PYRITE-CARBONATE MINERAL ASSOCIATION. SIGNS OF POST-DIAGENETIC PROCESSES IN PALAEOCENE FLYSCH DEPOSITS (SKYBOVA ZONE, UKRAINIAN CARPATHIANS)

Abstract

We studied post-diagenetic processes occurring in the Palaeocene sedimentary strata of the Skybova zone (Ukrainian Carpathians) to identify the relationship between the processes of litho- and ore-genesis. Our goal is to characterize the cata-metagenetic (post-diagenetic) pyrite-carbo-nate mineral association and to investigate its role in the processes of ore genesis. Geological, petrographic and mineralogical (pyrite, carbonate, quartz, sericite) studies of Palaeocene sedi-ments have been performed. The results of our previous lithological-stage and mineralogical-geochemical studies made it possible to determine different degrees of transformation of Palaeocene sediments on the exam-ple of the Yaremchanskyi horizon sandstones (Skybova zone). We distinguished progressive lithogenesis (100–175 °C), which covers the processes of catagenesis and metagenesis, and re-gressive lithogenesis (up to 100 °C), when hypergenesis processes complicated by low-tempera-ture hydrothermal manifestations took place. The following mineral associations have been distinguished: sedimentary-diagenetic pyrite-chrysocolla, cata- and metagenetic (or post-diagenetic) pyrite-carbonate and hydrothermal-sedi-mentary (low-temperature) chalcopyrite-bornite-malachite. The object of our research – post-diagenetic mineral association – is pyrite, carbonate, quartz and sericite. Minerals form streaky impregnations and fill the cement in the rock. Late pyrite grains often associate with carbonates, forming close intergrowths with them. Pe-ripheral parts of pyrite grains contain impregnations and microveinlets of carbonates. Instead, carbonate veinlets penetrate the pyrite grains to form a network of fine intergrowths. Sericite, which has been developed on glauconite, forms fine-grained flaky aggregates, sometimes forms gouges on the surface of pyrite grains and occurs in association with quartz and carbonate. Quartz evolved on chalcedony during its recrystallization, as evidenced by the unusu-ally sharp wavy extinction (in the sections under the microscope), which resembles chalcedony. Undoubtedly, the pyrite-carbonate association played an important role in the sequence of epigenetic mineralization formation in the Palaeocene sediments of the Skybova zone in the Ukrainian Carpathians.