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Drilling of the Kola Superdeep well (SG-3) was begun in May, 1970 on the Kola Peninsula above the Arctic Circle in northwestern U.S.S.R. This book presents the main results of studies to its present depth of 11,600 m. The work is divided into three parts: geology, geophysics, and drilling. Geology. The area of drill hole SG-3 is underlain by ancient igneometamorphic rocks of the Baltic shield. Archean crystalline basement is overlain by Proterozoic metamorphosed sedimentary and volcanic rocks. The Archean consists of the Kola Series and is divided into two sequences: biotite-plagioclase and biotite-amphibole-plagioclase gneisses and amphibolites at the base, and biotite plagioclase and muscovitebiotite-plagioclase gneisses containing high-alumina minerals (sillimanite, kyanite, garnet) above. The Proterozoic in drill hole SG-3 consists of metamorphosed tholeiitic metabasalt, metapyroxenite, metaperidotite, metatuffs, and a variety of metasedimentary rocks (sandstones, arkoses, carbonates) of the Pechenga Complex. Drill hole SG-3 is located in the Pechenga copper-nickel sulfide district. The greatest concentrations of ore minerals were found in zones of pyrrhotite mineralization of the Pechenga Complex. Commercialgrade copper-nickel ore was found in the 1665-1830 m depth interval. Three types of ores are found in the Pechenga Complex: disseminated ores in altered peridotite, breccia ores in disturbed zones, and veinlet and disseminated ores in phyllites. Ultramafic intrusives are doubtless the source of copper-nickel ores. The downward increase in temperature of metamorphism is accompanied by a transition from brittle to ductile deformation. However, one of the unexpected findings was' a wide distribution at all depths of fissures with various^ mineral fillings. It was found that mineralized zones of crushing, cataclasis, fracturing, and low temperature hydrothermal alteration, including sulfide mineralization, extend to depths 3 or 4 times what had been expected. Gas content of drilling mud and of cores was measured. Anomalous high concentrations of all components were detected down to 11,500 m. Methane content decreased .with depth from 0.05% in the Proterozoic rocks to 0.03-0.01% in the Archean rocks. Helium content tends to increase with depth. Drill hole SG-3 penetrates an ancient Proterozoic artesian basin. Gravitational water is distributed throughout the entire section of metamorphic rocks, marking the first time that ground water has been found under such conditions. This water is similar to d^_ep metamorphosed marine connate water of ancient platforms and intermentane basins. Ground water in the 0.8-7 km interval is of the sodium-chloride composition, salinities increasing with depth and reaching saturation in some intervals. Water in the 4.5-9 km interval is not connected hydraulically with the overlying zone; the water level immediately rose 80 m when this zone was penetrated. Below 7 km depth the water becomes calcium-chloride and calcium-sodium-chloride type. A constant inflow of water was observed d...

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