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.

Isotopic (S, Sr, Sm/Nd, D, Pb) evidences for multiple sources in the Early Jurassic Chaillac F-Ba ore deposit (Indre, France)

2009 ◽  
Vol 180 (2) ◽  
pp. 83-94 ◽  
Author(s):  
Stanislas Sizaret ◽  
Eric Marcoux ◽  
Alice Boyce ◽  
Michel Jebrak ◽  
Roos Stevenson ◽  
...  
Keyword(s):  
Fluid Inclusions ◽  
Hydrothermal Fluid ◽  
Western Europe ◽  
Isotopic Ratio ◽  
Deposition Process ◽  
Ore Deposits ◽  
French Massif Central ◽  
Multiple Sources ◽  
Massif Central ◽  
Ore Deposit

AbstractDuring the earliest Jurassic, a widespread hydrothermal event occurred in western Europe producing large veins and stratiform F-Ba-Pb-Zn ore deposits. Previous work argued about genetic processes involving circulation of mineralising brines. Two main alternative genetic models are proposed. The first one proposes a convection of brines through the crust to produce ore deposits, the second an early infiltration of brine in the basement followed by expulsion during Mesozoic extension. In the northern French Massif Central, new data on the F-Ba Chaillac deposit suggest that the genesis of these mineralising brines requires a new discussion.Located in the northern French Massif Central, the Chaillac barite and fluorite ore deposit is an exceptional site where a stratiform deposit is rooted onto a vein. The ore deposition is split in two stages: 1) precipitation of green and purple fluorite within the vein (Fg-p stage), with associated fluid inclusions indicating 135°C for deposition from a low salinity fluid, and 2) yellow fluorite and barite stage (Fy-Ba) filling the vein and forming the stratiform deposit. Fluid inclusions depict a mineralising brine at 110°C. The 87Sr/86Sr and 143Nd/144Nd isotopic ratios measured in the fluorite are compared to those of French Massif Central rocks. The ratios in green and purple fluorite are similar to those of monzogranite and granodiorite of the basement; those measured in yellow fluorite involve the granulites and other metamorphic rocks of the basement. Measurements of the Sr isotopic ratio and δ34SCDT in barite and δD in fluorite fluid inclusions suggest a deposition process by the mixing of a hydrothermal fluid with meteoric water.At the scale of the northern Massif Central district, the successive hydrothermal fluid salinities are highly contrasted as in Chaillac deposit. We propose that the two types of hydrothermal fluids have been produced by the boiling of a single fluid at depth.

Application of high resolution airborne geophysics to epithermal gold exploration in Northeast Queensland and Coromandel, New Zealand

1989 ◽  
Vol 20 (2) ◽  
pp. 99 ◽  
Author(s):  
S.S. Webster ◽  
R.W. Henley
Keyword(s):  
High Resolution ◽  
Regional Scale ◽  
Cost Effective ◽  
Gold Deposits ◽  
Ore Deposits ◽  
Magnetic Data ◽  
Mapping Technique ◽  
Epithermal Gold ◽  
Airborne Geophysics ◽  
Airborne Geophysical Data

High resolution airborne geophysical data over broad areas have been found to optimize exploration for epithermal gold deposits in differing geological environments.Genetic exploration models may be tested in favourable sites by the recognition of geophysical signatures. These signatures reflect structural, lithological and alteration patterns arising from controls on ore deposits and can be applied at regional or detailed scales, using the same data set.At regional scale (e.g. 1:100,000) the magnetic data reflect the regional tectonics and divide the area into domains for the application of appropriate genetic models. At prospect scale (e.g. 1:25,000) the radiometric data allow the extrapolation of poorly outcropping geology to provide a cost-effective mapping technique. The magnetic data can be used to supplement this interpretation or can be used to target deeper sources for direct investigation by drilling.

scholarly journals Abundance and Sources of Atmospheric Halocarbons in the Eastern Mediterranean

2017 ◽  
Author(s):  
Fabian Schoenenberger ◽  
Stephan Henne ◽  
Matthias Hill ◽  
Martin K. Vollmer ◽  
Giorgos Kouvarakis ◽  
...  
Keyword(s):  
Western Europe ◽  
Atmospheric Transport ◽  
Eastern Mediterranean ◽  
Stratospheric Ozone ◽  
Regional Scale ◽  
Top Down ◽  
Inversion Domain ◽  
Hfc 134A ◽  
Wide Range ◽  
Hfc 152A

Abstract. A wide range of anthropogenic halocarbons is released to the atmosphere, contributing to stratospheric ozone depletion and global warming. Using measurements of atmospheric abundances for the estimation of halocarbon emissions on the global and regional scale has become an important top-down tool for emission validation in the recent past, but many populated and developing areas of the world are only poorly covered by the existing atmospheric halocarbon measurement network. Here we present six months of continuous halocarbon observations from Finokalia on the island of Crete in the Eastern Mediterranean. The gases measured are the hydrofluorocarbons (HFCs), HFC-134a (CH2FCF3), HFC-125 (CHF2CF3), HFC-152a (CH3CHF2) and HFC-143a (CH3CF3), and the hydrochlorofluorocarbons (HCFCs), HCFC-22 (CHClF2) and HCFC-142b (CH3CClF2). The Eastern Mediterranean is home to 250 million inhabitants, consisting of a number of developed and developing countries, for which different emission regulations exist under the Kyoto and Montreal Protocols. Regional emissions of halocarbons were estimated with Lagrangian atmospheric transport simulations and a Bayesian inverse modelling system, using measurements at Finokalia in conjunction with those from Advanced Global Atmospheric Gases Experiment (AGAGE) sites at Mace Head (Ireland), Jungfraujoch (Switzerland) and Monte Cimone (Italy). Measured peak mole fractions at Finokalia showed generally smaller amplitudes for HFCs than at the European AGAGE sites, except periodic peaks of HFC-152a, indicating strong upwind sources. Higher peak mole fractions were observed for HCFCs, suggesting continued emissions from nearby developing regions such as Egypt and the Middle East. For 2013, the Eastern Mediterranean inverse emission estimates for the four analysed HFCs and the two HCFCs were 14.7 (6.7–23.3) Tg CO2eq yr-1 and 9.7 (4.3–15.7) Tg CO2eq yr-1, respectively. These emissions contributed 17.3 % (7.9–27.4 %) and 53 % (23.5–86%) to the total inversion domain, which covers the Eastern Mediterranean as well as Central and Western Europe. Greek bottom-up HFC emissions reported to the UNFCCC were much smaller than our top-down estimates, whereas for Turkey our estimates agreed with UNFCCC-reported values for HFC-125 and HFC-143a, but were much and slightly smaller for HFC-134a and HFC-152a, respectively. Sensitivity estimates suggest an improvement of the a posteriori emission estimates, i.e. a reduction of the uncertainties by 40–80 %, compared to an inversion using only the existing Central European AGAGE observations.

scholarly journals A modelling study of photochemical regimes over Europe: robustness and variability

2009 ◽  
Vol 9 (1) ◽  
pp. 1521-1560 ◽  
Author(s):  
M. Beekmann ◽  
R. Vautard
Keyword(s):  
Model Uncertainty ◽  
Mediterranean Basin ◽  
Western Europe ◽  
Regional Scale ◽  
Relative Sensitivity ◽  
Time Variability ◽  
Nox Emissions ◽  
The Mediterranean ◽  
North Western ◽  
The Mediterranean Basin

Abstract. The variability of the relative sensitivity to volatile organic compounds (VOC) or NOx emissions, the chemical regime, over Europe during summers 2001 to 2003 is simulated with a regional scale transport-chemistry model. The robustness of chemical regimes is shown. A VOC sensitive regime over North-Western Europe and a mainly NOx sensitive regime over the Mediterranean basin and Eastern Europe are found, confirming earlier published results. The chemical regime time variability, its robustness to several environmental factors (seasonality, interannual variability) and to model uncertainty are thoroughly analysed. The chemical regime spatial structure only slightly depends on the ozone target considered (daily ozone maximum or AOT40, SOMO35, ...). Differences between particular years and summer months are weak. Day to day variability is significant but does not change the occurrence of one or another chemical regime over North-Western Europe and the Mediterranean basin. Expected decreases in anthropogenic NOx emissions over Europe since the last and for the next few decades have shifted and will shift chemical regimes to more NOx sensitive. The predictive and explanatory use of chemical regime indicator species is also investigated. For all cases but near ship tracks over the Mediterranean basin, the spatial pattern of chemical regimes appears to be robust with respect to model uncertainty.

scholarly journals Conditions of ore formation of the Aunikskoye F-Be deposit (Western Transbaikal)

2019 ◽  
Vol 61 (1) ◽  
pp. 18-38
Author(s):  
L. B. Damdinova ◽  
B. B. Damdinov ◽  
M. O. Rampilov ◽  
S. V. Kanakin
Keyword(s):  
Pressure Range ◽  
Deposition Process ◽  
Isotopic Signature ◽  
Ore Deposits ◽  
Ore Formation ◽  
Ore Deposit ◽  
Temperature Range ◽  
Main Factors ◽  
Low Solubility

This study examines the compositions of the ore and the ore formation solutions, conditions of formation, and sources of Be mineralization using the Aunikskoye F-Be deposit, which is an integral part of the Western Transbaikal beryllium-bearing provinces, as a representative example. Further, the main factors responsible for the formation of beryllium mineralization were evaluated. The ore deposits are presented by the feldsparic–fluorspar–phenacite–bertrandite metasomatites formed in the carboniferous limestones during their metasomatic alternation with hydrothermal solutions by introducing F, Be, and other associated elements. The formation of early phenacite–fluorspar association occurred in high-fluorite СО2-containing solutions of elevated alkalinity with a salinity of ~10.5%–12% wt eq. NaCl in a temperature range of ~ 370–260 °С at pressures ranging from 1873 to 1248 bar. More recent fluorite and bertrandite deposits were formed by solutions with a salinity of 6.4%–7.7% wt eq. NaCl in a temperature range of ~156 °C–110 °C and a pressure range of 639–427 bar. The examination of the isotopic signature of the ore association minerals confirmed the apocarbonate nature of the main ore deposit and allowed the determination of the magmatogene nature of the ore-forming paleothermal springs, which are the source of subalkaline leucogranites. The primary factors that influenced the formation of the F-Be ore included the reduction of the F activity in solutions because of the binding of Ca and F in fluorite as well as because of the decrease in temperature during the ore deposition process. The elevated alkalinity of the ore-formation solutions resulted in the low solubility of the Be complexes, which caused a relatively low Be content in the ore and a relatively small amount of mineralization in the deposit.

Geoconservation

2005 ◽  
Author(s):  
Gerard Gonggrijp
Keyword(s):  
The Netherlands ◽  
Western Europe ◽  
Physical Geography ◽  
Policy And Practice ◽  
Human Welfare ◽  
Massif Central ◽  
Landscape Preservation ◽  
Visual Landscape ◽  
The Rich ◽  
North Western

The detailed descriptions of the physical geography in the previous chapters show the rich geodiversity of north-western Europe, reflected in its many geological landscapes (landscapes without the biological and cultural ‘furnishing’). The various geological forces, acting in time and space have created the foundation for this richness. The landscape’s framework has mainly been designed by such endogenic processes as tectonics, orogenesis, and volcanism, while its details have been sculptured by such exogenic processes as weathering, gravity, and glacial-, fluvial-, aeolian-, and marine activities. These modelling processes resulted in a very diverse geology, geomorphology, and pedology. The long scientific tradition and the rich geodiversity made north-western Europe one of the classical areas for geological research. It therefore includes many of the international case studies in earth sciences and became the cradle of numerous international reference localities such as Emsian (Rheinland-Pfalz, Germany), Dinantian (Ardennes, Belgium), Aptian (Provence, France), Danian—Dane is Latin for Denmark (Stevens Klint), Tiglian (Middle Limburg, The Netherlands), Eemian (river in western Netherlands), etc. The chronological division of glacial and fluvioglacial features is primarily based on type localities (villages, rivers, etc.) in Denmark, northern and southern Germany, and The Netherlands. Moreover, a multitude of Tertiary and Pre-Tertiary stages of the standard geological timetable have been named after type localities of geological and prehistoric sites in France. Geological landscapes such as the Maare system of the Eifel, the volcanoes on the Massif Central (France), the Saalian and Weichselian ice-pushed ridges of Germany, The Netherlands, and Denmark as well as the impressive dunes along the coast from France to the northernmost tip of Denmark have been subjects of detailed research. These geological landscapes form a unique geological patchwork. The activities of humans, especially in the last century, have damaged or destroyed many of these landscapes and sites of geological interest. However, selected sites and areas representing the geogenesis of the earth should be preserved for the benefit of science, education, and human welfare. In all European countries attention is given to landscape preservation; however, policy and practice have mainly been based on specific biological, historical-cultural, and visual landscape qualities.

scholarly journals Early Holocene Thermal Maximum recorded by branched tetraethers and pollen in Western Europe (Massif Central, France)

2020 ◽  
Vol 228 ◽  
pp. 106109 ◽  
Author(s):  
Céline Martin ◽  
Guillemette Ménot ◽  
Nicolas Thouveny ◽  
Odile Peyron ◽  
Valérie Andrieu-Ponel ◽  
...  
Keyword(s):  
Western Europe ◽  
Early Holocene ◽  
Massif Central ◽  
Holocene Thermal Maximum ◽  
Thermal Maximum

scholarly journals The Moroccan Massive Sulphide Deposits: Evidence for a Polyphase Mineralization

Minerals ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 156 ◽  
Author(s):  
Abderrahim Essaifi ◽  
Kathryn Goodenough ◽  
Fernando Tornos ◽  
Abdelhak Outigua ◽  
Abdelmalek Ouadjou ◽  
...  
Keyword(s):  
Lead Isotopes ◽  
Shear Zones ◽  
Structural Features ◽  
Isotopic Signature ◽  
Ore Deposits ◽  
Massive Sulphide ◽  
Isotopic Signatures ◽  
Crustal Block ◽  
Massive Sulphide Deposits ◽  
Sulphide Deposits

This work provides an overview of the geological, geochemical, and metallogenic data available up to date on the Moroccan massive sulphide deposits, including some new results, and then discusses the evidences for the epigenetic and syngenetic hypotheses. All of the ore deposits are located within a crustal block located at the intersection between two major shear zones and are characterized by a sustained and long-lived magmatic activity. The ore deposits are located within second-order shear zones, which played an important role in controlling the geometry of the mineralization. The mineralization lacks the unequivocal textural and structural features that are indicative of a sedimentary or diagenetic origin, and a syntectonic to late-tectonic pyrite-rich assemblage is superimposed on an earlier, pretectonic to syntectonic pyrrhotite-rich mineralization. Each deposit has a distinctive pyrrhotite sulfur isotopic signature, while the sulfur isotopic signature of pyrite is similar in all deposits. Lead isotopes suggest a shift from a magmatic source during the pyrrhotite-rich mineralization to a source that is inherited from the host shales during the pyrite-rich mineralization. The O/H isotopic signatures record a predominance of fluids of metamorphic derivation. These results are consistent with a model in which an earlier pyrrhotite-rich mineralization, which formed during transtension, was deformed and then remobilized to pyrite-rich mineralization during transpression.

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