Laurent BAILLY - Academia.edu (original) (raw)
Papers by Laurent BAILLY
Despite of the gold exploration since 150 years, there is a limited understanding of gold deposit... more Despite of the gold exploration since 150 years, there is a limited understanding of gold deposits in the French Guiana. To improve our knowledge, alluvial, eluvial and primary gold grains from the Sophie-Repentir and Saint-Elie goldfields (French Guiana) have been characterised by EPMA and LA-ICP-MS analyses. Preliminary results show a good discrimination between the two orogenic gold districts. Whereas the gold grains population of the Saint-Elie is characterised by a low content of silver (i.e. mainly less than 6 wt%), a suite of Bi mineral inclusions and a Sb-Bi-Cd fingerprint, gold from the Sophie-Repentir is enriched in silver (up to ~ 20 wt%), Cu-poor and associated with a wider range of tellurides. These features also allow matching an alluvial gold population to its corresponding lode source with confidence and raise questions about the processes controlling the trace elements behaviour.
Minerals, 2021
Monazite and rutile occurring in hydrothermally altered W mineralizations, in the Echassières dis... more Monazite and rutile occurring in hydrothermally altered W mineralizations, in the Echassières district of the French Massif Central (FMC), were dated by U-Pb isotopic systematics using in-situ Laser ablation-inductively coupled plasma–quadrupole mass spectrometry (LA-ICP-MS). The resulting dates record superimposed evidence for multiple percolation of mineralizing fluids in the same area. Cross-referencing these ages with cross-cutting relationships and published geochronological data reveals a long history of more than 50 Ma of W mineralization in the district. These data, integrated in the context of the Variscan belt evolution and compared to other major W provinces in the world, point to an original geodynamic-metallogenic scenario. The formation, probably during the Devonian, of a quartz-vein stockwork (1st generation of wolframite, called wolframite “a”; >360 Ma) of porphyry magmatic arc affinity is analogous to the Sn-W belts of the Andes and the Nanling range in China. Th...
Geochimica et Cosmochimica Acta, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Journal of Geochemical Exploration, 2021
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Journal of African Earth Sciences, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Mineralogical Magazine, 2018
ABSTRACTThe Conakry Igneous Complex is a mafic-ultramafic intrusion emplaced contemporaneously wi... more ABSTRACTThe Conakry Igneous Complex is a mafic-ultramafic intrusion emplaced contemporaneously with the opening of the Atlantic, forming a complex, 55 km x 5 km dyke-like body within which three main episodes of injection have been recognized, characterized by a lack of mineral layering. Unit 1 consists of dunite and related facies, Unit 2 of wehrlite and pyroxene peridotite and Unit 3 corresponds to various gabbro facies. Units 1 and 2 constitute the Kaloum Peninsula; Unit 3 is its NW extension, forming the 1010 m high Mount Kakoulima. Unit 3 intrudes the two previous units and corresponds to a tholeiitic liquid that crystallized in an almost closed system, and thus exhibits a strong differentiation trend, in contrast to Units 1 and 2. Mineral compositions suggest the existence of a deeper magma chamber where a first stage of differentiation occurred.Disseminated base-metal sulfides (BMS) are present in all units of the complex and earlier descriptions have mentioned a “massive sul...
Minerals, 2019
The Echassières district in central France contains complex rare-element ore deposits, whose form... more The Echassières district in central France contains complex rare-element ore deposits, whose formation is related to exotic igneous events and several hydrothermal episodes that are not entirely understood to date. Tungsten mineralization consists of three generations of wolframite, characterized by distinct Fe/Mn ratios (8.4; 3.5 and 0.3, for wolframite a, b and c, respectively), formed during three separate hydrothermal episodes related to the Variscan orogeny. Wolframite a occurs in quartz veins of the La Bosse stockwork where it crystallized before the Barrovian metamorphism that affected these veins and the host rock. After metamorphism, before intrusion of the Beauvoir and Colettes granites, wolframite b crystallized in the stockwork during massive topazification. High concentrations of wolframite c occur in the proximal quartz veins in the Mazet area, while only scant amounts are found in the La Bosse stockwork. In both settings, wolframite c precipitated from the fluid respo...
Karstologia : revue de karstologie et de spéléologie physique, 2005
Le rôle métallogénique des phénomènes karstiques est connu de longue date. Les principaux gisemen... more Le rôle métallogénique des phénomènes karstiques est connu de longue date. Les principaux gisements ainsi formés concernent l'aluminium, le plomb-zinc, le nickel et le cuivre. En Nouvelle-Calédonie, le climat tropical humide a développé divers types de karsts dans les formations carbonatées et dans les roches ultramafiques de l'ophiolite calédonien. Le nickel concentré dans les profils d'altération est exploité depuis le XIXème siècle. La mise en place de ces gisements a fait l'objet de nombreuses controverses. Divers modèles géologiques ont été proposés au cours du temps. Ils ont initialement été interprétés comme d'origine hydrothermale. On les a ensuite considérés comme supergènes où les fluides météoriques empruntent des réseaux de fractures préexistantes. Ils ont également été considérés comme contemporains d'une néotectonique en extension radiale. L'altération latéritique des péridotites s'est développée à partir d'une paléosurface d'âge...
Journal of African Earth Sciences, 2017
The petrology and mineralogy of the Itsindro complex in south-central Madagascar has been investi... more The petrology and mineralogy of the Itsindro complex in south-central Madagascar has been investigated through samples obtained from the 320.7 m-deep Lanjanina borehole. The section consists of a 254 m-thick pyroxenite unit with interbedded gabbro layers that overlies a gabbro unit and is itself overlain by a 19 m-thick granite unit. Most of the structures are sub-horizontal. A weak magmatic layering is locally observed but at the scale of the core, the intrusion does not appear to be a layered complex. Pyroxenite and gabbro show a systematic disseminated mineralization consisting of Fe-TiP oxides and Fe-(Cu-Ni) sulphides that takes the form of ilmenite-titanomagnetite±apatite and pyrrhotite±chalcopyrite±pentlandite. In the upper zone, from 90 to 72 m, sub-massive centimetre-to decimetre-sized layers of oxides and sulphides comprise a total of 16 m of sub-massive sulphide (the main mineralized zone). In this mineralized zone the oxide/sulphide ratio is close to 1/1. The sulphide is strongly dominated by pyrrhotite, which may locally contain inclusions of molybdenite crystals with the Re sulphide rheniite (ReS 2). Oxides are generally euhedral, included in or attached to the Fe-sulphide, and also locally form sub-massive centimetre-sized bands. Apatite as a cumulus phase is ubiquitous. Locally it may account for 30 % of the ore-rich samples and some samples consist of apatite-Fe-Ti oxides-Fe-Cu-Ni sulphides with virtually no silicate. Apatite is the main REE carrier but the total REE content remains low (<90 ppm). Mineral compositions and whole rock geochemistry indicate that the rocks are highly differentiated, and in spite of a relatively limited thickness, the differentiation process is observed. Two zones can be distinguished: from the bottom to 162.8 m we see a decrease in the Mg number of olivine and pyroxene, and a drop in TiO 2 and Al 2 O 3 for the latter. A reverse trend is then observed within the pyroxenite unit from the 162.8 m level upwards. The main mineralized zone is located in the upper part of this unit, about 70 m above this discontinuity. The highly differentiated Fe-TiP facies of the Lanjanina series in the Itsindro Gabbro Complex have been interpreted as corresponding to the Fe-TiP rich, Si-poor member remaining after an immiscible segregation of an evolved mafic magma. The granite dykes and the overlying granite unit represent the second, Si-rich member of the immiscibility process. The presence of large amounts of sulphide is attributed to sulphur contamination of the Fe-Ti-rich liquid. Fe-Ti oxides will tend to crystallize on the sulphide droplets and the accumulation of dense Fe-sulphides (liquid) and associated Fe-Ti oxides (solid) will result in this complex and unusual association taking the form of a net texture. Keywords Fe-Ti oxide ores, Fe-(Cu-Ni) sulphides, Fe-TiP rich liquid immiscibility, sulphide liquid immiscibility, mafic-ultramafic intrusion, Itsindro Gabbro, Madagascar characterized by late undifferentiated Archean migmatitic gneisses and schists (Tucker et al., 1999) and metamorphosed Mesoproterozoic sedimentary rocks of the Quarzto-Schisto-Calcaire series (Moine, 1968; 1974). The Itsindro gabbro gives an age of 790.1 ± 0.9 Ma (U-Pb on zircon and baddeleyite) and the age range obtained for other plutons in the region is
European Journal of Mineralogy, 2017
We present data available on rare metal and indium distributions in cassiterite and associated mi... more We present data available on rare metal and indium distributions in cassiterite and associated minerals from thirteen Sn ± W granite-related ore deposits in the western Variscan Belt (Massif Central and Armorican Massif, France; Galicia, Spain; and SW England). Cassiterite and associated minerals including sulfides and titanium oxides were analysed using an electron probe microanalyzer (EPMA). Significant indium contents were only measured in cassiterite from hydrothermal vein-type mineralizations associated with peraluminous granites of Montbelleux, Abbaretz (French Armorican Massif) and Marcofán (Galicia); they correlate with the highest Nb, Ta and Fe substitutions. Two coupled substitutions are proposed: (1) 2 (Sn 4þ , Ti 4þ) ↔ (Fe 3þ , In 3þ) þ (Nb 5þ , Ta 5þ) and (2) Fe 2þ þ (Nb, Ta) 5þ ↔ In 3þ þ (Ti, Sn) 4þ depending on Fe valence state. Sulfides (stannite, chalcopyrite, pyrite, arsenopyrite and sphalerite) and rutile associated with cassiterite contain significant amounts of indium, even when cassiterite is indium-free, suggesting preferential partitioning into the sulfides.
The Canadian Mineralogist, 2014
Abstract Certain basaltic flows of the Permian volcanism in the Esterel (France) are enriched at ... more Abstract Certain basaltic flows of the Permian volcanism in the Esterel (France) are enriched at their top and bottom in amygdules containing various minerals. Some of these amygdules appear to be particularly enriched in synchysite-(Ce), developed as fibrous aggregates together with chlorite and calcite. The rare earth element (REE) distribution pattern in individual amygdules appears very similar to that of the host basalt, suggesting that during the basalt9s late hydrothermal evolution the REE were coherently remobilized and reprecipitated in the amygdules in the form of REE minerals. In such an environment, enriched in carbonate and F, the most stable REE mineral to crystallize from the hydrothermal solution was synchysite-(Ce), whose REE pattern has strong similarities to the host basalt.
Studia Universitatis Babes-Bolyai, Geologia, 2000
The paper gives new evidences on some mineral species from Romanian epithermal ore deposits. Micr... more The paper gives new evidences on some mineral species from Romanian epithermal ore deposits. Microprobe analyses were used to identify the chemical composition of gangue and alteration minerals from Roşia Montană gold deposit. Special attention was given to rhodonite, rhodochrosite, and adularia.
International Journal of Earth Sciences, 2005
This article describes the formation of the principal French high-purity silica placer (source fo... more This article describes the formation of the principal French high-purity silica placer (source for electrometallurgy of silicon and ferrosilicon), the Boudeau deposit in Dordogne, and of one of its subordinate deposits, the Pays Bruˆle´deposit. Boudeau has always been considered to be a colluvial deposit, formed in a trap produced by extensional tectonism. The present work suggests a new genetic interpretation, based on a combined study of the deposits and their underlying rocks. It shows that the quartz gravel deposits, laid down by stream flow within braided channels, were reworked by karstic progressive sinking, and that the mechanism responsible for the increase in the thickness of the economic formations is cryptokarstic corrosion. This undercovers weathering process, which involves dissolution of karstifiable rocks (oolitic and bioclastic limestones) at their interface with a permeable, nonkarstifiable cover composed of chemically pure quartz gravels in a sandy-argillaceous matrix. A typological study of the gravels provides a basis for tackling the problem of their origin and their purity. They seem to be derived mainly from the synmetamorphic quartz mobilisates of the stripped metamorphic units (the lower and upper gneiss units forming the western edge of the Massif Central). Lastly, a dynamic model is suggested for the genesis of the high-purity silica deposits of Dordogne.
International Journal of Earth Sciences, 2002
Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science, 2000
The Au-Ag epithermal mineralization of the Shila Cordillera is dated at about 10.7 Ma (K/Ar on ad... more The Au-Ag epithermal mineralization of the Shila Cordillera is dated at about 10.7 Ma (K/Ar on adularia). The vein system is characterized by the association of a major ≈east-west vein and N120-135°E secondary fractures. The strike-slip faults controlling the veins indicate an initial NE-SW to ENE-WSW shortening direction, which is compatible with that generally accepted for this period. These structures were reopened during a second phase and channelized mineralizing fluids, the circulation of which may have began at the end of stage 1. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS Peru / Shila Cordillera / epithermal gold / vein / structural control / K/Ar ages Résumé-Âge K/Ar et contrôle structural de mise en place des veines épithermales à Au-Ag de la Cordillera Shila, Sud Pérou. Les minéralisations épithermales à Au-Ag de la Cordillera Shila sont datées à environ 10,7 Ma (K/Ar sur adulaire). Le système de veines est caractérisé par l'association entre une veine principale sensiblement est-ouest et des fractures satellites N120 à N135°E. Les décrochements contrôlant les veines indiquent une direction de raccourcissement initiale NE-SW à ENE-WSW, compatible avec celle généralement admise pour cette période. Dans un deuxième stade, ces structures sont ré-ouvertes pour servir de réceptacle aux fluides minéralisateurs, dont la circulation débute probablement dès la fin du stade 1.
Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science, 1998
The Au-Cu-Zn-Sb epithermal mineralisations of the Baia Mare district (north Romania) and their Mi... more The Au-Cu-Zn-Sb epithermal mineralisations of the Baia Mare district (north Romania) and their Mio-Pliocene talc-alkaline volcanic host rocks are linked to the presence, at depth, of the Baia Mare batholith, recognised by geophysical and field studies. The salinity and temperature evolution of fluid inclusions from Baia Sprie and Sasar deposits are interpreted as being linked to the thermal evolution of the underlying laccolith. The global evolution, however, shows many irregularities related to brittle tectonic activity and phreatomagmatism during mineral deposition. (0 AcadCmie des sciences / Elsevier, Paris.) Romania / epitbermal mineralisation / fluid inclusions Resume-Les minkralisations epithermales ?I Au-Cu-Zn-Sb du district de Baia Mare (Nord Roumanie) et les volcanitescalco-alcalines mio-plioc&nes encaissantes sont sous la dkpendance d'un laccolite sous-jacent reconnu par g&ophysique, par sondages et par la presence de cornbennes. Une ktude des inclusions fluides des gisements de Baia Sprie et Sasar montre une evolution de la salinite et des temperatures des fluides, interprhtee comme lice ?I I'histoire thermique du laccolite sous-jacent. Cette evolution globale est cependant perturbbe par une activite tectonique cassante, pksente tout au long du dbp6t des minkralisations et like 2 des episodes phreatomagmatiques. (0 Acadkmie des sciences / Elsevier, Paris.) Roumanie / mirkralisations Cpithermales / inclusions fluides Abridged version Geological setting The Baia Mare district, in the Eastern Carpathians of north Romania, is characterised by numerous Au-Cu-Zn-Sb epither-ma1 deposits of the low-sulfidation (adularia-sericite) type hosted by Mio-Pliocene talc-alkaline volcanic rocks (fi9ure I). These rocks form part of a Neogene volcanic belt (11.5 to 7.9 My, WAr ages) which extends for more than 350 km from the Ukraine (Berogovo district) to Romania. The magmatic and hydrothermal activity was related to the westward subduction of the Eurasiatic plate beneath the Pannonian block (Radulescu
Mineralium Deposita, 2002
Mineralium Deposita, 1999
The Pongkor gold-silver epithermal deposit with reserves of at least 98 tonnes of gold and 1026 t... more The Pongkor gold-silver epithermal deposit with reserves of at least 98 tonnes of gold and 1026 tonnes of silver, average grades 16.4 g/t Au and 171.2 g/t Ag is one of the most recent and largest gold and silver discoveries in Indonesia, proven within a short period (1988±1991). 40 Ar/ 39 Ar dating on adularia samples give an age of 2.05 0.05 Ma. The deposit is of the low-sul®dation epithermal type and consists of four main mineralized quartz veins located close to the internal rim of a volcano-tectonic depression (caldera). This resulted from an explosive ignimbritic eruption that produced pyroclastic¯ows and accretionary lapilli with rare intercalations of epiclastic rocks. This volcanic unit unconformably overlies Miocene subaqueous volcanic andesitic rocks with interbedded epiclastic rocks. The mineralized bodies are thick (average 4.2 m), steeply dipping, quartz-carbonate-adularia veins with a very low sul®de content (<0.5 wt.%). Their genesis is related to an extensional episode within a tectonic corridor showing NW-SE and NNE-SSW conjugate strike-slip faults, the major vein being located on the inner rim of the caldera. The vein ®ll reveals four successive stages of deposition marked by a speci®c facies: (1) carbonate-quartz breccia with dominant quartz and calcite and minor kutnahorite, rhodochrosite, and rhodonite (CQ facies), (2) a net
Mineralium Deposita, 2004
The natural deformation of stibnite in relation to the kinematic history of a regional fault is r... more The natural deformation of stibnite in relation to the kinematic history of a regional fault is resolved using microstructural analysis of massive stibnite along the Biards Fault in the Massif Central (France). Stibnite underwent intra-crystalline deformation associated with a strong linear and planar anisotropy. Lepidoblastic textures, undulatory extinction of oriented grains, growth of antimony between these grains, and a colour change of stibnite from white to black, result from dynamic recrystallisation. A range of asymmetric microstructures indicate non-coaxial deformation and a left-lateral sense of shear, related to the movement of the fault zone. The computed displacement corresponds to the geological offsets measured along the fault. We conclude that stibnite has microstructurally recorded the bulk kinematics of its host fault zone.
Despite of the gold exploration since 150 years, there is a limited understanding of gold deposit... more Despite of the gold exploration since 150 years, there is a limited understanding of gold deposits in the French Guiana. To improve our knowledge, alluvial, eluvial and primary gold grains from the Sophie-Repentir and Saint-Elie goldfields (French Guiana) have been characterised by EPMA and LA-ICP-MS analyses. Preliminary results show a good discrimination between the two orogenic gold districts. Whereas the gold grains population of the Saint-Elie is characterised by a low content of silver (i.e. mainly less than 6 wt%), a suite of Bi mineral inclusions and a Sb-Bi-Cd fingerprint, gold from the Sophie-Repentir is enriched in silver (up to ~ 20 wt%), Cu-poor and associated with a wider range of tellurides. These features also allow matching an alluvial gold population to its corresponding lode source with confidence and raise questions about the processes controlling the trace elements behaviour.
Minerals, 2021
Monazite and rutile occurring in hydrothermally altered W mineralizations, in the Echassières dis... more Monazite and rutile occurring in hydrothermally altered W mineralizations, in the Echassières district of the French Massif Central (FMC), were dated by U-Pb isotopic systematics using in-situ Laser ablation-inductively coupled plasma–quadrupole mass spectrometry (LA-ICP-MS). The resulting dates record superimposed evidence for multiple percolation of mineralizing fluids in the same area. Cross-referencing these ages with cross-cutting relationships and published geochronological data reveals a long history of more than 50 Ma of W mineralization in the district. These data, integrated in the context of the Variscan belt evolution and compared to other major W provinces in the world, point to an original geodynamic-metallogenic scenario. The formation, probably during the Devonian, of a quartz-vein stockwork (1st generation of wolframite, called wolframite “a”; >360 Ma) of porphyry magmatic arc affinity is analogous to the Sn-W belts of the Andes and the Nanling range in China. Th...
Geochimica et Cosmochimica Acta, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Journal of Geochemical Exploration, 2021
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Journal of African Earth Sciences, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Mineralogical Magazine, 2018
ABSTRACTThe Conakry Igneous Complex is a mafic-ultramafic intrusion emplaced contemporaneously wi... more ABSTRACTThe Conakry Igneous Complex is a mafic-ultramafic intrusion emplaced contemporaneously with the opening of the Atlantic, forming a complex, 55 km x 5 km dyke-like body within which three main episodes of injection have been recognized, characterized by a lack of mineral layering. Unit 1 consists of dunite and related facies, Unit 2 of wehrlite and pyroxene peridotite and Unit 3 corresponds to various gabbro facies. Units 1 and 2 constitute the Kaloum Peninsula; Unit 3 is its NW extension, forming the 1010 m high Mount Kakoulima. Unit 3 intrudes the two previous units and corresponds to a tholeiitic liquid that crystallized in an almost closed system, and thus exhibits a strong differentiation trend, in contrast to Units 1 and 2. Mineral compositions suggest the existence of a deeper magma chamber where a first stage of differentiation occurred.Disseminated base-metal sulfides (BMS) are present in all units of the complex and earlier descriptions have mentioned a “massive sul...
Minerals, 2019
The Echassières district in central France contains complex rare-element ore deposits, whose form... more The Echassières district in central France contains complex rare-element ore deposits, whose formation is related to exotic igneous events and several hydrothermal episodes that are not entirely understood to date. Tungsten mineralization consists of three generations of wolframite, characterized by distinct Fe/Mn ratios (8.4; 3.5 and 0.3, for wolframite a, b and c, respectively), formed during three separate hydrothermal episodes related to the Variscan orogeny. Wolframite a occurs in quartz veins of the La Bosse stockwork where it crystallized before the Barrovian metamorphism that affected these veins and the host rock. After metamorphism, before intrusion of the Beauvoir and Colettes granites, wolframite b crystallized in the stockwork during massive topazification. High concentrations of wolframite c occur in the proximal quartz veins in the Mazet area, while only scant amounts are found in the La Bosse stockwork. In both settings, wolframite c precipitated from the fluid respo...
Karstologia : revue de karstologie et de spéléologie physique, 2005
Le rôle métallogénique des phénomènes karstiques est connu de longue date. Les principaux gisemen... more Le rôle métallogénique des phénomènes karstiques est connu de longue date. Les principaux gisements ainsi formés concernent l'aluminium, le plomb-zinc, le nickel et le cuivre. En Nouvelle-Calédonie, le climat tropical humide a développé divers types de karsts dans les formations carbonatées et dans les roches ultramafiques de l'ophiolite calédonien. Le nickel concentré dans les profils d'altération est exploité depuis le XIXème siècle. La mise en place de ces gisements a fait l'objet de nombreuses controverses. Divers modèles géologiques ont été proposés au cours du temps. Ils ont initialement été interprétés comme d'origine hydrothermale. On les a ensuite considérés comme supergènes où les fluides météoriques empruntent des réseaux de fractures préexistantes. Ils ont également été considérés comme contemporains d'une néotectonique en extension radiale. L'altération latéritique des péridotites s'est développée à partir d'une paléosurface d'âge...
Journal of African Earth Sciences, 2017
The petrology and mineralogy of the Itsindro complex in south-central Madagascar has been investi... more The petrology and mineralogy of the Itsindro complex in south-central Madagascar has been investigated through samples obtained from the 320.7 m-deep Lanjanina borehole. The section consists of a 254 m-thick pyroxenite unit with interbedded gabbro layers that overlies a gabbro unit and is itself overlain by a 19 m-thick granite unit. Most of the structures are sub-horizontal. A weak magmatic layering is locally observed but at the scale of the core, the intrusion does not appear to be a layered complex. Pyroxenite and gabbro show a systematic disseminated mineralization consisting of Fe-TiP oxides and Fe-(Cu-Ni) sulphides that takes the form of ilmenite-titanomagnetite±apatite and pyrrhotite±chalcopyrite±pentlandite. In the upper zone, from 90 to 72 m, sub-massive centimetre-to decimetre-sized layers of oxides and sulphides comprise a total of 16 m of sub-massive sulphide (the main mineralized zone). In this mineralized zone the oxide/sulphide ratio is close to 1/1. The sulphide is strongly dominated by pyrrhotite, which may locally contain inclusions of molybdenite crystals with the Re sulphide rheniite (ReS 2). Oxides are generally euhedral, included in or attached to the Fe-sulphide, and also locally form sub-massive centimetre-sized bands. Apatite as a cumulus phase is ubiquitous. Locally it may account for 30 % of the ore-rich samples and some samples consist of apatite-Fe-Ti oxides-Fe-Cu-Ni sulphides with virtually no silicate. Apatite is the main REE carrier but the total REE content remains low (<90 ppm). Mineral compositions and whole rock geochemistry indicate that the rocks are highly differentiated, and in spite of a relatively limited thickness, the differentiation process is observed. Two zones can be distinguished: from the bottom to 162.8 m we see a decrease in the Mg number of olivine and pyroxene, and a drop in TiO 2 and Al 2 O 3 for the latter. A reverse trend is then observed within the pyroxenite unit from the 162.8 m level upwards. The main mineralized zone is located in the upper part of this unit, about 70 m above this discontinuity. The highly differentiated Fe-TiP facies of the Lanjanina series in the Itsindro Gabbro Complex have been interpreted as corresponding to the Fe-TiP rich, Si-poor member remaining after an immiscible segregation of an evolved mafic magma. The granite dykes and the overlying granite unit represent the second, Si-rich member of the immiscibility process. The presence of large amounts of sulphide is attributed to sulphur contamination of the Fe-Ti-rich liquid. Fe-Ti oxides will tend to crystallize on the sulphide droplets and the accumulation of dense Fe-sulphides (liquid) and associated Fe-Ti oxides (solid) will result in this complex and unusual association taking the form of a net texture. Keywords Fe-Ti oxide ores, Fe-(Cu-Ni) sulphides, Fe-TiP rich liquid immiscibility, sulphide liquid immiscibility, mafic-ultramafic intrusion, Itsindro Gabbro, Madagascar characterized by late undifferentiated Archean migmatitic gneisses and schists (Tucker et al., 1999) and metamorphosed Mesoproterozoic sedimentary rocks of the Quarzto-Schisto-Calcaire series (Moine, 1968; 1974). The Itsindro gabbro gives an age of 790.1 ± 0.9 Ma (U-Pb on zircon and baddeleyite) and the age range obtained for other plutons in the region is
European Journal of Mineralogy, 2017
We present data available on rare metal and indium distributions in cassiterite and associated mi... more We present data available on rare metal and indium distributions in cassiterite and associated minerals from thirteen Sn ± W granite-related ore deposits in the western Variscan Belt (Massif Central and Armorican Massif, France; Galicia, Spain; and SW England). Cassiterite and associated minerals including sulfides and titanium oxides were analysed using an electron probe microanalyzer (EPMA). Significant indium contents were only measured in cassiterite from hydrothermal vein-type mineralizations associated with peraluminous granites of Montbelleux, Abbaretz (French Armorican Massif) and Marcofán (Galicia); they correlate with the highest Nb, Ta and Fe substitutions. Two coupled substitutions are proposed: (1) 2 (Sn 4þ , Ti 4þ) ↔ (Fe 3þ , In 3þ) þ (Nb 5þ , Ta 5þ) and (2) Fe 2þ þ (Nb, Ta) 5þ ↔ In 3þ þ (Ti, Sn) 4þ depending on Fe valence state. Sulfides (stannite, chalcopyrite, pyrite, arsenopyrite and sphalerite) and rutile associated with cassiterite contain significant amounts of indium, even when cassiterite is indium-free, suggesting preferential partitioning into the sulfides.
The Canadian Mineralogist, 2014
Abstract Certain basaltic flows of the Permian volcanism in the Esterel (France) are enriched at ... more Abstract Certain basaltic flows of the Permian volcanism in the Esterel (France) are enriched at their top and bottom in amygdules containing various minerals. Some of these amygdules appear to be particularly enriched in synchysite-(Ce), developed as fibrous aggregates together with chlorite and calcite. The rare earth element (REE) distribution pattern in individual amygdules appears very similar to that of the host basalt, suggesting that during the basalt9s late hydrothermal evolution the REE were coherently remobilized and reprecipitated in the amygdules in the form of REE minerals. In such an environment, enriched in carbonate and F, the most stable REE mineral to crystallize from the hydrothermal solution was synchysite-(Ce), whose REE pattern has strong similarities to the host basalt.
Studia Universitatis Babes-Bolyai, Geologia, 2000
The paper gives new evidences on some mineral species from Romanian epithermal ore deposits. Micr... more The paper gives new evidences on some mineral species from Romanian epithermal ore deposits. Microprobe analyses were used to identify the chemical composition of gangue and alteration minerals from Roşia Montană gold deposit. Special attention was given to rhodonite, rhodochrosite, and adularia.
International Journal of Earth Sciences, 2005
This article describes the formation of the principal French high-purity silica placer (source fo... more This article describes the formation of the principal French high-purity silica placer (source for electrometallurgy of silicon and ferrosilicon), the Boudeau deposit in Dordogne, and of one of its subordinate deposits, the Pays Bruˆle´deposit. Boudeau has always been considered to be a colluvial deposit, formed in a trap produced by extensional tectonism. The present work suggests a new genetic interpretation, based on a combined study of the deposits and their underlying rocks. It shows that the quartz gravel deposits, laid down by stream flow within braided channels, were reworked by karstic progressive sinking, and that the mechanism responsible for the increase in the thickness of the economic formations is cryptokarstic corrosion. This undercovers weathering process, which involves dissolution of karstifiable rocks (oolitic and bioclastic limestones) at their interface with a permeable, nonkarstifiable cover composed of chemically pure quartz gravels in a sandy-argillaceous matrix. A typological study of the gravels provides a basis for tackling the problem of their origin and their purity. They seem to be derived mainly from the synmetamorphic quartz mobilisates of the stripped metamorphic units (the lower and upper gneiss units forming the western edge of the Massif Central). Lastly, a dynamic model is suggested for the genesis of the high-purity silica deposits of Dordogne.
International Journal of Earth Sciences, 2002
Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science, 2000
The Au-Ag epithermal mineralization of the Shila Cordillera is dated at about 10.7 Ma (K/Ar on ad... more The Au-Ag epithermal mineralization of the Shila Cordillera is dated at about 10.7 Ma (K/Ar on adularia). The vein system is characterized by the association of a major ≈east-west vein and N120-135°E secondary fractures. The strike-slip faults controlling the veins indicate an initial NE-SW to ENE-WSW shortening direction, which is compatible with that generally accepted for this period. These structures were reopened during a second phase and channelized mineralizing fluids, the circulation of which may have began at the end of stage 1. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS Peru / Shila Cordillera / epithermal gold / vein / structural control / K/Ar ages Résumé-Âge K/Ar et contrôle structural de mise en place des veines épithermales à Au-Ag de la Cordillera Shila, Sud Pérou. Les minéralisations épithermales à Au-Ag de la Cordillera Shila sont datées à environ 10,7 Ma (K/Ar sur adulaire). Le système de veines est caractérisé par l'association entre une veine principale sensiblement est-ouest et des fractures satellites N120 à N135°E. Les décrochements contrôlant les veines indiquent une direction de raccourcissement initiale NE-SW à ENE-WSW, compatible avec celle généralement admise pour cette période. Dans un deuxième stade, ces structures sont ré-ouvertes pour servir de réceptacle aux fluides minéralisateurs, dont la circulation débute probablement dès la fin du stade 1.
Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science, 1998
The Au-Cu-Zn-Sb epithermal mineralisations of the Baia Mare district (north Romania) and their Mi... more The Au-Cu-Zn-Sb epithermal mineralisations of the Baia Mare district (north Romania) and their Mio-Pliocene talc-alkaline volcanic host rocks are linked to the presence, at depth, of the Baia Mare batholith, recognised by geophysical and field studies. The salinity and temperature evolution of fluid inclusions from Baia Sprie and Sasar deposits are interpreted as being linked to the thermal evolution of the underlying laccolith. The global evolution, however, shows many irregularities related to brittle tectonic activity and phreatomagmatism during mineral deposition. (0 AcadCmie des sciences / Elsevier, Paris.) Romania / epitbermal mineralisation / fluid inclusions Resume-Les minkralisations epithermales ?I Au-Cu-Zn-Sb du district de Baia Mare (Nord Roumanie) et les volcanitescalco-alcalines mio-plioc&nes encaissantes sont sous la dkpendance d'un laccolite sous-jacent reconnu par g&ophysique, par sondages et par la presence de cornbennes. Une ktude des inclusions fluides des gisements de Baia Sprie et Sasar montre une evolution de la salinite et des temperatures des fluides, interprhtee comme lice ?I I'histoire thermique du laccolite sous-jacent. Cette evolution globale est cependant perturbbe par une activite tectonique cassante, pksente tout au long du dbp6t des minkralisations et like 2 des episodes phreatomagmatiques. (0 Acadkmie des sciences / Elsevier, Paris.) Roumanie / mirkralisations Cpithermales / inclusions fluides Abridged version Geological setting The Baia Mare district, in the Eastern Carpathians of north Romania, is characterised by numerous Au-Cu-Zn-Sb epither-ma1 deposits of the low-sulfidation (adularia-sericite) type hosted by Mio-Pliocene talc-alkaline volcanic rocks (fi9ure I). These rocks form part of a Neogene volcanic belt (11.5 to 7.9 My, WAr ages) which extends for more than 350 km from the Ukraine (Berogovo district) to Romania. The magmatic and hydrothermal activity was related to the westward subduction of the Eurasiatic plate beneath the Pannonian block (Radulescu
Mineralium Deposita, 2002
Mineralium Deposita, 1999
The Pongkor gold-silver epithermal deposit with reserves of at least 98 tonnes of gold and 1026 t... more The Pongkor gold-silver epithermal deposit with reserves of at least 98 tonnes of gold and 1026 tonnes of silver, average grades 16.4 g/t Au and 171.2 g/t Ag is one of the most recent and largest gold and silver discoveries in Indonesia, proven within a short period (1988±1991). 40 Ar/ 39 Ar dating on adularia samples give an age of 2.05 0.05 Ma. The deposit is of the low-sul®dation epithermal type and consists of four main mineralized quartz veins located close to the internal rim of a volcano-tectonic depression (caldera). This resulted from an explosive ignimbritic eruption that produced pyroclastic¯ows and accretionary lapilli with rare intercalations of epiclastic rocks. This volcanic unit unconformably overlies Miocene subaqueous volcanic andesitic rocks with interbedded epiclastic rocks. The mineralized bodies are thick (average 4.2 m), steeply dipping, quartz-carbonate-adularia veins with a very low sul®de content (<0.5 wt.%). Their genesis is related to an extensional episode within a tectonic corridor showing NW-SE and NNE-SSW conjugate strike-slip faults, the major vein being located on the inner rim of the caldera. The vein ®ll reveals four successive stages of deposition marked by a speci®c facies: (1) carbonate-quartz breccia with dominant quartz and calcite and minor kutnahorite, rhodochrosite, and rhodonite (CQ facies), (2) a net
Mineralium Deposita, 2004
The natural deformation of stibnite in relation to the kinematic history of a regional fault is r... more The natural deformation of stibnite in relation to the kinematic history of a regional fault is resolved using microstructural analysis of massive stibnite along the Biards Fault in the Massif Central (France). Stibnite underwent intra-crystalline deformation associated with a strong linear and planar anisotropy. Lepidoblastic textures, undulatory extinction of oriented grains, growth of antimony between these grains, and a colour change of stibnite from white to black, result from dynamic recrystallisation. A range of asymmetric microstructures indicate non-coaxial deformation and a left-lateral sense of shear, related to the movement of the fault zone. The computed displacement corresponds to the geological offsets measured along the fault. We conclude that stibnite has microstructurally recorded the bulk kinematics of its host fault zone.