Abstract
In 1990, the Sopcheozero Cr deposit was discovered in the Monchegorsk Paleoproterozoic layered mafic-ultramafic layered intrusion (Monchepluton). This stratiform early-magmatic deposit occurs in the middle part of the Dunite Block, which is a member of the Monchepluton layered series. The Cr2O3 average-weighted content in ordinary and rich ores of the deposit is 16.65 and 38.76 wt.%, respectively, at gradually changing concentrations within the rich, ordinary and poor ore types and ore body in general. The ores of the Sopcheozero deposit, having a ratio of Cr2O3/FeOtotal = 0.9–1.7, can serve as raw materials for the refractory and chemical industries. The ore Cr-spinel (magnochromite and magnoalumochromite) is associated with highly magnesian olivine (96–98 Fo) rich in Ni (0.4–1.1 wt.%). It confirms a low S content in the melt and complies with the low oxygen fugacity. The coexisting Cr-spinel-olivine pairs crystallized at temperatures from 1258 to 1163 °C, with accessory Cr-spinel crystallizing at relatively low, while ore Cr-spinel at higher temperatures. The host rock and ore distinguish with widespread plastic deformations of olivine at the postcrystallization phase under conditions of high temperature (above 400 °C) and pressure (5 kbar). At the post magmatic Svecofennian stage (1.84 Ga), the deposit, jointly with the Monchepluton, was subject to diverse tectonic deformations.
Highlights
The aim of this study is to define the genesis of the Cr-spinel mineralization and to detect the location of the Dunite Block in the Monchepluton based on geological-structural, geochronological, petrological and mineralogical data on the Sopcheozero deposit obtained at complex geological prospecting by drilling
The study of the mineral morphology, imaging in back-scattered electrons (BSEs) and preliminary chemical analyses were executed on polished sections with the use of the reflected light microscope Axioplan 2 Imaging (Karl Zeiss, Jena, Germany) and scanning electron microscope (SEM), LEO-1450 (Carl Zeiss, Oberkochen, Germany), with an energy dispersive X-ray analytical device (EDS) at the Laboratory of Physical Methods for Studying Rocks, Ores and Minerals of GI KSC RAS (Apatity, Russia)
We studied the composition of Cr-spinel phases in the cross-section of ore intervals in boreholes 1520, 1527 and 1585, cutting various sectors of the ore body through (Supplementary Materials, Table S1; Figure 7A–C)
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The largest chromite deposits are confined to the ophiolite formation and maficultramafic layered intrusions. In the results of comprehensive studies of the layered intrusions of the Fennoscandian Shield, the Sopcheozero chromite deposit was discovered. In 1992, geologists of the Central Kola Expedition (V.V. Sholokhnyov and G.F. Bakayev) performed general exploration work in promising areas under the contract with the OJSC “Severonickel Combine”. In 1995–1996, exploration work showed that the deposit has. Monchepluton is is aa typical typical 2.5. Ga layered layered intrusion intrusion containing containing deposits deposits and and. The prospects of chrome, sulfide Cu-Ni to prospects. (Figures22and and3)3)[6,7,8,9,10]. (Figures22and and3)3)[6,7,8,9,10]. [6,7,8,9,10].According According thethe U-Pb zircon
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