Michel Jébrak | Université du Québec à Montréal (original) (raw)

Papers by Michel Jébrak

The exclusive presence of porphyry-type deposits in Phanerozoic belts is becoming questionable, g... more The exclusive presence of porphyry-type deposits in Phanerozoic belts is becoming questionable, given the recent discoveries of porphyry deposits in Precambrian terrains (e.g., Troilus and Malartic, Québec; Spinifex ridge and Boddington, Western Australia). The Tilly property of Sirios Resources is one of the best examples of Precambrian porphyry systems in the Superior Province. The Tilly property is located in the Archean La Grande Subprovince, in the James Bay area.The local geology is dominated by a tonalite-granodiorite pluton in contact with a dioritic stock to the north, clastic sediments to the east and volcaniclatic rocks to the southeast (figure 1). Porphyric

Communication et grands projets, 2013

LPICo, Jun 1, 2010

Introduction: The suevite of the 14.35 Ma old, 25km wide Ries crater in southern Germany occurs i... more Introduction: The suevite of the 14.35 Ma old, 25km wide Ries crater in southern Germany occurs in 3 different geological settings: 1) the crater suevite in the central crater cavity inside the inner ring, 2) the outer suevite on top of the continuous ejecta blanket, 3) dikes in the crater basement and in displaced megablocks [1]. The mechanisms of transport of particles in the suevite remains poorly understood. In [2] the following processes are discussed: 1) "aerial" transport in a gaseous medium, 2) ground surging in a turbulent flow, 3) interaction of a temporary melt sheet in the central crater with surface water leading to "phreatomagmatic" explosions and subsequent aerial transport. We measured the shape and size distribution of particles in several drill core sections (thickness of suevite in parentheses): Nördlingen, inside the inner ring (300m); Enkingen, at the inner ring (80m); Wörnitzostheim, between inner ring and crater boundary (80m); and Otting, outside the crater (9m). The drill cores were studied by digital stereometric analysis. Grain sizes and shapes of lithic clasts and melt particles were measured on the plane surface of the half cores and on thin sections of the same core sections. The following grain parameters were measured in the size range of +2 to-6 phi (0.25 to 63mm): 1) particle content, 2) aspect ratio = minor axis/major axis, 3) maximum grain size = mean of the ten largest particles, 4) particle size distribution represented as fractal dimension [3]. Observation and subdivision of the Ries suevite: The crater suevites can be divided into stratigraphic subtypes. They differ in their stereometric parameters and show distinct differences between the central part and the outer part of the inner crater. The Nördlingen drill core can be subdivided into four suevite units: 1) Upper redeposited suevite (296-314m), 2) "Graded" suevite (314-330m), 3) Melt-rich suevite (331-520m), and 4) Melt poor suevite (520-602m). The Enkingen drill core can be subdivided into four units: 1) Upper suevite (21-40m), 2) Middle suevite (40-66m), 3) Lower suevite with intersection of coherent melt layers (66-86m), and 4) coherent impact melt (below 86m). The Wörnitzostheim drill core can be subdivided into three units: 1) Upper suevite (19-25m), 2) Melt-rich suevite (25-80m), 3) Melt-poor suevite (80-100m). The Otting drill core is homogenous. A comparison of the characteristics of all drill cores can be summarized as follows: 1) The suevite of

The choice of a model analogue of a radioactive waste repository requires precise definition of t... more The choice of a model analogue of a radioactive waste repository requires precise definition of the phenomena to be studied. The main problem to be solved by this approach is the development of low enthalpy geothermal systems near the repository, which would be likely to facilitate the migration of radionuclides towards the surface. A study has thus been undertaken on fossil geothermal systems in order to determine the various characteristics of migration of the elements analogous to the radionuclides (U, Th, REE, Sc, Sr).

HAL (Le Centre pour la Communication Scientifique Directe), Apr 16, 2020

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de

<p>The Richat Dome is a huge circular, slightly elliptical depression (~ 40 km in d... more <p>The Richat Dome is a huge circular, slightly elliptical depression (~ 40 km in diameter) in the Proterozoic to Cambro-Ordovician sedimentary series of the NE part of the Mauritanian Taoudeni basin. This structure consists of a central zone that corresponds to a complex of dolomitic limestones and sedimentary rocks of Neoproterozoic age, cut by breccia silica and felsic volcanic rocks. A peripheral zone comprising Neoproterozoic to Late Ordovician sandstones and pelites into which carbonatite veins and two gabbroic annular dykes are injected.</p><p>Generally, the carbonatites represent a relatively rare type of igneous rock composed mainly of primary carbonate minerals (calcite and/or dolomite > 50 vol % of the rock) associated with phosphate minerals, silicates, and oxides. They contain the highest concentrations of rare earth elements (REE) of all igneous rocks. The carbonatites are also the main source of REE especially the light REE (La, Ce, Pr and Nd) as well as some critical metals such as Nb and Ta.</p><p>The aim of this study is to present a preliminary work on the carbonatite dykes of the Richat Dome: (1) detailed geological mapping of the various dykes, (2) petrographic, (3) mineralogical and (4) geochemical characterizations. The results obtained will be cross-referenced with other strategic deposits around the world</p>

Mineralium Deposita, Jun 1, 2002

Mineralium Deposita, Jul 7, 1999

The Almade n district is the largest mercury concentration in the world, with a total content of... more The Almade n district is the largest mercury concentration in the world, with a total content of about 250 000 t of mercury, nearly one third of the known total mercury resources of the Earth. Mercury has been exploited since the Celtic and Roman times, with peak production during the Renaissance and between 1939± 1945. The district is hosted by a Paleozoic synclinorium overlying Precambrian rocks. The Paleozoic sequence comprises epicontinental quartz arenite rocks, including black shales and quartzites. Diatremes, alkaline lavas of dierent composition, and late tholeiitic diabases account for the Ordovician to Devonian magmatism. The tectonic setting of this complex suite corresponds to the intraplate type. The mercury deposits of Almade n can be classi®ed into two main types: type 1, early stratiform type ores characterized by cinnabar deposition on the lower Silurian quartzites (Criadero quartzite; e.g. the Almade n and El Entredicho deposits), and type 2, late discordant orebodies (e.g. Las Cuevas), largely hosted or related to diatremes (the`frailesca rocks') of alkaline basaltic composition. In type 1 cinnabar was deposited during diagenesis, in relation to hydrothermal circulation driven by magmatic activity. Type 2 include a variety of deposits having in common the discordant character of the orebodies (e.g. veins, stockworks, massive replacements), and their wide dispersion along the stratigraphic column, i.e. from Lower Silurian (e.g. Nueva Concepcio n) to Upper Devonian (e.g. Corchuelo).

Presses de l'Université du Québec eBooks, Sep 7, 2017

Journal of Metamorphic Geology, 1993

Archaean greenstone belts are often cut by major shear zones, for example the Cadillac tectonic z... more Archaean greenstone belts are often cut by major shear zones, for example the Cadillac tectonic zone (a) of the southern Abitibi region in north-westem Quebec. At McWatters, the CTZ contains slices of metavolcanic units bounded by comdors of highly strained and altered rocks. Mineral assemblages of the metabasites record the metamorphic evolution of the CLZ. The McWatters metabasalts and metagabbros have similar chemistry but different mineral assemblages consisting of variable amounts of actinolite, hornblende, chlorite, albite, epidote, quartz, carbonates, titanite, biotite, rutile, magnetite, ilmenite and sulphides. The different mineral assemblages, which coexist in a single tectonic slice, can be divided into three types, characterized by (A) presence of hornblende and actinolite, (B) presence of actinolite and epidote, and (C) absence of amphibole and epidote. Partial replacements indicate that these mineral assemblages are not in equilibrium. The hornblende of the least altered and deformed samples of the type A assemblage is a relict of a prograde metamorphic event, contemporaneous with the development of the main schistosity. The prograde conditions are estimated at P = 5 kbar, T = 475" C with low 4. The more altered and deformed samples of the type C assemblage record a later retrograde metamorphic event. Conditions of the later event are estimated at P = 4 kbar, T = 400" C with higher P,. Widespread calcite precipitation occurred during a later episode. The diversity of the mineral assemblages results from permeability variations along the high-strain zones of the Cl'Z.

The exclusive presence of porphyry-type deposits in Phanerozoic belts is becoming questionable, g... more The exclusive presence of porphyry-type deposits in Phanerozoic belts is becoming questionable, given the recent discoveries of porphyry deposits in Precambrian terrains (e.g., Troilus and Malartic, Québec; Spinifex ridge and Boddington, Western Australia). The Tilly property of Sirios Resources is one of the best examples of Precambrian porphyry systems in the Superior Province. The Tilly property is located in the Archean La Grande Subprovince, in the James Bay area.The local geology is dominated by a tonalite-granodiorite pluton in contact with a dioritic stock to the north, clastic sediments to the east and volcaniclatic rocks to the southeast (figure 1). Porphyric

Communication et grands projets, 2013

LPICo, Jun 1, 2010

Introduction: The suevite of the 14.35 Ma old, 25km wide Ries crater in southern Germany occurs i... more Introduction: The suevite of the 14.35 Ma old, 25km wide Ries crater in southern Germany occurs in 3 different geological settings: 1) the crater suevite in the central crater cavity inside the inner ring, 2) the outer suevite on top of the continuous ejecta blanket, 3) dikes in the crater basement and in displaced megablocks [1]. The mechanisms of transport of particles in the suevite remains poorly understood. In [2] the following processes are discussed: 1) "aerial" transport in a gaseous medium, 2) ground surging in a turbulent flow, 3) interaction of a temporary melt sheet in the central crater with surface water leading to "phreatomagmatic" explosions and subsequent aerial transport. We measured the shape and size distribution of particles in several drill core sections (thickness of suevite in parentheses): Nördlingen, inside the inner ring (300m); Enkingen, at the inner ring (80m); Wörnitzostheim, between inner ring and crater boundary (80m); and Otting, outside the crater (9m). The drill cores were studied by digital stereometric analysis. Grain sizes and shapes of lithic clasts and melt particles were measured on the plane surface of the half cores and on thin sections of the same core sections. The following grain parameters were measured in the size range of +2 to-6 phi (0.25 to 63mm): 1) particle content, 2) aspect ratio = minor axis/major axis, 3) maximum grain size = mean of the ten largest particles, 4) particle size distribution represented as fractal dimension [3]. Observation and subdivision of the Ries suevite: The crater suevites can be divided into stratigraphic subtypes. They differ in their stereometric parameters and show distinct differences between the central part and the outer part of the inner crater. The Nördlingen drill core can be subdivided into four suevite units: 1) Upper redeposited suevite (296-314m), 2) "Graded" suevite (314-330m), 3) Melt-rich suevite (331-520m), and 4) Melt poor suevite (520-602m). The Enkingen drill core can be subdivided into four units: 1) Upper suevite (21-40m), 2) Middle suevite (40-66m), 3) Lower suevite with intersection of coherent melt layers (66-86m), and 4) coherent impact melt (below 86m). The Wörnitzostheim drill core can be subdivided into three units: 1) Upper suevite (19-25m), 2) Melt-rich suevite (25-80m), 3) Melt-poor suevite (80-100m). The Otting drill core is homogenous. A comparison of the characteristics of all drill cores can be summarized as follows: 1) The suevite of

The choice of a model analogue of a radioactive waste repository requires precise definition of t... more The choice of a model analogue of a radioactive waste repository requires precise definition of the phenomena to be studied. The main problem to be solved by this approach is the development of low enthalpy geothermal systems near the repository, which would be likely to facilitate the migration of radionuclides towards the surface. A study has thus been undertaken on fossil geothermal systems in order to determine the various characteristics of migration of the elements analogous to the radionuclides (U, Th, REE, Sc, Sr).

HAL (Le Centre pour la Communication Scientifique Directe), Apr 16, 2020

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de

<p>The Richat Dome is a huge circular, slightly elliptical depression (~ 40 km in d... more <p>The Richat Dome is a huge circular, slightly elliptical depression (~ 40 km in diameter) in the Proterozoic to Cambro-Ordovician sedimentary series of the NE part of the Mauritanian Taoudeni basin. This structure consists of a central zone that corresponds to a complex of dolomitic limestones and sedimentary rocks of Neoproterozoic age, cut by breccia silica and felsic volcanic rocks. A peripheral zone comprising Neoproterozoic to Late Ordovician sandstones and pelites into which carbonatite veins and two gabbroic annular dykes are injected.</p><p>Generally, the carbonatites represent a relatively rare type of igneous rock composed mainly of primary carbonate minerals (calcite and/or dolomite > 50 vol % of the rock) associated with phosphate minerals, silicates, and oxides. They contain the highest concentrations of rare earth elements (REE) of all igneous rocks. The carbonatites are also the main source of REE especially the light REE (La, Ce, Pr and Nd) as well as some critical metals such as Nb and Ta.</p><p>The aim of this study is to present a preliminary work on the carbonatite dykes of the Richat Dome: (1) detailed geological mapping of the various dykes, (2) petrographic, (3) mineralogical and (4) geochemical characterizations. The results obtained will be cross-referenced with other strategic deposits around the world</p>

Mineralium Deposita, Jun 1, 2002

Mineralium Deposita, Jul 7, 1999

The Almade n district is the largest mercury concentration in the world, with a total content of... more The Almade n district is the largest mercury concentration in the world, with a total content of about 250 000 t of mercury, nearly one third of the known total mercury resources of the Earth. Mercury has been exploited since the Celtic and Roman times, with peak production during the Renaissance and between 1939± 1945. The district is hosted by a Paleozoic synclinorium overlying Precambrian rocks. The Paleozoic sequence comprises epicontinental quartz arenite rocks, including black shales and quartzites. Diatremes, alkaline lavas of dierent composition, and late tholeiitic diabases account for the Ordovician to Devonian magmatism. The tectonic setting of this complex suite corresponds to the intraplate type. The mercury deposits of Almade n can be classi®ed into two main types: type 1, early stratiform type ores characterized by cinnabar deposition on the lower Silurian quartzites (Criadero quartzite; e.g. the Almade n and El Entredicho deposits), and type 2, late discordant orebodies (e.g. Las Cuevas), largely hosted or related to diatremes (the`frailesca rocks') of alkaline basaltic composition. In type 1 cinnabar was deposited during diagenesis, in relation to hydrothermal circulation driven by magmatic activity. Type 2 include a variety of deposits having in common the discordant character of the orebodies (e.g. veins, stockworks, massive replacements), and their wide dispersion along the stratigraphic column, i.e. from Lower Silurian (e.g. Nueva Concepcio n) to Upper Devonian (e.g. Corchuelo).

Presses de l'Université du Québec eBooks, Sep 7, 2017

Journal of Metamorphic Geology, 1993

Archaean greenstone belts are often cut by major shear zones, for example the Cadillac tectonic z... more Archaean greenstone belts are often cut by major shear zones, for example the Cadillac tectonic zone (a) of the southern Abitibi region in north-westem Quebec. At McWatters, the CTZ contains slices of metavolcanic units bounded by comdors of highly strained and altered rocks. Mineral assemblages of the metabasites record the metamorphic evolution of the CLZ. The McWatters metabasalts and metagabbros have similar chemistry but different mineral assemblages consisting of variable amounts of actinolite, hornblende, chlorite, albite, epidote, quartz, carbonates, titanite, biotite, rutile, magnetite, ilmenite and sulphides. The different mineral assemblages, which coexist in a single tectonic slice, can be divided into three types, characterized by (A) presence of hornblende and actinolite, (B) presence of actinolite and epidote, and (C) absence of amphibole and epidote. Partial replacements indicate that these mineral assemblages are not in equilibrium. The hornblende of the least altered and deformed samples of the type A assemblage is a relict of a prograde metamorphic event, contemporaneous with the development of the main schistosity. The prograde conditions are estimated at P = 5 kbar, T = 475" C with low 4. The more altered and deformed samples of the type C assemblage record a later retrograde metamorphic event. Conditions of the later event are estimated at P = 4 kbar, T = 400" C with higher P,. Widespread calcite precipitation occurred during a later episode. The diversity of the mineral assemblages results from permeability variations along the high-strain zones of the Cl'Z.