This study considered the geology, mineralogy, geochemistry, formation and evolution of the heavy rare earth element (HREE) mineralised Lofdal alkaline carbonatite complex (LACC), which is located on the Bergville and Lofdal farms northwest of Khorixas, in the Kunene Region of the Republic of Namibia. . Field methods used included mapping, ground and hyperspectral airborne geophysics, and sampling. Analytical techniques used were optical petrography and CL, XRF, ICP-AES, backscattered and secondary electron imaging, electron microprobe, LA-ICP-MS, leaching, as well as carbon and oxygen stable isotope determination. The LACC comprises a swarm of dykes, mainly calcite carbonatite but also dolomite and ankerite carbonatite dykes (classified into five types) and two newly discovered plugs of calcite carbonatite (‘Main’ and ‘Emanya’), with associated dykes and plugs of phonolites, syenites and rare mafic rocks. These all intrude into the Huab Metamorphic Complex basement rocks within a NE-SW shear zone over 30 km long. The main HREE host mineral is xenotime-(Y). It occurs in highly oxidised iron-rich calcite carbonatite dykes mantling and replacing zircon, associated with hematite, thorite and apatite, or associated with monazite-(Ce), synchysite-(Ce), and parisite-(Ce), replacing the fluorocarbonates; it also forms aggregates in ankerite carbonatite. Although xenotime-(Y) occurs throughout the paragenetic sequence, there is much evidence for hydrothermal fluid activity at Lofdal, altering the dykes, and taking xenotime-(Y) into brecciated carbonate veins in albitised country rock (fenite). Radiogenic (Sr, Nd-Sm, U-Pb) and C and O stable isotope studies confirm that the carbonatite, derived from an enriched mantle, is the source of the REE. Mineralisation was contemporaneous with carbonatite emplacement at 765 ±16 Ma. Magmatic fluids >300°C were diluted with cool meteoric fluids. Abundant fluorite and carbonate indicate roles for F- and CO32- in addition to Cl- in REE transport. These ligands form the most stable complexes with HREE and since xenotime is soluble in concentrated alkali halide solutions, they could have preferentially transported and then deposited xenotime. Many of the features of Lofdal are common to other REE-rich carbonatite complexes but the xenotime-(Y) abundance is so far unique. The high amount of fluid activity in shear zones around the dyke swarm and probably a higher proportion of HREE in the original magmas seem to be the main differentiating features.

Der Band fasst den Kenntnisstand zu den Komplexlagerstätten östlich von Pöhla zusammen. Behandelt werden die Nebengesteinsverhältnisse mit der Tektonik, die Vererzungsverhältnisse und Fragen zu den geophysikalischen Arbeiten in der Lagerstätte, zur Hydrogeologie und zur Ingenieurgeologie. Die Untersuchungen zur Entwicklung der Rohstoffbasis zeigen, dass noch beträchtliche Vorräte in der Tiefe verblieben sind, insbesondere an Zinn.

Rare earth elements (REE) are considered as critical and non-substitutable metals for electronics and green technology. A greater diversity of supply is needed and the REE occur in a wide range of REE- and REE-bearing minerals within different ore deposit types. The beneficiation processes for REE ores can vary widely based on their mineralogy and texture. It is, therefore, essential to understand the mineralogical characteristics when designing processing routes. Little research was carried out on this topic until the last few years, apart from bastnäsite, monazite, and xenotime, and most REE minerals in deposits currently under exploration are poorly understood in terms of processing characteristics. This geometallurgical study brings together the results of process mineralogy and minerals processing to recover synchysite-(Ce) and apatite from the carbonatite at Songwe Hill, Malawi. This deposit is unusual because it is a potential carbonatite source of both LREE and HREE. Results from previous flowsheet development studies on this deposit suggest that flotation is the most promising processing route and therefore this study concentrated on testing this hypothesis. It sought to understand the mineralogy better in order to predict processing response and carried out a series of flotation experiments to improve the processing efficiency. It also investigated the fundamental magnetic properties of the rare earth fluorcarbonate minerals (including synchysite) and established for the first time that there is a systematic variation in their properties that can be applied to minerals processing. Eight samples of REE carbonatite drill core, crushed to 1700 μm, and a composite sample ground to 53 μm and 38 μm were used throughout this research. Automated mineralogy (QEMSCAN®) was applied to determine the mineralogical characteristics of the ore deposit. This utilised a novel species identification protocol (SIP) for REE minerals in carbonatites, which was validated by electron microscopy (SEM-EDS), and electron probe microanalysis (EPMA). The principal REE minerals at Songwe are the REE fluorcarbonates, synchysite-(Ce) and also parisite-(Ce). These are challenging minerals for automated mineralogical techniques owing to their chemical similarity and common occurrence either as bladed (needle-like) crystals, which is the main textural type at Songwe Hill, or as syntaxial intergrowths. However, using the SIP developed in this study, the QEMSCAN® can distinguish between these minerals based on the Ca content and can also recognise syntaxial intergrowths on a scale of about > 20 μm. The Songwe Hill carbonatite hosts about 6 wt% to 10 wt% of REE- and REE-bearing minerals. Apatite hosts the more valuable HREE in addition to P2O5, followed by synchysite-(Ce)/parisite-(Ce) (mainly synchysite-(Ce)), and minor florencite-(Ce), which host the LREE. These minerals are commonly associated with the predominant gangue minerals, ankerite and calcite, and, to a lesser extent Fe- Ox/CO3 and K-feldspar, strontianite and baryte. Fundamental magnetic properties of pure REE fluorcarbonate single crystal minerals using a vibrating sample magnetometer (VSM) were determined. The magnetic susceptibility is highly dependent on the mineral composition. It is positive (paramagnetic) for bastnäsite-(Ce) and gradually decreases as the amount of Ca increases in parisite-(Ce), becoming negative (diamagnetic) for the Ca-rich member of the series, röntgenite. Synchysite-(Ce) in this deposit was experimentally determined by magnetic separation and behaved as a diamagnetic mineral. This can be explained by the layered structure common to the REE fluorcarbonate series minerals. Selected laboratory scale mineral processing experiments including magnetic separation and froth flotation were performed. Pre-concentration tests by magnetic separation showed a recovery of 84% for P2O5, 80% for Y2O3, and 76% for Ce2O3 in the non-magnetic product, with gangue minerals rejection of about 49% for ankerite and 48% for Fe-Ox/CO3 to the magnetic product. Apatite and synchysite-(Ce) loss to the magnetic product is mainly the result of their association with the paramagnetic minerals i.e. ankerite and Fe-Ox/CO3 as indicated by automated mineralogy. A spectrophotometer was utilised to measure the solubility of the organic chemical reagents including fatty acids and lignin sulphonate in different alkaline solutions and to determine the appropriate operating parameters for bench flotation tests. The results indicated that the solubility of fatty acids increased with increasing the pH value from 8.5 to 10.5, while the opposite was observed for lignin sulphonate. 35 bench-scale froth flotation tests under a wide range of chemical and operating conditions including pH modifiers and dosages, soluble and insoluble collectors, depressants, temperature, and conditioning time were performed. The results demonstrated that fatty acids and lignin sulphonate are sensitive to changes in pH, conditioning time, and temperature. These factors significantly affected flotation efficiency. A recovery of 86% for P2O5 and 74% for both of Y2O3 and Ce2O3 with TREO upgrading from 1.6 wt% to 3.8 wt% at a mass pull of 31% were achieved under a constant pulp pH of 9.5, elevated temperature, and long conditioning time. This study suggests that combining magnetic separation and froth flotation techniques to pre-concentrate and upgrade the REE- and REE-bearing minerals, should be considered further to minimise the cost of the chemical reagents used in froth flotation and gangue leaching.

Microarrays on gold have been used to develop new methodologies for biocatalysis and proteomic applications. The technology applies the logic of solid phase supported chemistry using self-assembled monolayers (SAMs) on a gold chip. The advantages of this technology are: i) an easy to handle platform, ii) parallel screening (64 reactions at once), iii) microliter scale reactions (1µL per sample), iv the use of mild conditions (buffers and t=37 °C), v) the absence of purification steps (only chip washing is required), vi) quick and accurate analysis by MALDI ToF MS.The metallopeptidase thermolysin was studied in peptide-coupling reactions to profile reactivity and specificity (Chapter 2). Reactivity was further investigated in transpeptidation reactions. Comparing the serine peptidase chymotrypsin with the zinc dependent thermolysin, it was found that transpeptidations proceed via N-transacylation reactions independent of a specific enzymatic catalytic mechanism (Chapter 3). These transacylations may be exploited for modifications of biocompatible and selective surfaces in ‘bottom-up’ bionanofabrication technologies. Selected peptidases with different catalytic mechanism were also arrayed to investigate polymerisation ability of dipeptides (Chapter 4). It was shown that oligomerisation can be obtained under mild conditions and a set of peptides was synthesised. Chapter 5 describes a new chemical methodology by which crude tryptic peptide digests can be trapped on chip and analysed by MALDI ToF MS without further purification steps. This dramatically improves time and cost efficiency.Finally, a new stepwise native chemical ligation methodology is proposed for amino acids, and peptides containing N-terminal cysteine residues (Chapter 6).

Strongly correlated metals are known to give rise to a variety of exotic states. In particular, if a system is tuned towards a quantum critical point, new ordered phases may arise. Sr₃Ru₂O₇ is a quasi-two dimensional metal in which field-tuned quantum criticality has been observed. In very pure single crystals of this material, a phase with unusual transport properties forms in the vicinity of its quantum critical point. Upon the application of a small in-plane field, electrical resistivity becomes anisotropic, a phenomenon which has led to the naming of this phase as an `electron nematic'. The subject of this thesis is a study of the electrical transport in high purity crystals of Sr₃Ru₂O₇. We modified an adiabatic demagnetisation refrigerator to create the conditions by which the entire temperature-field phase diagram can be explored. In particular, this allowed us to access the crossover between the low-temperature Fermi liquid and the quantum critical region. We also installed a triple axis `vector magnet' with which the applied magnetic field vector can be continuously rotated within the anisotropic phase. We conclude that the low- and high-field Fermi liquid properties have a complex dependence on magnetic field and temperature, but that a simple multiple band model can account for some of these effects, and reconcile the measured specific heat, dHvA quasiparticle masses and transport co-efficients. At high temperatures, we observe similarities between the apparent resistive scattering rate at critical tuning and those observed in other quantum critical systems and in elemental metals. Finally, the anisotropic phase measurements confirm previous reports and demonstrate behaviour consistent with an Ising-nematic, with the anisotropy aligned along either of the principal crystal axes. Our observations are consistent with the presence of a large number of domains within the anisotropic phase, and conclude that scattering from domain walls is likely to contribute strongly to the large measured anisotropy.

Le tungstène est défini comme “ressource minérale critique” par la Commission Européenne. La province de Jiangxi, située au sud-est de la Chine, dans le bloc Cathaysia, représente 90 % des réserves en tungstène chinoises. Ce travail est basé sur l’étude des gisements hydrothermaux à W-Sn de Maoping et Piaotang, tous deux situés dans le district de Dayu (sud de la province de Jiangxi). Cette thèse a permis de (i) développer des traceurs pétrographiques et minéralogiques de processus minéralisateurs à travers des études paragénétiques détaillées et la géochimie des micas lithinifères et donc d’apporter un modèle impliquant des fluides multiples se chevauchant dans le temps et associés à plusieurs épisodes distincts de mise en place de minéralisations en métaux rares, (ii) définir par l’étude d’inclusions fluides deux processus fluides comme seul responsables de la précipitation de la minéralisation dans ces gisements « géants » : la différenciation magmatique de granites peralumineux et des processus de mélange, et (iii) de développer des approches de datation associés à ces systèmes montrant que la minéralisation en tungstène se met en place aux alentours de 160 Ma, antérieurement à la plupart des âges obtenus sur les minéraux de gangue datés dans cette zone et défini alors une remise à zéro majeure des systèmes isotopiques par de multiples circulations fluides entre 150 et 155 Ma. De plus, les stades post-minéralisations ont pu être définis pour la première fois et révèlent l’implication de magmatisme peralcalin impliqué dans la précipitation de minéralisations à Nb-Ta-Y-REE aux alentours de 130 Ma. A la lumière de cette observation, cette thèse s’est aussi tournée vers le développement de méthodes de datation in situ sur columbo-tantalite / Tungsten is defined as a “critical mineral resource” by the European Commission. The Jiangxi province, located in the southeastern part of China, in the Cathaysia block, represents 90% of the Chinese tungsten resources. This work is based on the study of the Maoping and Piaotang W-Sn hydrothermal deposits located in the Dayu district (southern Jiangxi). This thesis managed to (i) develop mineralogical and petrological tracers of ore-forming processes through detailed paragenetic sequences and geochemistry of Li-micas and shows that multiple overlapping fluids associated to several and distinct rare-metal mineralizing stages, (ii) distinguish by fluid inclusions studies that peraluminous magmatic differentiation and mixing processes are the only prequisite for the formation of these giant deposits, and (iii) develop dating approaches associated to these systems to demonstrate that the W mineralization formed at ca. 160 Ma, prior to most ages obtained on gangue minerals in the area, defining a major resetting of isotopic systems due to multiple fluid circulations around 150-155 Ma. Moreover, post-“silicate-oxide” stages have been defined for the first time and reveal the implication of peralkaline new fluid sources involved in the precipitation of Nb-Ta-Y-REE minerals at ca. 130 Ma. In the light of these results, this thesis gives new developments for in situ direct dating of ore-bearing minerals such as columbo-tantalite

In the UK, large quantities of intermediate level waste pose complex radiological remediation challenges. Chemical understanding of uranium in these Mg-rich sludges is vital. Previous studies have examined uranium uptake by calcium carbonate minerals (calcite and aragonite) under conditions pertinent to both natural and anthropogenically perturbed systems. However, research on uranyl uptake by magnesium-rich minerals such as magnesite [MgCO3], brucite [Mg(OH)2], nesquehonite [MgCO3·3H2O] and hydromagnesite-[Mg5(CO3)4(OH)2·4H2O] has not, to the best of our knowledge, been previously conducted. Such experiments will improve our understanding of the mobility of uranium and other actinides in natural lithologies such as dolomitic limestones or mafic igneous emplacements, as well as provide key information applicable to nuclear waste repository strategies involving Mg-rich phases. By two EXAFS techniques, we determined: (1) where uranyl (UO22+) is adsorbed, and (2) how uranyl is attached to the mineral surface. Therefore powder experiments of U(VI) were performed with magnesite, brucite, nesquehonite and hydromagnesite. The second experiment (GIXAFS) consisted of single crystals of magnesite (10.4) and brucite (0001). The powders were reacted in solution pH ~8.5 with U(VI)nitrate for 48 hrs. under ambient PCO2 = -3.5. The single crystals were reacted under ambient and reduced PCO2 ~ -4.5 for 48 hrs. with concentrations of U(VI)chlroride above (500; 50 ppm) and below (5 ppm) solubility of schoepite [UO2(OH)2·H2O]. The GIXAFS measurements were made at χ = 0˚ and χ = 90˚ relative to the synchrotron beam polarisation to uequivocally determine the adsorbate structures. Kd values for Mg-carbonate phases were comparable to or exceeded those published for calcium carbonates. GIXAFS results clearly showed polarisation for both ambient and reduced PCO2. XANES results showed uranyl is oriented with the axial oxygens perpendicular to the mineral surface. This implies, using also X-ray reflectivity and diffuse scatter, local hydrated bayleyite [Mg2(UO2)(CO3)3∙18H2O] and possible rutherfordine-like [UO2CO3] regions, which will be useful to predict uranium behaviour in various remediation processes.

Ce travail présente une étude multi-échelle des relations entre altération et minéralisation en uranium le long de la bordure Sud Est du bassin Méso-Protérozoïque du Thelon, au Nunavut, Canada. Les altérations associées aux minéralisations sont développées dans une série volcano-sédimentaire Archéenne appartenant à la ceinture de roche verte du Woodburn Lake Group (WLG). Elles s'expriment majoritairement par un assemblage à illite (polytypes 1Mcis & 1Mtrans) ± sudoite ± hématite et phosphates sulfates d'aluminium hydratés (APS). De plus des composés carbonés, cogénétiques des minéralisations, ont été identifiés comme des produits des réactions hydrothermales. La signature de l'altération, fortement guidées par les structures Est-Ouest du corridor de Kiggavik-Andrew Lake, apparaît alors très similaire à celle rencontrée dans les roches de socles des parties profondes des autres gisements d'uranium de type discordance du bassin d'Athabasca (Canada) ou de la Kombolgie (Australie). L'étude des marqueurs minéralogiques tels que les APS ont permis de mettre en évidence les transferts élémentaires au cours des processus métallogéniques et de distinguer les caractéristiques pétrographique et chimiques des processus diagénétiques et hydrothermaux. Enfin la compréhension fine de l'expression de marqueurs cristallographiques issus de l'irradiation naturelle des minéraux argileux donne de nouvelles pistes pour le traçage et la compréhension des circulations des radios-éléments à l'échelle géologique. / This work presents a multi-scale study of the relationships between alteration and uranium mineralization along the South Eastern margin of the Meso-Proterozoic Thelon Basin, Nunavut, Canada. The ore associated alterations are hosted in an Archean volcano-sedimentary sequence belonging to the Woodburn Lake Group (WLG). Their main expression is a mineral assemblage composed of dominant illite (1Mcis & 1Mtrans polytypes) together with sudoite ± hematite and aluminum phosphate sulfate minerals. Moreover carbonaceous materials cogenetic with the uranium mineralization have been identified as potential indicators of the hydrothermal conditions. At a regional scale, alteration is strongly controlled via East-West faults forming the main frame of the Kiggavik-Andrew Lake structural trend. Then from the regional to the mineral scale, alterations signatures at Kiggavik are similar to the ones described in deep basement rocks of unconformity type uranium deposits in both Athabasca (Canada) and Kombolgie (Australia) Paleoproterozoic basins. In addition mineralogical markers studies (APS minerals) lead to the distinction between hydrothermal and diagenetic processes as well as elemental transfers during fluid rock interaction. Finally, detailed studies on radiation induced defects on illite revealed new ways to tracing and better understanding the radio elements mobility in such deep seated natural systems.

Les gisements à Sn-W de type veine et greisen sont des systèmes magmatiques-hydrothermaux dont l’exploitation fournit une part importante de la production mondiale de tungstène et qui représentent également une source importante d’étain. La formation de ces gisements résulte d’un continuum de processus magmatiques et hydrothermaux et implique un transport efficace et la focalisation des fluides minéralisateurs. Cette étude vise àaméliorer la compréhension des processus hydrodynamiques et géologiques impliqués lors du transport et du dépôt de métaux conduisant à la formation de ces gisements. Nous avons réalisé une étude pluridisciplinaire combinant (i) travail de terrain (étude géologique et structurale), (ii) reconstruction des paléo-circulations hydrothermales via l’analyse texturale des bandes de croissance des tourmalines, (iii) détermination expérimentale des changements de perméabilité induits par la greisenisation et (iv) modélisation numérique des écoulements péri-granitiques prenant en compte l’évolution de la perméabilité dynamique lors des interactions fluide-roche. Cette méthodologie a été appliquée au cas du gisement W-Sn-(Cu) de Panasqueira, qui constitue un site de référence pour étudier les processus magmatiques e thydrothermaux conduisant à la formation de gisements à Sn-W de classe mondiale. Les résultats obtenus démontrent que l’expulsion des fluides magmatiques minéralisés a déclenché la greisenisation des parties apicales (coupoles etapex) de l’intrusion granitique, entraînant la création de porosité (~ 8,5%) qui améliore significativement la perméabilité(de 10-20 à 10-17 m²) au sein du greisen massif composant le toit de l’intrusion. Le développement de ce niveau perméable constitue un drain important favorisant l'expulsion et la focalisation des fluides magmatiques minéralisateurs exsolvés lors de la cristallisation du granite sous-jacent. Cette focalisation des décharges hydrothermales (i) améliore significativement le transport des métaux, et (ii) favorise l'établissement de conditions de pression de fluide élevées qui couplées aux contraintes régionales compressives causent l'ouverture des veines minéralisées au toit de l’intrusion.Cette étude souligne l’importance des rétrocontrôles entre perméabilité dynamique et altération hydrothermale. Ces derniers constituent des mécanismes majeurs permettant d’améliorer significativement la circulation des fluides minéralisateurs et donc la formation de gisements hydrothermaux de grandes tailles / The vein and greisen Sn-W deposits are magmatic-hydrothermal systems that provide an important part of theworld W production and represent an important source of Sn. The formation of these deposits involves continuum ofmagmatic-hydrothermal processes and implies the transfer and the focusing of a large amount of mineralizing fluids. Thisstudy aims to improve understanding of hydrodynamic and geological processes involved during the transport and thedeposition of metals leading to the formation of these deposits. We have performed a complete study combining (i) fieldworks (geological and structural studies), (ii) fluid flow reconstruction via the textural analysis of tourmaline growth bands,(iii) experimental determination of permeability changes during greisenization, and (iv) numerical modeling of peri-graniticfluid flow accounting for magmatic fluid production and dynamic permeability related to fluid-rock interactions. Thismethodology was applied in the case of the world-class W-Sn-(Cu) Panasqueira deposit, which represents a referencesite to study magmatic-hydrothermal processes leading to the formation of large vein and greisen deposit. Our resultsdemonstrate that the releasing and the expulsion of ore-bearing magmatic fluids triggered greisenization of the apicalpart of granite intrusion, which caused generation of porosity (~8.5%) and therefore a significant increase of permeability(from 10-20 to 10-17 m²) in massive greisen composing the granite’s roof. The development of this permeable pathwayconstitutes an important drain promoting the expulsion and the focusing of magmatic fluids produced during thecrystallization of the underlying granite. This enhancement of magmatic fluids expulsion (i) promotes significantly fluidflux and transfer of metals, and (ii) the establishment of high fluid pressure conditions, which coupled with the regionalcompressive crustal regime, triggered the opening of mineralized veins above the granite roof. Finally, this studyemphasizes that reactive hydrothermal fluids are able to generate their own pathways in initially impermeable rocks. Thisprocess represents an important mechanism to enhance fluid flow and promote the formation of large hydrothermaldeposits.

Cette thèse est centrée sur la ceinture orogénique Attico-Cycladique formée durant l'orogénèse Alpine. Par une approche multi-méthodes et multi-échelles combinant géologie structurale, pétrographie, thermobarométrie des assemblages minéraux, géochimie élémentaire et isotopique, et données PVTX des inclusions fluides associées, ce travail vise à caractériser et comprendre les relations entre circulations fluides, interactions fluides/roches, déformation, et mobilisation-transport-dépôt des métaux. Les marbres et schistes de la péninsule du Lavrion et de l'île d'Eubée témoignent d'une évolution orogénique complexe marquée par une phase d'enfouissement à l'Eocène suivie par deux phases d'exhumation successives syn-et post-orogéniques. Les minéralisations de type Cu-Pb-Zn-Fe-Ag de la région du Lavrion sont synchrones de l’activation du détachement post-orogénique et de la mise en place de plutons de granodiorite. Leurs positions structurales témoignent d’un piégeage depuis un régime de déformation ductile jusqu'à fragile. Les minéralisations mises en place durant le régime de déformation ductile à ductile-fragile (skarn et remplacement de carbonate) sont associées à la décarbonatation des niveaux de marbres et à la circulation des fluides magmatiques. L'exhumation progressive de la racine orogénique se traduit par la transition des roches depuis une déformation ductile vers un régime fragile associé à l’ouverture du système aux fluides de surface et notamment aux fluides météoriques. Cette circulation est responsable d’une remobilisation des métaux des minéralisations primaires permettant alors une seconde phase de précipitation dans un régime cassant (veines épithermales) / This thesis is focused on the Attico-Cycladic orogenic wedge formed during the Alpine orogeny. From a multi-method and multi-scale approach using structural geology, petrography, mineral thermobarometry, element and isotope geochemistry, and PVTX data of associated fluid inclusions, this study deciphers the relationships between fluid circulation, fluid-rock interactions and mobilisation-transport-deposits of metals. Marbles and schists from the Evia Island and the Lavrion peninsula testify to a complex orogenic history marked by an Eocene burial phase followed by syn- and post-orogenic exhumation. Cu-Pb-Zn-Fe-Ag mineralisations from the Lavrion area are synchronous with the formation of the low-angle post-orogenic detachment and the emplacement of granodioritic magmas. The structural position of the deposits attests of an emplacement during ductile to brittle deformation conditions. Deposits associated with ductile to ductile-brittle deformation (skarn, carbonate replacement) are related to a marble decarbonation and magmatic fluid circulation. The progressive exhumation of the orogenic wedge allows the transition toward brittle conditions and opens the system to surficial meteoritic fluids. This meteoritic fluid circulation is responsible to remobilisation of metals from primary deposits allowing thus a second phase of deposition in a pure brittle deformation (epithermal veins)