Szekessy Vilmos (szerk.): A Magyar Természettudományi Múzeum évkönyve 57. (Budapest 1965)

Csalogovits, I. J.: Geological and petrological conditions of the Szanda - Bercel area

occur not too frequently in the interior of the veins. These indicate intense oxidation, and chloritization is replaced here by opacitization. The simultaneous appearance of highly oxidized opacitites and chloroandesites in the veins is indicative of extreme fluctuations of pH values of the hydrothermal solutions and of local changes in pH values. Considering, however, that the hydroandesites to be characterized by chloritic decomposition represent about 96% of the endometavulcanites and, further, that the montmorillonite dominating in the hydrothermal material, and the gel-forming opal material of the last generations are doubtless indicative of an alkaline medium, the decomposition character of alkaline-medium hydrothermal solutions can be regarded as acting in the direction of chlorovulcanitization. b. Chloritization of a lesser extent appearing in andésite that is in contact with the veins is an intense montmorillonitization. # c. Feldspar is the montmorillonitization especially of porphyric interbeddings. 3. Exometavulcanitic (weathering) hydroandesites. Hydroandesites formed in the course of weathering occur in the greatest quantities in the crushed zones of dikes that were loosened and shifted by horizontal movements: in small quantities they appear in other places of andésite occurrence on the surfaces of jointing form. Various phases of the process are shown in the crushed zones by andésite blocks of spherical structure. The initial phase of weathering is indicated by opacitization, and by the montmorillonitization of porphyric plagioclases as the process was going on, and the decomposition of the matrix was followed by the dissolution of silicic acid. In the initial phases of decomposition the decrease of iron content, a relative enrichment in silicic acid, the dissolution of silicic acid under the effect of alkaline rock that appears simulTable I. Distribution of the water content of the contact andésite and its country rock. (Szanda) * andésite country rock (sandy clay) ** ""'-'•--^^^ 20 6 3.6 j 1.8 0.6 0.15 0.05 0 0.15 0.30 0.6 1.20 2.40 Quarry sap condition 4.11 8.94 9.5 17.8 24.2 27.7 Air-dry condition 3.4 4.1 5.5 13.7 18.3 18.3 20-105° C w. content 1.6 2.4 1.7 3.2 4.2 1.4 1.0 0.8 3.9 4.0 4.0 7.2 7.3 105 — 1000° C w. content 0.8 1.4 1.4 2.9 3.4 1.1 0.8 0.6 0.8 3.5 3.2 3.3 3.0 * Distance from the contact line in meters. ** Water content of the semples( %).