Desilicated pegmatite with OH-rich fluorapatite and niobian rutile from Utín near Havlíčkův BrodArticle PDF
Desilicated pegmatite with OH-rich fluorapatite and niobian rutile from Utín near Havlíčkův Brod
Mineral assemblages of strongly desilicated granitic pegmatite at Utín near Havlíčkův Brod were examined. The pegmatite crosscuts a small serpentinite body. Prevailing mineral of the pegmatite is a massive chlorite; it encloses relics of plagioclase, fresh phlogopite and accumulations of phlogopite with macroscopically red apatite, colored by thin veinlets of Fe-oxides. Hyalophane (K, Ba-feldspar), scheelite, Nb-rutile, uraninite and zircon were found in microscopic grains. Chlorite occurs in at least three generations, chlorite I and II replaces plagioclase, chlorite III fills fissures in older minerals. Plagioclase is preferentially replaced along twinning lamellae. Phlogopite is a primary mineral; it remained stable during replacement processes. Apatite is a member of fluorapatite-hydroxylapatite (FAp0.6–0.7HAp0.3–0.4) solid solution with slightly elevated content of Fe, Mn and Mg, and low content of Y+REE. Nb-rutile contains 7.33 wt. % of Nb2O5, 2.03 wt. % Ta2O5 and 1.49 wt. % SnO2. Desilication of the pegmatite is most probably related to the hydrothermal alteration processes in the host serpentinite.
Jan Cempírek, Moravian Museum, Dept. of Mineralogy and Petrography, Zelný trh 6, 659 37 Brno; e-mail: firstname.lastname@example.org
Vladimír Strunga, Institute of Geological Sciences, Masaryk University, Kotlářská 2, 61137 Brno
Radek Škoda, Institute of Geological Sciences, Masaryk University, Kotlářská 2, 61137 Brno