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Vol. 21 (2018 year), No. 1, DOI: 10.21443/1560-9278-2018-21-1

Groshev N. Yu. , Malygina A. V., Timofeeva M. G.
Study of the nature of high-magnesian xenoliths of the Gabbro-10 massif, Monchegorsk Complex, the Kola Region

The results of studying geology, petrography and geochemistry of chlorite-amphibole rocks and fine-grained metagabbro in the Gabbro-10 massif have been presented. Chlorite-amphibole rocks are found as large fragments of irregular shape. They have a porphyraceous texture, a schistose structure and are enriched in magnesium and chromium (19 and 0.3 wt % respectively) concerning the metagabbro prevailing in the massif. According to the classification and variation diagrams of main elements, as well as to the diagrams of the trace-element composition normalized to primitive mantle, the chlorite-amphibole rocks are metamorphosed xenoliths of melanocratic norites of the Nyud-Poaz massif. Fine-grained metagabbros, on the other hand, occur in the form of numerous angular fragments concentrated near the lower contact of the intrusion. These massive rocks of the blastogabbroic texture are less enriched in magnesium and chromium (8 and 0.02 wt % respectively) and correspond to the composition of mesocratic gabbronorites. According to the spectra of trace elements normalized to the primitive mantle, fine-grained metagabbro, with pronounced negative Nb-Ta & Zr-Hf anomalies and positive Sr & Eu anomalies, corresponds to the rocks of the marginal zones of the NKT and Nude-Poaz massifs. However, the greatest similarity is established between these rocks and the schistose gabbroids of the marginal zone of the Gabbro-10 massif. Thus, the fragments of fine-grained metagabbro are possibly autoliths of the intrusion. Collectively, the obtained data have indicated the late intrusion of the Gabbro-10 massif following the crystallization of the Nude-Poaz rocks, and the presence of autoliths of its own marginal zone in the massif points at several magmatic impulses during its formation.

(in Russian, стр.12, fig. 8, tables. 3, ref 7, adobe PDF, adobe PDF 0 Kb)

Vol. 28 (2025 year), No. 1, DOI: 10.21443/1560-9278-2025-28-1

Groshev N. Yu., Sushchenko A. M., Raevsky A. B., Ivanov A. N., Chernyavsky A. V.
Micromagnetic survey experience in the mapping of the South Sopcha platinum-bearing intrusion, Monchegorsk ore district

The norite-pyroxenite zone hosting platinum group element (PGE) mineralization is located at the base of the South Sopcha intrusion being a part of the Monchegorsk layered complex. The complex geological structure of the norite-pyroxenite zone, dipping at angles from 20° to 80°, is defined by frequent alternation of pyroxenites and taxitic gabbroids of mafic composition. There is an assumption that the first group of rocks of this zone, represented by pyroxenites with peridotites interlayers, was formed before the rocks of the second group, including mineralized taxitic mafic gabbroids distributed throughout the whole zone in the form of lenticular vein-like bodies. Micromagnetic survey used for the first time in the Kola Region is an effective tool for studying objects with such complex structures. The results of the micromagnetic survey at two detailed sites located within the Arvarench PGE occurrence, surveyed in 2011 and 2024 using 5×1 m and 4×1 m grids, respectively, are presented in our paper. The analysis based on a comparison of the loss of information when using less detailed grids shows that the loss in the case of grid discharge is significant and the effectiveness of the magnetic survey for mapping is greatly reduced. The results of petrophysical measurements and micromagnetic survey together lead to the following assumptions about the magnetic field over the norite-pyroxenite zone: 1) high-amplitude positive anomalies are associated with peridotites; 2) mineralized taxitic mafics containing a high proportion of magnetite along with disseminated sulfides are characterized by medium-amplitude anomalies; 3) the lower contact of the intrusion with less magnetic Archean gneisses is fixed in the magnetic field by a negative curve-shaped anomaly; 4) tectonic zones probably consisting of remagnetized rocks are marked by linear negative anomalies. It is argued that micromagnetic survey in combination with detailed magnetometry can be used for geological mapping of layered intrusions and prospecting for PGE mineralization.

(in Russian, стр.14, fig. 7, tables. 1, ref 28, AdobePDF, AdobePDF 0 Kb)