Diabazy z wiercenia Kurowo-2 koło Koszalina

Wiesław Heflik, Marek Muszyński

Abstract


DIABASES DRILLED AT KUROWO-2, NEAR KOSZALIN

Summary

Basic magmatic rocks (diabases) have for the first time been encountered at a depth of 2147,0-2171,2 m in the Western Pomerania area, by bore hole Kurowo-2, situated approximately 30 km SE of Koszalin (Fig. 1). These rocks are immediately overlain with black dolomites, locally impregnated with calcite and pyrite, and higher up with dark ashen-grey schists with anhydrite or dolomite veinlets. This complex, along with the magmatic rocks (from 2129,0 to 2171,2 m), has been referred to the Carboniferous . Under the microscope, the diabase reveals a holocrystalline, ophitic texture, locally intersertal or poikilitic. Two varieties can be distinguished here: finecrystalline and mesocrystalline (Tables I and II). Plagioclase (labradorite and Basic oligoclase) and pyroxenes (diposide augite) are the main components of these rocks. Magnetite, ilmenite, apatite and biotite are subordinate ones. Of considerable importance are also secondary minerals like chlorites, talc, and, subordinately, calcite. The average mineral composition of these rocks is shown in Table 1. The chlorites occur in two varieties: olive-green (prochlorite) and grass-green (pennintite). The chlorites are accompanied by abundant ore minerals: magnetite, ilmenite (Table 2), pyrite and chalcopyrite. Apatite is developed in the form of elongated columns, small rods or needles. X-ray examinations (Table 3) and spectrophotometric analyses in infra-red radiation (Fig. 2) point that it belongs to the fluorine variety. It results from the research works that the crystallization of intrusion of the diabase pierced by bore hole Kurowo-2 at a depth of 2147,0-2171,2 m took place at insignificant temperature changes. Due to this, two diabase varieties crystallized: fine-crystalline diabase and medium-crystalline diabase. During the final phase of the formation of this intrusion some autohydrothermal phenomena developed, leading to the complete or partial chloritization of pyroxenes, the development of calcite, and the mineralization of these rocks with pyrite and chalcopyrite. These alternation processes comparised mainlythe medium-crystalline variety of the diabases, the crystallization of which, as compared with the fine-crystallization variety, took place most probably at an earlier period. Such conditions may have occurred in near-surface intrusion, i. e. in the discussed rocks pierced by bore hole Kurowo-2. The crystallization of the rocks under examination, particularly that of the fine-crystalline variety, was accompanied by a considerable amount of titanium and phosphorus, i. e. chemical elements which first of all entered the composition of both ilmenite and apatite. The investigations carried out prove the previous observations, pointing to the existence of basic magmatism in all the Carboniferous occurrences known at present in the areas of Poland.


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