Stopy magmaticke flotace v “iserinu” z ricky Jizerky v Jizerskych horach

The Jizerka Rivulet in the Jizerské hory Mts is the best known gemstone alluvial placer in the Czech Republic at least since the 16^th century (Fig. 1). Dominant tracker of sapphires and zircons (hyacinth) is “iserine” (Mg-Fe³⁺-rich variety of ilmenite), which is the most common heavy mineral originally described from Jizerská louka (Iser meadow), Jizerské hory Mts. (Iser Mts.) by Klaproth in the 19^th century (Klaproth 1810).
This article deals especially with the traces of the magmatic flotation in nodules of the “iserine” mineral assemblage from the Jizerka Rivulet in the Jizerské hory Mts. The process of the magmatic mineral separation is documented with the bubble-shaped concave imprints onto “iserine” grains, resembling the slag texture. Deep sink of the fluid bubbles into soft “iserine” nodules indicates the coexistence of this mineral association with the magmatic melt in thermodynamic equilibrium at the temperature above 1000° C. Actually, ilmenite is a liquidus mineral, which is the first or among the first mafic minerals to crystallize in Fe-Ti rich magmas. Herein documented massive invasion of the fluid bubbles onto minerals of the “iserine” assemblage produced their magmatic flotation and accumulation at the roof of the magma chamber. Deep seated basaltic melt at the basement of the Krkonoše-Jizera Granite Massif facilitated fast transport of “iserine” nodules/aggregates with the assistance of fluid bubbles via volcanic diatremes on the ground surface. A weak abrade of the bubble imprints into “iserine” nodules indicates short transport of the “iserine” mineral association from the volcanic source to the Jizerka Rivulet. This model represents another link of the Pytlacká Hollow volcanic diatreme with occurrence of the “iserine” mineral association in the neighbouring Jizerka Rivulet.