Petrographic structures: Khibiny ijolites and urtites

In addition to the standard description of the structures and textures of crystalline rocks the mathematical approaches have been proposed based on a rigorous determination of the petrographic structure through the probabilities of binary intergrain contacts. In general, the petrographic structure is defined as an invariant aspect of rock organization, algebraically expressed by the canonical diagonal form of the symmetric Pij matrix and geometrically visualized by structural indicatrices - surfaces of the 2nd order. The agreed nomenclature of possible petrographic structures for an n-mineral rock is simple: the symbol Snm means that there are exactly m positive numbers in the canonical diagonal form of the Pij matrix. New types of barycentric diagrams have been proposed. To describe the massive texture, the concept of Hardy - Weinberg equilibrium has been proposed. This boundary classifies barycentric diagrams into areas within which canonical types of Рij matrices and topological types of structural indicatrices are preserved. The change in the organization of the rock within a type is quantitative, the transition from one type to another means structural restructuring. The methods are used to describe ijolites and urtites of the Khibiny massif, the Kola Peninsula. In the modern taxonomy of rocks, the boundaries between them are mostly conditional and are drawn according to the contents of rock-forming minerals, for example, between ijolites and urtites - according to the contents of nepheline and pyroxene. The strict definition of the petrographic structure proposed by the authors makes it possible to introduce into petrography the constitutional principle (structure + composition), which is successfully acting in mineralogy.

Seismic productivity of blasts: A case-study of the Khibiny Massif

The authors study the property of production-scale blasts to induce seismic events classified as micro shocks, rock bursts and earthquakes caused by sudden slips along faults. The study area is the production performance zone of Apatit’s Kirovsk Branch. It is situated in the southeast of the Khibiny Massif on the Kola Peninsula and is subjected to continuous autonomous seismicity monitoring. The subject of the research is the production blasts and seismic events recorded by the seismic monitoring station of Apatit’s Kirovsk Branch between January 1996 and June 2019. Blasting-induced seismic events were identified using the nearest neighbor method and the seismicity-dependent proximity function of the space–time–magnitude (energy), calculated with respect to the blasts. The threshold of the proximity function to assume a seismic event as the blast-induced event was selected using the model-independent method of seismic catalog randomization. It is shown that the number of blasting-induced seismic events—blasting productivity—obeys an exponential distribution irrespective of magnitudes or occurrence depths of the studied events. The obtained result conforms with the earlier determined productivity law for natural earthquakes on a global and regional scale, as well as for mining-induced seismicity in the Khibiny Massif. Accordingly, the productivity distribution is governed by the properties of a medium and is independent of the source mechanism of a triggering event (explosion, seismicity). The paper presents the research findings supported by the Russian Foundation for Basic Research, Project No. 19-05-00812, and in the framework of State Contract No. 007-00186-18-00 with the Kola Branch of the Geophysical Service of the Russian Academy of Sciences.

New geochemical criterion of rare metal mineralization in the peralkaline magmas (Lovozero mineral deposit, Kola Peninsula)

Detailed studies have shown that changing the forms of eudialyte release (and the time of its crystallization) is a new geochemical criterion for the ore - bearing of alkaline magmas for rare metal (eudialyte ores). A new ore-bearing principle of alkaline magmas has been formulated: a prerequisite for the formation of an ore deposit is the early saturation of alkaline magmas with respect to the ore mineral. If the concentration of the ore component is significantly lower than the cotectic concentration (saturation), then the melt saturation and crystallization of the ore mineral will be carried out at the later stages of rock formation in a small volume of interstitial melt, when the phenomena of convective-gravity differentiation and segregation of mineral phases in the form of ore deposits are hampered. This leads to the dispersion of ore components in the form of xenomorphic forms of accessory minerals. Rocks of the differentiated complex (lower zone of the Lovozero deposit), and of the Khibiny massif, containing xenomorphic eudialyte, are not promising for eudialyte ores. Eudialyte deposits are associated with the upper zone of the Lovozero intrusion containing idiomorphic early eudialyte. The saturation of the initial magma in relation to eudialyte occurs after crystallization of about 80% of the intrusion. The proposed criterion is applicable to the largest alkaline massifs in the world. With the Ilimaussaksky massif (Greenland), in the rocks of which early, crystallized, idiomorphic eudialyte, there is a superlarge eudialyte ore deposit while in the Khibiny eudialyte ore is absent.