scholarly journals The Distribution of Rare Metals in the LCT Pegmatites from the Giraúl Field, Angola

Minerals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 580
Author(s):  
Gonçalves ◽  
Melgarejo ◽  
Alfonso ◽  
Amores ◽  
Paniagua ◽  
...  
Keyword(s):  
Grain Size ◽  
Hydrothermal Fluids ◽  
Granitic Pegmatite ◽  
Rare Metals ◽  
Accessory Minerals ◽  
Critical Elements ◽  
Incompatible Elements ◽  
Pegmatite Body ◽  
Quartz Core ◽  
Oxide Minerals

The Giraúl granitic pegmatite field in Angola is composed of five pegmatite types, the most evolved belong to the beryl-columbite, beryl-columbite-phosphate and spodumene types. Pegmatites are concentrically zoned with increased grain size toward a quartz core; the most evolved pegmatites have well-developed replacement units. These pegmatites are rich in Nb-Ta oxide minerals and the field has a moderate interest for critical elements such as Ta and Hf. Tourmaline, garnet and micas occur as accessory minerals. The abundance of Zr and Nb-Ta minerals increases with the evolution of the pegmatites, as well as the proportions of beryl and Li-rich minerals. The Ta/(Ta + Nb) ratio in Nb-Ta oxide minerals and the Hf/(Hf + Zr) ratio in zircon also increase with the evolution of the pegmatites and within each pegmatite body from border to inner zones, and especially in the late veins and subsolidus replacements. Textural patterns and occurrence of late veins with Ta-rich minerals suggest that Nb and especially Ta can be enriched in late hydrothermal fluids exsolved from the magma, along with Hf and other incompatible elements as Sn, U, Pb, Sb and Bi.

scholarly journals Komplexní magmaticko-hydrotermální vývoj columbitu, mikrolitu a fersmitu z beryl-columbitového pegmatitu D6e u Maršíkova, Česká republika

2020 ◽  
Vol 28 (1) ◽  
pp. 23-34 ◽  
Author(s):  
Štěpán Chládek ◽  
Pavel Uher
Keyword(s):  
Czech Republic ◽  
Granitic Pegmatite ◽  
Accessory Minerals ◽  
Partial Dissolution ◽  
Pegmatite Body ◽  
Magmatic Fluids ◽  
Compositional Variations ◽  
Homogeneous Pattern ◽  
Oscillatory Zonation

The recently rediscovered small D6e granitic pegmatite body, enclosed in amphibole gneiss of the Sobotín amfibolite massif (Jeseníky Mountains, Czech Republic), is characterized by numerous accessory minerals, including common columbite group minerals (CGM) and minor microlite and fersmite related to blocky K-feldspar unit. The CGM show complex internal zoning. Primary magmatic columbite-(Mn) occurs as corroded domains of prevailing homogeneous pattern, followed by less evolved oscillatory zonation. Primary CGM were overprinted by extensive recrystallization controlled by late-magmatic to post-magmatic fluids and leading to a formation of complex patchy and convolute oscillatory domains of secondary (hydrothermal) CGM. Primary columbite-(Mn) shows significantly limited Ta/(Ta+Nb) and Mn/(Mn+Fe) ratios, whereas secondary columbite-(Fe) to -(Mn) show slightly wider Fe-Mn and Nb-Ta compositional variations. Complex textures and the element fluctuations indicate a partial dissolution-reprecipitation of primary CGM caused by late- to post-magmatic fluids. Moreover, late calciomicrolite I, II and fersmite precipitated on the cracks of columbite crystals. Rare U-rich calciomicrolite I was extensively replaced by fersmite and oscillatorily zoned U-poor calciomicrolite II, slightly enriched in F. Their formation sequestrated part of hydrotermally released Na, Ca, U and represents the final subsolidus fluid-driven stage of the pegmatite evolution. Textural and compositional variations of Nb-Ta mineralization point to a complex magmatic to hydrothermal evolution of the D6e beryl-columbite pegmatite similar to other pegmatites in this region.

scholarly journals Sandstone-Hosted Uranium Deposits as a Possible Source for Critical Elements: The Eureka Mine Case, Castell-Estaó, Catalonia

Minerals ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 34 ◽  
Author(s):  
Montgarri Castillo-Oliver ◽  
Joan Carles Melgarejo ◽  
Lisard Torró ◽  
Cristina Villanova-de-Benavent ◽  
Marc Campeny ◽  
...  
Keyword(s):  
Organic Matter ◽  
Low Temperature ◽  
Black Shales ◽  
Hydrothermal Fluids ◽  
Uranium Deposits ◽  
Critical Metals ◽  
Fine Grained ◽  
Critical Elements ◽  
By Products ◽  
Red Bed

The Eureka deposit in Castell-estaó in the Catalan Pyrenees is a Cu–U–V deposit, hosted by Triassic red-bed sandstones, and classified here as a low-temperature, sandstone-hosted stratabound metamorphite U deposit. The main mineralisation is stratabound, related to coal-bearing units and produced during the Alpine deformation by migration of hydrothermal fluids. In this stage, the original sedimentary and diagenetic components (quartz and calcite, micas, hematite and locally apatite) were replaced by a complex sequence of roscoelite, fine-grained REE phosphates, sulphides and Ni–Co arsenides and sulpharsenides, Ag–Pb selenides, bismuth phases, sulphosalts and uraninite. The black shales of the Silurian sediments underlying the deposit and the nearby Carboniferous volcanoclastic rocks are interpreted as the source of the redox-sensitive elements concentrated in Eureka. The sulphur source is related to leaching of the evaporitic Keuper facies. The REE transport would be facilitated by SO4-rich solutions. The reduction of these solutions by interaction with organic matter resulted in the widespread precipitation of REE and redox-sensitive elements, including many critical metals (V, Bi, Sb, Co), whereas barite precipitated in the oxidized domains. The occurrence of similar enrichments in critical elements can be expected in other similar large uranium deposits, which could be a source of these elements as by-products.

Mn-rich graftonite, ferrisicklerite, staněkite and Mn-rich vivianite in a granitic pegmatite at Soè Valley, central Alps, Italy

2007 ◽  
Vol 71 (5) ◽  
pp. 579-585 ◽  
Author(s):  
A. Guastoni ◽  
F. Nestola ◽  
G. Mazzoleni ◽  
P. Vignola
Keyword(s):  
Single Crystal ◽  
Cell Volume ◽  
Unit Cell Volume ◽  
Unit Cell ◽  
Hydrothermal Fluids ◽  
Granitic Pegmatite ◽  
Single Crystal Xrd ◽  
Central Alps ◽  
X Ray Diffraction ◽  
X Ray

AbstractMn-rich graftonite, (Ca,Mn2+)(Fe2+,Mn2+)2(PO4)2, ferrisicklerite, Li1–x(Fe3+,Mn2+)PO4, manganoan apatite, (Ca,Mn2+,Fe2+Mg)(PO4)3Cl, staně kite, Fe3+Mn2+O(PO4) and Mn-rich vivianite, (Fe2+)3(PO4)2·8H2O, occurring in a granitic pegmatite at Soè Valley (central Alps, Italy) were characterized by powder and single-crystal X-ray diffraction (XRD) and electron microprobe analyses. Geochemically, the Mn-rich graftonite phases are poorly evolved Fe/Mn-phosphates of rare-earth elements-lithium (REE-Li) granitic pegmatites. The assemblage Mn-rich graftonite + ferrisicklerite + staněkite has rarely beendocumen ted in pegmatites. Inthe Soè Valley pegmatite, ferrisicklerite forms exsolution lamellae with Mn-rich graftonite associated with manganoan apatite and staněkite. Graftonite is associated with Mn-rich vivianite. Powder and single-crystal XRD data indicate that the unit-cell volume of graftonite increases as a function of Mn2+content. Staněkite shows a distinctly smaller unit-cell volume with respect to previously reported staněkites, probably due to reduced Mn2+. Vivianite with significant Mn2+has a unit-cell volume similar to nearly Mn-free vivianite. The formation of Mn-rich graftonite and manganoan apatite is related to destabilization of Mn-rich almandine and biotite during pegmatite formation. Ferrisicklerite forms exsolution lamellae along the 010 cleavage planes of Mn-rich graftonite, whereas staněkite forms by alterationof ferrisicklerite and Mn-rich vivianite due to circulation of late-stage hydrothermal fluids.

The occurrence of niobian zirconolite, pyrochlore and baddeleyite in the Kovdor carbonatite complex, Kola Peninsula, Russia

1996 ◽  
Vol 60 (401) ◽  
pp. 639-646 ◽  
Author(s):  
C. Terry Williams
Keyword(s):  
Kola Peninsula ◽  
Incompatible Element ◽  
Fluid Composition ◽  
Carbonatite Complex ◽  
Compositional Zoning ◽  
Accessory Minerals ◽  
Element Ratios ◽  
Backscattered Electron ◽  
Oxide Minerals ◽  
High Concentrations

AbstractThe compositions and textural relationships of the oxide minerals zirconolite, pyrochlore and baddeleyite are described. These occur as accessory minerals, often intergrown with each other, from a phoscorite rock associated with the Kovdor carbonatite complex. Both the zirconolite and baddeleyite have relatively high concentrations of Nb and Ta; the pyrochlore is rich in U and Ta. Backscattered electron images, coupled with detailed microprobe analyses, reveal complex compositional zoning in zirconolite and pyrochlore which reflect changes in the fluid composition during growth of these minerals. A comparison is made of incompatible element ratios Zr/Hf, Nb/Ta and Th/U between the three accessory minerals.

Fluid-mediated alteration of (Y,REE,U,Th)–(Nb,Ta,Ti) oxide minerals in granitic pegmatite from the Evje-Iveland district, southern Norway

2016 ◽  
Vol 110 (5) ◽  
pp. 581-599 ◽  
Author(s):  
Charley J. Duran ◽  
Anne-Magali Seydoux-Guillaume ◽  
Bernard Bingen ◽  
Sophie Gouy ◽  
Philippe de Parseval ◽  
...  
Keyword(s):  
Granitic Pegmatite ◽  
Oxide Minerals ◽  
Southern Norway

Fe-Mn phosphate associations as indicators of the magmatic-hydrothermal and supergene evolution of the Jálama batholith in the Navasfrías Sn-W District, Salamanca, Spain

2012 ◽  
Vol 76 (1) ◽  
pp. 1-24 ◽  
Author(s):  
T. Llorens ◽  
M.C. Moro
Keyword(s):  
Hydrothermal Fluids ◽  
Granitic Pegmatite ◽  
Metamorphic Rocks ◽  
Low Grade ◽  
Magmatic Differentiation ◽  
Metasedimentary Rocks ◽  
Quartz Veins ◽  
Ore Minerals

AbstractThe residual melts that remained after the consolidation of the Jálama batholith crystallized to form a group of intra-granitic pegmatite dykes, which are hosted by its outermost facies (the External Unit), and the most evolved residual melts migrated through fractures to form the Cruz del Rayo field of pegmatite dykes, which are hosted by pre-Ordovician low-grade metasedimentary rocks. The increasing activity of phosphorus as magmatic differentiation took place led to the crystallization of primary phosphates, including members of the triplite–zwieselite and the amblygonite–montebrasite series. A strong albitization of the granitic and pegmatite rocks led to the replacement of the primary assemblage by other phosphates such as alluaudite. The influx of post-magmatic hydrothermal fluids, produced quartz veins, gave rise to the crystallizationof ore minerals and triplite, and altered the granites, aplites and pegmatites, replacing some of the phosphate minerals and feldspars and depositing goyazite, montebrasite and childrenite–eosphorite. The interaction of the residual hydrothermal fluids with those from the surrounding metamorphic rocks during later alteration events resulted in the influx of large quantities of Ca and Mg, and produced phosphate assemblages enriched in those elements. Finally, late goyazite, hydroxylapatite and an unidentified Fe-rich phosphate were formed as a result of supergene alterationby percolating meteoric waters, which added Ca, Sr and other elements into the system, and increased fO2.

scholarly journals Rare-element granitic pegmatite of Miocene age emplaced in UHP rocks from Visole, Pohorje Mountains (Eastern Alps, Slovenia): accessory minerals, monazite and uraninite chemical dating

2014 ◽  
Vol 65 (2) ◽  
pp. 131-146 ◽  
Author(s):  
Pavel Uher ◽  
Marian Janák ◽  
Patrik Konečný ◽  
Mirijam Vrabec
Keyword(s):  
Late Miocene ◽  
Volcanic Rocks ◽  
Eastern Alps ◽  
Granitic Pegmatite ◽  
Fault System ◽  
Rare Element ◽  
Accessory Minerals ◽  
Precipitation Temperature ◽  
The Alps ◽  
Chemical Dating

Abstract The granitic pegmatite dike intruded the Cretaceous UHP rocks at Visole, near Slovenska Bistrica, in the Pohorje Mountains (Slovenia). The rock consists mainly of K-feldspar, albite and quartz, subordinate muscovite and biotite, while the accessory minerals include spessartine-almandine, zircon, ferrocolumbite, fluorapatite, monazite- (Ce), uraninite, and magnetite. Compositions of garnet (Sps48-49Alm45-46Grs + And3-4 Prp1.5-2), metamict zircon with 3.5 to 7.8 wt. % HfO2 [atom. 100Hf/(Hf + Zr) = 3.3-7.7] and ferrocolumbite [atom. Mn/(Mn + Fe) = 0.27-0.43, Ta/(Ta + Nb) = 0.03-0.46] indicate a relatively low to medium degree of magmatic fractionation, characteristic of the muscovite - rare-element class or beryl-columbite subtype of the rare-element class pegmatites. Monazite-(Ce) reveals elevated Th and U contents (≤11 wt. % ThO2, ≤5 wt. % UO2). The monazite-garnet geothermometer shows a possible precipitation temperature of ~495 ± 30 °C at P~4 to 5 kbar. Chemical U-Th-Pb dating of the monazite yielded a Miocene age (17.2 ± 1.8 Ma), whereas uraninite gave a younger (~14 Ma) age. These ages are comtemporaneous with the main crystallization and emplacement of the Pohorje pluton and adjacent volcanic rocks (20 to 15 Ma), providing the first documented evidence of Neogene granitic pegmatites in the Eastern Alps. Consequently, the Visole pegmatite belongs to the youngest rare-element granitic pegmatite populations in Europe, together with the Paleogene pegmatite occurrences along the Periadriatic (Insubric) Fault System in the Alps and in the Rhodope Massif, as well as the Late Miocene to Pliocene pegmatites in the Tuscany magmatic province (mainly on the Island of Elba).

scholarly journals Minerály skupiny columbitu a mikrolitu v granitovom pegmatite pri Liešťanoch: prvý výskyt vzácnoprvkovej Nb-Ta mineralizácie v Strážovských vrchoch (Slovenská republika)

2020 ◽  
Vol 28 (2) ◽  
pp. 347-352
Author(s):  
Pavel Uher ◽  
Martin Števko ◽  
Sergii Kurylo
Keyword(s):  
Crystalline Basement ◽  
Western Carpathians ◽  
Granitic Pegmatite ◽  
Chemical Compositions ◽  
Accessory Minerals ◽  
Magmatic Origin ◽  
Euhedral Crystal ◽  
Compositional Variations ◽  
Central Western Carpathians

Accessory minerals of columbite and microlite groups were identified in granitic pegmatite dike intruded into parental Carboniferous (~350 Ma) leucogranites of the crystalline basement of the Tatric Unit, Central Western Carpathians. The pegmatite is situated on E slope of Bystrý Hill near Liešťany village, the Strážovské vrchy Mts., Slovakia. Primary columbite-(Fe) forms euhedral crystal (~3 mm across) with diffuse internal zoning reflecting a relatively small compositional variations: Mn/(Mn + Fe) = 0.40 - 0.45 and Ta/(Ta + Nb) = 0.21 - 0.24. Secondary anhedral domains of Ta-rich columbite-(Fe) to tantalite-(Fe) (≤200 μm) with Mn/(Mn + Fe) = 0.45 - 0.47 and Ta/(Ta + Nb) = 0.45 - 0.62 partly replace primary columbite-(Fe) along crystal rims. Moreover, secondary subhedral crystals of microlite-group minerals (≤25 μm) form fracture fillings in columbite-(Fe). The microlites show uniform high Ta/(Ta + Nb) ratio (0.77 - 0.80) and U content (7.7 - 10.2 wt.% UO2; 0.18 - 0.21 U apfu) but different contents of F, Ca, Na and Pb: central parts locally show fluorcalciomicrolite composition (~2 wt.% F, ~9.5 wt.% CaO, 2.2 - 2.7 wt.% Na2O), whereas main microlite mass forms zero-valent-dominant microlite with inclusions (≤8 μm) of Pb-rich zero-valent-dominant microlite (16.8 - 19.7 wt.% PbO; 0.46 - 0.56 Pb apfu). Textural relationships and chemical compositions of Nb-Ta minerals indicate primary magmatic origin of columbite-(Fe) and post-magmatic (early subsolidus to late hydrothermal) formation of secondary Ta-rich columbite-(Fe) to tantalite-(Fe) and microlite-group minerals.

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