-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.

V-Cr-spinel of wide composition range is present as a rock-forming or accessory mineral in parametamorphic rocks of the Sludyanka Complex (South Baikal area, Siberia, Russia). The spinel can be subdivided into two large groups: magnesian spinel and ferroan spinel. In this paper we describe ferroan spinel. It is subdivided into three groups: (1) Zn-V-bearing and vanadian (up to 5 wt.% ZnO and up to 19.5 wt.% V2O3); (2) V-bearing zinc spinel and vanadian zincochromite (up to 6 wt.% V2O3 and 5.0-20.3 wt.% ZnO); and (3) Zn-V spinel and zincochromite (>6 wt.% V2O3 and 5.0-22.2 wt.% ZnO). A separate small group of ferroan spinel is represented by ternary chro-mite-coulsonite-magnetite solid solution. In addition to the Slyudyanka spinel, we present a summary of metamorphogenic chromium and vanadium spinel from other deposits. The behavior of Cr, V, and Zn in metamorphic and magmatic spinel is discussed.

—We present data on the mineral and geochemical compositions of metasedimentary Mn-bearing rocks of the Itantsa Formation of the Ikat terrane. According to the mineral composition, the studied quartz–spessartine rocks of the formation are referred to as gondites. The main Mn-concentrating minerals are garnet, pyrophanite, and Mn-ilmenite, and the secondary ones are rhodonite and Mn-amphibole. Two Mn-bearing objects of the Itantsa Formation (Usutai deposit and Almarnatol occurrence) show differences in chemical and mineral compositions, related to different sources of their material, different distances from the mouth of a hydrothermal vent, and different degrees of postsedimentary alteration. The Mn-bearing deposits of the formation accumulated in a sedimentary basin in the immediate vicinity of continental provenance areas in the Late Neoproterozoic (Ediacaran), under synchronous volcanic activity.

new mineral was discovered in Cr–V-bearing marbles of the Sludyanka Complex from the Pereval marble quarry, Sludyanka district, southern Baikal region, Russia. It was named vanadio-pargasite as vanadium-bearing analog of pargasite according to the amphibole supergroup classification and CNMNC recommendations. Black Cr–V-spinel (magnesiocoulsonite–magnesiochromite), red Cr–V-bearing spinel, calcite, dolomite, Cr–V-bearing diopside and chlorite, phlogopite, and forsterite are associated minerals. Vanadio-pargasite occurs as subhedral long- and short-prismatic crystals 0.10–0.8 × 0.05–0.10 mm in size, with (110) and (010) faces and perfect cleavage by (110). Macroscopically, the new mineral is bright green to emerald green with vitreous luster; in thin sections and powder, it is pale green, without pleochroism. The new mineral is biaxial, positive, 2 V = 86° ± 2°, γ = 1.659(2), β = 1.651(2), α = 1.643(2). The Mohs hardness is 6, average VHN50;100 is 795; range 752–824 kg/mm2. The measured and calculated density is 3.05(5) and 3.112 g/cm3, respectively. In a thermogram over the range 654–1081°С, H2O is released with a endothermic effect. Over the range 900–1183°C, the main endothermic effect is caused by water and, possibly, F release, as well as melting of the mineral (1020°C). The absorption bands in the IR spectrum are, cm–1: 3445, 1633, 980, and 469. Vanadio-pargasite is monoclinic, space group 2C/m; the unit cell parameters are: a = 9.914(3), b = 18.003(2), c = 5.300(2) Å, β = 105.69(3)°, V = 910.7(5) Å 3 , Z = 2. The strongest reflections in the X-ray diffraction pattern are [d, Å (I) (hkl)]: 8.98 (15) (020), 8.43 (40) (110), 3.27 (30) (240), 3.14 (100) (310), 2.82 (35) (330), 2.70 (18) (151), 2.34 (15) ( 4.101̅ ), 1.898 (15) (510), 1.445 (25) (4.101). The average chemical composition (528 point analyses) is, wt

—A continuous solid-solution series between the end-members eskolaite (98 wt.% Cr2O3) and karelianite (93 wt.% V2O3) has been revealed in Cr–V-bearing rocks of the Slyudyanka metamorphic complex. Chromium and vanadium oxides crystallized as karelianite-eskolaite minerals during regional high-temperature prograde (granulite facies) metamorphism and participated in the formation of other Cr–V and Cr–V-bearing phases. Ferrian karelianite (up to 12 wt.% Fe2O3) and three-component solid solutions Esk12–50Kar45–60Hem6–30 occur in metamorphic rocks that have particular protolith compositions (Fe–Kar) and in later metasomatic rocks ((Cr, V, Fe)2O3). Natural eskolaite and karelianite are discussed in terms of paragenesis, and their crystallization conditions are compared with the conditions of their laboratory synthesis.

A new mineral was discovered in Cr–V-bearing marbles of the Sludyanka Complex from the Pereval marble quarry, Sludyanka district, southern Baikal region, Russia. It was named vanadio-pargasite as vanadium-bearing analog of pargasite according to the amphibole supergroup classification and CNMNC recommendations. Black Cr–V-spinel (magnesiocoulsonite–magnesiochromite), red Cr–V-bearing spinel, calcite, dolomite, Cr–V-bearing diopside and chlorite, phlogopite, and forsterite are associated minerals. Vanadio-pargasite occurs as subhedral long- and short-prismatic crystals 0.10–0.8 × 0.05–0.10 mm in size, with (110) and (010) faces and perfect cleavage by (110). Macroscopically, the new mineral is bright green to emerald green with vitreous luster; in thin sections and powder, it is pale green, without pleochroism. The new mineral is biaxial, positive, 2V = 86° ± 2°, γ = 1.659(2), β = 1.651(2), α = 1.643(2). The Mohs hardness is ~ 6, average VHN50;100 is 795; range 752–824 kg/mm2. The measured and calculated density is 3.05(5) and 3.112 g/cm3, respectively. In a thermogram over the range 654–1081°С, H2O is released with a endothermic effect. Over the range 900–1183°C, the main endothermic effect is caused by water and, possibly, F release, as well as melting of the mineral (1020°C). The absorption bands in the IR spectrum are, cm–1: 3445, 1633, 980, and 469. Vanadio-pargasite is monoclinic, space group 2C/m; the unit cell parameters are: a = 9.914(3), b = 18.003(2), c = 5.300(2) Å, β = 105.69(3)°, V = 910.7(5) Å3, Z = 2. The strongest reflections in the X-ray diffraction pattern are [d, Å (I) (hkl)]: 8.98 (15) (020), 8.43 (40) (110), 3.27 (30) (240), 3.14 (100) (310), 2.82 (35) (330), 2.70 (18) (151), 2.34 (15) ( $$4.10\bar 1$$ ), 1.898 (15) (510), 1.445 (25) (4.101). The average chemical composition (528 point analyses) is, wt %: 42.75 SiO2, 0.14 TiO2, 12.75 A12O3, 0.44 Cr2O3, 5.92 V2O3, 19.15 MgO, 0.03 FeO, 0.01 MnO, 12.52 CaO, 3.45 Na2O, 0.41 K2O, 0.74 F (wet chem.) 1.75 H2O (calc.); the total is 99.91. The simplified formula is K0.1Na0.9Ca2.0Mg4.0V0.7Al0.3(Si6.1Al1.9)8.0O22(OH1.7F0.3)2.0. Holotype material has been deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia (registration nos. 5035/1, 5035/2, and 5035/3).

Mannardite was found in a type of Cr–V–bearing metamorphic rock of the Slyudyanka complex (South Baikal region). The X-ray data of the mineral are recalculated for three scenarios taking into account possible variations of the mannardite structure. The mean chemical composition is as follows (14 analyses, wt %): 0.11 SiO2, 52.08 TiO2, 6.19 VO2, 13.51 V2O3, 5.50 Cr2O3, 0.24 Al2O3, 0.16 Fe2O3, 0.05 MgO, 20.09 BaO, 2.09 H2O (the H2O, VO2, and V2O3 contents are recalculated). The formula of the mean composition is (Ba1.06H2O0.94)(Ti5.27Si0.21V0.614+V1.453+Cr0.59Fe0.02Mg0.01)O16. Mannardite is characterized by the presence of different valent V. The mineral can be hydrous with molecular H2O or hydroxylion in tunnels or anhydrous. Mannardite can be considered an indicator of the hydroxyl or oxygen regime of petrogenetic processes.

The results of U—Th—Pb (LA-ICP-MS) geochronological studies of detrital zircons from terrigenous rocks of the Dzhida terrane of the Central Asian Fold Belt (CAFB) are presented. The data obtained allow us to distinguish the following age maxima (Ma): 578 and 634 (Vendian); 720, 823, and 919 (Late Riphean); 1922, 2090, 2225, and 2321 (Early Proterozoic). A number of zircons have Late Archean age in the interval of 2670–2980 Ma. Taking into account Late Cambrian age (504–506 Ma) of intrusive rocks that intruded the Dzhida terrane, a possible sedimentation period of sequences of this terrane is estimated to be in the interval of 580–510 Ma (from Vendian to Late Cambrian). The possible provenance areas of terrigenous sediments are proposed and the previously proposed models of geodynamic evolution of the Dzhida terrane are correlated with new geochronological data.

The results of geochemical, mineralogical, and isotope (U–Pb and Sm–Nd) studies of metasedimentary manganese-bearing rocks from the Itantsa Formation of the Ikat terrane are presented. It is found that the carbonate-effusive-shale complex of the Itantsa Fm. formed under the continental margin environment, with volcanic activity accompanying sedimentation, in the interval of 650–540 Ma ago.

Felsic rocks of the Khamsara terrane in Tyva (southern Siberia) have been studied in terms of major-and trace-element compositions and U-Pb isotope geochronology. The Khamsara Formation rocks have compositions of A(2)-subtype within-plate anorogenic volcanics derived from molten continental crust and SIMS U-Pb zircon ages of 463.9 +/- 2.8 and 461.7 +/- 3.1 Ma of two rhyolite porphyry samples. The Khamsara volcanics are compared with subvolcanic granitoids of the Ognit complex in the Biryusa terrane (Sharyzhalgai basement inlier of the Siberian craton) adjacent to the Khamsara terrane. The volcanics and the granites are coeval and share compositional similarity. The Khamsara Formation is interpreted as a cap complex that marks the upper age bound of the accretionary-collisional events when amalgamated terranes in this part of the Central Asian orogen accreted to the Siberian craton. (C) 2017, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

The paper presents data on accessory rutile in Cr–V-rich metamorphic rocks of the Slyudyanka crystalline (granulite) complex in the southern Baikal region. The geochemical features of the studied rutile are unique in combining isomorphic admixtures typical of the mineral from either mafic (Cr) or felsic igneous and associated metasomatic rocks (W), as well as the Nb and V contents, which are abnormally high for metamorphic rocks. The highest concentrations of these elements are as follows, wt %: 15.38 V2O3, 4.33 Cr2O3, 11.09 Nb2O5, 12.36 WO3. These high W and V contents have never been measured in natural rutile. The studied rutile is compared to that from other Cr–V-bearing rocks in the world and various genetic types. The optimal isomorphic substitutions and probable conditions of their realization are discussed.

Cr-V-bearing rocks of the Sludyanka metamorphic complex in the Southern Baikal area contain accessory niobian rutile with Nb contents unusually high for metamorphic rocks (10-12 to 20-25 wt.% Nb2O5, or, occasionally, up to 36-37 wt.%). Incorporation of Nb5+ into the rutile structure is balanced by Cr3+ and V3+, which reach 16 wt.% Cr2O3 and 8 wt.% (or, rarely, up to 20 wt.%) V2O3. The distribution of Nb, Cr, and V in ruffle is very uneven, down to the microscale. It does not depend on PT conditions, being rather controlled by crystallization kinetics of minerals competing with rutile in the paragenesis. (C) 2016, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.