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Geochemical characteristics of spherules from the Pivdenna kimberlite pipe, East Azov region (Ukraine) : implications for their sources and origin

Yatsenko Ivan, Poberezhskyy Andriy, Stupka Oksana, Bekesha Serhii

Geological Quarterly

2023

Vol. 67, No. 1

art. no. 6

The composition of spherules and particles of native metals from the Pivdenna kimberlite pipe, Ukraine, was studied using the SEM/EDS method. Three varieties of spherules have been distinguished: titanium-manganese-iron-silicate (TMIS) spherules, Ca-rich silicate spherules, and magnetite-wustite-iron (MW-I) spherules. TMIS spherules are composed of homogeneous glass, some having a native iron core. Large TMIS spherules may contain a crystalline phase with needle-like armalcolite. Ca-rich silicate spherules can be subdivided into two subtypes: calcium-silicate (CS) spherules where SiO2 and CaO are the dominant constituents, and calcium-iron-silicate (CIS) spherules with significant FeO content. CS spherules may contain a core consisting of native phases (Fe, Fe-Si, and Mn-Si-Fe). Native metal particles are represented by native Cu and native Zn. The spherule varieties from the Pivdenna pipe are similar to those from other kimberlite pipes in the world. We infer that the formation of spherules occurred in gas-melt streams, separately from the kimberlites, and propose a model for the formation of the most common variety of spherules (TMIS and MW-I varieties) in the region of the core-mantle boundary (CMB). First, a melt of the Fe-Ti-Mn-Si-O system was formed in ultra-low-velocity zones (ULVZ) as a result of thermochemical reactions (reduction) between the molten core and solid oxide-silicate rocks. The melt then migrates to shallower levels, where a decrease in temperature initiates oxidation with the formation of SiO2-TiO2-FeO-MnO-Fe0 melt, i.e. parent melt of TMIS and MW-I spherules. We interpret the formation of native metals in kimberlites as a result of the decomposition of nitrides, which came from the Earth’s core via intratelluric flows.

Złoża kimberlitowe i aluwialne w rejonie Kimberley : 155 lat od odkrycia diamentów w Afryce Południowej

Jarmolowicz-Szulc Katarzyna, Kozłowska Aleksandra

Przegląd Geologiczny

2021

Vol. 69, nr 3

174--178

For 155 years, the world's most famous diamond deposits have been known from South Africa. The first discoveries that had a casual character took place in the second half of the 19th century in the Kimberley region where diamonds are associated either with kimberlite pipes or occur as secondary deposits of the river alluvia. Minerals that formed in the upper mantle under high p-T conditions were transported to the surface by magmas and deposited around craters due to lava explosions. Surfice waters leached and transported diamonds either to the crater or to the neighbourhood. These processes have led to diamond production both from the deep and open-pit mines which is presented in the paper.

Analysis of Distribution of Secondary Minerals and their Associations on The Surface of Diamonds and in Derrivative Products of Metasomatically Altered Kimberlites

Dvoichenkova Galina, Chanturiya Valentin, Morozov Valery, Podkamenny Yury, Kovalchuk Oleg

Inżynieria Mineralna

2019

R. 21, nr 1

43--46

The theoretical and experimental studies resulted in establishing regularities in the distribution of secondary minerals and their associations in metasomatically altered diamond-bearing kimberlites and products of their processing. Based on integrated mineralogical research, it was found out that the composition of the altered kimberlites and the fine-dispersed clayey slurries formed during their processing constituted the basis of hydrophilic formations on the surface of diamond crystals not recovered by the methods of grease and froth separation. Particles of these minerals concentrate in fine-dispersed slurry products of kimberlite ore processing, interact with the crystal surface, reduce their hydrophobic properties and, accordingly, recovery in processes of grease and froth separations into concentrates.

Przeprowadzono analizę teoretyczną i badania eksperymentalne w celu ustalenia prawidłowości w rozkładzie minerałów wtórnych i ich związków w metasomatycznie zmienionych diamentach kimberlitowych i produktach ich przetwarzania. Na podstawie zintegrowanych badań mineralogicznych stwierdzono, że zmienione kimberlity i drobnoziarniste produkty ich metamorfozy stanowiły hydrofilowe formacje na powierzchni kryształów diamentu, które nie zostały odzyskane metodami flotacji pianowej. Cząstki tych minerałów koncentrują się w drobno zdyspergowanych produktach przerobu rudy kimberlitowej, oddziałują z powierzchnią kryształu, redukują ich właściwości hydrofobowe i odpowiednio przechodzą w procesach flotacji do koncentratów.