Compositional and textural variations of columbite-group minerals from beryl-columbite pegmatites in the Maršíkov District, Bohemian Massif, Czech Republic: Magmatic versus hydrothermal evolution
Abstract:We studied compositional variations in columbite group minerals (CGM) from several granitic pegmatites of the beryl-columbite subtype in the Maršíkov district, Silesian Domain of the Bohemian Massif, Czech Republic. The CGM are characterized by distinct zoned patterns in BSE images. Primary magmatic homogeneous to oscillatory zoning is preserved in corroded crystal cores, whereas the majority of the crystal volume is replaced by secondary complexly zoned domains formed via post-magmatic processes. The primary … Show more
“…Fig. 1.Geological map of the Silesian Domain and the Maršíkov District with individual pegmatite occurrences (modified after Cháb et al , 2007 and on-line map application of the Czech Geological Survey 2019, Chládek et al , 2020). …”
Section: Geological Settingmentioning
confidence: 99%
“…Fig. 2.Idealised cross-sections of the pegmatites: (a) Maršíkov – Schinderhübel I (Chládek et al , 2020, modified); (b) Maršíkov – Scheibengraben (Novák et al , 2003, modified); (c) Sobotín – Bienergraben (Chládek et al , 2020, modified).…”
Section: Internal Structure Petrography and Mineralogy Of Pegmatitesmentioning
confidence: 99%
“…All the pegmatites investigated contain very similar mineral assemblages and they correspond to the LCT family and beryl–columbite subtype of rare-element granitic pegmatites ( sensu stricto Černý and Ercit, 2005). Accessory minerals include common garnet (almandine–spessartine), zircon, fluorapatite, gahnite and uraninite together with other, mostly rare, minerals (Pokorný and Staněk, 1951; Dostál, 1966; Kruťa, 1966; Chládek et al , 2020; Dolníček et al , 2020a,b). Beryl is the only primary magmatic Be mineral together with rare metamorphic chrysoberyl and common secondary bavenite and bohseite.…”
Section: Internal Structure Petrography and Mineralogy Of Pegmatitesmentioning
confidence: 99%
“…Beryl is the only primary magmatic Be mineral together with rare metamorphic chrysoberyl and common secondary bavenite and bohseite. Niobium–tantalum oxide minerals are represented by relatively common columbite–tantalite and microlite, whereas Nb–Ta-rich rutile, titanite, tapiolite-(Fe), rynersonite, and fersmite are less common (Čech, 1973; Černý et al , 1992, 1995; Novák et al , 2003; Novák and Dosbaba, 2006; Chládek et al , 2020). Most granitic pegmatites in the Maršíkov District are relatively poor in B, F and P (Novák, 1988, 2005; Novák et al , 2003), only the most fractionated Scheibengraben body also contains accessory schorl, topaz and triplite (Pokorný and Staněk, 1951).…”
Section: Internal Structure Petrography and Mineralogy Of Pegmatitesmentioning
confidence: 99%
“…We have investigated beryl–columbite pegmatites from the Maršíkov District, Bohemian Massif which are relatively poor in volatile elements (F, B or P). They contain accessory Nb–Ta oxide minerals (maily members of CGM), which have been the object of several investigations (Černý et al , 1992, 1995; Novák et al , 2003; Novák and Dosbaba, 2006; Chládek et al , 2020), though these have had only minor focus on the microlite-group minerals replacing columbite–tantalite. The microlite-group minerals, which can form a variety of textural and compositional types, precipitated at least three different stages, which reflect complex subsolidus processes in the host pegmatite.…”
Microlite-group minerals occur as common replacement products after primary and secondary columbite-group minerals (CGM) in albitised blocky K-feldspar and in coarse-grained, muscovite-rich units of the Schinderhübel I, Scheibengraben and Bienergraben beryl–columbite pegmatites in the Maršíkov District (Silesian Unit, Bohemian Massif, Czech Republic). Textural and compositional variations of microlite-group minerals were examined using electron probe micro-analyses and microRaman spectroscopy (μRS). A complex post-magmatic evolution of the pegmatites and the following microlite populations (Mic) and related processes were found: (1) precipitation of U, Na-rich and F-poor Mic I on cracks in CGM; (2) alteration of Mic I to U-rich together with Na- and F-poor Mic II; and (3) partial replacement of Mic I and II by Mic III with a distinct Na, U and Ti loss and Ca and F gain. Stage (2) includes an extensive leaching of Na, without U loss. The final stage (3) produced euhedral-to-subhedral oscillatory zoned Ca and F enriched Mic III with distinctly different composition to the previous F-poor and A-site vacant Mic II. Aggregates of fersmite are associated commonly with Mic III. Distal Mic IIId occurs locally on cracks in K-feldspar or quartz, with compositions analogous to Mic III. Compositional variations and textural features of microlite-group minerals during dissolution–reprecipitation processes serve as sensitive tracers of post-magmatic evolution in granitic pegmatites recording complex interactions between magmatic pegmatite units and externally derived, hydrothermal metamorphic fluids.
“…Fig. 1.Geological map of the Silesian Domain and the Maršíkov District with individual pegmatite occurrences (modified after Cháb et al , 2007 and on-line map application of the Czech Geological Survey 2019, Chládek et al , 2020). …”
Section: Geological Settingmentioning
confidence: 99%
“…Fig. 2.Idealised cross-sections of the pegmatites: (a) Maršíkov – Schinderhübel I (Chládek et al , 2020, modified); (b) Maršíkov – Scheibengraben (Novák et al , 2003, modified); (c) Sobotín – Bienergraben (Chládek et al , 2020, modified).…”
Section: Internal Structure Petrography and Mineralogy Of Pegmatitesmentioning
confidence: 99%
“…All the pegmatites investigated contain very similar mineral assemblages and they correspond to the LCT family and beryl–columbite subtype of rare-element granitic pegmatites ( sensu stricto Černý and Ercit, 2005). Accessory minerals include common garnet (almandine–spessartine), zircon, fluorapatite, gahnite and uraninite together with other, mostly rare, minerals (Pokorný and Staněk, 1951; Dostál, 1966; Kruťa, 1966; Chládek et al , 2020; Dolníček et al , 2020a,b). Beryl is the only primary magmatic Be mineral together with rare metamorphic chrysoberyl and common secondary bavenite and bohseite.…”
Section: Internal Structure Petrography and Mineralogy Of Pegmatitesmentioning
confidence: 99%
“…Beryl is the only primary magmatic Be mineral together with rare metamorphic chrysoberyl and common secondary bavenite and bohseite. Niobium–tantalum oxide minerals are represented by relatively common columbite–tantalite and microlite, whereas Nb–Ta-rich rutile, titanite, tapiolite-(Fe), rynersonite, and fersmite are less common (Čech, 1973; Černý et al , 1992, 1995; Novák et al , 2003; Novák and Dosbaba, 2006; Chládek et al , 2020). Most granitic pegmatites in the Maršíkov District are relatively poor in B, F and P (Novák, 1988, 2005; Novák et al , 2003), only the most fractionated Scheibengraben body also contains accessory schorl, topaz and triplite (Pokorný and Staněk, 1951).…”
Section: Internal Structure Petrography and Mineralogy Of Pegmatitesmentioning
confidence: 99%
“…We have investigated beryl–columbite pegmatites from the Maršíkov District, Bohemian Massif which are relatively poor in volatile elements (F, B or P). They contain accessory Nb–Ta oxide minerals (maily members of CGM), which have been the object of several investigations (Černý et al , 1992, 1995; Novák et al , 2003; Novák and Dosbaba, 2006; Chládek et al , 2020), though these have had only minor focus on the microlite-group minerals replacing columbite–tantalite. The microlite-group minerals, which can form a variety of textural and compositional types, precipitated at least three different stages, which reflect complex subsolidus processes in the host pegmatite.…”
Microlite-group minerals occur as common replacement products after primary and secondary columbite-group minerals (CGM) in albitised blocky K-feldspar and in coarse-grained, muscovite-rich units of the Schinderhübel I, Scheibengraben and Bienergraben beryl–columbite pegmatites in the Maršíkov District (Silesian Unit, Bohemian Massif, Czech Republic). Textural and compositional variations of microlite-group minerals were examined using electron probe micro-analyses and microRaman spectroscopy (μRS). A complex post-magmatic evolution of the pegmatites and the following microlite populations (Mic) and related processes were found: (1) precipitation of U, Na-rich and F-poor Mic I on cracks in CGM; (2) alteration of Mic I to U-rich together with Na- and F-poor Mic II; and (3) partial replacement of Mic I and II by Mic III with a distinct Na, U and Ti loss and Ca and F gain. Stage (2) includes an extensive leaching of Na, without U loss. The final stage (3) produced euhedral-to-subhedral oscillatory zoned Ca and F enriched Mic III with distinctly different composition to the previous F-poor and A-site vacant Mic II. Aggregates of fersmite are associated commonly with Mic III. Distal Mic IIId occurs locally on cracks in K-feldspar or quartz, with compositions analogous to Mic III. Compositional variations and textural features of microlite-group minerals during dissolution–reprecipitation processes serve as sensitive tracers of post-magmatic evolution in granitic pegmatites recording complex interactions between magmatic pegmatite units and externally derived, hydrothermal metamorphic fluids.
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