I. A. Bryzgalov

New nickel-uranium-arsenic mineral species from the oxidation zone of the Belorechenskoye deposit, Northern Caucasus, Russia: I. Rauchite, Ni(UO2)2(AsO4)2·10H2O, a member of the autunite group

Rauchite, ideally Ni(UO 2 ) 2 (AsO 4 ) 2 ·10H 2 O (IMA no. 2010-037), a new arsenate mineral species of the autunite group, was found at the Belorechenskoye deposit, Adygea Republic, Northern Caucasus, Russia. It is a supergene mineral associated with dymkovite, annabergite and goethite in cavities of a dolomite vein with primary uraninite (pitchblende), nickeline and gersdorffite. Rauchite forms pseudo-tetragonal lamellar crystals (the main form is {001}) up to 0.5 mm across, typically split, like a fan or open book, and their clusters or crusts as large as 2 mm. Rauchite is transparent to translucent and light yellowish-green. The lustre is vitreous. The mineral is brittle, the Mohs’ hardness is ca. 2. The cleavage is {001} perfect. D calc is 3.427 g cm −3 . Rauchite is optically biaxial (−), α = 1.550(3), β = 1.578(1), γ = 1.581(1), 2 V meas = 40(5)°, 2 V calc = 36°. The average chemical composition (mean of eight electron-microprobe analyses) is (in wt%): MgO = 0.71, CoO = 0.07, NiO = 5.38, ZnO = 0.08, P 2 O 5 = 1.08, As 2 O 5 = 20.26, UO 3 = 54.22, H 2 O calc = 17.10, and the total = 98.90. The empirical formula calculated on the basis of 22 O apfu is: (Ni 0.76 Mg 0.19 Co 0.01 Zn 0.01 ) ∑ 0.97 U 2.00 O 4 (As 1.86 P 0.16 ) ∑2.02 O 8 ·10H 2 O. Rauchite is triclinic, space group I -1, a = 7.100(3), b = 7.125(3), c = 19.955(8) A, α = 92.406(14), β = 94.924(14), γ = 90.420(6)°, V = 1004.7(7) A 3 , Z = 2. [parameters of the reduced P cell are: a = 7.100(3), b = 7.125(3), c = 10.751(4) A, α = 106.855(7), β = 104.366(7), γ = 90.420(6)°, V = 502.4(4) A 3 , Z = 1]. The crystal structure was refined from single-crystal X-ray diffraction data obtained at 153 K ( R 1 = 0.089). The structure is based upon autunite-type [(UO 2 )[AsO 4 ]] − layers with Ni 2+ coordinated by six H 2 O molecules and located in the interlayer space. The strongest lines in the powder X-ray diffraction pattern are [ d in A( I )( hkl )]: 9.97(100)(002), 6.641(22)(003), 4.936(62)(004, 01-3, −111), 4.533(41)(−112), 3.539(93)(020, 200, 20-1, 01-5, 02-1), 3.388(43)(20-2, 015, 02-2, 105), 2.488(27)(220, 2-21, −125, 1-25, 22-2, −222), and 2.233(27)(1-31, 3-10, 13-1, 31-1, 31-2, 2-24, 13-2, 21-7). The structure of rauchite corresponds to the 1 A -type stacking arrangement of uranyl arsenate layers in the autunite group of minerals and synthetic compounds. The mineral is named in accordance with the naming rules accepted for the autunite group as the hydrated analogue of metarauchite, Ni(UO 2 ) 2 (AsO 4 ) 2 ·8H 2 O.

Natural Mg-Fe clinochlores: Enthalpies of formation and dehydroxylation derived from calorimetric study

Abstract This paper presents the results of the first experimental thermochemical investigation of two natural trioctahedral chlorites (clinochlores). The study was performed with the help of a high-temperature heat-flux Tian-Calvet microcalorimeter. The samples were characterized by X ray spectroscopy analysis, X ray powder diffraction, thermal analysis, and FTIR spectroscopy. The enthalpies of formation of clinochlores were found using the melt solution calorimetry method to be: –8806 ± 16 kJ/mol for composition (Mg4.9Fe0.32+

Minerals of the Au-Ag-Pb-Te-Se-S system of porphyry-copper-molybdenum deposits from the Nakhodka ore field, Chukchi Peninsula, Russia

{\text{Fe}}_{0.3}^{2 + }

Tourmaline from deposits of the Birgil’da-Tomino ore cluster, South Urals

Al0.8)[Si3.2Al0.8O10](OH)8 and –8748 ± 24 kJ/mol for composition (Mg4.2Fe0.62+

New nickel-uranium-arsenic mineral species from the oxidation zone of the Belorechenskoye deposit, Northern Caucasus, Russia: II. Dymkovite, Ni(UO2)2(As3+O3)2·7H2O, a seelite-related arsenite

{\text{Fe}}_{0.6}^{2 + }

Calorimetric Study of Natural Anapaite

Al1.2)[Si2.8Al1.2O10](OH)8. The experimental data for natural samples allowed calculating the enthalpies of formation for end-members and intermediate members of the clinochlore (Mg5Al)[Si3AlO10](OH)8 and chamosite (Fe5Al)[Si3AlO10](OH)8 series. An important feature of the clinochlore structure is the presence of two distinct hydroxyl-containing octahedral layers: the interlayer octahedral sheet and octahedral 2:1 layer; the enthalpies of water removal from these positions in clinochlore structure were determined as: 53 ± 20 kJ/(mol·H2O) and 131 ± 10 kJ/(mol·H2O), respectively. These obtained first thermodynamic characteristics of Mg-Fe clinochlores can be used for quantitative thermodynamic modeling of geological and industrial processes including clinochlores of different composition.

Thermochemical Study of Mg-Fe Chlorites

The Nakhodka ore field located 220 km south of the Bilibino town, Chukchi Peninsula, Russia comprises Cu-Mo-porphyry (Malysh and Vesennii) and Mo-Cu-porphyry (Nakhodka, III Vesennii) deposits. The late epithermal mineralization with native gold of low fineness (498–766) of the first group deposits refers to the IS (intermediate sulfidation) type, which is characterized by the occurrence of petzite; stutzite; acanthite; pearceite; and minerals of the Pb-Bi-Ag-Se-Te, Ag-Te-Se, and Ag-Bi-Se systems, as well as by native tellurium. The epithermal mineralization forms at fTe2(−19...−18) and fS2(−14...−13) and temperatures <200°C. The second group deposits do not exhibit epithermal mineralization; telluride mineralization is present as only native tellurium and altaite.

Thermodynamic study of calcic amphiboles

Tourmalines from the Kalinovka porphyry copper deposit with epithermal bismuth-gold-basemetal mineralization and the Michurino gold-silver-base-metal prospect have been studied in the South Urals. Tourmaline from the Kalinovka deposit occurs as pockets and veinlets in quartz-sericite metasomatic rock and propylite. The early schorl-“oxy-schorl” [Fetot/(Fetot + Mg) = 0.66−0.81] enriched in Fe3+ is characterized by the homovalent isomorphic substitution of Fe3+ for Al typical of propylites at porphyry copper deposits. The overgrowing tourmalines of the second and third generations from propylite and quartz-sericite metasomatic rock are intermediate members of the dravite-magnesio-foitite solid solution series [Fetot/(Fetot + Mg) = 0.05−0.46] with homovalent substitution of Mg for Fe2+ and coupled substitution of X▭ + YAl for XNa + YMg. These substitutions differ from the coupled substitution of YAl + WO2− for YFe2+ + WOH− in tourmaline from quartz-sericite rocks at porphyry copper deposits. At the Michurino prospect, the tourmaline hosted in the chlorite-pyrite-quartz veins and veinlets with Ag-Au-Cu-Pb-Zn mineralization is an intermediate member of the dravite-magnesio-foitite solid solution series [Fetot/(Fetot + Mg) = 0.20−0.31] with homovalent substitution of Mg for Fe2+ and coupled substitutions of X▭ + YAl for XNa + YMg identical to that of late tourmaline at the Kalinovka deposit. Thus, tourmalines of the porphyry and epithermal stages are different in isomorphic substitutions, which allow us to consider tourmaline as an indicator of super- or juxtaposed mineralization.

Thermochemical study Mg–Fe amphiboles

A new arsenite mineral species dymkovite, ideally Ni(UO 2 ) 2 (As 3+ O 3 ) 2 ·7H 2 O (IMA no. 2010-087), was found at the Belorechenskoye deposit, Adygea Republic, Northern Caucasus, Russia. It is a supergene mineral associated with rauchite, annabergite, and goethite in cavities of a dolomite vein with primary uraninite (pitchblende), nickeline, and gersdorffite. Dymkovite forms long-prismatic, lath-shaped to acicular crystals (≤0.5 mm long, ≤0.05 mm thick), which are elongated along [010]. They are combined in sprays or open-work, chaotic groups up to 1.5 mm across; crusts up to 2 × 2 mm 2 and up to 0.05–mm-thick also occur. Dymkovite crystals are transparent and bright yellow, whereas crusts are translucent and light yellow to light greenish-yellow. The luster is vitreous. The mineral is brittle, the Mohs’ hardness is ca. 3. Cleavage was not observed. D calc is 3.806 g cm −3 . Dymkovite is optically biaxial (−), α = 1.625(2), β = 1.735(5), γ = 1.745(3), 2 V meas = 20(10)°, 2 V calc. = 32°. Dispersion is strong, r > v . Pleochroism is strong: X = very pale yellowish-green, Y ≈ Z = light greenish yellow. In the IR spectrum, bands of As 3+ O 3 anions are strong, whereas bands of As 5+ O 4 anions are very weak. The average chemical composition (electron microprobe) is (in wt%): MgO = 1.11, FeO = 0.24, NiO = 5.40, ZnO = 0.23, As 2 O 3 = 19.57, P 2 O 5 = 0.58, UO 3 = 59.43, H 2 O calc = 13.44, total = 100.00. The empirical formula, calculated on the basis of 17 O apfu, is: (Ni 0.69 Mg 0.26 Fe 0.03 Zn 0.03 ) ∑1.01 U 1.97 (As 3+ 1.88 P 0.08 ) ∑1.96 O 9.94 ·7.06H 2 O. Dymkovite is monoclinic, space group C 2/ m , a = 17.99(3), b = 7.033(7), c = 6.633(9) A, β = 99.62(11)°, V = 827(3) A 3 , Z = 2. The crystal structure was refined from single-crystal X-ray diffraction data ( R 1 = 0.063). The structure is based upon the [(UO 2 )(As 3+ O 3 )] − sheets formed by chains of edge-sharing [UO 7 ] pentagonal bipyramids and (As 3+ O 3 ) triangular pyramids, which are linked through hydrogen bonds involving disordered [Ni(H 2 O) 6 ] 2+ octahedra and additional H 2 O molecules in the interlayer. The strongest lines of the powder X-ray pattern [ d in A ( I )( hkl )] are: 8.93(100)(200), 4.463(34)(111, 400), 3.523(23)(020), 3.276(21)(220), 3.008(26)(11-2), 2.846(27)(112, 221, 31-2). Dymkovite is a Ni-dominant, almost arsenate-free analogue of seelite, Mg(UO 2 ) 2 [(As 3+ O 3 ) 1.4 (As 5+ O 4 ) 0.6 ]·7H 2 O. The mineral is named in honor of the Russian mineralogist Yuriy Maksimovich Dymkov (b. 1926), a specialist in U mineralogy, the geology of U deposits, and problems of mineral formation, who was one of the first researchers of the U ores of the Belorechenskoye deposit.

Enthalpy of formation of natural amesite

The thermochemical study of natural hydrous calcium and iron phosphate, anapaite Ca2Fe(PO4)2 · 4H2O (Kerch iron ore deposit, Crimea, Russia), was carried out using high-temperature melt solution calorimetry with a Tian-Kalvet microcalorimeter. The enthalpy of formation of the mineral from elements was obtained to be Δ fHel°(298.15 K) =–4812 ± 16 kJ/mol. The values of the standard entropy and the Gibbs energy of anapaite formation are S°(298.15 K) = 404.2 J/K mol and Δ fGel°(298.15 K) =–4352 ± 16 kJ/mol, respectively.