Dosage du potassium, de l'uranium, du radium et du thorium, par spectrometrie gamma dans les laves d'Auvergne, du Velay et de la province sicilienne

1963 ◽  
Vol S7-V (2) ◽  
pp. 218-231 ◽  
Author(s):  
Jean Louis Cheminee ◽  
Daniel Nordemann
Keyword(s):  
Hydrothermal Alteration ◽  
Volcanic Rocks ◽  
Statistical Dependence ◽  
Direct Proportion ◽  
Radioactive Elements ◽  
Spectrometry Analysis ◽  
Functional Relations ◽  
South Central ◽  
Intrusive Rocks ◽  
Radioactive Minerals

Abstract Fifty samples of volcanic rocks from south-central France, ranging from basalts to rhyolites, were subjected to gamma spectrometry analysis for the purpose of determining the proportions and relationships of the constituent radioactive elements. Zircon, sphene and apatite generally contained less thorium and uranium than the less abundant accessory minerals such as allanite, monazite and xenotime. Results of the analysis also show that the percentage of radioactive minerals is greater in the acidic lavas than in the intrusive rocks, suggesting that the latter were subjected to hydrothermal alteration. The percentage of potassium varies in direct proportion to the variation in the percentage of silica. The increase in thorium as a function of silica is more rapid than that of uranium. Graphically, no correlation exists between the percentage of radium and silica. The concentrations of uranium and thorium do not vary independently but seem to have a statistical dependence whose functional relations are not yet apparent.

Evolution of the south-central segment of the Archean Abitibi Belt, Quebec. Part III: Plutonic and metamorphic evolution and geotectonic model

1983 ◽  
Vol 20 (9) ◽  
pp. 1374-1388 ◽  
Author(s):  
Erich Dimroth ◽  
Laszlo Imreh ◽  
Normand Goulet ◽  
Michel Rocheleau
Keyword(s):  
Hydrothermal Alteration ◽  
High Intensity ◽  
Thermal Contact ◽  
Volcanic Rocks ◽  
Metamorphic Grade ◽  
Contact Metamorphism ◽  
Metamorphic Evolution ◽  
South Central ◽  
Central Segment ◽  
Basin System

Textural criteria permit distinction between the pre-Kenoran and Kenoran phases of plutonism and metamorphism. The pre-Kenoran plutons and pre-Kenoran metamorphic phases are directly related to the volcanic evolution. Synvolcanic tonalite–trondhjemite plutons and swarms of mafic and felsic dykes core central volcanic complexes. The volcanic rocks underwent three types of pre-Kenoran metamorphism, namely, a pervasive alteration, a thermal contact metamorphism that affected narrow aureoles around synvolcanic plutons, and a high-intensity hydrothermal alteration that affected cross-cutting pipes in central volcanic complexes.Synkinematic Kenoran metamorphism resulted in the growth of minerals (chlorite, actinolite, etc.) parallel to schistosities. Synkinematic metamorphic grade ranges form the pumpellyite–prehnite facies to the amphibolite facies. Late- to post-kinematic metamorphic phases resulted in the growth of minerals across schistosities. Syn- to post-kinematic plutons are not voluminous in the part of the Abitibi Belt described here, but they underlie vast areas in the Bellecombe Belt. They range from gneissose early synkinematic plutons to late-kinematic plutons that have well preserved igneous textures.The paleogeographic, tectonic, plutonic, and metamorphic histories of the Abitibi and Bellecombe belts are reviewed and we conclude that the belts are analogous to an island arc – fore-arc basin system.

Hydrothermal alteration of volcanic rocks in Seival Mine Cu–mineralization – Camaquã Basin – Brazil (part I): Chloritization process and geochemical dispersion in alteration halos

2017 ◽  
Vol 177 ◽  
pp. 45-60 ◽  
Author(s):  
Eduardo Fontana ◽  
André S. Mexias ◽  
Christophe Renac ◽  
Lauro V.S. Nardi ◽  
Rodrigo W. Lopes ◽  
...  
Keyword(s):  
Hydrothermal Alteration ◽  
Volcanic Rocks ◽  
Geochemical Dispersion

scholarly journals Mineralogical and Fluid Inclusions Study of Epithermal Type Veins Intruding the Volcanic Rocks of the Kornofolia Area, Evros, NE Greece.

2019 ◽  
Vol 55 (1) ◽  
pp. 202
Author(s):  
Foteini Aravani ◽  
Lambrini Papadopoulou ◽  
Vasileios Melfos ◽  
Triantafillos Soldatos ◽  
Triantafillia Zorba ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Fluid Inclusion ◽  
Hydrothermal Alteration ◽  
Fluid Inclusions ◽  
Volcanic Rocks ◽  
The Other ◽  
Calc Alkaline ◽  
Ft Ir ◽  
Host Rocks

The volcanic rocks of Kornofolia area, Evros, host a number of epithermal-type veins. The host rocks are Oligocene calc-alkaline andesites to rhyo-dacites. The andesites form hydrothermal breccias and show hydrothermal alteration. The veins comprise mainly silica polymorphs such as quartz, chalcedony and three types of opal (milky white, transparent and green). Amethyst also forms in veins at the same area. Apart from the silica polymorphs, the veins are accompanied by calcite and zeolites. The main aim of this study is the characterization of the silica polymorphs. Using FT-IR analyses, variations in the crystal structure of the three opals were recognized. The green opal is found to be more amorphous than the other two types. Fluid-inclusion measurements were performed in calcite and were compared with amethyst from previous studies. The Th is between 121-175 °C and the Te between -22.9 and -22.4 °C. The salinities range from 0.9 to 4.5 wt % NaCl equiv.

A rock magnetic fingerprint of hydrothermal alteration in volcanic rocks - An example from the Los Azufres Geothermal Field, Mexico

2019 ◽  
Vol 91 ◽  
pp. 260-271
Author(s):  
Kailasa Pandarinath ◽  
Rajasekhariah Shankar ◽  
E. Santoyo ◽  
Shwetha B. Shetty ◽  
America Yosiris García-Soto ◽  
...  
Keyword(s):  
Hydrothermal Alteration ◽  
Volcanic Rocks ◽  
Geothermal Field

Evolution of the south-central segment of the Archean Abitibi Belt, Quebec. Part II: Tectonic evolution and geomechanical model

1983 ◽  
Vol 20 (9) ◽  
pp. 1355-1373 ◽  
Author(s):  
Erich Dimroth ◽  
Lazlo Imreh ◽  
Normand Goulet ◽  
Michel Rocheleau
Keyword(s):  
Tectonic Evolution ◽  
Anisotropic Plate ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Normal Fault ◽  
Geomechanical Model ◽  
Southwestern Part ◽  
South Central ◽  
Central Segment ◽  
Volcanic Terrain

In this paper, we describe the relations between the paleogeographic and tectonic evolution of the southwestern part of the Archean Abitibi and Bellecombe belts. Volcanism in the Abitibi Belt created a very thick, anisotropic plate composed of competent volcanic rocks and broken by the Duparquet–Destor break. The depocenters of the upper division of diverse volcanic rocks subsided about 10 km relative to their surroundings, and some central volcanic complexes within this division were consolidated by synvolcanic plutons and their thermal metamorphic aureole. The Cadillac break, a normal fault, separated the Abitibi and Bellecombe belts. The latter consisted of comparatively incompetent sedimentary rocks on top of a basement composed of ultramafic–mafic flows.North–south compression of the volcanic terrain during the Kenoran Orogeny produced a set of flexure folds, F1, that curve around the consolidated cores of central volcanic complexes generally in an easterly direction. Synclinoria nucleated at the deeply subsident depocenters of the upper diverse division. Further north–south flattening and subvertical stretching produced the east-trending F2 folds, their axial-plane schistosity S2, and local superposed schistosities S3 and S4. Southward verging recumbent folds suggest that the Bellecombe Belt simultaneously was pulled northward below the Abitibi Belt. During the orogeny, the Duparquet–Destor and Cadillac breaks were transformed to thrust faults; the Duparquet–Destor break also shows minor (< 3 km) right-lateral strike slip. Diapiric rise of late- to post-kinematic plutons locally distorted earlier schistosities.

The Duck Pond and Boundary Cu–Zn deposits, Newfoundland: new insights into the ages of host rocks and the timing of VHMS mineralization

2010 ◽  
Vol 47 (12) ◽  
pp. 1481-1506 ◽  
Author(s):  
Vicki McNicoll ◽  
Gerry Squires ◽  
Andrew Kerr ◽  
Paul Moore
Keyword(s):  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Isotopic Data ◽  
Sulphide Ores ◽  
Intrusive Rocks ◽  
Felsic Volcanic ◽  
Host Rocks ◽  
Felsic Volcanic Rocks

The Duck Pond Cu–Zn–Pb–Ag–Au deposit in Newfoundland is hosted by volcanic rocks of the Cambrian Tally Pond group in the Victoria Lake supergroup. In conjunction with the nearby Boundary deposit, it contains 4.1 million tonnes of ore at 3.3% Cu, 5.7% Zn, 0.9% Pb, 59 g/t Ag, and 0.9 g/t Au. The deposits are hosted by altered felsic flows, tuffs, and volcaniclastic sedimentary rocks, and the sulphide ores formed in part by pervasive replacement of unconsolidated host rocks. U–Pb geochronological studies confirm a long-suspected correlation between the Duck Pond and Boundary deposits, which appear to be structurally displaced portions of a much larger mineralizing system developed at 509 ± 3 Ma. Altered aphyric flows in the immediate footwall of the Duck Pond deposit contained no zircon for dating, but footwall stringer-style and disseminated mineralization affects rocks as old as 514 ± 3 Ma at greater depths below the ore sequence. Unaltered mafic to felsic volcanic rocks that occur structurally above the orebodies were dated at 514 ± 2 Ma, and hypabyssal intrusive rocks that cut these were dated at 512 ± 2 Ma. Some felsic samples contain inherited (xenocrystic) zircons with ages of ca. 563 Ma. In conjunction with Sm–Nd isotopic data, these results suggest that the Tally Pond group was developed upon older continental or thickened arc crust, rather than in the ensimatic (oceanic) setting suggested by previous studies.

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