scholarly journals Controls on chemical evolution and rare element enrichment in crystallising albite-spodumene pegmatite and wallrocks: Constraints from mineral chemistry

Lithos ◽  
2020 ◽  
Vol 352-353 ◽  
pp. 105289 ◽  
Author(s):  
Renata Barros ◽  
David Kaeter ◽  
Julian F. Menuge ◽  
Radek Škoda
Keyword(s):  
Chemical Evolution ◽  
Mineral Chemistry ◽  
Rare Element ◽  
Element Enrichment

scholarly journals Rhenium - rich molybdenites in Thracian porphyry Mo±Cu occurrences, NE - Greece

2001 ◽  
Vol 34 (3) ◽  
pp. 1015 ◽  
Author(s):  
Β. ΜΕΛΦΟΣ ◽  
Π. ΒΟΥΔΟΥΡΗΣ ◽  
Κ. ΑΡΙΚΑΣ ◽  
Μ. ΒΑΒΕΛΙΔΗΣ
Keyword(s):  
Chemical Composition ◽  
Hydrothermal Alteration ◽  
Fluid Inclusions ◽  
Mineral Chemistry ◽  
Rare Element ◽  
Alteration Zones ◽  
Porphyry Cu ◽  
Mineral Assemblages ◽  
Host Rocks

The present study correlates both the mineralogy of the hydrothermal alteration and the mineral chemistry of molybdenites from three porphyry Mo ± Cu occurrences in Thrace: Melitena, Pagoni Rachi/Kirki and Ktismata/ Maronia. The mineralisations are genetically related to calcalkaline, subvolcanic bodies of Tertiary age. According to their mineralogical and chemical composition the host rocks are characterized as dacite (Melitena), dacitic andésite (Pagoni Rachi) and porphyry microgranite (Ktismata/Maronia). The molybdenites occur in disseminated form, as fracture fillings, as well within quartz stockworks crosscuting the central alteration zones of the intrusives. They are accompanied by the following mineral assemblages: quartz, sericite, pyrophyllite, diaspore, Ca-Ba-rich alunite, pyrite (Melitena); quartz, albite/K-feldspar, biotite, actinolite, magnetite (Pagoni Rachi); and sericite, kaolinite, pyrophyllite, chlorite (Ktismata). Preliminary microthermometric results showed homogenisation temperatures from 352° to 390 °C for Pagoni Rachi area and from 295° to 363 °C for Melitena area. The salinities range between 4.5 and 6.1 wt% eq. NaCl and between 2.7 and 3.4 wt% eq. NaCl, respectively. Detailed study on over 400 fluid inclusions from the porphyry Cu-Mo deposit in Maronia area revealed formation temperatures from 300° to 420 °C, whereas salinities are distincted in two different groups from 6 to 16 wt% eq. NaCl and from 28 to 55 wt% eq. NaCl. The chemical composition of the molybdenites from the three porphyry Mo±Cu deposits in Thrace was studied with 155 microprobe analyses. The results revealed unusual high and variable Re concentrations in the studied molybdenites. Re content in molybdenite from Melitena area vary from 0.21 to 1.74 wt%, 0.79 wt% on average. The highest values were measured in samples from Pagoni Rachi (0.45-4.21 wt%, 1.98 wt% on average). Finally, microprobe analyses from molybdenite in Ktismata/Maronia showed Re content between 0.12 and 2.88 wt% (0.76 wt% on average). Rhenium is a very rare element with many definite uses, and is mainly associated with molybdenite in porphyry type deposits. According to the data published so far the Re content in molybdenite reaches up to 0.42 wt%. It is obvious therefore that such high Re concentrations (0.12 to 4.22 wt%) from the studied molybdenites in Thrace, are very ineresting for a possible future exploitation.

Crystal chemistry and microfeatures of gadolinite imprinted by pegmatite formation and alteration evolution

2020 ◽  
Vol 105 (11) ◽  
pp. 1647-1655
Author(s):  
Nenad Tomašić ◽  
Radek Škoda ◽  
Vladimir Bermanec ◽  
Marin Šoufek
Keyword(s):  
Rare Earth ◽  
Chemical Properties ◽  
Mineral Chemistry ◽  
Complexing Agent ◽  
Textural Features ◽  
Rare Element ◽  
Backscattered Electron ◽  
Mineral Matrix ◽  
Southern Norway

Abstract Gadolinite [REE2Fe2+Be2Si2O10] is a common mineral in certain types of rare element and rare earth element (REL-REE) pegmatites. Changes in pegmatite environment during and after gadolinite formation may be devised by studying its crystal-chemical properties and a thorough observation of microfeatures in the mineral matrix. Post-crystallization processes in pegmatite might trigger alteration mechanisms in gadolinite like in other REE-rich pegmatite minerals, whereby various late-magmatic or metasomatic events may affect mineral chemistry. Three gadolinite samples originating from various pegmatite occurrences in southern Norway offer an excellent opportunity in studying post-crystallization evolution of the pegmatites; by determining their crystallographic, chemical, and micro-textural features, imprints of the related processes in the pegmatites have been characterized in this study. Relevant mineral information was collected in recrystallization experiments of fully or slightly metamictized gadolinite samples and subsequent XRD analyses. Micro-Raman spectroscopy, electron microprobe analysis (EMPA), and scanning electron microscope–backscattered electron–energy-dispersive X-ray spectroscopy (SEM-BSE-EDS) analyses were employed to retrieve micro-chemical properties and related micro-textural features of the mineral matrix. With a reference to the gadolinite supergroup, a general alteration path can be envisaged outlining the pegmatite evolution and suggesting the occurrence of the secondary REE mineral phases: altered gadolinite domains prove Ca enrichment with a tendency toward the hingganite composition, while a slight fluorine increase and sporadic secondary fluorite occurrence imply a significant role of fluorine as a complexing agent in the dissolution-reprecipitation mechanism of metasomatic alteration in the mineral. Micro-Raman spectra show improved vibration statistics for the altered gadolinite domains, which could be linked to the substitution of rare earth elements (REE) by Ca and a possible increase of structural ordering within the gadolinite structure, being at the same time an indication of structural healing of metamictized domains by metasomatic processes. A study of microfeatures in the complex silicates like gadolinite proves to be an excellent tool to trace post-crystallization processes in a pegmatitic environment. With a slight redistribution of radionuclides during an alteration in gadolinite, a moderate precaution has to be taken when selecting gadolinite for U-Th-Pb dating.

scholarly journals Nb–Ta–(Ti–Sn) oxide mineral chemistry as tracer of rare-element granitic pegmatite fractionation in the Borborema Province, Northeastern Brazil

2007 ◽  
Vol 43 (2) ◽  
pp. 207-228 ◽  
Author(s):  
Hartmut Beurlen ◽  
Marcelo R. R. Da Silva ◽  
Rainer Thomas ◽  
Dwight R. Soares ◽  
Patrick Olivier
Keyword(s):  
Mineral Chemistry ◽  
Northeastern Brazil ◽  
Granitic Pegmatite ◽  
Rare Element ◽  
Oxide Mineral ◽  
Borborema Province

scholarly journals Comparison of Cretaceous granitoids of the Chaun tectonic zone to those of the Taigonos Peninsula, NE Asia: rock chemistry, composition of rock forming minerals, and conditions of formation

2009 ◽  
Vol 4 ◽  
pp. 289-311 ◽  
Author(s):  
P. L. Tikhomirov ◽  
M. V. Luchitskaya ◽  
I. R. Kravchenko-Berezhnoy
Keyword(s):  
Volcanic Belt ◽  
Mineral Chemistry ◽  
Trace Element Composition ◽  
Melt Crystallization ◽  
Tectonic Zone ◽  
Source Regions ◽  
Transitional Type ◽  
Chukotka Volcanic Belt ◽  
Element Enrichment ◽  
Late Stages

Abstract. The Cretaceous granitoid complexes of the Eastern Taigonos and the Prybrezhny Taigonos belts (southern part of the Taigonos Peninsula), Tanyurer pluton of the Okhotsk-Chukotka volcanic belt, and the Peekiney, Moltykan, and Telekay plutons of the Chaun tectonic zone are discussed in relation to their structural position, petrography, rock and mineral chemistry and physicochemical conditions of melt crystallization. These granitoid plutons were generated through melting of a compositionally heterogeneous crustal source, with direct contribution from mafic melts produced in the mantle wedge above active or extinct Benioff zones. Variations of the trace-element composition of granitoids are controlled to a greater extent by local compositional peculiarities of the source regions than by the geodynamic regime as such. The final crystallization of these plutons occurred at comparatively shallow depths, between 1–2 and 6–7 km, in a temperature interval of 700–770°C. The depth of emplacement of the bodies decreases with increasing distance from the areas with oceanic and transitional type crust, as does the degree of incompatible element enrichment of the mantle and crustal sources of melts. Variations in fo2 values at the late stages of crystallization of the plutons reach 3–4 orders of magnitude, exceeding the limits of the quartz-fayalite-magnetite (QFM) and nickel-nickel oxide (NNO) buffer equilibria, which likely results from local variations of the source composition.

scholarly journals Some aspects of the chemical evolution of 4He in the Galaxy: the He/H radial gradient and the ΔY/ΔZ enrichment ratio

2000 ◽  
Vol 198 ◽  
pp. 204-213
Author(s):  
W. J. Maciel
Keyword(s):  
Chemical Evolution ◽  
Heavy Element ◽  
Planetary Nebulae ◽  
Enrichment Ratio ◽  
Radial Gradient ◽  
The Galaxy ◽  
Element Enrichment ◽  
Progenitor Stars

Two aspects of the chemical evolution of 4He in the Galaxy are considered on the basis of a sample of disk planetary nebulae by the application of corrections due to the contamination of 4He from the progenitor stars. First, the He/H radial gradient is analyzed, and then, the helium to heavy element enrichment ratio is determined for metallicities up to the solar value.

Chemical evolution of Nb-Ta oxides and zircon from the Koktokay No. 3 granitic pegmatite, Altai, northwestern China

2004 ◽  
Vol 68 (5) ◽  
pp. 739-756 ◽  
Author(s):  
A. C. Zhang ◽  
R. C. Wang ◽  
H. Hu ◽  
H. Zhang ◽  
J. C. Zhu ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Chemical Evolution ◽  
Electron Microprobe ◽  
The Other ◽  
Northwestern China ◽  
Granitic Pegmatite ◽  
Hydrothermal Conditions ◽  
Rare Element ◽  
Other Hand ◽  
Backscattered Electron

AbstractThe Koktokay No. 3 granitic pegmatite, Altai, northwestern China, is a strongly zoned rare-element granitic pegmatite, where the petrographic zones were distinguished into two groups: outer zones (I to IV) and inner zones (V to IX). Nb-Ta oxides and zircon are investigated in this paper by using quantitative electron-microprobe analyses (EMPA) and backscattered-electron (BSE) imaging. Columbite-tantalite and zircon occur in most textural zones, whereas tapiolite and uranmicrolite are mainly restricted to zone VII. Manganocolumbite and zircon from the outer zones (zones II and IV) are homogeneous except for a few exceptions, whereas manganotantalite and hafnian zircon from the inner zones (V–VII) are obviously heterogeneous and strongly zoned. Chemically, Ta/(Nb+Ta) in columbite-tantalite and Hf/(Zr+Hf) in zircon increase from the outer to the inner zones on one hand, and from core to rim in single zoned crystals on the other hand. Observations of intra-zonal variations of the chemical composition of Nb-Ta oxides and zircon in the Koktokay No. 3 granitic pegmatite may suggest that the outer zones crystallize under magmatic conditions, whereas the inner zones crystallize under fluid-rich magmatic conditions, and locally under hydrothermal conditions. The extreme enrichments of columbite-tantalite in Ta, and of zircon in Hf, as well as the occurrence of uranmicrolite and tapiolite, indicate an elevated evolution of the Koktokay No. 3 granitic pegmatite.

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