will be to identify the clay signature of FZs in the granitic basement. These preliminary results aim to calibrate the shortwave infrared (SWIR) data acquired in the GIL-1 well. This innovative SWIR method already demonstrated its applicability to the granitic basement of the URG with the Soultz and Rittershoffen case studies whose examples will also be presented (Glaas et al., 2019; Vidal et al., 2018a).

IE TCD MSS 4026-4028 are three manuscript volumes detailing Daniel Augustus Beaufort’s ‘tour through part of Ireland’ in 1787.

IE TCD MS 4033 is a journal of a tour in the north of Ireland, 9 October-8 November 1807, and a journal of another tour in the west of Ireland, 9 August-8 October 1808, with a few added entries for October 20. Kept by Daniel Augustus Beaufort.

IE TCD MSS 4029-4030 are two volumes of a journal of a tour of Ireland begun on 3 July 1788 and ended on September 17th 1788 by Daniel Augustus Beaufort, 1739-1821, vicar of Collon.

IE TCD MS 4031 is a diary kept by Daniel Augustus Beaufort, mapmaker and vicar of Collon, 1739-1821. Diary vol. V, 19 November 1786 - 30 April 1790. Includes some sketches.

IE TCD MS 4037: a diary of Daniel Augustus Beaufort, vicar of Collon, with entries dated 18 September 1818 to 30 November 1820.Extent: 127 folios

IE TCD MS 4029 is a journal of a tour of Ireland begun on 3 July 1788 and ended on September 17th 1788 by Daniel Augustus Beaufort, 1739-1821, vicar of Collon. This volume includes entries for 3 July-14 August 1788.Extent: 90 folios. The first of two volumes: see also IE TCD MS 4030. MSS 4029 and 4030 is published in Gerard J Lyne, 'Rev Samuel Beaufort's tour of Kerry 1788' in Journal of the Kerry Archaeological and Historical Society, 18 (1985) and some of this is due to be republished in Cornelius Kelly and Penny Durrell, The grand tour of Kerry (Cailleach Books, 2001).Cornelius Kelly, The grand tour of Galway (Cailleach Books, 2002) uses extracts from 17 September 1787, 20 Sept, 4 October 1787, and from this MS 2 August 1788. County Clare passages are published in Brian Ó Dálaigh, The stranger's gaze: travels in County Clare 1534-1950 (Ennis: Clasp Press, 1998), pp 127-134.

International audience; The high potential of the Upper Rhine Graben (URG) for geothermal relies on more than 30 years of expertise in crystalline geothermal reservoirs developed in Soultz (France), the near presence of direct users in the area of the Eurometropolis of Strasbourg and undeniably, the acceptance of the population and the presence of investors. Hence, Strasbourg area is very attractive and is very active in the development of deep geothermal plants. In this context, this study proposes an innovative method of geothermal exploration to detect the highly hydrothermally altered zones corresponding to permeable fracture zones (FZ). They are acting as natural pathways for the fluid in the crystalline rocks of the URG. Applied on cuttings of granite samples with reduced costs and time, the short wave infrared (SWIR) spectroscopy method was realized on geothermal wells from Northern Alsace (Soultz, Rittershoffen) for calibration. Indeed, the FZ of these wells were first characterized by structural and mineralogical studies done from borehole image logs and cuttings analysis respectively. In the Rittershoffen wells, the occurrence of small crystallites of illite and illite-smectite mixed layers minerals (

International audience; The early stage of oil exploration in sedimentary basins is based both on large scale tectono-stratigraphic approachfrom previous workss and conventional industrial data mostly well-logs and 2D seismic. In particular geologistsface to the lack of model to be able to better predict the reservoir presence and quality of undrilled basins.The source-to-sink studies (“S2S”) on modern or recent systems are particular interest because they aim tounderstand and quantify the link from the source/hinterland area (drainage area, nature of the bedrock, climateand topography) to the sink/basin (slope gradient, shelf size, subsidence, eustasy and sedimentary process). Theapplication of this S2S approach on ancient sedimentary systems is challenging because of the lack of constraintsof some controlling factors like the climate, the composition of the source material, the location and altitude ofpaleo-reliefs or the extent of the drainage area.Our aim is to constraint the causes of major changes in basin sedimentation of the well documented ZambeziS2S system through times using a combination of mineralogical/petrographical analysis tools. Here, we proposeto combine petrographical and heavy minerals quantifications with U/Pb on detrital Zircon and the evolution ofclays minerals association on cuttings from two offshore wells through the Meso-cenozoic to constraint changesin provenance or weathering conditions.Our first petrographycal and HM results through the basin series show four mains HM assemblages, a clear evolutionof sandstone composition in Quartz, Feldspars and volcanic fragments content trough time (QFL diagram),and six U/Pb age reflecting the erosion and recycling of six Units which signal in sediment change in space andtime. An evolution of sediments provenance is proposed with the erosion of permo-triassic volcano/sedimentaryseries during earliest Cretaceous following by a syn-sedimentary alcalin-volcanic event probably Aptian in ageand an increase of recycling of older sedimentary cycles quartz-rich through time. On-going clay analysis showchanges in clays association suggesting change in chemical VS physical weathering conditions through times.Even if the base of the serie is diagenetically impacted, the Cretaceous to Pliocene clays series evolutions indicatesan increase of physical weathering condition since the end of the early cretaceous to Pliocene sediments probablyinterrupted during Paleocene-Eocene times.

Fil: Pons, María J. Universidad Nacional de Río Negro. Instituto de Investigación en Paleobiología y Geología; Argentina Fil: Pons, María J. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Patagónico de Estudios Metalogenéticos. Instituto de Investigación en Paleobiología y Geología; Argentina Fil: Franchini, Marta B. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Patagónico de Estudios Metalogenéticos; Argentina Fil: Giusiano, Adolfo. Dirección Provincial de Hidrocarburos y Energía de la Provincia del Neuquén; Argentina Fil: Patrier, Praticia. Université de Poitiers. IC2MP. CNRS-UMR 7285. Hydrasa; Francia Fil: Beaufort, Daniel. Université de Poitiers. IC2MP. CNRS-UMR 7285. Hydrasa; Francia Fil: Impiccini, Agnes. Universidad Nacional del Comahue. Facultad de Ingeniería. Departamento de Geología y Petróleo; Argentina Fil: Rainoldi, Ana L. Universidad Nacional del Sur. Departamento de Geología; Argentina Fil: Meinert, Lawrence. EGRU. School of Earth and Environmental Sciences. James Cook University; Australia Fil: Franchini, Marta. Universidad Nacional del Comahue; Argentina The Tordillos sediment-hosted Cu deposit is located in the north-central sector of the Huincul High structure, in the Neuquén Basin, Argentina. It is hosted in sedimentary rocks of the Huincul Formation, an Upper Cretaceous redbed sequence deposited in a fluvial environment. Field mapping, petrography, and chemical analysis of the authigenic clay, sulfate, carbonate, and sulfide minerals at Tordillos have identified systematic variation in alteration and paragenesis with time and with respect to the main feeder zones. The alteration associated with Cu mineralization provides evidence of a multistage infiltration of fluids spatially associated with paleo-hydrocarbon migration driven by Tertiary tectonism. Early diagenesis formed hematite, kaolinite, and calcite1 that have been preserved in the reddish brown mudstones. Later influx of hydrocarbons and warm, reduced formation waters from deeper reservoir rocks is associated with dissolution of early cements and clasts and precipitation of new minerals. In the thickest paleochannels of the Huincul Formation, dissolution of early cements (hematite, kaolinite, calcite1 and barite1) and clasts locally increased the porosity of sandstones up to 24% and destroyed hematite that changed sandstones and conglomerates from red to yellowish-grey. Bitumen impregnations are abundant along with calcite2, 3, and 4, pyrite, minor montmorillonite, quartz overgrowth, and coarse barite2 crystals with primary organic fluid inclusions at the contact with hydrocarbon tubes. The MnO enrichment of calcite in stages 3 and 4 reflects their precipitation under reduced conditions. Grey and greenish-grey sandstoneswithmontmorillonite, V-hematite, smectite-chlorite group minerals and pyrite, respectively are exposed between the reddish-brown mudstones and the yellowish-grey sandstones and conglomerates. The grey and greenish-grey horizons are representative of abrupt changes in Eh-pH conditions, between regional early oxidizing solutions responsible for the formation of early diagenetic redbeds and later infiltration of reducing fluids responsible for alteration of sedimentary rocks. Copper mineralization is located inside the altered sandstones and conglomerates zones, forming halos surrounding vertical tubes containing bitumen. These tubes are interpreted as the conduits through which migrated hydrocarbons, formation waters, and subsequent chloride and metal-rich fluids. In these places, pyrite, calcite, and barite cements of the altered rocks, have been dissolved and replaced by copper- rich sulfides and then by late supergene Cu minerals. Interconnection among stacked permeable paleo-channels in the mid-section of the Huincul Formation facilitated the migration of several generations of fluids during early diagenesis, hydrocarbon up flow, and exhumation of the Neuquén Group, resulting in the development of alteration halos and Cu mineralization that can be used, both in outcrop and drill core, during exploration for sediment-hosted Cu mineralization. The Tordillos sediment-hosted Cu deposit is located in the north-central sector of the Huincul High structure, in the Neuquén Basin, Argentina. It is hosted in sedimentary rocks of the Huincul Formation, an Upper Cretaceous redbed sequence deposited in a fluvial environment. Field mapping, petrography, and chemical analysis of the authigenic clay, sulfate, carbonate, and sulfide minerals at Tordillos have identified systematic variation in alteration and paragenesis with time and with respect to the main feeder zones. The alteration associated with Cu mineralization provides evidence of a multistage infiltration of fluids spatially associated with paleo-hydrocarbon migration driven by Tertiary tectonism. Early diagenesis formed hematite, kaolinite, and calcite1 that have been preserved in the reddish brown mudstones. Later influx of hydrocarbons and warm, reduced formation waters from deeper reservoir rocks is associated with dissolution of early cements and clasts and precipitation of new minerals. In the thickest paleochannels of the Huincul Formation, dissolution of early cements (hematite, kaolinite, calcite1 and barite1) and clasts locally increased the porosity of sandstones up to 24% and destroyed hematite that changed sandstones and conglomerates from red to yellowish-grey. Bitumen impregnations are abundant along with calcite2, 3, and 4, pyrite, minor montmorillonite, quartz overgrowth, and coarse barite2 crystals with primary organic fluid inclusions at the contact with hydrocarbon tubes. The MnO enrichment of calcite in stages 3 and 4 reflects their precipitation under reduced conditions. Grey and greenish-grey sandstoneswithmontmorillonite, V-hematite, smectite-chlorite group minerals and pyrite, respectively are exposed between the reddish-brown mudstones and the yellowish-grey sandstones and conglomerates. The grey and greenish-grey horizons are representative of abrupt changes in Eh-pH conditions, between regional early oxidizing solutions responsible for the formation of early diagenetic redbeds and later infiltration of reducing fluids responsible for alteration of sedimentary rocks. Copper mineralization is located inside the altered sandstones and conglomerates zones, forming halos surrounding vertical tubes containing bitumen. These tubes are interpreted as the conduits through which migrated hydrocarbons, formation waters, and subsequent chloride and metal-rich fluids. In these places, pyrite, calcite, and barite cements of the altered rocks, have been dissolved and replaced by copper- rich sulfides and then by late supergene Cu minerals. Interconnection among stacked permeable paleo-channels in the mid-section of the Huincul Formation facilitated the migration of several generations of fluids during early diagenesis, hydrocarbon up flow, and exhumation of the Neuquén Group, resulting in the development of alteration halos and Cu mineralization that can be used, both in outcrop and drill core, during exploration for sediment-hosted Cu mineralization.

Depuis une quarantaine d'années, la reconstitution de l'histoire thermique des bassins sédimentaires s'appuie sur les propriétés chimiques, physiques et moléculaires de la matière organique présente dans les sédiments. Puis progressivement, des marqueurs minéraux se sont avérés être d'excellents témoins de cette histoire thermique. Ce livre (inspiré d'un séminaire de formation continue de l'Université de Paris-Sud) a pour but de présenter d'abord toutes les méthodes organiques et minérales actuellement disponibles incluant celles qui sont apparues très récemment et de se focaliser sur les marqueurs minéraux qui ont atteint un degré de maturité suffisant. L'histoire thermique est reconstituée à partir de géothermomètres, de chronomètres, de chronothermomètres et enfin de géothermomètres cinétiques ou cumulatifs. La combinaison de toutes ces méthodes aboutit à des histoires dont les implications géodynamiques, pétrolières, minières, environnementales sont très importantes. Il n'existe pas une démarche unique puisque les méthodes utilisées ont des domaines d'application différents, des précisions variables et dépendent de la nature des sédiments. De niveau master, cet ouvrage s'adresse aux étudiants et aux enseignants mais également à tous les géologues qui s'intéressent à la thermicité des bassins et qui se demandent quelles sont les méthodes qui peuvent permettre de résoudre leurs énigmes.

The Bouillante geothermal field, located on the west coast of Guadeloupe (Lesser Antilles), was explored in the 1970s, developed in the 1980s, brought into production in 1986, and expanded in 2005 to currently produce up to 15 MWe. In addition to its electricity-producing role, the Bouillante field is an outstanding research laboratory for improving our knowledge of a reference high temperature (260°C) geothermal system in island-arc environment. A great deal of scientific research and exploration investigation have been carried out on the Bouillante geothermal field for 10 years, including geological investigation (volcanism), structural analysis of the fluid conduits, geophysical investigations both offshore (magnetics and high-resolution shallow seismics, see Calcagno et al.) and onshore (gravimetry, electrical resistivity tomography profile and passive seismic, see Gailler et al.), characterization of the surface and deep hydrothermal manifestations, numeric geological modelling of the developed field, fluid geochemistry and tracer tests (Sanjuan et al.) and hydrogeological modelling. This large range of multidisciplinary data has made it possible to develop an innovative conceptual model of this type of high-temperature geothermal system. The model highlights the major influence of structural control on the development of the geothermal activity at different scales and especially on the geometry of the reservoir. It also explores new ideas concerning the geothermal system in terms of heat source, fluid circulation and spatio-temporal scenario. This scenario takes into account all events from the early magmatic activity of the Bouillante volcanic Chain (~500,000 y) up to the beginning of the geothermal field some 250,000 years later, having probably started with a phreatic explosion in the bay of Bouillante (see Patrier-Mas et al., Verati et al.). This 2D geothermal resource conceptual model will be used as an exploration tool to reduce geological risks for the next exploration drilling campaign. This work is supported by the French Agency for Energy and Environment (ADEME).

International audience; The crystal structure and crystal chemistry of dioctahedral smectites in high enthalpy geothermal systems was investigated through 2 wells drilled in the Bouillante geothermal area in order to understand the factors which control their vertical variation. Smectites were examined by optical and scanning electron microscopy, electron microprobe analysis, X-ray diffraction (after Ca, Li, alkylammonium saturations), Fourier transform infrared spectrometry (after Li, NH4 + saturations) and oxygen isotope analysis. Smectites predominate within the upper part of the drill holes (up to 260m depth - temperature range : 67-160°C). The XRD, FTIR and punctual chemical analysis clearly demonstrate a transition from montmorillonite to beidellite with increasing depth and temperature which proceeded through interstratification of beidellite-like and montmorillonite-like layers. Montmorillonite predominates at temperatures lower than 100°C while beidellite predominates between 110 and 170°C. However, this transition is not explained by a thermally controlled beidellitization process but seems related to the hydrothermal solutions from which precipitated these smectites. The δ18O values of the equilibrated fluids indicate that beidellitic smectite precipitated from the hot geothermal fluid associated with minor amounts of residual solutions resulting from local boiling and that montmorillonitic smectite precipitated from reacting solutions whose origin has to be searched in the phreatic water table associated with minor amounts of liquids resulting from the condensation of vapors escaped from the boiling zones. The mixing rate of Mg-free geothermal fluid with meteoric waters exerted a major influence on the montmorillonite versus beidellite ratio of the smectite material as underlined by the irregular depth related smectite transition

International audience; Des études récentes portant sur la chaîne hercynienne marocaine ont essayé de démontrer par de nombreux arguments d'ordre métamorphique, magmatique et structural qu' à une période de collision succède une évolution induite par le retour vers un équilibre thermique et gravitaire d'une croûte sur-épaissie. Par cette étude nous nous attacherons à mettre en évidence ce caractère généralisé de la tectonique extensive post-collision. Dans le massif hercynien des Rehamna, les veines de quartz à disthène sont encaissées dans des métapélites affectées par un métamorphisme à caractère barrovien, qui atteint les conditions du faciès des amphibolites et, de façon synchrone, la fusion partielle qui a engendré les granitoïdes de la région. De nouvelles observations de terrain appuyées par des travaux de laboratoire ont permis de mettre en évidence les caractères suivants : (i) les veines ou les filons de quartz à disthène sont clairement sécants et donc tardifs par rap-port à la stratification et la foliation régionale S0-1 associée à la première phase tectonothermale qui est synchrone de la collision hercynienne ; donc ces veines quartzitiques à disthène sont liées à une structuration plus récente. (ii) la structure pegmatitique et l'orientation des paragenèses minérales (disthène + quartz + micas blancs +/- tourmaline) dans les veines suggèrent une cristallisation qui correspond à une précipitation de minéraux à partir d'une solution hydrothermale riche en silice dans des ouvertures macroscopiques. (iii) presque toujours les veines discordantes de quartz contenant ce silicate d'alumine sont associées à des zones métamorphiques marquées par une forte activité hydrothermale d'origine magmatique, et de ce fait elles sont considérées comme pénécontemporaines des pegmatites tardi-magmatiques, des veines de tourmalinite et des dykes de greisen minéralisés en béryl, rutile et cassitérite. Dans le cadre régional, le premier apport de cette étude est de susciter une hypothèse : le disthène n'est pas attribué à la pression lithostatique, c'est-à-dire à la profondeur, mais plutôt à la pression de fluide engendrée par une solution hydrothermale en surpression. La présente note s'attache précisément à proposer un processus géodynamique où sont intégrés d'une part les veines ou filons synmétamorphiques de quartz à disthène, et d'autre part, l'amincissement crustal post-orogénique, considéré comme élément structural majeur dont le développement s'est accompagné de plu-sieurs manifestations hydrothermales de grande ampleur, vraisemblablement associées à un magmatisme granitique qui contrôle la distribution de la quasi-totalité des minéralisations dans le massif hercynien des Rehamna. Recent studies on the Moroccan Hercynian Belt have used metamorphic, magmatic and structural evidence to demonstrate that the post-collisional period was driven by return of the thickened crust towards thermal and gravi-tational equilibrium. In this study, we aim to characterize this general post-collisional extensional tectonic event. In the Rehamma Hercynian Massif, quartz-kyanite veins are found in association with amphibolite facies Barrovian metapelites. This metamorphism is synchronous with the partial melting episode which generated granitoids in the same region. Both experimental studies and field observations have led to the following conclusions: (i) quartz-kyanite veins or sills occurred later than the stratification and the regional foliation S0-1, which are associated with the first tectonothermal stage of the Hercynian collision. These veins are therefore contemporaneous with a more recent tectonic event. (ii) In the veins, both the pegmatitic structure and orientation of the paragenetic assemblage (kyanite + quartz + muscovite +/- tourmaline) suggest that the minerals precipitated from silica-rich hydrothermal solutions within macroscopic cracks. (iii) Discordant quartz-kyanite veins are usually found in association with metamorphic zones which have been altered by intense hydrothermal activity of magmatic origin. These kyanite-quartz veins can be viewed as penecontemporaneous with other late-magmatic pegmatites, tourmaline veins and greisen dykes rich in beryl, rutile and cassiterite. In this study, we suggest that kyanite growth was induced by high-pressure hydrothermal fluids rather than by litho-static pressure alone (i.e. depth). We show that both quartz-kyanite veins/sills and post-orogenic crustal thinning can be integrated into a single geodynamic process. Significant hydrothermal events are contemporaneous with post-orogenic crustal thinning and are probably associated with the granitic magmatism which controls the distri-bution of almost all the mineralisation in the Rehamna Hercynian Massif.

International audience; Des études récentes portant sur la chaîne hercynienne marocaine ont essayé de démontrer par de nombreux arguments d'ordre métamorphique, magmatique et structural qu' à une période de collision succède une évolution induite par le retour vers un équilibre thermique et gravitaire d'une croûte sur-épaissie. Par cette étude nous nous attacherons à mettre en évidence ce caractère généralisé de la tectonique extensive post-collision. Dans le massif hercynien des Rehamna, les veines de quartz à disthène sont encaissées dans des métapélites affectées par un métamorphisme à caractère barrovien, qui atteint les conditions du faciès des amphibolites et, de façon synchrone, la fusion partielle qui a engendré les granitoïdes de la région. De nouvelles observations de terrain appuyées par des travaux de laboratoire ont permis de mettre en évidence les caractères suivants : (i) les veines ou les filons de quartz à disthène sont clairement sécants et donc tardifs par rap-port à la stratification et la foliation régionale S0-1 associée à la première phase tectonothermale qui est synchrone de la collision hercynienne ; donc ces veines quartzitiques à disthène sont liées à une structuration plus récente. (ii) la structure pegmatitique et l'orientation des paragenèses minérales (disthène + quartz + micas blancs +/- tourmaline) dans les veines suggèrent une cristallisation qui correspond à une précipitation de minéraux à partir d'une solution hydrothermale riche en silice dans des ouvertures macroscopiques. (iii) presque toujours les veines discordantes de quartz contenant ce silicate d'alumine sont associées à des zones métamorphiques marquées par une forte activité hydrothermale d'origine magmatique, et de ce fait elles sont considérées comme pénécontemporaines des pegmatites tardi-magmatiques, des veines de tourmalinite et des dykes de greisen minéralisés en béryl, rutile et cassitérite. Dans le cadre régional, le premier apport de cette étude est de susciter une hypothèse : le disthène n'est pas attribué à la pression lithostatique, c'est-à-dire à la profondeur, mais plutôt à la pression de fluide engendrée par une solution hydrothermale en surpression. La présente note s'attache précisément à proposer un processus géodynamique où sont intégrés d'une part les veines ou filons synmétamorphiques de quartz à disthène, et d'autre part, l'amincissement crustal post-orogénique, considéré comme élément structural majeur dont le développement s'est accompagné de plu-sieurs manifestations hydrothermales de grande ampleur, vraisemblablement associées à un magmatisme granitique qui contrôle la distribution de la quasi-totalité des minéralisations dans le massif hercynien des Rehamna. Recent studies on the Moroccan Hercynian Belt have used metamorphic, magmatic and structural evidence to demonstrate that the post-collisional period was driven by return of the thickened crust towards thermal and gravi-tational equilibrium. In this study, we aim to characterize this general post-collisional extensional tectonic event. In the Rehamma Hercynian Massif, quartz-kyanite veins are found in association with amphibolite facies Barrovian metapelites. This metamorphism is synchronous with the partial melting episode which generated granitoids in the same region. Both experimental studies and field observations have led to the following conclusions: (i) quartz-kyanite veins or sills occurred later than the stratification and the regional foliation S0-1, which are associated with the first tectonothermal stage of the Hercynian collision. These veins are therefore contemporaneous with a more recent tectonic event. (ii) In the veins, both the pegmatitic structure and orientation of the paragenetic assemblage (kyanite + quartz + muscovite +/- tourmaline) suggest that the minerals precipitated from silica-rich hydrothermal solutions within macroscopic cracks. (iii) Discordant quartz-kyanite veins are usually found in association with metamorphic zones which have been altered by intense hydrothermal activity of magmatic origin. These kyanite-quartz veins can be viewed as penecontemporaneous with other late-magmatic pegmatites, tourmaline veins and greisen dykes rich in beryl, rutile and cassiterite. In this study, we suggest that kyanite growth was induced by high-pressure hydrothermal fluids rather than by litho-static pressure alone (i.e. depth). We show that both quartz-kyanite veins/sills and post-orogenic crustal thinning can be integrated into a single geodynamic process. Significant hydrothermal events are contemporaneous with post-orogenic crustal thinning and are probably associated with the granitic magmatism which controls the distri-bution of almost all the mineralisation in the Rehamna Hercynian Massif.

Beaufort Daniel, Cassagnabere Alain, Lacharpagne Jean-Claude. La transition kaolinite/dickite dans les réservoirs gréseux : exemples des réservoirs à hydrocarbures de Froy et Rind (Mer du Nord, Norvège). In: Transferts dans les systèmes sédimentaires : de l'échelle du pore à celle du bassin. Réunion spécialisée SGF-TRABAS/CNRS, Paris 27-28 septembre 1999. Résumés. Strasbourg : Institut de Géologie – Université Louis-Pasteur, 1999. pp. 11-14. (Sciences Géologiques. Mémoire, 99)

A major problem in ore prospecting on granitic terrains is to make a distinction between clay mineral assemblages due to weathering and those due to hydrothermal alteration. The most outstanding features of these two types of transformation are : 1. Potassic beidellite is typical of hydrothermal alteration. 2. Low iron content mineral assemblages in the presence of large amounts of kao-linite is typical of hydrothermal alteration. 3. Argillan veins and pore coatings are typical of weathered rocks. The control of microprobe analyses by X-ray diffraction on small quantities of matter is very useful for the identification of clay assemblages., Meunier Alain, Velde Bruce, Dudoignon P., Beaufort D. Identification of weathering and hydrothermal alteration in acidic rocks : petrography and mineralogy of clay minerals. In: Pétrologie des altérations et des sols. Vol. II : Pétrologie des séquences naturelles. Colloque international du CNRS, Paris 4-7 juillet 1983. Strasbourg : Institut de Géologie – Université Louis-Pasteur, 1983. pp. 93-99. (Sciences Géologiques. Mémoire, 72)