Cr-spinels in carbonate veins of Ongurensky complex (Western Baikal region)

Savelieva V. B., Bazarova E. P., Khromova E. A.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2019. V. 148. N 5. P. 89-112

https://doi.org/10.30695/zrmo/2019.1485.05

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Language: Russian 

Abstract

Cr-spinels in carbonate veins of the Ongurensky complex (Eastern Siberia, Western Baikal region) are mainly represented by ferrichromite and crommagnetite (MgO ≤0.3 wt %, Mg# ≤0.04, Al₂O₃ ≤2.5 wt%; Cr# 0.91—1.00, Fe²⁺/Fe³⁺ 0.8—1.4) with a high content of ZnO (0.9—4.6 wt %). In the calcite vein, titanium chrommagnetite is transformed into chromium-containing titanomagnetite, which decomposes into less titanium magnetite and ilmenite at 970—1000 °С and f_O2 is about +0.5 ÷ +0.7 QFM. In the dolomite vein, ferrichromite and chrommagnetite grains contain relic cores of subferrialumochromite (Al₂O₃ 10.6—14.4 wt %, Cr# 0.63—0.73, Fe²⁺/Fe₃₊ 4.1—5.2, MgO ≤0.52 wt %) with increased amounts of ZnO (3.7—5.1 wt %), TiO₂ (3.2—4.1 wt %), and MnO (0.6—1.1 wt %). Ferrichromite and chrommagnetite are formed during high-temperature (>600 °C) metamorphism of the vein. Superimposed deformations in conditions of greenschist facies lead to the formation of magnetite rims around the grains of chromomagnetite.

Key words: ferrichromite, chrommagnetite, subferrialumochromite, titanomagnetite, carbonate veins, Western Baikal Region