P.M. Goryainov

3D mineralogical mapping of the Kovdor phoscorite–carbonatite complex (Russia)

The Kovdor baddeleyite–apatite–magnetite deposit in the Kovdor phoscorite–carbonatite pipe is situated in the western part of the zoned alkali-ultrabasic Kovdor intrusion (NW part of the Fennoscandinavian shield; Murmansk Region, Russia). We describe major intrusive and metasomatic rocks of the pipe and its surroundings using a new classification of phoscorite–carbonatite series rocks, consistent with the IUGS recommendation. The gradual zonation of the pipe corresponds to the sequence of mineral crystallization (forsterite–hydroxylapatite–magnetite–calcite). Crystal morphology, grain size, characteristic inclusions, and composition of the rock-forming and accessory minerals display the same spatial zonation pattern, as do the three minerals of economic interest, i.e. magnetite, hydroxylapatite, and baddeleyite. The content of Sr, rare earth elements (REEs), and Ba in hydroxylapatite tends to increase gradually at the expense of Si, Fe, and Mg from early apatite–forsterite phoscorite (margins of the pipe) through carbonate-free, magnetite-rich phoscorite to carbonate-rich phoscorite and phoscorite-related carbonatite (inner part). Magnetite displays a trend of increasing V and Ca and decreasing Ti, Mn, Si, Cr, Sc, and Zn from the margins to the central part of the pipe; its grain size initially increases from the wall rocks to the inner part and then decreases towards the central part; characteristic inclusions in magnetite are geikielite within the marginal zone of the phoscorite–carbonatite pipe, spinel within the intermediate zone, and ilmenite within the inner zone. The zoning pattern seems to have formed due to both cooling and rapid degassing (pressure drop) of a fluid-rich magmatic column and subsequent pneumatolytic and hydrothermal processes.

FRACTAL ANALYSIS OF SEISMIC AND GEOLOGICAL DATA

Abstract Continental lithosphere is a highly organised physical medium which can be investigated by seismic methods to obtain objective information. The use of fractal representation offers new possibilities to determine quantitative parameters of the structural arrangement of the lithosphere and to compare tectonic structures composed of a similar set of “participants” i.e. structural complexes with a relatively homogeneous range of rocks. Fractals as a universal property of continental crust are shown to be an important tool for a comparative study of geological and seismic sections on a quantitative basis, and also in reassessing many of the previous interpretations of seismic and geological structures.

Structural and compositional zoning and formation conditions of the Greater Eastern Litsa BIF occurrence, Kola Peninsula

New geological and geochronological data on the Greater Eastern Litsa banded iron formation (BIF) occurrence demonstrate its similarity to the BIF of the Olenegorsk iron district in geology (lenticular orebodies with exponential distribution of their sizes), age (2.8 Ga), and typical structural and compositional zoning of orebodies. The temperature of ore formation (600–780°C) and BIF composition depend on the intensity of folding expressed in the fractal dimension D = 1.0–1.3 of a single layer. All BIF deposits of the Kola-Norwegian Megablock, including the Greater Eastern Litsa occurrence pertain to the one system. Variation m their composition is controlled by the size of orebodies (capacity of oxygen buffer) and the energy of metamorphic reactions, which strongly depend on the intensity of folding.

Native elements in rocks of the banded iron formation, Kola Peninsula

Eleven native minerals and intermetallic alloys were identified in rocks of the banded iron formation (BIF) in the Kola Peninsula: copper, silver, gold, electrum, auricupride, cuproauride, tetraauricupride, bismuth, sulfur, tellurium, and graphite. Graphite is a common mineral of sulfide-bearing BIF and gneiss. Sulfur occurs in supergene-altered sulfide-bearing BIFs together with Fe- and Ca-sulfates. Gold of low fineness (electrum) in association with electrum, acanthite, auricupride, volynskite, hessite, cervelleite, pavonite, petzite, and bismuth is related to the areas of hydrothermally altered skarnoids with greenalite, chamosite, aegirine, and Na-Ca amphibole. Redeposited gold of high fineness associated with auricupride, hessite, silver, electrum, kostovite, cuproauride, tetraauricupride, and sperrylite occurs in low-temperature zonal hydrothermal segregations hosted in aluminous gneiss and which formed under the effect of alkalized, highly siliceous solutions at the regressive stage of BIF metamorphism.