Papers by Antonio Benedicto
Draining faults propagating from carbonates to clay layers could significantly impact the safety ... more Draining faults propagating from carbonates to clay layers could significantly impact the safety of nuclear waste storages, as investigated in the Bure Underground Research Laboratory (URL, France). In this study, we show that the draining properties of such faults seem to depend mainly of the fault throw magnitude. The results obtained on the Maltese Islands indicate that large faults (throw >50m) as well as small faults (throw <5m) does not lead to fluid circulation. On the opposite, intermediate faults propagates in the clay formation and lead to significant fracturation and fluid flows, including associated mineralisations.
En la cuenca neogena extensiva del Valles-Penedes, numerosas fallas muestran figuras de disolucio... more En la cuenca neogena extensiva del Valles-Penedes, numerosas fallas muestran figuras de disolucion (cavidades) y relleno de tipo carstico (sedimento, espelotemas). Estas figuras coexisten con rocas de falla (brechas y cataclasitas) y fracturas bien cementadas (calcita) en la zona de falla. El objetivo de este trabajo es el estudio de las relaciones entre el sistema carstico como medio de aporte de fluidos meteoricos y la deformacion y cementacion en una zona de falla afectando rocas carbonatadas. El trabajo aqui presentado se centra en un afloramiento de la falla del Valles-Penedes, limite occidental del semigraben del Valles- Penedes, situado en Castellvi de la marca. En este resumen se presentan los resultados preliminares del estudio estructural de la zona de falla.
Geofluids
Petrographic and geochemical analyses (δ18O, δ13C, 87Sr/86Sr, clumped isotopes, and elemental com... more Petrographic and geochemical analyses (δ18O, δ13C, 87Sr/86Sr, clumped isotopes, and elemental composition) coupled with field structural data of synkinematic calcite veins, fault rocks, and host rocks are used to reconstruct the episodic evolution of an outstanding exposed thrust zone in the Southern Pyrenees and to evaluate the fault behavior as a conduit or barrier to fluid migration. The selected thrust displaces the steeply dipping southern limb of the Sant Corneli-Bóixols anticline, juxtaposing a Cenomanian-Turonian carbonate unit against a Coniacian carbonate sequence. Successive deformation events are recorded by distinct fracture systems and related calcite veins, highlighting (i) an episodic evolution of the thrust zone, resulting from an upward migration of the fault tip (process zone development) before growth of the fault (thrust slip plane propagation), and (ii) compartmentalization of the thrust fault zone, leading to different structural and fluid flow histories in th...
Mineralium Deposita
The Kiggavik area is located on the eastern boundary of the Paleo- to Mesoproterozoic Thelon Basi... more The Kiggavik area is located on the eastern boundary of the Paleo- to Mesoproterozoic Thelon Basin (Nunavut, Canada) and hosts uranium mineralization in Archean basement rocks. The major fault/fracture network in the Kiggavik area is mainly oriented ENE-WSW and NE-SW, consisting of polyphased fault zones initiated during the Thelon and Trans-Hudsonian orogenies (ca. 1900–1800 Ma). These faults were subsequently mineralized in four stages referred to as U0, U1, U2, and U3. The first event U0 is inferred to be of magmatic origin and is related to microbrecciation and weak clay alteration under a WSW-ENE σ1. U0 is a ca. 1830 event which predates intense quartz brecciation (QB) and veining at ca. 1750 Ma. QB is associated with emplacement of the Kivalliq Igneous Suite and caused pervasive silicification of former fault zones, which in turn controlled subsequent fracture development and behaved as barriers for later U mineralizing fluids (U1 to U3). U1, U2, and U3 postdate deposition of the Thelon Basin. U1 and U2 occurred under a regional strike-slip stress regime, with the direction of σ1 evolving from WNW-ESE (U1) to NE-SW /ENE-WSW (U2); both formed at ~ 1500–1330 Ma and are related to circulation of Thelon-derived uranium-bearing basinal brines. A post U2, but pre-Mackenzie dykes (ca. 1270 Ma), extensional/transtensional stress regime with σ3 oriented NE-SW caused normal-dextral offset of the orebodies by reactivating NNW-SSE and E-W trending faults. This fracturing event triggered circulation of hot (~ 300 °C), probably acidic, fluids that dissolved quartz, and caused illitization and bleaching of the host rocks. Finally, U3 records remobilization of the previous mineralization along redox fronts through percolation of low-temperature meteoric fluids during two main tectonic events at ca. 550 and 350 Ma. This study provides evidences for the presence of a primary, pre-Thelon Basin uranium stock within the Kiggavik prospects, and a strong structural control on mineralization in the Kiggavik area. Our study also shows a nearly similar evolution of uranium mineralization in this area compared to the world-class uranium district of the Athabasca Basin (Saskatchewan, Canada).
Journal of Structural Geology, 2015
ABSTRACT A multidisciplinary study investigates the influence of different parameters on fault ro... more ABSTRACT A multidisciplinary study investigates the influence of different parameters on fault rock architecture development along normal faults affecting non-porous carbonates of the Corinth rift southern margin. Here, some fault systems cut the same carbonate unit (Pindus), and the gradual and fast uplift since the initiation of the rift led to the exhumation of deep parts of the older faults. This exceptional context allows superficial active fault zones and old exhumed fault zones to be compared. Our approach includes field studies, micro-structural (optical microscope and cathodoluminescence), geochemical analyses (δ13C, δ18O, trace elements) and fluid inclusions microthermometry of calcite sin-kinematic cements. Our main results, in a depth-window ranging from 0 m to about 2500 m, are: i) all cements precipitated from meteoric fluids in a close or open circulation system depending on depth; ii) depth (in terms of P/T condition) determines the development of some structures and their sealing; iii) lithology (marly levels) influences the type of structures and its cohesive/non-cohesive nature; iv) early distributed rather than final total displacement along the main fault plane is the responsible for the fault zone architecture; v) petrophysical properties of each fault zone depend on the variable combination of these factors.
Proceedings, 2012
The analysis of three cataclastic band sets from Provence (France) reveals that the band density,... more The analysis of three cataclastic band sets from Provence (France) reveals that the band density, their conjugate angles, their ratio of shear displacement to compaction, and the amount of cataclasis are different and can be expressed as a function of tectonic setting and petrophysical properties. We identify (1) a dense and closely spaced network of shear enhanced (reverse) compaction bands, (2) a regularly spaced less dense network of reverse compactional shear bands, and (3) a localized network of normal shear bands. The field data show that the localization of strain is favored in an extensional setting and is characterized by shear bands with a large shear to compaction ratio and a low conjugate band angle. In contrast, distributed strain is favored in a contractional setting and is characterized by compactional bands with a low ratio of shear to compaction and a large conjugate band angle. To explain the mechanical origin of this strain localization, we quantify the yield strength and the stress evolution in extensional and contractional regimes. We propose a model of strain localisation in porous sandstone as a function of tectonic stresses, burial depth, material properties, strain hardening and fluid pressure.
2nd EAGE International Conference on Fault and Top Seals - From Pore to Basin Scale 2009, 2009
Geological Society, London, Special Publications, 2008
... The process zone moves with the fault tip, leaving ... The location and geometry of damage zo... more ... The process zone moves with the fault tip, leaving ... The location and geometry of damage zones are important as they may contribute to compartmentalization, or provide fracture-controlled fluid flow pathways in addition to the master fault in a reservoir (eg, Knott et al. ...
Field observations of highly porous and permeable sandstone in the Orange area (S-E Basin, France... more Field observations of highly porous and permeable sandstone in the Orange area (S-E Basin, France) show that networks of shear-enhanced compaction bands can form in a contractional regime at burial depths of about 400 m AE 100 m. These bands show equal compaction and shear displacements, are organized in conjugate and densely distributed networks, and are restricted to the coarse-grained (mean grain diameter of 0.6 AE 0.1 mm) and less porous (porosity of 26 AE 2%) sand layers. The bands are crush microbreccia with limited grain comminution and high grain microfracture density. They show reductions of permeability (mD) ranging from 0 to little more than 1 order of magnitude. They show no control on the alteration products related to meteoric water flow, which suggests that these shear-enhanced compaction bands have no or only negligible influence on subsurface fluid flow. Their selective occurrence and small (20%) reduction in transmissibility in densely populated layers prevented them from compartmentalizing the sandstone reservoirs. A comparison with compaction-band populations in the Navajo and Aztec sandtsones (western U.S.) emphasizes the role of burial depth and the presence of chemical compaction processes for the sealing potential of deformation bands.
Marine and Petroleum Geology
Geochemistry: Exploration, Environment, Analysis
Uranium mineralization in the Patterson Lake corridor (southwestern Churchill province, Canada) i... more Uranium mineralization in the Patterson Lake corridor (southwestern Churchill province, Canada) is hosted in the metamorphosed Paleoproterozoic basement covered to the north by the flat-lying sandstone formations of the Athabasca Basin. The mineralization is exclusively contained within inherited ductile structures that were reactivated under a brittle regime. Petrographic and micro-structural studies of drill core samples from the Spitfire discovery (Hook Lake project) reveal the linkages between structural evolution of the basement, alteration and mineralization. During basement exhumation, localization of non-coaxial deformation led to the formation of a large anastomosing shear zone system made of mylonitic rocks. Strain localization associated with fluid circulation induced strong mineralogical and rheological changes, forming discontinuities in mechanical anisotropy. During and post-deposition of the Athabasca Basin after 1.80 Ga, these zones of anisotropy localized brittle re...
Economic Geology
The structural controls on unconformity-related uranium deposits of the Athabasca basin, Saskatch... more The structural controls on unconformity-related uranium deposits of the Athabasca basin, Saskatchewan, Canada, are a matter of debate regarding the role of inherited fault systems and their reactivation. This can be related to the lack of outcrops allowing for direct observations, the strong clay alteration halos wrapping deposits that often obliterate structures, and the poor core recovery related to drilling strongly altered and mineralized intervals, which limits observation of structures and reliable oriented measurements. Borehole imaging technology is an invaluable alternative for obtaining oriented data through challenging drilling intervals. The use of borehole Acoustic Televiewer (ATV) has been integrated in recent exploratory campaigns in the Athabasca basin by Orano Canada. Here, we present the inputs and benefits of the use of the ATV in the exploration of unconformity-related uranium deposits and the structural analysis of oriented data from seven inclined diamond drill...
Geofluids
The occurrence of unconformity-related uranium mineralization requires the combination of three c... more The occurrence of unconformity-related uranium mineralization requires the combination of three components: fluids with the right composition, geochemical traps with the right agents that produce precipitation, and structural traps with the right geometry. In the Athabasca Basin unconformity-related uranium deposits, while basinal brines are commonly accepted as the principal mineralized fluids and graphite and gases (CH4, CO2, and H2S) are well known as the reductants, only few case studies describing structural traps are published. A number of recent works, including numerical modelling, have improved the understanding of the role of inherited shear zones on fluid flow and the development of uranium deposits at a micro- and regional-scale. Nevertheless, there is still a lack of knowledge about the meso- or deposit-scale structural controls that lead to the present (and potentially predictive) localization of uranium deposits along a given shear zone. The present work examines new ...
Minerals
Pb-isotopes have been proposed as pathfinders for sandstone-hosted unconformity-related U deposit... more Pb-isotopes have been proposed as pathfinders for sandstone-hosted unconformity-related U deposits, with isotope ratios providing information on mineralization timing and element remobilization and migration. Pb-isotopes proximal to mineralization display radiogenic signatures, often with ‘excess Pb’ suggestive of derivation from greater U concentrations than are currently present. The U deposits in the Kiggavik project area (west of Baker Lake, NU, Canada) are basement-hosted, contain several generations of pitchblende mineralization, display a strong structural control, and are located in fault-related fracture systems and foliation-parallel veinlets. Drill core samples were analysed by Inductively-Coupled Plasma-Mass Spectrometer (ICP-MS) for Pb isotopes following multi-acid total-digestion, reverse Aqua Regia partial-digestion, and weak-acid-leach attacks, to evaluate the utility of the respective dissolution methods in Pb-isotope pathfinder geochemistry. Partial-digestion resul...
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Papers by Antonio Benedicto