Pneumatolytic and hydrothermal activity in the Karkonosze-Izera block

Abstract

The Karkonosze-lzera block in the Sudetes Mts (Southern Poland), consisting of the Karkonosze ganite massif and its gneiss-schist cover, named the lzera area, bears numerous pegmatites and pneumatolytic-hydrothermal bodies: veins, silicified cataclastic zones, and metasomatites (leucogranites, greisens and tourmaline nests). A scheme of the formation of early zones of pegmatites by metasomatic recrystallization of aplite under pneumatolytic conditions is presented, being established on textural features. The mode of crystallization of the individual types of veins depended on the type of fracture and the changes of temperature during the fracture filling with minerals. Both pegmatites and veins from Karkonosze formed originally under action of pneumatolytic, and subsequently of hydrothermal fluids, contrary to veins and metasomatites in the Izera area, formed by an activity of essentially hydrothermal fluids. Measurements of temperatures of the homogenization of fluid inclusions and evaluation of the pressure permitted a discussion of real temperatures of the crystallization of hydrothermal mineral assemblages. Geochemistry of major elements in the inclusion fillings i.e. sodium, potassium, calcium, magnesium, aluminum, iron and chlorine, was characterized. High fluorine content in inclusions, expressed as atomic ratio l000F/Cl is typical of metasomatites and ore-bearing rocks in the Izera area, being a possible prospecting tool. Minor and trace elements in inclusion flulids, especially Li, Be and B, have characteristic regional distribution. Bromine content in inclusions gives some genetic suggestions on the origin of mineral-forming solutions. Discussed are also possible relations between diverse hydrothermal deposits in the metamorphic lzera cover and the Karkonosze granite massif.