Wstępne wyniki badań izotopowych δ13C i δ34S nad genezą mineralizacji siarczkowej, węglanowej i grafitowej w skałach zasadowych w masywie suwalskim (NE Polska)

Janina Wiszniewska, Mariusz O. Jędrysek

Abstrakt


PRELIMINARY δ13C AND δ34S ISOTOPE STUDY ON THE GENESIS OF SULPHIDE, CARBONATES AND GRAPHITE MINERALIZATION IN THE MAFIC ORE-BEARING ROCKS OF SUWAŁKI MASSIF (NE POLAND)

Summary
Proterozoic Suwałki Anorthosite Massif is mineralized by Fe-Ti-V oxide-ores, that locally, in the vicinity of Krzemianka and Udryń, have economic significance (Fig. 1). Metal oxides are accompanied by Fe, Cu, Co and Ni sulphides. The origin of the sulphide mineralization either related to magmatic or hydrothermal processes has been considered in this paper. The origin of accessory graphite accompanying sulphides and carbonates has also been discussed. The paper presents δ13CPDB and δ34SCDT values of the samples mineralized with sulphides, carbonates and graphites. The results of isotope examinations are presented in Tables 1,2 and diagrams (Fig. 2 and 3). Microscopic observations indicate that pyrrhotite and chalcopyrite from Krzemianka IG-20 borehole, originated as primary, magmatic minerals together with oreoxides (Fig. 4, 5). This is also confirmed by δ34S values (close to zero), characteristic for magmatic sulphide minerals (Tab. 1). On the other hand, pyrite is a typical, secondary mineral formed in the process of pyritization of pyrrhotite or hydrothermal processes as a filling of fissures and cracks in the rocks (Fig. 6). Its δ34S value is higher than primary sulphides (Tab.l). Nelsonite from Łopuchowo borehole is a veiny ore-apatite rock enriched in ilmenite, magnetite and sulphides: pyrrhotite, chalcopyrite and pentlandite (Fig. 7). The δ34S value (-1,85‰) of chalcopyrite from nelsonite is the lowest one of all the examined sulphides. The presence of graphite indicates a low activity of oxygen. It builds ribbon-like forms together with carbonates around sulphides (Fig. 8 and 9). The results of isotope study of carbonates and graphites support the hypothesis on the origin of graphite from the reduction of siderite.

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