Low-hafnium zircon from alluvial and colluvial placeres of northern Bohemia: composition and possible sorces

• Autorzy: Ulrych J. , Her P.
• Języki publikacji: EN

Abstrakty

EN

Low-hafnium zircon is, together with pyrope, sapphire and magnesian ferri-ilmenite, a widespread heavy mineral in three historical placers of precious stones in N Bohemia. The chemical compositions of zircon from all three localities (Třebenice area, Jizerská louka Meadow, Sýkoří důl Valley) are appreciably similar. Zircon forms large, 1 to 7 mm long homogeneous or oscillatory zoned crystals, generally low in Hf (0.45-1.27; aver. 0.77 wt.% HfO2), Y, REE, U, Th and Ca. The genetic association of this zircon with nepheline syenite or pegmatite is doubtful as zircon from this rock found in xenoliths in a nearby alkali basalt pipe breccia from Košťálov Hill represents the Hf-rich type (1.57-1.97; aver. 1.73 wt.% HfO2). Consequently, low-hafnium zircon most probably originated from unknown coarse-grained products of early magmatic crystallisation of an alkali basalt magma forming explosive pipe breccias.

Słowa kluczowe

EN

zircon; Zr/Hf ratios; placer deposits; Bohemia; Czech Republic

• Wydawca: Instytut Nauk Geologicznych PAN ; Instytut Nauk Geologicznych Uniwersytetu Wrocławskiego
• Czasopismo: Geologia Sudetica
• Rocznik: 1999
• Tom: Vol. 32, nr 2
• Strony: 139--146

Twórcy

autor

Ulrych J.

autor

Her P.

• Institute of Geology, Academy of Sciences of the Czech Republic, Rozvojová 135, 165 02 Praha 6, Czech Republic