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Getting reliable geophysical and geological 3D models of the subsurface is an absolute necessity for successful resources exploration. Here, we show how novel UAV-borne geophysical mapping can be extremely valuable for mapping potential new exploration areas that are difficult to access by foot, such as hard rock inter-tidal zones and boulder beaches. We show the results from a multidisciplinary geophysical campaign of highly magnetic dikes and granites along a boulder beach in Brittany, France. Our mapping is carried out using customized geophysical sensor systems with high quality sensors. These include in particular a special designed UAV-towed magnetometer bird and multispectral system for large area mapping purposes. The UAV-borne mapping is supplemented by ground-based gamma-ray spectrometry data and ground-based magnetic gradiomety data. The results clearly demonstrate the value of UAV-borne systems in difficult areas as compared to traditional mapping methods as well as the value of combining various geophysical sensors for exploring the economic geology. All UAV-borne data were collected during two days, while the groundbased data - covering only the inner and dry part of the beach - were collected over seven days.

Contains fulltext : 103363.pdf (publisher's version ) (Closed access)

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Contains fulltext : 103363.pdf (publisher's version ) (Closed access)

Contains fulltext : 103363.pdf (publisher's version ) (Closed access)

A method is proposed for the simulation of non-stationary geological patterns, using 2D conditional simulation based on wavelet decomposition of geophysical data and geological model analogues. The method is outlined and then applied to a synthetic channel to generate two models. One represents the real geological model while the other is the model analogue. The results show that wavelet simulation of geology is in good agreement with the synthetic model, in terms of both amplitudes and shape of the channels., A method is proposed for the simulation of non-stationary geological patterns, using 2D conditional simulation based on wavelet decomposition of geophysical data and geological model analogues. The method is outlined and then applied to a synthetic channel to generate two models. One represents the real geological model while the other is the model analogue. The results show that wavelet simulation of geology is in good agreement with the synthetic model, in terms of both amplitudes and shape of the channels.

Contains fulltext : 60272.pdf (preprint version ) (Open Access)

Contains fulltext : 32487.pdf (publisher's version ) (Open Access)

Contains fulltext : 60272.pdf (preprint version ) (Open Access)

Contains fulltext : 32487.pdf (publisher's version ) (Open Access)

Contains fulltext : 60272.pdf (preprint version ) (Open Access)

Contains fulltext : 32487.pdf (publisher's version ) (Open Access)

Contains fulltext : 60341.pdf (publisher's version ) (Open Access), We have studied dissociative multiphoton ionization of NO2 by time-resolved velocity map imaging in a two-color pump-probe experiment using the 400 and 266 nm harmonics of a regeneratively amplified titanium-sapphire laser. We observe that most of the ion signal appears as NO+ with similar to0.28 eV peak kinetic energy. Approximately 600 fs period oscillations indicative of wave packet motion are also observed in the NO+ decay. We attribute the signal to two competitive mechanisms. The first involving three-photon 400 nm absorption followed by dissociative ionization of the pumped state by a subsequent 266 nm photon. The second involving one-photon 400 nm absorption to the B-2(2) state of NO2 followed by two-photon dissociative ionization at 266 nm. This interpretation is derived from the observation that the total NO+ ion signal exhibits biexponential decay, 0.72 exp(-t/90+/-10)+0.28 exp(-t/4000+/-400), where t is the 266 nm delay in femtoseconds. The fast decay of the majority of the NO+ signal suggests a direct dissociation via the bending mode of the pumped state. (C) 2004 American Institute of Physics.

Contains fulltext : 60341.pdf (publisher's version ) (Open Access), We have studied dissociative multiphoton ionization of NO2 by time-resolved velocity map imaging in a two-color pump-probe experiment using the 400 and 266 nm harmonics of a regeneratively amplified titanium-sapphire laser. We observe that most of the ion signal appears as NO+ with similar to0.28 eV peak kinetic energy. Approximately 600 fs period oscillations indicative of wave packet motion are also observed in the NO+ decay. We attribute the signal to two competitive mechanisms. The first involving three-photon 400 nm absorption followed by dissociative ionization of the pumped state by a subsequent 266 nm photon. The second involving one-photon 400 nm absorption to the B-2(2) state of NO2 followed by two-photon dissociative ionization at 266 nm. This interpretation is derived from the observation that the total NO+ ion signal exhibits biexponential decay, 0.72 exp(-t/90+/-10)+0.28 exp(-t/4000+/-400), where t is the 266 nm delay in femtoseconds. The fast decay of the majority of the NO+ signal suggests a direct dissociation via the bending mode of the pumped state. (C) 2004 American Institute of Physics.

This article aims to show how science on metallogenic models can modify the idea of numerous interior zones regarded as of little or no potential. Re-interpretation of data considered from a new angle may lead to new discoveries on old deposit sites. For example Sn was classically considered to be concentrated in continental crust and most exploitations follow this model. However the most important Sn concentration in the form of cassiterite is localised in a volcanogenic massive sulphide (Neves Corvo in Portugal) formed on an oceanic plate. In mainland France, mining potential is indisputable for three metals: tungsten, antimony and gold. Reserves calculated in the past need to be reconsidered as more important resources may be found deeper. New types of gold mineralisation associated with granitic intrusions in Sn-W orogenic provinces have emerged since the end of the nineties. Recent studies propose a spatial relationship between mineralisation and the presence of mafic intrusions in depth that constitute the source of metals such as Au and Sb. Buried mafic bodies easily identifiable by geophysics could possibly increase significantly the reserves of these metals., This article aims to show how science on metallogenic models can modify the idea of numerous interior zones regarded as of little or no potential. Re-interpretation of data considered from a new angle may lead to new discoveries on old deposit sites. For example Sn was classically considered to be concentrated in continental crust and most exploitations follow this model. However the most important Sn concentration in the form of cassiterite is localised in a volcanogenic massive sulphide (Neves Corvo in Portugal) formed on an oceanic plate. In mainland France, mining potential is indisputable for three metals: tungsten, antimony and gold. Reserves calculated in the past need to be reconsidered as more important resources may be found deeper. New types of gold mineralisation associated with granitic intrusions in Sn-W orogenic provinces have emerged since the end of the nineties. Recent studies propose a spatial relationship between mineralisation and the presence of mafic intrusions in depth that constitute the source of metals such as Au and Sb. Buried mafic bodies easily identifiable by geophysics could possibly increase significantly the reserves of these metals.

Resource estimation of French deposits are very different since mining operations terminated in the nineties and economics have evolved. Exploitation of the major metals is lower. Resource assessment of studied deposits could be much higher. To evaluate these variations a study was carried out on the tungsten deposit of Fumade in the Montagne Noire. Morphology of skarns is variable and deposits can vary from 100 000s to a few 1 000 tonnes of ore. Prospection in Fumade permitted three economic targets: one surficial target and two buried targets, Fedial and Fumade deep. The first step into re-estimation was integration of available data within the GIS to develop a 3D model of the deposit. Different levels of mineralisation have been distinguished at the Fumade deep target. By cutting the levels into blocks during the refinement of the model, geostatistics allows an estimation of the content of WO3 to an economic value of 0.3%. For all three targets the estimation of resources has risen to 22 000 t of tungsten. More exploration is needed to characterise more clearly the potential of this deposit., Resource estimation of French deposits are very different since mining operations terminated in the nineties and economics have evolved. Exploitation of the major metals is lower. Resource assessment of studied deposits could be much higher. To evaluate these variations a study was carried out on the tungsten deposit of Fumade in the Montagne Noire. Morphology of skarns is variable and deposits can vary from 100 000s to a few 1 000 tonnes of ore. Prospection in Fumade permitted three economic targets: one surficial target and two buried targets, Fedial and Fumade deep. The first step into re-estimation was integration of available data within the GIS to develop a 3D model of the deposit. Different levels of mineralisation have been distinguished at the Fumade deep target. By cutting the levels into blocks during the refinement of the model, geostatistics allows an estimation of the content of WO3 to an economic value of 0.3%. For all three targets the estimation of resources has risen to 22 000 t of tungsten. More exploration is needed to characterise more clearly the potential of this deposit.

Research into favourable areas for the presence of tungsten in the Montagne Noire allows two predictive mapping methods to be illustrated: the classic weights of evidence (WoE) and the more novel cell-based association (CBA) developed at BRGM. It appears that these two methods underline broadly the same areas of interest with, first of all, the mountains of Lacune between Bouissas and Fumade where advanced research demonstrates the strong potential of some deposits (more defined by CBA then WoE) and the dome of Montredon-Labessonnie with the deposits of l'Hom-haut and Moulinas. In the Montagne Noire example, only indicative data and geology were used. The results could be refined by adding supplementary information, geochemistry and geophysics. The Geographic Information Systems (GIS) allows taking into account other constraints implicating conflicts of interest for the use of soil and underground, and environmental constraints that could restrict prospective zones determined by the predictive mapping techniques., Research into favourable areas for the presence of tungsten in the Montagne Noire allows two predictive mapping methods to be illustrated: the classic weights of evidence (WoE) and the more novel cell-based association (CBA) developed at BRGM. It appears that these two methods underline broadly the same areas of interest with, first of all, the mountains of Lacune between Bouissas and Fumade where advanced research demonstrates the strong potential of some deposits (more defined by CBA then WoE) and the dome of Montredon-Labessonnie with the deposits of l'Hom-haut and Moulinas. In the Montagne Noire example, only indicative data and geology were used. The results could be refined by adding supplementary information, geochemistry and geophysics. The Geographic Information Systems (GIS) allows taking into account other constraints implicating conflicts of interest for the use of soil and underground, and environmental constraints that could restrict prospective zones determined by the predictive mapping techniques.

The National Mining Inventory has led to major discoveries, most of which have not been exploited yet, but may be considered as national strategic stock. Prospective areas have not been explored with the old methods allowing for valuable potential. Going deeper led to discovery of deposits such as Mo porphyry type sites at Beauvain in lower Normandy and Breitenbach in the Vosges, as well as real metallogenic provinces such as base and precious metals in St. Georges-sur-Loire, new gold districts in the Pyrenees or the fault of Argentat. Data extracted over the last seventeen years have kept their intrinsic value but access remains complex because of the scale of realised works. Methodically, the Inventory has permitted a large development in the French subsoil but also an update in new methods of prospecting, particularly in multi-element geochemistry, as well as the establishment of an export methodology for Italy, Spain and Latin American countries., The National Mining Inventory has led to major discoveries, most of which have not been exploited yet, but may be considered as national strategic stock. Prospective areas have not been explored with the old methods allowing for valuable potential. Going deeper led to discovery of deposits such as Mo porphyry type sites at Beauvain in lower Normandy and Breitenbach in the Vosges, as well as real metallogenic provinces such as base and precious metals in St. Georges-sur-Loire, new gold districts in the Pyrenees or the fault of Argentat. Data extracted over the last seventeen years have kept their intrinsic value but access remains complex because of the scale of realised works. Methodically, the Inventory has permitted a large development in the French subsoil but also an update in new methods of prospecting, particularly in multi-element geochemistry, as well as the establishment of an export methodology for Italy, Spain and Latin American countries.

The purpose of this series is to present an overall view of mining potential, with the exception of energy resources such as uranium, carbon or hydrocarbons, beginning with principal available data, mostly from the Mining Inventory, and then demonstrating through some examples how the evolution of economics, ideas and new learning methods could increase its value significantly. French mining activity is very old, so an historical evaluation is presented from Prehistory to present days. Development of geographic information systems (GIS) permits predictions to be made which allows targetting areas of interest for exploration or using existing data to determine geological parameters controlling mineralisation on a regional scale or in a geodynamic context. Critical metals are defined as a result of tensions in the supply markets. These critical metals find their applications in high technology areas and are often considered by-products of other metals. There is also a renewed interest in mining potential in Guyana with new approaches in identification of signatures for gold exploration., The purpose of this series is to present an overall view of mining potential, with the exception of energy resources such as uranium, carbon or hydrocarbons, beginning with principal available data, mostly from the Mining Inventory, and then demonstrating through some examples how the evolution of economics, ideas and new learning methods could increase its value significantly. French mining activity is very old, so an historical evaluation is presented from Prehistory to present days. Development of geographic information systems (GIS) permits predictions to be made which allows targetting areas of interest for exploration or using existing data to determine geological parameters controlling mineralisation on a regional scale or in a geodynamic context. Critical metals are defined as a result of tensions in the supply markets. These critical metals find their applications in high technology areas and are often considered by-products of other metals. There is also a renewed interest in mining potential in Guyana with new approaches in identification of signatures for gold exploration.

Leaching of uranium-fertile granites represents a major source of uranium, as uraninite is easily dissolved in oxygenated aqueous solutions, but this phenomenon remains poorly documented for granites at depth. It is proposed that surface-derived oxidised hydrothermal fluids leached uranium from uraninite in the Questembert peraluminous granite of the Armorican massif, NW France, at temperatures greater than 70-160 degrees C. This Variscan synkinematic granite is characterised by development of vertical and permeable C-S (shear-schistosity) structures, which are likely to have facilitated the infiltration of oxidised hydrothermal fluids from the surface, their circulation at depth, and the subsequent fluid-rock interaction in the granite. Published oxygen isotope data shows that it has undergone subsolidus fluid-rock interaction, dated between 312 and 303 Ma by 40-Ar/39-Ar analysis on muscovite. These interactions were responsible for the concomitant decrease of the feldspar 18-O values together with uranium leaching. Mass-balance calculations suggest that this hydrothermal event could have liberated from the Questembert granite several hundred thousand tonnes of uranium, which may have been dispersed in Early Permian intramontane basins and therefore disseminated over large areas. A specific and systematic sampling is required to constrain the proposed model better., Leaching of uranium-fertile granites represents a major source of uranium, as uraninite is easily dissolved in oxygenated aqueous solutions, but this phenomenon remains poorly documented for granites at depth. It is proposed that surface-derived oxidised hydrothermal fluids leached uranium from uraninite in the Questembert peraluminous granite of the Armorican massif, NW France, at temperatures greater than 70-160 degrees C. This Variscan synkinematic granite is characterised by development of vertical and permeable C-S (shear-schistosity) structures, which are likely to have facilitated the infiltration of oxidised hydrothermal fluids from the surface, their circulation at depth, and the subsequent fluid-rock interaction in the granite. Published oxygen isotope data shows that it has undergone subsolidus fluid-rock interaction, dated between 312 and 303 Ma by 40-Ar/39-Ar analysis on muscovite. These interactions were responsible for the concomitant decrease of the feldspar 18-O values together with uranium leaching. Mass-balance calculations suggest that this hydrothermal event could have liberated from the Questembert granite several hundred thousand tonnes of uranium, which may have been dispersed in Early Permian intramontane basins and therefore disseminated over large areas. A specific and systematic sampling is required to constrain the proposed model better.

The classification and general characteristics of rare-metal (Be, Li and other) granites and pegmatites are summarised in a table and a brief illustrated account given of their locations in France as well as those of tin-tungsten veins and skarns: Chavence, Montebras, Beauvoir, Chabannes, Margnac, Chedeville, Villeder, Roha, Kerdu and others. Industrial rocks and minerals associated with granites are also considered with reference to Glomel andalusite and various kaolin quarries that may be visited by collectors of quartz crystals., The classification and general characteristics of rare-metal (Be, Li and other) granites and pegmatites are summarised in a table and a brief illustrated account given of their locations in France as well as those of tin-tungsten veins and skarns: Chavence, Montebras, Beauvoir, Chabannes, Margnac, Chedeville, Villeder, Roha, Kerdu and others. Industrial rocks and minerals associated with granites are also considered with reference to Glomel andalusite and various kaolin quarries that may be visited by collectors of quartz crystals.