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Gor'Kovets V.Ya.,Russian Academy of Sciences | Rudashevskii N.S.,OOO PC | Rudashevskii V.N.,OOO PC | Popov M.G.,Russian Academy of Sciences | Antonov A.V.,Karpinskii All Russia Geological Research Institute VSEGEI
Doklady Earth Sciences

The mineralogy of a new lamproitic diatreme 200-250 m in diameter and 3 ga in area is studied in detail. The chemical and 3-D mineralogical analysis identify the diatreme rocks as strongly altered olivine lamproites with a large volume (50-60%) of xenoliths of strongly altered spinel (garnet) lherzolites and harzburgites-dunites. Numerous grains-xenocrysts of indicator minerals of diamond have been extracted from the heavy concentrates (the weight of the initial product is 742 g and the size is 100-500 μm) as a result of hydroseparation: (1) subcalcium (CaOav. 2.6 wt %) high-Cr (Cr 2O3 av. 5.3 wt %) pyrope (50 grains); (2) chrome diopside (7 and 8 mol % of kosmochlor and jadeite components, respectively, >40 grains); (3) high-Cr chromite (Cr2O3 > 62 wt %); and (4) picroilmenite (MgO 12-13.8 wt %) and Cr-rutile (Cr2O3 1.1 wt %). Xenocrysts prove the mantle endogene (the level of garnet lherzolites) source of the magmatic center of lamproites and forecast the diamond potential of the new diatreme in the Kostomuksha ore district. © 2013 Pleiades Publishing, Ltd. Source

Morozov A.F.,Federal Agency of the Russian Federation for Treatment of Resources of the Earthss Interior | Khakhaev B.N.,NPTs Nedra Public Joint Stock Company | Petrov O.V.,Karpinskii All Russia Geological Research Institute VSEGEI | Gorbachev V.I.,Karpinskii All Russia Geological Research Institute VSEGEI | And 6 more authors.
Doklady Earth Sciences

A thick (200 m) rock salt mass covering Late Archean granitoids was exposed for the first time in the Early Proterozoic volcanogenic-sedimentary formations in the Onega trough of the east Baltic Shield by the Onega parametric well. The mineral composition of salts, their geochemical features, and the isotopic composition of carbonate carbon and oxygen have been studied. After fluid inclusions present in salts, their metamorphism temperature and isotopic composition of helium and argon were determined. The obtained results give evidence of the fact that rock salts and magnesites associated with them were formed in an evaporate basin with participation of deep crustal processes. The age of the underlying granitoids (2.716 ± 9 Ma) is determined using the Pb-Pb method. © 2010 Pleiades Publishing, Ltd. Source

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