Nowe dane o pegmatytach hybrydalnych w serpentynitach kopalni magnezytu Wiry (Dolny Śląsk)
Abstract
NEW DATA ON HYBRID PEGMATITES IN SERPENTINITES OF THE WIRY MAGNESITE MINE (LOWER SILESIA, SW POLAND)
Summary
Desilicated (hybridic) pegmatites, which occur within serpentinites in the Wiry magnesite mine (Fig. 1), are in many respects similar to the classic pegmatites of this type in the Urals Mts. Pegmatites from Wiry are genetically related to the nearby Variscan Strzegom-Sobótka granitic pluton. Reactions between the intruding pegmatitic melt and host serpentinites caused the depletion of the melt in Si and K and its contamination with Mg (Fig. 3). As the result of that process the pegmatitic veins are built up predominantly of Ca-rich albite (over 90 voI. %) and, therefore, can be called plagioclasites. Reaction rims developed at the contact between pegmatites and serpentinites. They consist of the phlogopite, chlorite-vermikulite, and talc zones (Fig. 2). The presence of beryl (Fig. 7) in the hybridic pegmatites is a mineralogical evidence for their granitic origin. Beryl from the Wiry mine has a peculiar EPR spectrum indicative of slow crystalization under relatively high pressure. Electron microprobe analyses of beryl contain about 1 wt. % MgO (Table 2) due to contamination of the melt by Mg derived from the reacting serpentinites. Accessory minerals of the pegmatites include also fluorapatite (Fig. 6, Tables 2 and 3), Mn-almandine , phlogopite (Table 2, Fig. 4), muscovite (Table 2), corundum, cordierite, Mn-c1inozoisite (thulite), zircon, cassiterite and heulandite. Crystallization of apatite and beryl in the pegmatites may have been related to the extensive albitization of pegmatites. Based on the chemical analyses of Ca-rich albites and secondary albites one can calculate that 22 g of plagioclase was necessary to provide Ca to crystallize 1 g of apatite. Mass balance calculations, based on both chemical analyses and density determinations of bulk samples, suggest that between 13 and 28 g of Si per 100 g of rock was released from the melt during the intrusion into serpentinites. Gains and losses of other elements are shown in Figure 8 in respect of volume changes.
Summary
Desilicated (hybridic) pegmatites, which occur within serpentinites in the Wiry magnesite mine (Fig. 1), are in many respects similar to the classic pegmatites of this type in the Urals Mts. Pegmatites from Wiry are genetically related to the nearby Variscan Strzegom-Sobótka granitic pluton. Reactions between the intruding pegmatitic melt and host serpentinites caused the depletion of the melt in Si and K and its contamination with Mg (Fig. 3). As the result of that process the pegmatitic veins are built up predominantly of Ca-rich albite (over 90 voI. %) and, therefore, can be called plagioclasites. Reaction rims developed at the contact between pegmatites and serpentinites. They consist of the phlogopite, chlorite-vermikulite, and talc zones (Fig. 2). The presence of beryl (Fig. 7) in the hybridic pegmatites is a mineralogical evidence for their granitic origin. Beryl from the Wiry mine has a peculiar EPR spectrum indicative of slow crystalization under relatively high pressure. Electron microprobe analyses of beryl contain about 1 wt. % MgO (Table 2) due to contamination of the melt by Mg derived from the reacting serpentinites. Accessory minerals of the pegmatites include also fluorapatite (Fig. 6, Tables 2 and 3), Mn-almandine , phlogopite (Table 2, Fig. 4), muscovite (Table 2), corundum, cordierite, Mn-c1inozoisite (thulite), zircon, cassiterite and heulandite. Crystallization of apatite and beryl in the pegmatites may have been related to the extensive albitization of pegmatites. Based on the chemical analyses of Ca-rich albites and secondary albites one can calculate that 22 g of plagioclase was necessary to provide Ca to crystallize 1 g of apatite. Mass balance calculations, based on both chemical analyses and density determinations of bulk samples, suggest that between 13 and 28 g of Si per 100 g of rock was released from the melt during the intrusion into serpentinites. Gains and losses of other elements are shown in Figure 8 in respect of volume changes.