THE SYSTEM Fe-Nb-S AND ITS GEOLOGICAL IMPLICATIONS

Abstract

Phase relations within the system Fe-Nb-S were studied experimentally by the technique of evacuated silica glass tubes in the temperature interval 400-1000°C. The dominant field in the system is a broad solid-solution Fe x Nb y S 2 (0 < x < 0.5, 1.0 < y < 1.4) that includes the composition of the mineral edgarite. Also, it forms stable assemblages with pyrrhotite and pyrite. The iron sulfides dissolve limited amounts of Nb: pyrrhotite dissolves up to 1.13 at.% Nb, and pyrite, only 0.02 at.% Nb. We refined the crystal structure of five samples of the Fe x Nb y S 2 solid solution, and established the relation between the unit-cell volume and Fe/(Fe + Nb). The occurrence of edgarite can be expected in associations with other sulfides crystallizing under extremely low fugacity of oxygen.

Role of structural factors in formation of chiral magnetic soliton lattice in Cr1/3NbS2

“…As initial data for calculations of the sign and strength of magnetic interactions, we used crystallographic parameters and coordinates of intercalate atoms: M 1/3 NbS 2 (M ¼ Cr, 15 V, 31 Ti, 31 Ni, 32 Co, 33 Fe, 34 and Mn (Ref. 32)), M 1/3 NbSe 2 (M ¼ Cr, 35 Rh, 15 V, 35 Ti, 15 The crystal lattice of magnetic Cr 3þ ions comprises flat triangular planes parallel to the ab plane ( Fig.…”

“…As initial data for calculations of the sign and strength of magnetic interactions, we used crystallographic parameters and coordinates of intercalate atoms: M 1/3 NbS 2 (M = Cr 15 , V 31 , Ti 31 , Ni 32 , Co 33 , Fe 34 and Mn 32 ), M 1/3 NbSe 2 (M = Cr 35 , Rh [ 15 ], V 35 , Ti 15 and Co 35 ), M 1/3 ТаS 2 (M = Cr 15 , V 15 and Rh 15 ), and M 1/3 TaSe 2 (M = Cr 15 and V 15 ) at room temperature and ion radii determined in Ref. 36.…”

“…That is why in this case one should know the valence state of the magnetic ion, whose radius and, therefore, that of the local space, increase along with the valence decrease. Besides, the FM J4 couplings strength could, in addition, be dramatically increased upon shifting of S(Se) ions to In the compounds of the fifth group (Fe 1/3 NbS 2 34 (16) and Mn 1/3 NbS 2 32 (17)) with large magnetic ions Fe +2 and Mn +2 , the interplane FM J3 init (0.047 Fe Å -1 and 0.045 Mn Å -1 ) and J3 displ (0.048 Fe and 0.046 Mn Å -1 ) and intraplane intraplane FM J4 displ (0.055 Fe and 0.067 Mn Å -1 ) couplings are stronger than the AFM J6 (-0.041 Fe and -0.040 Mn Å -1 ) couplings in left-handed helices. The reasons of strengthening of the FM J3 and FM J4 displ couplings are teh same like in the fourth and thrid groups, respectively.…”

“…It is worth mentioning that, according to our calculations, in Cs 2 CuBr 4 such value (J′ 2 /J 2 = 0.74) is obtained for nextnearest-neighbor J 2 (J 2 = -0.0151 Å -1 , d(Cu-Cu) = 15.930 Å) and J' 2 (J' 2 = -0.0112 Å -1 , d(Cu-Cu) = 15.191 Å) couplings in linear chains along respective triangle sides (Fig.1), not for the ratio between nearest neighbors in the triangular lattice. About the same ratio J′ 2 /J 2 = 0.70 (J 2 = -0.0148 Å -1 , d(Cu-Cu) = 15.214 Å and J' 2 = -0.0104 Å -1 , d(Cu-Cu) = 14.531 Å) was obtained for Cs 2 CuCl 4 .As initial data for calculations of the sign and strength of magnetic interactions, we used crystallographic parameters and coordinates of intercalate atoms: M 1/3 NbS 2 (M = Cr 15 , V 31 , Ti 31 , Ni 32 , Co 33 , Fe34 and Mn 32 ), M 1/3 NbSe 2 (M = Cr35 , Rh [ 15 ], V35 , Ti 15 and Co35 ), M 1/3 ТаS 2 (M = Cr 15 , V 15 and Rh 15 ), and M 1/3 TaSe 2 (M = Cr 15 and V 15 ) at room temperature and ion radii determined in Ref 36…”

Ekplexite (Nb,Mo)S2·(Mg1−xAlx)(OH)2+x, kaskasite (Mo,Nb)S2·(Mg1−xAlx)(OH)2+x and manganokaskasite (Mo,Nb)S2·(Mn1−xAlx)(OH)2+x, three new valleriite-group mineral species from the Khibiny alkaline complex, Kola peninsula, Russia

“…This fenite locality is unique in terms of sulfide mineralization and formation conditions: high activity of S 2À and, unusually for terrestrial objects, extremely low oxygen fugacity (Barkov et al, 1997;Drábek et al, 2010;Yakovleva et al, 2010). These conditions lead to some lithophile metals such as W, Nb and Ti demonstrating chalcophile behaviour resulting in the formation of sulfides.…”