Chromite mineralization in the sopcheozero deposit (Monchegorsk layered intrusion, fennoscandian shield)

Abstract

In 1990, the Sopcheozero Cr deposit was discovered in the Monchegorsk Paleoprotero-zoic 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 °С, 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 °С) and pressure (5 kbar). At the post magmatic Svecofennian stage (1.84 Ga), the deposit, jointly with the Monch-epluton, was subject to diverse tectonic deformations.