Processes Driving Iron and Manganese Dispersal From the TAG Hydrothermal Plume (Mid-Atlantic Ridge): Results From a GEOTRACES Process Study

Hydrothermal vents are a recognized source of trace elements to the ocean inventory. Nevertheless, the contribution of slow-spreading ridges remains poorly resolved. To address this, high-resolution dissolved (<0.45 μm) iron (dFe) and manganese (dMn) samples were collected during the GEOTRACES HERMINE GApr07 process study at the Mid Atlantic Ridge. Samples were collected at nine stations, from the TAG vent site to 75 km south-southwest following the neutrally buoyant plume. Concentrations of dMn and dFe ranged from 71 ± 6 and 51 ± 2 nmol kg–1 right above the vent site to 0.43 ± 0.01 and 1.56 ± 0.02 nmol kg–1 at the most distal station, respectively. Using a 5-box model coupled with our data, we show that as the plume traveled away from the vent, aggregation processes controlled dFe concentrations in the first 2 km, with an aggregation rate averaging between 8.0 ± 0.6 and 0.11 ± 0.04 nmol L–1 d–1, respectively in the first and second kilometer. Aggregation, likely of small colloidal particles, led to partitioning of the size fractionated Fe pool, as 6% of the dFe was moved into the particulate size fraction. Further away, disaggregation processes became more prevalent, with rates ranging from 0.27 ± 0.02 to 0.008 ± 0.001 nmol L–1 d–1, enriching the dFe pool by 10%. The computed decrease of hydrothermal Fe within the neutrally buoyant plume was likely caused by flocculation of small Fe oxyhydroxide particles. This process resulted in Fe aggregate formation with radii estimated to range between 14 and 20 μm in the first km from TAG. Between 2 and 30 km from the vent site, the radii ranged between 2 and 4 μm

Origin and Composition of Ferromanganese Deposits of New Caledonia Exclusive Economic Zone

Located in the South-West Pacific, at the northern extremity of the mostly submerged Zealandia continent, the New Caledonian Exclusive Economic Zone (EEZ) covers 1,470,000 km² and includes basins, ridges and seamounts where abundant ferromanganese crusts have been observed. Several investigations have been conducted since the 1970s on the nature and composition of ferromanganese crusts from New Caledonia’s seamounts and ridges, but none have covered the entire EEZ. We present data from 104 ferromanganese crusts collected in New Caledonia’s EEZ during twelve oceanographic cruises between 1974 and 2019. Samples were analysed for mineralogy, geochemical compositions, growth rates, and through a statistical approach using correlation coefficients and factor analysis. Crust thicknesses range from 1 mm to 115 mm, with growth rates between 0.45 mm/Ma and 102 mm/Ma. Based on textures, structures, discrimination plots, and growth rates, we distinguish a group of hydrogenetic crusts containing the highest mean contents of Co (0.42 wt%), Ni (0.31 wt%), and high contents of Mo, V, W, Pb, Zn, Nb, from a group of hydrothermal and/or diagenetic deposits showing high mean contents of Mn (38.17 wt%), Ba (0.56 wt%) and low contents of other trace metals. Several samples from this later group have exceptionally high content of Ni (0.7 wt%). The data shows that crusts from the southern part of the EEZ, notably seamounts of the Loyalty Ridge and the Lord Howe Rise, present high mineral potential for prospectivity owing to high contents of valuable metals, and constitute a great target for further investigatio

Géologie, géochimie et géochronologie du gisement aurifère de Tamlalt-Menhouhou (Haut-Atlas oriental)

Because of its particular location at the edge of the West African Craton, Morocco has experienced a complex geodynamic history, starting in the Palaeoproterozoic and continuing until the most recent alpine events. This polyphase history resulted in the formation of mineralizations that overlap in time and space. The Tamlalt-Menhouhou gold deposit is located on the southern edge of the Neoprotérozoic-Palaeozoic Tamlalt inlier (Eastern High- Atlas), just north of the limit between the Atlasic intra-cratonic High-Atlas belt and the Panafrican Anti-Atlas belt. Mineralizations are enclosed in Ediacaran volcano-sedimentary formations (U/Pb age: 569 ± 8 Ma) which were probably produced in a back-arc basin. The Neoproterozoic felsic rocks reveal the fertile character of the Upper Neoproterozoc crust and include both barite mineralization and an iron-bearing mineralization that can be described as a “Banded Iron Formation”. The Tamlalt-Menhouhou gold deposit is crosscut by many shear faults compatible with a dextral shearing phase. Two different gold mineralizations were identified: (i) a primary gold mineralization of the type “Iron Oxide Copper Gold deposit” (IOCG) characterized by a strong sodic (± calcic) alteration and (ii) a secondary gold mineralization corresponding to a “Shear zone related gold deposit” and related to a strong argillic and phyllic alteration localized along the shear faults. A detailed ion microprobe study of hydrothermal zircons genetically associated with albitization provide a Late Ordovician age (449 ± 8 Ma) for primary gold mineralization. This age is confirmed by 40Ar/39Ar dating of two muscovite mono-grains, which underscores the potential of zircons to record hydrothermal events, and the interest of these phases for metallogeny. A Late Variscan age (293 ± 7 Ma) is defined by 40Ar/39Ar analysis of phengites from the phyllic alteration synchronous with auriferous quartz vein development, and which is assumed to represent the age of gold mineralization. This age is in agreement with the Late Variscan dextral shearing phase, and demonstrates the consequences of the Variscan orogeny for the re-mobilization of metalliferous pre-concentrations.En raison de sa localisation particulière en bordure du craton Ouest Africain, le Maroc révèle une histoire géodynamique complexe qui commence au Paléoprotérozoïque et qui se poursuit jusqu'aux derniers évènements alpins. Ce polyphasage se traduit notamment par la formation de minéralisations télescopées dans le temps et dans l'espace. Le gisement aurifère de Tamlalt-Menhouhou se situe sur la bordure sud de la boutonnière paléozoïque de Tamlalt (Haut-Atlas oriental), jouxtant la limite entre la chaîne intra-cratonique atlasique du Haut- Atlas et la chaîne panafricaine de l'Anti-Atlas. Les minéralisations sont encaissées dans des formations volcano-sédimentaires de l'Ediacarien (âge U/Pb : 569 ± 8 Ma) probablement mise en place dans un contexte d'arrière-arc. Les roches felsiques néoprotérozoïques ont révélé le caractère fertile de la croûte néoprotérozoïque supérieure avec la présence d'une minéralisation barytique et d'une minéralisation ferrifère de type "Banded Iron Formations". Le secteur aurifère de Tamlalt-Menhouhou est recoupé par de nombreux décrochevauchements compatibles avec une tectonique cisaillante dextre. Deux minéralisations aurifères ont pu être identifiées : (i) une minéralisation aurifère primaire de type "Iron Oxide Copper Gold deposit" (IOCG) associée à un altération sodique (± calcique) caractérisée par un enrichissement en Au, Cu, Fe, Co, Ni, Mo, As, Sb, ± Bi, et (ii) une minéralisation aurifère secondaire de type "Shear zone related gold deposit" associée aux altérations argilleuses et phylliteuses localisées le long des décro-chevauchements. L'étude détaillée à la microsonde ionique effectuée sur les zircons hydrothermaux génétiquement associés au phénomène d'albitisation permet d'obtenir un âge Ordovicien supérieur de 449 ± 8 Ma pour la minéralisation aurifère primaire, ce qui constitue une première au Maroc. Cet âge est confirmé par la datation 40Ar/39Ar sur deux mono-grains de muscovites soulignant le potentiel des zircons à enregistrer des évènements hydrothermaux, et leur intérêt en métallogénie. La minéralisation aurifère secondaire est datée à 293 ± 7 Ma (Stéphano-autunien) par géochronologie 40Ar/39Ar sur des phengites associées à l'altération argilleuse et phylliteuse et aux veines de quartz aurifères. Cet âge est en accord avec celui proposé pour la phase cisaillante dextre tardi-varisque, et souligne l'importance de cette orogenèse pour la remobilisation de pré-concentrations métallifères

Geology, geochemistry and geochronology of the tamlalt-menhouhou gold deposit (easterrn high-atlas)

Le gisement aurifère de Tamlalt-Menhouhou se situe sur la bordure sud de la boutonnière paléozoïque de Tamlalt (Haut-Atlas oriental), jouxtant la limite entre la chaîne du Haut-Atlas et la chaîne de l'Anti-Atlas. Les minéralisations sont encaissées dans des formations volcano-sédimentaires de l'Ediacarien (âge U/Pb : 569 ± 8 Ma). Deux minéralisations aurifères ont pu être identifiées : (i) une minéralisation aurifère primaire de type "Iron Oxide Copper Gold deposit" (IOCG) associée à un altération sodique (± calcique) caractérisée par un enrichissement en Au, Cu, Fe, Co, Ni, Mo, As, Sb, ± Bi, et (ii) une minéralisation aurifère secondaire de type "Shear zone related gold deposit" associée aux altérations argilleuses et phylliteuses localisées le long des décro-chevauchements. L'étude détaillée à la microsonde ionique effectuée sur les zircons hydrothermaux génétiquement associés au phénomène d'albitisation permet d'obtenir un âge Ordovicien supérieur (449 ± 8 Ma) pour la minéralisation aurifère primaire. Cet âge est confirmé par la datation 40Ar/39Ar sur deux mono-grains de muscovites et souligne le potentiel des zircons à enregistrer des évènements hydrothermaux, et leur intérêt en métallogénie. La minéralisation aurifère secondaire est datée au Stéphano-autunien (293 ± 7 Ma) par géochronologie 40Ar/39Ar sur des phengites associées à l'altération argilleuse et phylliteuse et aux veines de quartz aurifères. Cet âge souligne l'importance de cette orogenèse pour la remobilisation de pré-concentrations métallifères.The Tamlalt-Menhouhou gold deposit is located on the southern edge of the Neoprotérozoic-Palaeozoic Tamlalt inlier (Eastern High-Atlas), just north of the limit between the High-Atlas belt and the Anti-Atlas belt. Mineralizations are enclosed in Ediacaran volcano-sedimentary formations (U/Pb age: 569 ± 8 Ma). Two different gold mineralizations were identified: (i) a primary gold mineralization of the type “Iron Oxide Copper Gold deposit” (IOCG) characterized by a strong sodic (± calcic) alteration and (ii) a secondary gold mineralization corresponding to a “Shear zone related gold deposit” and related to a strong argillic and phyllic alteration localized along the shear faults. A detailed ion microprobe study of hydrothermal zircons genetically associated with albitization provide a Late Ordovician age (449 ± 8 Ma) for primary gold mineralization. This age is confirmed by 40Ar/39Ar dating of two muscovite mono-grains, and underscores the potential of zircons to record hydrothermal events, and the interest of these phases for metallogeny. A Late Variscan age (293 ± 7 Ma) is defined by 40Ar/39Ar analysis of phengites from the phyllic alteration synchronous with auriferous quartz vein development, and which is assumed to represent the age of gold mineralization. This age demonstrates the consequences of the Variscan orogeny for the re-mobilization of metalliferous pre-concentrations

Géologie, géochimie et géochronologie du gisement aurifère de Tamlalt-Menhouhou (Haut-Atlas oriental)

Le gisement aurifère de Tamlalt-Menhouhou se situe sur la bordure sud de la boutonnière paléozoïque de Tamlalt (Haut-Atlas oriental), jouxtant la limite entre la chaîne du Haut-Atlas et la chaîne de l'Anti-Atlas. Les minéralisations sont encaissées dans des formations volcano-sédimentaires de l'Ediacarien (âge U/Pb : 569 +- 8 Ma). Deux minéralisations aurifères ont pu être identifiées : (i) une minéralisation aurifère primaire de type "Iron Oxide Copper Gold deposit" (IOCG) associée à un altération sodique (+- calcique) caractérisée par un enrichissement en Au, Cu, Fe, Co, Ni, Mo, As, Sb, +- Bi, et (ii) une minéralisation aurifère secondaire de type "Shear zone related gold deposit" associée aux altérations argilleuses et phylliteuses localisées le long des décro-chevauchements. L'étude détaillée à la microsonde ionique effectuée sur les zircons hydrothermaux génétiquement associés au phénomène d'albitisation permet d'obtenir un âge Ordovicien supérieur (449 +- 8 Ma) pour la minéralisation aurifère primaire. Cet âge est confirmé par la datation 40Ar/39Ar sur deux mono-grains de muscovites et souligne le potentiel des zircons à enregistrer des évènements hydrothermaux, et leur intérêt en métallogénie. La minéralisation aurifère secondaire est datée au Stéphano-autunien (293 +- 7 Ma) par géochronologie 40Ar/39Ar sur des phengites associées à l'altération argilleuse et phylliteuse et aux veines de quartz aurifères. Cet âge souligne l'importance de cette orogenèse pour la remobilisation de pré-concentrations métallifères.The Tamlalt-Menhouhou gold deposit is located on the southern edge of the Neoprotérozoic-Palaeozoic Tamlalt inlier (Eastern High-Atlas), just north of the limit between the High-Atlas belt and the Anti-Atlas belt. Mineralizations are enclosed in Ediacaran volcano-sedimentary formations (U/Pb age: 569 +- 8 Ma). Two different gold mineralizations were identified: (i) a primary gold mineralization of the type Iron Oxide Copper Gold deposit (IOCG) characterized by a strong sodic (+- calcic) alteration and (ii) a secondary gold mineralization corresponding to a Shear zone related gold deposit and related to a strong argillic and phyllic alteration localized along the shear faults. A detailed ion microprobe study of hydrothermal zircons genetically associated with albitization provide a Late Ordovician age (449 +- 8 Ma) for primary gold mineralization. This age is confirmed by 40Ar/39Ar dating of two muscovite mono-grains, and underscores the potential of zircons to record hydrothermal events, and the interest of these phases for metallogeny. A Late Variscan age (293 +- 7 Ma) is defined by 40Ar/39Ar analysis of phengites from the phyllic alteration synchronous with auriferous quartz vein development, and which is assumed to represent the age of gold mineralization. This age demonstrates the consequences of the Variscan orogeny for the re-mobilization of metalliferous pre-concentrations.NANCY-INPL-Bib. électronique (545479901) / SudocSudocFranceF

Trace element determinations in Fe–Mn oxides by high resolution ICP-MS after Tm addition

International audienc

ARCHIMEDE - A new software for management of geological and biological samples

Since 2003, IFREMER manages the marine geology database of Brest (BGMB) which includes information on geological samples (sediment cores and rocks) and geotechnical measurements collected by IFREMER teams and/or resources and related analyses (stratigraphy, lithology, chemistry, grain size). In the same way, the IFREMER Deep Sea Lab database (BIOCEAN) gathers data about biological, sediment and hydrological samples collected by IFREMER biologists and ecologists since 1967. These databases which include several thousands of operations and samples require having a better visibility for the scientific community through the improvement of existing software tools and services. Indeed, according to the current scientific projects and future applications (e.g. management of mining licenses, implementation of the Nagoya Protocol, observatory of mineral raw materials, data dissemination), it becomes crucial to access to: • the geographic position of sampling operations, • the samples description (preservation, identifications,…) and related analyses, • the samples physical location. In this context, a project was initiated in order to: • improve archiving and maintenance of marine samples collected during expensive marine cruises all over the world, • make visible and accessible the available information (data and samples) to the whole scientific community, • rationalise and optimise the logistic for cruise preparation for the French and international community. As part of this, a study about management of marine geological and biological samples and related data in a unique system has been undertaken. The main objective is to save all information about the technical and scientific work during the operational phase in the field and in the lab. All metadata and data about handling and curating of sampled materials have to be collated as well. In that aim, new tools and services have been developed: • A new database was designed by merging and adapting BGMB and BIOCEAN schemas. It allows management of multi-points operations, in-situ measures and observations. Different types and subsampling levels of samples (cores, fluids, organisms…) can be stored in relation with their physical place and transfers. The analyses on samples could also be managed following this new schema. • The onboard software SEALOG allows recording and reporting events and operations and tracking samples from cruises, dives and moorings operated by biologists and geologists. Back on land, these data are loaded into the central database. However they must be completed after processing of samples and performing analyses. • The graphical user interface connected to the new database, ARCHIMEDE, can be used in the lab, downstream the early acquisition at sea. This software was developed through four structuring functions: (1) Data input; (2) Visual display of data and query; (3) Data import; (4) Data export. So far these functionalities enable processing of information about surface operations, diving operations and samples (acquisition date-time, positions, equipment, originator, description…). The marine samples physical location and movements (transfers, loans…) can already be tracked with ARCHIMEDE whereas the features for the management of analyses on samples will be added by 2017. A module dedicated to geographical sites is planned to be integrated in a longer term. • A website has been developped (soon available) in order to make visible and accessible to the whole scientific community all the information stored in the database. It is based on Sextant infrastructure (http://sextant.ifremer.fr/en/) which allows data display using the OGC Web Map Service protocol (WMS). Thanks to this website, scientists and general public will be able to locate geological and biological material from sea floor and archived in different French repositories. They will have access to related data (analyses) and images according to restriction rules. This initiative was conducted through a collaborative relationship with field operators as well as laboratory staff in order to answer their needs and to offer user-oriented solutions. Besides providing a way for scientists and data managers to enhance the currently existing data flows, this project aims to improve our capabilities in data and information security, management, use and delivery. This is of vital importance for marine researchers, industry and policy-makers in the context of various studies, from the climate change prediction, marine resources assessment, to off shore engineering, and to make evidence-based decisions in France and globally. The presentation will focus primarily on the software ARCHIMEDE, related developments and perspectives

Element distribution in the root zone of ultramafic-hosted black smoker-like systems: Constraints from an Alpine analog

Fluid-rock interactions at Mid-Oceanic Ridges lead to metal deposition in the so-called seafloor massive sulfides at ultramafic-hosted systems. Due to restricted access to the seafloor and scarcity of 3D exposures, these systems are poorly understood at-depth. A way to access the vertical dimension is to focus on fossil analogs preserved on-land such as the one preserved in serpentinites from the Platta nappe (SE Switzerland). For this example, we document the element distribution in the mineralized rocks at three distinct levels in the rock column using both whole rock chemical analyses and LA-ICPMS analysis of sulfide (chalcopyrite and pyrrhotite) and magnetite. We bring, for the first time, chemical signatures of the mineralization in the root zone of ultramafic-hosted black smokers. At any given depth, the Co/Ni ratio is maximum in the most mineralized samples indicating that this ratio is linked to the intensity of hydrothermal alteration. Additionally, the Co/Ni ratio decreases in mineralized rocks towards the paleosurface, whereas the Se content increases. An episode of carbonation recorded in the highest structural level of the system was responsible for a slight remobilization of the former Cu stock. We propose a model in which the uprising mineralizing fluid mixed with seawater within the host serpentinites, before venting at the paleoseafloor

Origin and Evolution of the Fatu Kapa Magmatic System (North-Western Lau Back-arc Basin): Insight on the Genesis of High-Silica Lavas

International audienceAbstract The South Eastern Futuna Volcanic Zone (SEFVZ; 50 km × 80 km) is located in the NW of the Lau back-arc basin at the northern boundary of the Futuna and YAO microplates. Fatu Kapa is an area (∼15 km × 10 km) of diffuse volcanic activity at the center of the SEFVZ and at the intersection of two volcanic axes with the Futuna fracture zone. At this place, the volcanic, tectonic, and hydrothermal activities are enhanced. The most differentiated volcanic series of the whole Futuna region are found in the Fatu Kapa area. Based on major and trace element data, four groups of volcanic rocks are distinguished in the Fatu Kapa area. The main groups form a well-defined transitional suite from basalts to andesitic and dacitic lavas that display enrichments in Zr, Cl and heavy rare earth elements. The most mafic lavas of this group are extracted from an Indian-type depleted mantle mixed with a component with trace element and isotopic characteristics similar to the nearby Samoa mantle plume. There is no evidence of subduction input. Petrological modelling shows that the mafic melts of the main group (Group 1A) evolve towards trachyandesites through fractional crystallization coupled with assimilation of 10 % of a Cl-rich and Th-poor melt generated by low-degree (≤2 %) partial melting of a hydrothermally altered basaltic crust. Rocks of Groups 1B(a) and 1B(b) were then generated by mixing of a mafic melt from Group 1A with a melt obtained by partial melting of andesitic and hydrothermally altered wallrock in shallow magma chambers. Extremely high Cl concentrations can be explained by assimilation of interstitial K- and Cl-rich brines in the pore water of the hydrothermally altered volcanic rocks before melting of these rocks. This is in good agreement with unusual extension of the Fatu Kapa hydrothermal area and indicates that, in the north of the Lau basin, the microplate boundaries are privileged zones to generate a complex felsic magmatism within areas of widespread hydrothermal alteration. Our study confirms the importance of assimilation and fractional crystallization and mixing processes in generating high-silica lavas in back-arc environments decoupled from subduction