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Russian Geology and Geophysics

2005 year, number 12


S.I. Mityukhin and Z.V. Spetsius
ALROSA Co. Ltd., 6 ul. Lenina, Mirny, 678170, Russia
Keywords: Diamonds, inclusions, sulfides, kimberlites, Yakutia
Pages: 1225-1236


This study was given to specific features and compositions of mineral inclusions in diamonds from the Botuobinskaya pipe. The initial collection of diamonds (91 specimens taken of the three hundred diamonds inspected) was represented by colorless and transparent crystals, chiefly, of octahedral shape, 3-4 mm in size. The imprisoned minerals were exposed to the day by polishing of diamonds and were instrumentally studied in situ.
The suite of revealed mineral inclusions combines a group of silicates and oxides, which were established in 28 crystals, and sulfides present in 65% of the crystals from the studied lot of diamonds. The silicate minerals are dominated by Cr-spinels with more than 61.0 wt.% Cr2O3, with subordinate amounts of garnet and olivine. Rutile, phlogopite, and sanidine are present as solitary inclusions. Sulfides are represented by pyrrhotite, pentlandite, and monosulfide solid solutions with scarce blocks and thin rims of chalcopyrite.
Analysis of compositions of mineral inclusions in diamonds of the Botuobinskaya pipe, with the sulfide phases taken into account, shows that the eclogite paragenesis makes up more than 50% of the bulk of inclusions in diamonds of this kimberlite body. The ultrabasic paragenesis makes up 45%, and about 3.5% of the crystals belong to the pyroxenite association. The high percentage of eclogite paragenesis among inclusions in diamonds is anomalous in the diamond populations in kimberlite pipes of the Yakutian Diamond Province. This suggests a specific composition of the medium of diamond formation and, correspondingly, upper mantle in the region of the new Nakyn kimberlite field.