Vanadian–Chromian Spinels (Sludyanka Metamorphic Complex, South Baikal Area). Magnesian Spinel

Abstract

—The paper presents data on two groups of magnesian Cr–V spinel occurring as rock-forming minerals in various types of Cr–V bearing rocks of the Sludyanka metamorphic complex (South Baikal area, Siberia, Russia): (i) low-Al magnesiochromite–magnesiocoulsonite spinels and (ii) Al spinels varying from V-bearing aluminous magnesiochromite and Al–Cr coulsonite to spinel proper with minor contents of Cr and V, and with complex zoning patterns. Spinels in the Sludyanka rocks are also present as iron-magnesian accessories, among which high-Cr varieties are compositionally similar to mantle-derived spinel from igneous rocks and to inclusions in diamonds. Comparison of formation conditions for mantle spinels in igneous lithologies and spinel phases in metamorphic rocks shows that their mineral chemistry is mainly controlled by the bulk composition of the igneous and sedimentary protoliths, respectively. Detrital spinel may be a false indicator poorly applicable to paleogeodynamic reconstructions and diamond potential evaluation.