Microlite-group minerals: tracers of complex post-magmatic evolution in beryl–columbite granitic pegmatites, Maršíkov District, Bohemian Massif, Czech Republic
| Authors | |
|---|---|
| Year of publication | 2021 |
| Type | Article in Periodical |
| Magazine / Source | Mineralogical Magazine |
| MU Faculty or unit | |
| Citation | |
| Web | https://www.cambridge.org/core/journals/mineralogical-magazine/article/microlitegroup-minerals-tracers-of-complex-postmagmatic-evolution-in-berylcolumbite-granitic-pegmatites-marsikov-district-bohemian-massif-czech-republic/B2D8DBE1935150ABEAD88BE8EF2442 |
| Doi | http://dx.doi.org/10.1180/mgm.2021.58 |
| Keywords | granitic pegmatites; beryl-columbite subtype; Nb-Ta minerals; microlite; columbite; tantalite; fersmite; crystal chemistry; hydrothermal alteration; recrystallisation |
| Description | 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 Schinderhubel I, Scheibengraben and Bienergraben beryl-columbite pegmatites in the Marikov 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 (mu RS). 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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