Composition of quartz-muscovite shales from pre-Jurassic basement of the West Siberian megabasin (West-Yarotinskaya area, Yamal)

Geological studies of the West Siberian megabasin are a priority, since the hydrocarbon deposits of this vast re¬gion are extremely important for the Russian economy. The paper describes in detail the mineralogy and trace element composition of quartz-muscovite shales from the basement of the Yamal Peninsula (well West-Yarotinskaya 303). The mineral composition of the rocks is as follows: quartz, muscovite, donbassite, albite, dolomite, siderite, calcite, dravite, schorl, rutile, zircon, fluorapatite, pyrite, chalcopyrite, sphalerite, galena, violarite, goyazite, flo¬rensite-(Ce). The florensite-(Ce) determined by us is the first find for rocks from the basement of the West Siberian Plate. The distribution of rare, trace, and rare-earth ele¬ments in the studied rocks is similar to that of metamor¬phic shales from the basement of the Arctic (Lenzitskaya area and Verkhnerechenskaya area) and Cis-Ural (Shaim¬sko-Kuznetsovskmeganticlinorium shales) parts of the West Siberian megabasin. Probably, the studied metape¬lites were formed as a result of heating of the sedimen¬tary rocks by a granite intrusion located in the immediate vicinity on the territory of the Verkhnerechenskaya area. Later, the rocks underwent propilitization with the forma¬tion of secondary carbonate, goyazite, florensite-(Ce) and sulfides.