Występowanie, petrografia i geneza dolomitu granicznego w cechsztynie okolic Lubina.
Abstract
Occurrence, petrography and genesis of the boundary dolomite in the Zechstein near Lubin
Abstract
The paper presents results of investigations of the so-called boundary dolomite occurring west of Lubin. The boundary dolomite appears at the base of the first Zechstein cyclothem (P21). Its appearance disturbs typical lithological succession in the cyclothems, thus one may distinguish subcyclothem P21'. There are two megascopic varieties of the boundary dolomite: light-gray and gray-black, developing in different sedimentary environments. Microscopic studies allow to distinguish three microfacial varieties, namely microsparite, biomicrite, and sandy dolomite. Studies performed on rock samples and in the mine excavations allow to conclude that the boundary dolomite developed in troughs of a shallow sea basin. Increased salinity promoted dolomitization of a newly deposited calcite mud. Then, in further stages of diagenesis took place recrystallization and mineralization. The chief ore mineral of the boundary dolomite is chalcopyrite. Bornite, galena and pyrite are less common. Chemical analyses showed that the boundary dolomite is composed of pure dolomite and dolomite impured with sandy and clayey-coal matter.