Acta Mineralogica-Petrographica, Abstract Series 1, Szeged, 2003 THE PECTOLITE SKARN FROM MIĘDZYRZECZE (BIELSKO-BIAŁA REGION) IN THE POLISH CARPATHIANS KARWOWSKI, Ł. & WŁODYKA, R. Department of Geochemistry and Petrology, University of Silesia, ul. Będzińska 60, PL-41-200 Sosnowiec, Poland. E-mail: [email protected] In the western part of the Outer Polish Carpathians, be- There are two genetic types of pectolite: open-space fill- tween Bielsko-Biała and Cieszyn, the occurrence of ing and metasomatic. Pectolite, like datolite, can crystallize teschenite sills and related rocks (diabase, picrite and lam- only from solutions with very low concentrations of CO2, i.e. prophyre) were observed. They are widely distributed in the in zones of reduced pressure, where degassing of CO2 takes flysch sediments of the Cieszyn Subnappe (Cieszyn beds, place. In the veins intersecting the skarn body pectolite forms Upper Kimmeridgian to Hauterivian). irregular massive aggregates of radial or fan-arranged crys- In Międzyrzecze Górne near Bielsko-Biała, close to the tals with size between a few millimeters and 12 cm. Large, top of the picrite sill, the presence of a pectolite skarn was up to 6 cm long, fibrous (with diameter below 0.01 mm) or stated. The pectolite endoskarn forms a lenticular body that is needle-shaped (up to 0.03 mm) crystals are white and silky. up to 2 m thick, 5 m wide and 12 m long. Abundant carbon- The second, metasomatic type of pectolite forms the endo- ate veins (up to 30 cm thick) intersect the central part of the skarn body. The formula of the fibrous pectolite from the skarn filling the tectonic fissures and cracks. The pectolite centres of vein in endoskarn is Na0.98Ca2.00H1.01Si2.99P0.01O9. skarn consists mainly of elongated (up to 2 mm long and to There are small chemical differences between two genetic 0.5 mm wide) pectolite crystals which poikilitically enclose types of pectolite. The metasomatic type is enriched in abundant inclusions of Ti-garnets, diopside, analcime and Al2O3, FeO, MnO, and MgO compared to the open-spaces aegirine. Poikilitic biotite crystals with inclusions of Ti- filling type. Pectolite from the Międzyrzecze sill is triclinic garnets sometimes coexist with other minerals such as natro- with the following lattice parameters: a = 7.986 Å, b = 7.017 lite, calcite, apatite and titanite. Veins cutting the skarn body Å, c = 7.021 Å and α = 90.399o, β = 95.208o, γ = 102.554o. contain calcite, pectolite, natrolite, analcime, datolite, Ti- In the pectolite skarn, two types of Ti-bearing garnet can garnet and apophyllite. The spatial relationships between the be distinguished: above mentioned minerals suggest that natrolite and anal- 1. Brown-black euhedral crystals (<0.02 mm) forming in- cime were the first to crystallize forming the vein margins, clusions in pectolite, biotite, titanite and diopside or filling being followed by calcite. Pectolite, likewise datolite and open spaces in veins. apophyllite always formed after calcite had filled open 2. Larger (up to 0.7 mm across) atoll-shaped garnets spaces in the vein centres. showing narrow black-light brown rims completely distinct Datolite from Międzyrzecze occurs mainly as granular from cores consisting of spicular aegirine and a cryptocrys- aggregate, rarely as automorphic crystals up to 1 cm in size, talline mixture of natrolite and analcime. These garnets are pale green in colour. Three morphological types of datolite clearly metasomatic type Ti-garnets. Both types of garnet crystals were distinguished: pseudo-bipyramidal, prismatic from the pectolite skarn show very restricted changes in TiO2 and pinacoidal. Most of the datolite crystals are 0.5–0.8 cm content (12–15 wt%). Textural and chemical evidence shows in size and belong to the second type. They crystallized on that the atoll garnets reflect replacement, mainly by analcime the walls of miarolitic cavities within calcite. On basal pina- and natrolite, progressing from the garnet interior towards coid faces of datolite numerous fluorapophyllite crystals the garnet margins. The garnet compositions plotted on the appear. Its chemical composition follows the crystallochemi- schorlomite (2R4+) – andradite (2R3+) – morimotoite (R2+R4+) cal formula (K0.86Na0.03)0.89 Ca4.03 (Si7.91Al0.04P0.03)7.98 (F0.83 diagram show that they are titanian andradites according to OH0.17)1.00O19.92 • 8.08 H2O. The datolite habit changes from the nomenclature of DEER et al. (1982). The data obtained pseudo-bipyramidal through prismatic to pinacoidal with pH support the conclusion that the schorlomite substitution was decrease. In the Międzyrzecze skarn, in individual cavities, the major factor in the formation of Ti-bearing garnet in the datolite crystals of different habit coexisted. This situation skarn from the Międzyrzecze sill. may reflect the local, labile conditions of datolite crystalliza- tion in the open system. The studied datolite has monoclinic References symmetry with the following lattice parameters: a = 4.8316 DEER, W. A., HOWIE, R. A. & ZUSSMAN, J. (1982). Å, b = 7.6054 Å, c = 9.6287 Å and β = 90.143o. Its chemical Rock-forming minerals. Vol. 1A. Orthosilicates (2nd ed.) composition is close to the theoretical one, among trace ele- KUDĚLÁSEK, F., MATYSEK, D. & KLIKA, Z. (1987). ments barium and strontium predominate. Datolite from Čas. Mineral. Geolog., 32(2): 169-174. Międzyrzecze is similar in composition to those from Žer- manice and Řepiště (Northen Moravia) (KUDĚLÁSEK et al., 1987). 50.