pdf № 314, February

DOI: 10.19110/geov.2021.2.1

Based on the obtained evidence of hot heterogeneous accretion of the Earth and the calculated quantitative model of kimberlite magmas, the nature of the main features of kimberlites is explained. Their presence only within ancient cratons is conditioned by the crystallization of the magma ocean. The formation of kimberlites from residual melts in the bottom peridotite layer resulted in the enrichment of kimberlites with melt-like components, the presence of diamonds in them, the small volume of bodies and the scattered distribution. Decompression solidification of magmas at the shallow stage of ascent is the cause of the explosion under the influence of the preserved pressure of the gas phase and the absence of kimberlite lavas.

Keywords: origin of kimberlites, magmatic ocean, model of kimberlite magmas.

pdf  Download full text (248 KB)

DOI: 10.19110/geov.2021.2.2

The article presents the impact of contact metamorphism on the ores of the large Novo-Uchaly Cu-Zn massive sulfide deposit (South Urals) as well as structural features of the contact zone and change in mineral composition of the ore and dikes. The study of contact metamorphism is also of practical interest because the ores are enriched in precious metals and rare elements in the local contact areas.

The author together with geologists from the Uchaly Mining and Processing Plant carried out a geological and mineralogical mapping of the deposit (underground mine). The analytical studies were based on using optical and scanning electron microscopes.

The results of detailed geological mapping are as follows: the thick gabbro-diorite dike is alterated by chloritization, hematitization and silicification, and contains quartz-carbonate-sulfide veinlets. The exocontact zones are usually thin, with thickness less than 10 cm, rarely reach 2 m.

The signs of the contact metamorphism of the ores: cataclasis, recrystallization of sulfides; the appearance of the increased amount of rare minerals (magnetite, fahlore, galena); violation of the geochemical zoning caused by local redistribution of chemical elements. These factors characterize the ore transformation by the processes — local contact metamorphism and the subsequent hydrothermal mineralization caused by the remobilization of the ore substance.

Keywords: contact metamorphism, dikes, VMS deposit, mineralogy, South Urals.

Download full text

DOI: 10.19110/geov.2020.2.3

The article presents the results of mineral thermobarometry and physico-chemical simulation of the formation of garnet-enstatite gneiss from the Mesoproterozoic metamorphic suite of the Bunger Hills, East Antarctica. As a result, the water activity, temperature and pressure of rock formation were estimated. It is shown that the peak temperature of metamorphism could reach 900 °С or more. Such temperature conditions indicate the prerequisites for the occurrence of UHT-metamorphism during the formation of the East Antarctic Shield.

Keywords: thermobarometry, granulites, gneiss, Bunger Hills, East Antarctica.

Download full text

DOI: 10.19110/geov.2020.2.4

It is shown by the example of the fences of Saint Petersburg that they combine the borders of all seven symmetry groups in different ways. A criterion is proposed: a lattice is harmonious if the symmetry groups of the borders are subordinate, otherwise it is eclectic. According to the author’s experience, such an approach on the border of crystallography and architecture facilitates the perception of the topic on the subordination of 32 point symmetry groups in the university course of crystallography. The article is dedicated to the memory of the outstanding scientist and popularizer of mineralogy Professor A. G. Bulakh.

Keywords: point symmetry groups, border symmetry groups, subordination of groups, lattices.

Download full text