Mineralizacja osadów doggeru na przykładzie otworu Głogowiec

Abstract

MINERALIZATIONS OF DOGGER DEPOSITS IN THE BORE HOLE GŁOGOWIEC

Summary

The bore hole Głogowiec is situated in the area of the eastern limb of the Kłodawa-Lęczyca anticline, about 20 km: NE of Kłodawa (Kujawy - Pomeranian, anticlinorium). At the top part of the Bathonian deposits at Głogowiec, intercalations rusty-cherry in colour were found to occur among grey sandstones at a depth from 621 to 600 metres (Fig. 11). It appeared that these arenaceneous-carbonate rocks, rich in iron compounds mostly fine-grained or middle-grained quartz  sandstones with dolomite-ankerite cement. Arenaceous ankerite, dolomites are rarely found. Quartz (Tabl. I; Fig. 2) is here the main detrital mineral and feldspars, muscovite, zircon, tourmaline, sandstone and siltstone fragments, ferruginous oolites and dolomitized fragments of echinoderms and pelecypods appear subordinately. These rocks contain more than 10,4%  Fe₂O₃ that occurs in the form of goethite (Tabl. I, Fig. 3) and up to 10,2% FeO bound in ankerite.
Feldspar grains reveal regeneration rims characterized by idiomorphic outlines (Tabl. II, Figs. 4 and 5). Both grains and rims are represented by microcline with an angle of optical axes amounting to 2V₂ = 80–85°. Feldspar grams and rims, also quartz grams, are frequently corroded by alkali solutions (Tabl. III, Figs. 6 and 7). Feldspars with rims are most frequently found in the middle, most ferruginous part of the section under examination, whereas at the bottom and top, they occur sporadically.
The remaining Bathonian sandstones, grey and grey-greenish in colour, that were found in the bore hole Głogowiec at a depth from 630 m to 600 m, resemble the cherry sandstones described above, but they contain far less iron (up to 2,6%, F₂O₃ and 3,9% FeO).
The results of total analyses of the 1114 selected arenaceous-carbonate rock samples are given in Tab. 1, Tab. 2 shows the results of spectral analysis of 33 samples. For the highest contents of some trace elements their chemical compositions were determined (Cu – 0,01%, Cr –0,06%, Mo – 0,002%, Pb – 0,03%.
These values exceed the clarks of the above chemical elements in sedimentary rocks and salts (L. Vinogradov, 1962, S. Katshenkov, 1964, H. Born, 1934).
Both microscope and chemical examinations show that the rocks described above are not primary formations. Their development is not typical of the Bathonian deposits of the Polish Lowland area. Certain concentration of trace elements, regeneration rims around feldspar grains, irregular arrangement of iron hydroxide and carbonate concretions in rocks and relict character of clay cement in some samples are here of particular significance. In all probability, initially, these were slightly compact, porous quartz sandstones that were then mineralized and cemented due to the activity of solutions. To the I stage of mineralization belong: feldspathization, geothitization and concentration of copper and other trace elements. This stage should be referred to the period of early diagenesis. Mineralizing solutions contained mainly such ions as K^+l, Fe⁺³, as well as Cu⁺¹, Pb⁺², Cr⁺³ and others, pH value being about 8. The next stage of transformations followed the process of hardening of Bathonian sediments, and began after the crystallization of feldspar rims. To the stage of mineralization belong: dolomitization of deposit, and formation of ankerite. The mineralizing solutions were characterized mainly by the presence of Ca⁺², Mg⁺², CO₂^–2 ions and of little H₂S, and concentration of hydrogen ions ranging from 9 to 10. These solutions were also responsible for a partial dissolution of feldspars and quartz.
Taking into account the situation of the bore hole Głogowiec, located within the Kłodawa-Łęczyca anticline, one can suppose that brines had been here mineralizing solutions, since similar phenomena, e.g. dolomitization or mineralization with pyrite, were found in this area in several bore holes (J. Znosko, 1957, R. Krajewski, 1957). The I stage of mineralization can be related to an outflow of brines in the uplifted salt masses at the Bathonian time. The II stage of mineralization is connected with an intense outflow of magnesium brines which, according to J. Znosko (1957), took place in the Kujawy region, during the young Cimmerian orogeny.