Picroilmenite from Kimberlite Pipes of Central Yakutia

• Published in: IOP Conference Series: Earth and Environmental Science
• Main Authors: Oparin, Nikolay, Oleynikov, Oleg
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: IOP Publishing 2020
• Subjects: Khompu; Yakutia
• Online Access: http://dx.doi.org/10.1088/1755-1315/609/1/012028; https://iopscience.iop.org/article/10.1088/1755-1315/609/1/012028/pdf; https://iopscience.iop.org/article/10.1088/1755-1315/609/1/012028

Abstract Picroilmenite is one of the most important indicator minerals of kimberlite rocks, which can be used in solving petrological problems and in the search for diamond deposits. The present study shows the results of studying picroilmenite grains from the Manchary and Aprelskaya pipes within the Khompu-May kimberlite field (Central Yakutia). The rocks composing the pipes are represented by porphyritic kimberlite and kimberlite breccia, between which there are gradual transitions. Rocks forming the upper pipe horizons are highly carbonatized and supergenetically altered. Porphyritic segregations are represented by carbonatized serpentine pseudomorphs from macro-, megacrysts and olivine phenocrysts. Pyrope, picroilmenite mega-, macrocrysts and chromospinellide macrocrysts are found in both pipes. Most weakly altered parts of mesostasis are microgranular and formed mostly by phlogopite, with xenomorphic segregations of calcite and serpentine. Picroilmenite in both kimberlite bodies occurs as irregular and rounded macrorysts ranging from 0.7 to 10 mm and megacrysts ranging from 10 to 25 mm. Micrograins of this mineral were not diagnosed in the mesostasis. Individual grains of picroilmenite from the Manchary pipe are surrounded by a polymineral rim composed of either ferrospinel and magnetite, or perovskite and magnetite. High-and low-chromium varieties which correspond to two parageneses are identified among the picroilmenite grains from the Manchary pipe. Crystallization trend of high-chromium ilmenites from the Manchary pipe is clearly seen in the diagram in the coordinates Fe 2 O 3 -FeTiO 3 -MgTiO 3 and associated with the presence of Cr-rich phlogopite from lherzolites xenoliths. Picroilmenite grains from the Aprelskaya kimberlite pipe are more magnesian in comparison with similar grains from the Manchary pipe. Picroilmenite from both pipes in the coordinates Fe 2 O 3 -FeTiO 3 -MgTiO 3 is characterized by a magmatic kimberlite trend of the mineral composition evolution. The distribution of mineral ...