scholarly journals Spanish Bentonites: A Review and New Data on Their Geology, Mineralogy, and Crystal Chemistry

Minerals ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 696 ◽  
Author(s):  
Emilia García-Romero ◽  
Eva María Manchado ◽  
Mercedes Suárez ◽  
Javier García-Rivas
Keyword(s):  
Hydrothermal Alteration ◽  
Compositional Variation ◽  
Volcanic Area ◽  
Crystal Chemical ◽  
Initial Composition ◽  
Sedimentary Deposits ◽  
Crystal Chemical Data ◽  
Structural Formulae ◽  
Trioctahedral Smectites ◽  
Representative Samples

A review and a synthesis of the geological, mineralogical, and crystal chemical data available in the literature on active Spanish bentonitic exploitations were done, and at the same time, new data are provided from a set of representative samples from these deposits. They were located in three different areas with different geological origins: (1) Miocene sedimentary deposits from the Tajo Basin (Madrid–Toledo provinces) in the center of the Iberian Peninsula, where bentonites appear in two different units named for their colors (Green Clays and Pink Clays); (2) samples from Tamame de Sayago (Zamora province) originating from the hydrothermal alteration of granitic Variscan rocks; and 3) Miocene deposits originating from the hydrothermal alteration of volcanic or subvolcanic rocks from the Cabo de Gata volcanic area (Almería Province) in the southern part of Spain, where the three main deposits (Cortijo de Archidona, Los Trancos, and Morrón de Mateo) were studied. The bentonites from the Tajo Basin were formed mainly by trioctahedral smectites, and there were significant mineralogical differences between the Green and Pink Clays, both in terms of the contents of impurities and in terms of smectite crystallochemistry and crystallinity. The smectites from Tamame de Sayago were dioctahedral (montmorillonite–beidellite series), and they appeared with kaolinite, quartz, and mica in all possible proportions, from almost pure bentonite to kaolin. Finally, the compositions of the bentonites from the three studied deposits in Cabo de Gata were quite similar, and zeolites and plagioclases were the main impurities. The structural formulae of the smectites from Cortijo de Archidona and Los Trancos showed a continuous compositional variation in beidellite–montmorillonite, while in Morrón de Mateo, the smectites were mainly montmorillonite, although there was continuous compositional variation from Al montmorillonites to Fe–Mg-rich saponites. The variation in the smectite composition is due to the intrusion of a volcanic dome, which brings new fluids that alter the initial composition of the smectites.

scholarly journals Geochemistry of Sphalerite from the Permian Volcanic-Hosted Massive Sulphide (VHMS) Deposits in the Tasik Chini Area, Peninsular Malaysia: Constraints for Ore Genesis

Minerals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 728
Author(s):  
Mohd Basril Iswadi Basori ◽  
Sarah E. Gilbert ◽  
Khin Zaw ◽  
Ross R. Large
Keyword(s):  
Variable Temperature ◽  
Mineral Chemistry ◽  
Peninsular Malaysia ◽  
Massive Sulphide ◽  
Compositional Variation ◽  
Volcanic Origin ◽  
Sedimentary Deposits ◽  
Depositional Processes ◽  
Tasik Chini ◽  
Vhms Deposits

The Bukit Botol and Bukit Ketaya deposits are two examples of volcanic-hosted massive sulphide (VHMS) deposits that occur in the Tasik Chini area, Central Belt of Peninsular Malaysia. The mineralisation is divided into subzones distinguished by spatial, mineralogical, and textural characteristics. The primary sulphide minerals include pyrite, chalcopyrite, sphalerite, and galena, with lesser amounts of Sn- and Ag-bearing minerals, with Au. However, pyrrhotite is absent from both deposits. This study presents the results of sphalerite chemistry analysed by using an electron microprobe. Two types of sphalerite are recognised: sphalerite from the Bukit Botol deposit reveals a range of <DL to 24.0 mole% FeS, whereas sphalerite from the Bukit Ketaya deposit shows a range of <DL to 3 mole% FeS. Significant variations are shown in Zn, Cu, Cd, and Ag levels. Although the sphalerite has a wide variation in composition, a discernible decreasing Fe trend is exhibited from the stringer zone towards massive sulphide. This compositional variation in sphalerites may in part reflect variable temperature and activity of sulphur in the hydrothermal fluids during ore formation. Alternatively, the bimodal composition variations suggest that mineral chemistry relates to contrasting depositional processes. The Zn/Cd ratios for sphalerite from both these deposits are similar to those exhibited by volcano−sedimentary deposits with a volcanic origin. Therefore, the consistently low Cd concentrations and moderate to high Zn/Cd ratios suggest mixing of seawater and minor magmatic fluids controlling the chemistry of sphalerite at both deposits during their formation.

Lithium-Bearing Hydrothermal Alteration Phyllosilicates Related to Portalet Fluorite Ore (Pyrenees, Huesca, Spain)

Clay Minerals ◽  
1993 ◽  
Vol 28 (2) ◽  
pp. 275-283 ◽  
Author(s):  
J. M. Gonzlez Lopez ◽  
I. Subias Pirez ◽  
C. Fernandez-Nieto ◽  
I. Fanlo Gonzalez
Keyword(s):  
Hydrothermal Alteration ◽  
Half Cell ◽  
Ore Bodies ◽  
Alteration Minerals ◽  
Structural Formulae

AbstractPhyllosilicate associations in hydrothermally altered fluorite ore bodies are: Li-chlorite ± pyrophyllite ± interstratified minerals ± muscovite +± kaolinite. Chlorites, the main alteration minerals, are dioctahedral, d060 = 1.489-1-490/~,, of Ia polytype. The structural formulae indicate substitution of AI for Si from 0.61-0.78 atoms. The total octahedral occupancy ranges from 4.52-4-71 atoms, with 0.49-0-69 Li atoms per half cell unit. This composition indicates that the chlorites are intermediate members of the donbassite-cookeite series proposed by Sudo (1978). The mineralogical associations and textural relations suggest that after intensive silicification which produced alkali alteration under acid conditions, pyrophyllite was produced at the expense of muscovite and then Li-bearing donbassite formed from the pyrophyllite. The Li needed for the formation of the chlorites could be genetically related to granitic batholiths which occur close to the fluorite ores.

Behaviour of ThSiO4 during hydrothermal alteration of raremetal rich lithologies from peralkaline rocks

2017 ◽  
Vol 81 (4) ◽  
pp. 873-893 ◽  
Author(s):  
R. Macdonald ◽  
B. Bagiński ◽  
P. M. Kartashov ◽  
D. Zozulya
Keyword(s):  
Low Temperature ◽  
Hydrothermal Alteration ◽  
Late Stage ◽  
Great Majority ◽  
Hydrothermal Fluids ◽  
Element Mobility ◽  
Limited Mobility ◽  
Fluid Infiltration ◽  
Geochemical Indicators ◽  
Structural Formulae

AbstractThe behaviour of ThSiO4 during low-temperature alteration has significance for element mobility and redistribution. Here we describe five types of alteration of ThSiO4 by hydrothermal fluids: (1) primary ThSiO4 associated with chevkinite-(Ce) in a quartz-epidote metasomatite; (2) during alteration of monazite-(Ce) in a quartzolite; (3) during alteration of fergusonite-(Y) in a quartz-epidote metasomatite; (4) following exsolution from chevkinite-(Ce); and (5) associated with cerite-(Ce) and with ilmenite and bastnäsite-(Ce) in late-stage veinlets in a syenitic pegmatite and a metasomatite. The great majority of crystals have been strongly altered compositionally, with variable degrees of replacement of formula elements by non-formula elements, such as Ca, Fe, P and REE. The most reliable geochemical indicators of hydrothermal alteration are low analytical totals and non-stoichiometric structural formulae. The alteration is variably ascribed to dissolution-reprecipitation and pervasive fluid infiltration along cracks. Thorium appears to have shown limited mobility in these samples.

scholarly journals Tectonic structure and volcanic centers at the eastern edge of the aegean volcanic arc around Nisyros island

2001 ◽  
Vol 34 (1) ◽  
pp. 289 ◽  
Author(s):  
D. PAPANIKOLAOU ◽  
P. NOMIKOU
Keyword(s):  
Volcanic Activity ◽  
Recent Volcanic Activity ◽  
Volcanic Area ◽  
The South ◽  
Tectonic Structure ◽  
General Direction ◽  
Volcanic Arc ◽  
Sedimentary Deposits ◽  
The North ◽  
Eastern Edge

The recent volcanic activity at the eastern edge of the Aegean Volcanic Arc is limited within a neotectonic graben structure which is developed in an E-W general direction between the alpine basement of Kos Island to the north and the alpine basement of Tilos Island to the south. In between the boundary faults of the neotectonic graben there is an extended volcanic area comprising several individual volcanic centers, which penetrate through the thick post-alpine sedimentary deposits of the graben.

Compositional variation in minerals of the chevkinite group

2002 ◽  
Vol 66 (6) ◽  
pp. 1075-1098 ◽  
Author(s):  
R. Macdonald ◽  
H. E. Belkin
Keyword(s):  
Negative Correlation ◽  
Linear Array ◽  
General Relationship ◽  
Igneous Rocks ◽  
Compositional Variation ◽  
Strong Negative Correlation ◽  
Intermediate Composition ◽  
Structural Formulae ◽  
Charge Balancing

Abstract The composition of chevkinite and perrierite, the most common members of the chevkinite group, is closely expressed by the formula A4BC2D2Si4O22, where A = (La,Ce,Ca,Sr,Th), B = Fe2+, C = (Fe2+,Fe3+,Ti,Al,Zr,Nb) and D = Ti. The A site is dominated by a strong negative correlation between (Ca+Sr) and the REE. Chondrite-normalized REE patterns are very variable, e.g. in LREE/HREE and Eu/Eu*. The C site is dominated by Ti, Al and Fe2+, in very variable proportions. Most chevkinites and perrierites are close to stoichiometric, with cation sums between 12.9 and 13.5, compared to the theoretical 13. There is no single, generally applicable charge balancing substitution scheme in the group; however, the general relationship defines a linear array with r2 = 0.91. Chevkinite and perrierite are shown to be compositionally distinct on the basis of CaO, FeO*, Al2O3 and Ce2O3 abundances. Chevkinite forms mainly in chemically evolved parageneses, such as syenites, rhyolites and fenites associated with carbonatite complexes. Perrierite is more commonly recorded from igneous rocks of mafic to intermediate composition. The compositional characteristics and possible structural formulae of other members of the chevkinite group are reviewed briefly.

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