scholarly journals Multiple Generations of Wolframite Mineralization in the Echassieres District (Massif Central, France)

Minerals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 637 ◽  
Author(s):  
Loïs Monnier ◽  
Stefano Salvi ◽  
Jérémie Melleton ◽  
Laurent Bailly ◽  
Didier Béziat ◽  
...  
Keyword(s):  
Host Rock ◽  
Ore Deposits ◽  
Variscan Orogeny ◽  
Rare Element ◽  
Massif Central ◽  
Multiple Generations ◽  
Quartz Veins ◽  
Negligible Amount ◽  
High Concentrations ◽  
Tungsten Mineralization

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 responsible for greisen alteration that massively affected the Beauvoir granite. In the La Bosse stockwork, greisen alteration is characterized by hydrothermal topaz that is texturally and chemically distinct from that precipitated during topazification. Supergene alteration responsible for kaolinization of Beauvoir and Colettes granites caused remobilization of a non-negligible amount of tungsten (W) during replacement of wolframite by W-rich goethite in all units of the Echassières district. This model for multiple W mineralizing events is novel and can prove essential in distinguishing potential economic deposits worldwide.

scholarly journals Transport and Evolution of Supercritical Fluids During the Formation of the Erdenet Cu–Mo Deposit, Mongolia

Geosciences ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 201 ◽  
Author(s):  
Geri Agroli ◽  
Atsushi Okamoto ◽  
Masaoki Uno ◽  
Noriyoshi Tsuchiya
Keyword(s):  
Fluid Inclusion ◽  
Supercritical Fluids ◽  
Hydrothermal System ◽  
Host Rock ◽  
Fluid Injection ◽  
Sector Collapse ◽  
Fluid Inclusion Data ◽  
Multiple Generations ◽  
Quartz Veins

Petrological and fluid inclusion data were used to characterize multiple generations of veins within the Erdenet Cu–Mo deposit, Mongolia, and constrain the evolution of fluids within the magmatic–hydrothermal system. Three types of veins are present (from early to late): quartz–molybdenite, quartz–pyrite, and quartz. The host rock was emplaced at temperatures of 700–750 °C, the first quartz was precipitated from magma-derived supercritical fluids at 650–700 °C, quartz–molybdenite and quartz–pyrite veins were formed at ~600 °C, and the quartz veins were precipitated in response to retrograde silica solubility caused by decreasing temperatures at <500 °C. We infer that over-pressured fluid beneath the cupola caused localized fluid injection, or that accumulated stress caused ruptures and earthquakes related to sector collapse; these events disrupted impermeable layers and allowed fluids to percolate through weakened zones.

Tectonic evolution of the Cevennes para-autochthonous domain of the Hercynian French Massif Central and its bearing on ore deposits formation

2001 ◽  
Vol 172 (6) ◽  
pp. 687-696 ◽  
Author(s):  
Michel Faure ◽  
Xavier Charonnat ◽  
Alain Chauvet ◽  
Yan Chen ◽  
Jean-Yves Talbot ◽  
...  
Keyword(s):  
Tectonic Evolution ◽  
Ore Deposits ◽  
French Massif Central ◽  
Magmatic Evolution ◽  
Coal Basin ◽  
Massif Central ◽  
Quartz Veins ◽  
The North ◽  
Gravimetric Data ◽  
Gold Bearing

Abstract The Cevennes area belongs to the para-autochthonous domain of the Hercynian Belt of the French Massif Central. Three lithological series, namely: sandstone-pelite, black micaschist and gneiss-micaschist, are identified. They form an imbrication of five tectonic units which overthrust the unmetamorphosed Viganais Paleozoic units to the south and the gneissic Mamejean Unit to the north. The structural, metamorphic and magmatic evolution of the Cevennes area is characterized by three events, namely: (1) southward shearing coeval to a MP/MT metamorphism dated around 340 Ma; (2) post nappe anatexis (T&lt;750 degrees C, P&gt;5 kb); (3) Namurian (ca 315 Ma) E-W extensional tectonics and plutonism. The structure of the Mt-Lozere-Borne granitic complex is constrained by new AMS and gravimetric data. The plutons are the driving power of the hydrothermal convective circulations responsible for an early deposition of diffuse arsenopyrite in the thermal aureole. Gold bearing sulfides are afterwards concentrated in quartz veins along brittle normal and wrench faults around the granite. Lastly, ore bearing quartz pebbles are sedimented in the Stephanian Ales coal basin.

scholarly journals HERMIONE, EVOLUTION OF ATe-BEARING EPITHERMAL MINERALIZATION, ARGOLIS, HELLAS

2007 ◽  
Vol 40 (2) ◽  
pp. 996 ◽  
Author(s):  
S. Tombros ◽  
K. St. Seymour
Keyword(s):  
Sedimentary Rocks ◽  
Ore Deposits ◽  
Stage I ◽  
Stage Ii ◽  
Quartz Veins ◽  
Minor Contribution ◽  
Epithermal Mineralization ◽  
Ore Bodies ◽  
Calcite Veins ◽  
Sandstone Formation

The Cu-Te-bearing pyrite deposits of Hermione, Argolis are hosted in Miocenic ophiolites. The ophiolites are overlain by a shale-sandstone formation with intercalations of limestones and manganiferous sedimentary rocks. The ore deposits form irregular lenticular or stratiform ore bodies, and veins. These ore bodies are related to volcanic activity in an arc-related rift at the margins of a palaeocontinent. Late N- to NNE-trending, sinistral, milky quartz-pyrite-calcite veins cut the host ophiolites. Alteration haloes of quartz-calcite, albite-sericitechlorite, and chalcedony-epidote-clay minerals are developed in the lavas as concentric shells, or as envelops that parallel the quartz veins. The telluriumbearing mineralization is developed in two successive stages, characterized by the assemblages: pyrite-(pyrrhotite)-magnetite-chalcopyrite-sphalerite (Stage I) and galena-sphalerite-freibergite-marcasite-chalcocite (Stage II), followed by a supergene stage. The cobaltiferous pyrite-chalcopyrite geothermometer defined two ranges of last-equilibration temperatures: 220° to 250°Cfor Stage I, and 120° to 195°Cfor Stage II. The calculated δ18 Ο and SD compositions of the mineralizing fluids, at 200° and 250°C, reflect the dominance of a magmatic component. The calculated δ SH2S fluid values reveal a magmatic source for the sulphur, with minor contribution from submarine sediments, whereas tellurium is proposed to be derived from a mafic-ultramafic source.

Mineral deposits and chalcogen gases

1993 ◽  
Vol 57 (389) ◽  
pp. 599-606 ◽  
Author(s):  
Martin Hale
Keyword(s):  
Ore Deposits ◽  
Anomalous Dispersion ◽  
Mineral Deposits ◽  
Oxidation Reactions ◽  
Sulphide Minerals ◽  
Sulphide Ore ◽  
Dispersion Patterns ◽  
Sulphide Deposits ◽  
High Concentrations ◽  
And Migration

AbstractSulphide minerals and their analogues yield gases as a result of oxidation reactions. Even where sulphide minerals are in contact with mildly reducing groundwaters, S2- ions pass into solution and their dispersion patterns can be detected in soil as acid-released H2S. In more oxidising conditions, the metastable gases COS and CS2 are generated. Anomalous dispersion patterns of COS have been reported in soils above more than ten sulphide ore deposits, many of them concealed beneath transported exotic overburden. High concentrations of CS2 occur in the soils over several of the same deposits and uniquely reflect others. Anomalies of SO2 over sulphide deposits are confined to arid terrains. Certain anomalous dispersion patterns of arsenic and tellurium in soils are attributed to the generation and migration of unspecified gases from the oxidation of arsenide and telluride minerals.

scholarly journals Uraninite, Coffinite and Ningyoite from Vein-Type Uranium Deposits of the Bohemian Massif (Central European Variscan Belt)

Minerals ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 123 ◽  
Author(s):  
Miloš René ◽  
Zdeněk Dolníček ◽  
Jiří Sejkora ◽  
Pavel Škácha ◽  
Vladimír Šrein
Keyword(s):  
Chemical Composition ◽  
Electron Microprobe ◽  
Bohemian Massif ◽  
Uranium Deposit ◽  
Ore Deposits ◽  
Metamorphic Rocks ◽  
Uranium Deposits ◽  
Massif Central ◽  
Vein Type ◽  
Ore District

Uraninite-coffinite vein-type mineralisation with significant predominance of uraninite over coffinite occurs in the Příbram, Jáchymov and Horní Slavkov ore districts and the Potůčky, Zálesí and Předbořice uranium deposits. These uranium deposits are hosted by faults that are mostly developed in low- to high-grade metamorphic rocks of the basement of the Bohemian Massif. Textural features and the chemical composition of uraninite, coffinite and ningyoite were studied using an electron microprobe. Collomorphic uraninite was the only primary uranium mineral in all deposits studied. The uraninites contained variable and elevated concentrations of PbO (1.5 wt %–5.4 wt %), CaO (0.7 wt %–8.3 wt %), and SiO2 (up to 10.0 wt %), whereas the contents of Th, Zr, REE and Y were usually below the detection limits of the electron microprobe. Coffinite usually forms by gradual coffinitization of uraninite in ore deposits and the concentration of CaO was lower than that in uraninites, varying from 0.6 wt % to 6.5 wt %. Coffinite from the Jáchymov ore district was partly enriched in Zr (up to 3.3 wt % ZrO2) and Y (up to 5.5 wt % Y2O3), and from the Potůčky uranium deposit, was distinctly enriched in P (up to 8.8 wt % P2O5), occurring in association with ningyoite. The chemical composition of ningyoite was similar to that from type locality; however, ningyoite from Potůčky was distinctly enriched in REE, containing up to 22.3 wt % REE2O3.

Role of rheological heterogeneities in vein-ore localization

1993 ◽  
Vol 30 (1) ◽  
pp. 113-123 ◽  
Author(s):  
C. Castaing ◽  
D. Cassard ◽  
Y. Gros ◽  
M. Moisy ◽  
J. C. Chabod
Keyword(s):  
Lower Order ◽  
Shear Zones ◽  
Ore Deposits ◽  
Second Order ◽  
Massif Central ◽  
First Order ◽  
Ore Localization ◽  
Ore Minerals ◽  
Partial Destruction

Structural studies of the Saint-Salvy zinc deposit and other Hercynian, veinhosted ore deposits in the French Massif Central and Pyrénées reveal a fourstage evolution of mineralized structures under rheological control: (i) localization of potential mineralized areas, guided by the presence of first-order lithological or structural heterogeneities that caused stress and strain perturbations; (ii) creation of second-order heterogeneities, corresponding to indurated shear zones that acted as rheological discontinuities; (iii) tectonic activation of these second-order heterogeneities, opening voids that allowed circulation of hydrothermal fluids and periodic trapping of ore minerals; (iv) reworking and partial destruction of the mineralized structures, caused by the reactivation of anisotropic surfaces acting as zones of weakness. The interaction between preexisting, first-order heterogeneities and regional shear strain caused instability, which in turn produced second-order and then lower-order heterogeneities. Such progressively smaller heterogeneities induced an increasingly focused, centripetal localization of structural disturbances that enabled hydrothermal fluid channelling. This is the reason that lower-order and late structures preferentially bear economic mineralization.

Galena-Bearing Pyrite Nodules in the Nelway Formation, Salmo, British Columbia

1974 ◽  
Vol 11 (4) ◽  
pp. 495-502 ◽  
Author(s):  
Joseph W. Mills
Keyword(s):  
British Columbia ◽  
Low Temperature ◽  
Host Rock ◽  
Ore Deposits ◽  
Middle Cambrian ◽  
Stratigraphic Position

Pyrite nodules composed of radiating elongate pyrite crystals and including some galena are found in the sparry dolomite matrix of a dolomite breccia within the middle Cambrian Nelway Formation, Salmo map-area, British Columbia.Similar textures, mineralogy, host rock, and stratigraphic position for the nodules and some pyritic zinc-lead ores in northeastern Washington are taken to indicate a common lineage. Favored is an hypothesis calling for the formation of solution-collapse breccias and their filling by dolomite and sulfides precipitated from low temperature solutions. Later deformation and metamorphism erased or concealed the record of these early events in many of the ore deposits.

scholarly journals Tectonic-thermal constraints on the Pb-Zn ore deposits from southeastern French Central Massif by K-Ar and Pb-Pb dating of illite

2020 ◽  
Vol 28 (2) ◽  
pp. 307-321
Author(s):  
Theofilos Toulkeridis ◽  
Nicole Liewig
Keyword(s):  
Western Europe ◽  
Regional Scale ◽  
Isotopic Signature ◽  
Ore Deposits ◽  
Massif Central ◽  
Sedimentary Sequences ◽  
New Information ◽  
Heat Transfers ◽  
Thermal Pulses ◽  
Hydrothermal Activities

Illite-rich size-fractions (<0.2, <0.4, 0.4-1, 0.4-2 and <2 µm) of Cambrian, Permian, Triassic and Jurassic calcschists, shales and dolostones from Pb-Zn ore-district of the southeastern French Massif Central were dated by the K-Ar method, and some by the Pb-Pb method after removal of the Pb external to the illite particles. The combined mineralogical and isotopic determinations show that illitization occurred successively at 285 ± 5, 240 ± 20, 185 ± 15, 140 ± 10 and 105 ± 5 Ma in the district. These tectonic-thermal pulses, which were also reported at a larger regional scale, did not systematically release Pb-mineralizing fluids. The mineralizing episodes seem to have only contributed to contemporaneous illitization and Pb precipitation at 191 ± 41 Ma, by Pb-Pb dating of illite, and at 105 ± 5 Ma in a reactivated fault containing illite mixed with Pb precipitates. The scatter of the Pb-Pb data suggests an incompletely equilibrated Pb isotopic signature when incorporated into the illite structure during crystallization. Pb-isotopic determinations of barren illite-type minerals provide new information about the circulation timing of the mineralizing hydrothermal fluids. The fluid migrations related to recurrent hydrothermal activities occurred within a segment of a continental margin that was located away from main rift zones and far (more than 500 km) from major orogenic zones of Western Europe. The lack of major geodynamic activities near metal deposits needs to hypothesize periodic migrations of hot -fluids in the underneath continental crust. Metals were concentrated at specific places, but not necessarily during each tectonic-thermal pulse recorded by illite. These tectonic-thermal activities confirm local geodynamic re-activations of previously occurring events with effects on local mass and heat transfers in the plutonic basements, as well as in the sedimentary sequences.

scholarly journals Geochemistry of Gold Ores Mined During Celtic Times from the North-Western French Massif Central

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Sandrine Baron ◽  
Călin G. Tămaș ◽  
Marion Rivoal ◽  
Béatrice Cauuet ◽  
Philippe Télouk ◽  
...  
Keyword(s):  
Western Europe ◽  
Gold Mining ◽  
Isotope Geochemistry ◽  
Ore Deposits ◽  
Mining District ◽  
French Massif Central ◽  
Massif Central ◽  
Gold Ores ◽  
The North ◽  
Field Evidence

AbstractThe Celtic culture of Western Europe left magnificent gold objects, such as jewellery and weapons from nobility graves and hoarded coins, as well as field evidence of pre-Roman gold mining and metallurgical workshops that attest to the mining of local ores. This is the case of Central France where many precious metallic ores have been mined throughout the ages from the Prehistoric times onwards. One of the lingering problems in assessing the provenance of gold artefacts and coins is the lack of relevant data on the isotope geochemistry and mineralogy of ore sources. Forty gold ores samples were collected and studied from Limousin (French Massif Central), a very significant gold mining district from the Celtic times. Their Pb isotope compositions clearly show a local dichotomy i.e. two distinct groups of ores, one of Late Proterozoic to Early Paleozoic Pb model age and another associated to Variscan ages and consistent with field relationships, mineralogy and elemental analyses. The use of Cu and Ag isotopes, and their coupling with Pb isotopes, will refine the tracing of future metal provenance studies, but also highlight some metallurgical practices like deliberate metal additions to gold artefact or debasement of gold coins. The newly acquired Pb, Ag, and Cu isotopic data on gold ores improves our understanding of ore deposits geology and provide clarifications on the provenance of Celtic gold from this area and its economic importance.

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