Mineralogical and geochemical features of volcanics from the pre-Jurassic basement of the western part of Yamal

Abstract

Relevance of the work. The Arctic part of the West Siberian megabasin is the main source of oil and gas in Russia, therefore, the study of the geological structure of this region is extremely important. Recently, Russia has lodged an application to extend its territory in the Arctic Ocean along the ridges that stretch from the continental shelf. Unfortunately, at the same time, we know little about the geological structure of the Arctic in the region of Western Siberia, where the thickness of the sedimentary cover is very high (about 3–4 km), therefore, the study of the basement of the Yamal Peninsula seems to be extremely urgent. The purpose of this work is mineralogical, petrological and geochemical study of dolerites from the pre-Jurassic basement of the Bovanenkovskaya area (well No. 114) within the territory of the gas condensate field of the same name, located in the western part of the Yamal Peninsula. Scope of the work. This work can be useful in constructing geological maps of the pre-Jurassic basement of the Yamal Peninsula. Results and conclusions. We have studied the mineralogical and geochemical features of dolerites from the pre-Jurassic basement of the Bovanenkovskaya area (well No. 114, sampling depth – 3210 m) of the West Siberian megabasin. The mineralogy of the rocks is represented by augite, diopside, albite, magnesian chamosite, ferrous hornblende, calcite, siderite, dolomite, anorthoclase, grossular, zeolite (gmelenite-K), pyrite, chalcopyrite, and rare lead chloride – cotunnite. The rocks underwent minor transformations in the conditions of the lower greenschist metamorphism, as well as secondary alterations in the form of superimposed propylitization. As a result of this low-temperature metasomatic process, zeolite, carbonate (calcite, dolomite, and siderite) and sulfide mineralization composed of pyrite and chalcopyrite, as well as cotunnite, which apparently replaced the dissemination of galena, were formed in the rock. Judging by geological position of the region, these dolerites are most likely formed at shallow depths during continental rifting. Remelting of the Paleozoic island arc substrate during the Early Triassic rifting and volcanism provided some closeness to the island arc trend in the geochemical features of these rift volcanics.