The Khibiny and Lovozero massifs—the world’s largest alkaline massifs—contain deposits with unique reserves of phosphorus and rare metals, respectively. The reduced gas content in the rocks and, especially, the ore deposits of these massifs is unusually high for igneous complexes, thus representing both geochemical and practical interests. There are three morphological types (or occurrence forms) of the gas phase in these deposits: occluded (predominantly in vacuoles of micro-inclusions in minerals), diffusely dispersed, and free. All three morphological types have the same qualitative chemical gas composition. Methane is the main component, and molecular hydrogen (which sometimes dominates) and ethane are the subordinate constituents. Heavier methane homologs (up to and including pentanes), alkenes, helium, and rarely carbon oxide and dioxide are present in minor or trace amounts. All three morphological types of gases are irregularly distributed in space to various degrees. Free gases also show a release intensity that varies in time. The majority of researchers recognize that the origin of these gases is abiogenic and mostly related to the formation of the massifs and deposits. However, the relative time and mechanism of their generation are still debated. Emissions of combustible and explosive hydrogen–hydrocarbon gases pose hazards during the underground mining of ore deposits. Therefore, the distinctive features of gas-bearing capacity are an essential part of the mining and geological characterization of such deposits because they provide a basis for establishing and implementing special measures of the gas regime during mining operations.

Gas chromatography and other analytical techniques (EMR, PMR, and IR spectroscopy) were used to examine volatile components (CH₄, C₂-C₃, CO₂, CO, H₂, H₂O, and others) in alkaline rocks and minerals from the Ukrainian Shield (eight massifs and dikes of grorudites) and from the Khibina and Lovozero massifs in the Baltic Shield. The alkaline rocks from the Ukrainian Shield are mostly of Proterozoic (1.7–2.1 Ga) age. The alkaline rocks from the Kola Peninsula were confirmed to be rich in methane (21 ± 14 μl/g on average) and other hydrocarbons, whereas the analogous rocks from the Ukrainian Shield are poor in methane (2.1 ± 1.6 μl/g on average at a maximum of 14 μl/g). The latter rocks are richer in CO₂, which is one of the major volatile components of alkaline rocks, including agpaitic nepheline syenites from the Kola Peninsula. The rocks from the Ukrainian Shield often have elevated contents of nitrogen (up to 20 μl/g). The reasons for the differences in the composition of volatile components of rocks from the Kola Peninsula and Ukrainian Shield are as follows: the agpaitic crystallization trends of large massifs in the Kola Peninsula and much less clearly pronounced agpaitic trends in the small massifs in the Ukrainian Shield, the affiliation of these rocks with different complexes, the deeper erosion levels of the Ukrainian alkaline massifs, different ages of these rocks, etc.

Relationships between methane and its homologues mainly contained in fluid microinclusions have been studied in 332 monomineralic fractions from the Khibiny and Lovozero alkaline plutons. Hydrocarbon gases (HCG) were extracted for subsequent chromatographic analysis using the bulk method of sample comminution. The molecular weight distribution (MWD) of gaseous alkanes in the same and associated minerals is different depending on geological setting of the samples. The molecular mass of HCG increases (i) with decrease in temperature and capture of fluid inclusions in the course of transformation of primary magmatic minerals and the formation of late minerals as products of intensified postmagmatic processes; (ii) in the direction from khibinite at the margin and foyaite in the core of the Khibiny pluton to the central ring structure; and (iii) from the bottom to top of the differentiated complex in the Lovozero pluton. The results obtained coupled with other geochemical data suggest multistage generation and transformation of hydrocarbons from the magmatic to the final low-temperature hydrothermal stage. The MWD of hydrocarbon components in gases occluded by minerals can serve as an indicator of conditions characteristic of rock and ore formation, as well as of the consecutive formation and transformation of associated minerals revealing ambiguous and controversial relationships.

The composition and concentrations of gases disseminated in rocks (and moving through them mainly via diffusion) and characteristics of their release from these rocks were studied in the Khibina and Lovozero massifs in the Kola Peninsula. Similar to fluid inclusions occluded in vacuoles in minerals and unlike local “jet” gas exhalations, diffusively disseminated gases (DDG) ubiquitously occur in the massifs in variable concentrations. Along with predominant methane and hydrogen, subordinate amounts of methane homologues, and helium, DDG most commonly contain carbon dioxide (in higher concentrations than gases in other modes of their occurrence). One of the most important factors controlling the spontaneous release character of diffusively disseminated gases and their proportions of individual components is the geomechanical state of the rocks. It is proved that the distributions of all modes of gas occurrence in the rocks are generally not interrelated, and hence, it is senseless to utilize the contents of occluded and forcibly extracted gases to predict hazardous gas emissions in mines during the development of mineral deposits related to nepheline syenite complexes.