The Hiendelaencina mining district (Guadalajara,Spain)

The Hiendelaencina mining district (Guadalajara, Spain), includes the ore deposits of the Hiendelaencina, La Bodera and Congostrina areas. In this paper a general overview of this district is given, with special emphasis on the parageneses, mineralizing stages and chemical characteristics of the sulphides and sulphosalts. These deposits contain silver in Sb-rich sulphosalts such as freibergite, pyrargyrite, polybasite, stephanite, freieslebenite and the Bi-rich sulphosalt, aramayoite. Three mineralizing stages have been detected in Hiendelaencina and Congostrina: (1) As-Fe; (2) Cu-Zn-Fe-Sb-Ag; and (3) Pb-Sb-Ag (±Bi) but only two in La Bodera (stages 2 and 3). The average sulphosalt formulas are: freibergite (Cu_0.5 Ag_5.9) (Fe_1.42 Zn_0.66) (Sb_4.49 As_0.02) S₁₃; pyrargyrite Ag_3.38 Sb_1.0 S₃; polybasite (Ag_16.3Cu_0.15) (Sb_2.8 As_0.15) S₁₁; stephanite Ag_6.7 Sb_1.38 S₄; freieslebenite Ag_1.1 Sb_0.83 Pb_1.05 S₃ and aramayoite Ag_1.06 Bi_{0. 35} Sb_0.7 Pb_0.03 S₂. The compositional patterns of these sulphosalts (mainly based on the Sb/(Sb + Ag), Ag/ (Ag + Cu), Sb(Ag + As) and Ag/(Ag + Cu) ratios) are outlined, pointing broadly to similar tendencies in their chemistry and genetic conditions.     

Fe-Zn exchange reaction between tetrahedrite and sphalerite in natural environments

Microprobe and fluid inclusion analyses of hydrothermal ore deposits containing the subassemblage sphalerite+ tetrahedrite-tennantite [(Cu, Ag)₁₀(Fe, Zn)₂(As,Sb)₄S₁₃] reveal that the Gibbs energies of the reciprocal reaction Cu₁₀Zn₂Sb₄S₁₃ + Cu₁₀Fe₂As₄S₁₃ = Cu₁₀Fe₂Sb₄S₁₃ + Cu₁₀Zn₂As₄S₁₃ and the Fe-Zn exchange reaction 1/2Cu₁₀Fe₂Sb₄S₁₃ + ZnS = 1/2Cu₁₀Zn₂Sb₄S₁₃ + FeS are within the uncertainties of the values established by Sack and Loucks (1985) and Raabe and Sack (1984), 2.59±0.14 and 2.07±0.07 kcal/gfw. However, this study suggests that the Fe-Zn exchange reaction between sphalerite and Sb and Ag-rich tetrahedrites does not obey the simple systematics suggested by Sack and Loucks (1985) wherein tetrahedrite is assumed to behave as an ideal reciprocal solution. Instead these studies show that the configurational Gibbs energy of this exchange reaction,RTln[(X _Fe/X _Zn)^TET(X _ZnS/X _FeS)^SPH], corrected for sphalerite nonideality exhibits both a local maximum and minimum as a function of Ag/(Cu+Ag) ratio at a givenX _FeS ^SPH and temperature. The local maximum forX _FeS ^SPH 0.10 corresponds to the position of the cell edge maximum established for natural tetrahedrites by Riley (1974), Ag/(Ag+Cu)0.4. These studies and the results of structural refinements of Ag-bearing tetrahedrites suggest that in low silver tetrahedrites Ag is preferentially incorporated in trigonal-planar sites but that in tetrahedrites with intermediate and greater Ag/(Ag+Cu) ratio, Ag is preferentially incorporated in tetrahedral sites. A nonconvergent site ordering model for tetrahedrite is developed to quantify and extrapolate these predictions.     

Some electrical properties of fahlore Cu10(Zn,Fe)2(As,Sb)4S13

Natural Zn-tennantite Cu_10.10Ag_0.04(Zn_1.29-Fe_0.67)_1.96(As_3.04Sb_0.89)_3.93S_12.98 from Beresovskoe, Urals, behaves as an ordinary semiconductor in the temperature range 300–400 K and frequency range 10⁸–2.8·10¹⁰ Hz, and no ionic component conductivity is observed. This contrasts with the behaviour of synthetic tetrahedrites (both Cu-rich and Cu-poor) which are solid electrolytes. These results can be related to the number of vacancies per formula unit and the substitution scheme for the divalent metals in fahlore.     

The role of Fe2+ and Fe3+ in synthetic Fe-substituted tetrahedrite

Summary Tetrahedrites with the composition between Cu₁₂Sb₄S₁₃ and Cu₁₀Fe₂Sb₄S₁₃ were synthesized at 457 °C and 500 °C from the elements and carefully studied by Mössbauer spectroscopy of⁵⁷Fe. Between Cu₁₂Sb₄S₁₃ and Cu₁₁Fe₁Sb₄S₁₃ iron is predominantly ferric. Between Cu₁₁Fe₁Sb₄S₁₃ and Cu₁₀Fe₂Sb₄S₁₃ iron is predominantly ferrous and occupies the tetrahedral M1-sites.

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Zusammenfassung Die Rolle von Fe²⁺ und Fe³⁺ in synthetischen Tetraedriten mit Fe-Substitution Tetraedrite mit einer Zusammensetzung zwischen Cu₁₂Sb₄S₁₃ and Cu₁₀Fe₂Sb₄S₁₃ wurden bei 457 °C und 500 °C aus den Elementen synthetisiert und sorgfdltig mit Mössbauer-Spektroskopie von⁵⁷Fe untersucht. Zwischen Cu₁₂Sb₄S₁₃ and Cu₁₁Fe₁Sb₄S₁₃ ist Eisen überwiegend dreiwertig. Zwischen Cu₁₁Fe₁Sb₄S₁₃ and Cu₁₁Fe₂Sb₄S₁₃ ist Eisen überwiegend zweiwertig und besetzt die tetraedrisch koordinierten M1-Plätze.

     

Fahlore thermochemistry: Gaps inside the (Cu,Ag)<Subscript>10</Subscript>(Fe,Zn)<Subscript>2</Subscript>(Sb,As)<Subscript>4</Subscript>S<Subscript>13</Subscript> cube

Possible topologies of miscibility gaps in arsenian (Cu,Ag)₁₀(Fe,Zn)₂(Sb,As)₄S₁₃ fahlores are examined. These topologies are based on a thermodynamic model for fahlores whose calibration has been verified for (Cu,Ag)₁₀(Fe,Zn)₂Sb₄S₁₃ fahlores, and conform with experimental constraints on the incompatibility between As and Ag in (Cu,Ag)₁₀(Fe,Zn)₂(Sb,As)₄S₁₃ fahlores, and with experimental and natural constraints on the incompatibility between As and Zn and the nonideality of the As for Sb substitution in Cu₁₀(Fe,Zn)₂(Sb,As)₄S₁₃ fahlores. It is inferred that miscibility gaps in (Cu,Ag)₁₀(Fe,Zn)₂As₄S₁₃ fahlores have critical temperatures several °C below those established for their Sb counterparts (170 to 185°C). Depending on the structural role of Ag in arsenian fahlores, critical temperatures for (Cu,Ag)₁₀(Fe,Zn)₂(Sb,As)₄S₁₃ fahlores may vary from comparable to those inferred for (Cu,Ag)₁₀(Fe,Zn)₂As₄S₁₃ fahlores, if the As for Sb substitution stabilizes Ag in tetrahedral metal sites, to temperatures approaching 370°C, if the As for Sb substitution results in an increase in the site preference of Ag for trigonal-planar metal sites. The latter topology is more likely based on comparison of calculated miscibility gaps with compositions of fahlores from nature exhibiting the greatest departure from the Cu₁₀(Fe,Zn)₂(Sb,As)₄S₁₃ and (Cu,Ag)₁₀(Fe,Zn)₂Sb₄S₁₃ planes of the (Cu,Ag)₁₀(Fe,Zn)₂(Sb,As)₄S₁₃ fahlore cube.     

Phase relations in the systems Ag2S-Cu2S-PbS and Ag2S-Cu2S-Bi2S3 and their mineral assemblages

Phase relations in the ternary systems Ag₂S-Cu₂S-PbS and Ag₂S-Cu₂S-Bi₂S₃ were studied using the silica vacuum technique. In the system Ag₂S-Cu₂S-Bi₂S₃ the phase relations are dominated by join-lines from galena to f.c.c. (Ag_x Cu_2−xS) and b.c.c. (Cu_x Ag_2−xS) at 500°C. With decreasing temperature, galena can coexist with all the phases on the Ag₂S-Cu₂S join. There are six solid solutions, and one new phase, i.e., “C” whose composition is Ag_1.1 Cu_4.8Bi_5.8S₁₂ in the system Ag₂S-Cu₂S-Bi₂S₃ at 500°C. The pavonite (AgBi₃S₅) contains 14 mole% Cu₂S in solid solution, but only 3.0 mole% Ag₂S in CuBi₃S₅ solid solution. The Cu₃Bi₅S₉ ss and wittichenite (Cu₃BiS₃) ss can form join-lines with pavonite as and have the maximum contents of 9.0 and 18 mole% Ag₂S. The most striking feature is the presence of bejaminite as a stable phase with a chemical formula of Ag₂Bi₄S₇ on the Ag₂S-Bi₂S₃ join. AgBiS₂ of the PbS type occupies a fairly large field with a maximum of 23 mole% Cu₂S.     

The kinetics of oxygen exchange between the GeO4Al12(OH)24(OH2)12(aq) molecule and aqueous solutions

We report rates of oxygen exchange with bulk solution for an aqueous complex, ^IVGeO₄Al₁₂(OH)₂₄(OH₂)₁₂⁸⁺(aq) (GeAl₁₂), that is similar in structure to both the ^IVAlO₄Al₁₂(OH)₂₄(OH₂)₁₂⁷⁺(aq) (Al₁₃) and ^IVGaO₄Al₁₂(OH)₂₄(OH₂)₁₂⁷⁺(aq) (GaAl₁₂) molecules studied previously. All of these molecules have ε-Keggin-like structures, but in the GeAl₁₂ molecule, occupancy of the central tetrahedral metal site by Ge(IV) results in a molecular charge of +8, rather than +7, as in the Al₁₃ and GaAl₁₂. Rates of exchange between oxygen sites in this molecule and bulk solution were measured over a temperature range of 274.5 to 289.5 K and 2.95 < pH < 4.58 using ¹⁷O-NMR.Apparent rate parameters for exchange of the bound water molecules (η-OH₂) are k_ex²⁹⁸ = 200 (±100) s⁻¹, ΔH^‡ = 46 (±8) kJ · mol⁻¹, and ΔS^‡ = −46 (±24) J · mol⁻¹ K⁻¹ and are similar to those we measured previously for the GaAl₁₂ and Al₁₃ complexes. In contrast to the Al₁₃ and GaAl₁₂ molecules, we observe a small but significant pH dependence on rates of solvolysis that is not yet fully constrained and that indicates a contribution from the partly deprotonated GeAl₁₂ species.The two topologically distinct μ₂-OH sites in the GeAl₁₂ molecule exchange at greatly differing rates. The more labile set of μ₂-OH sites in the GeAl₁₂ molecule exchange at a rate that is faster than can be measured by the ¹⁷O-NMR isotopic-equilibration technique. The second set of μ₂-OH sites have rate parameters of k_ex²⁹⁸ = 6.6 (±0.2) · 10⁻⁴ s⁻¹, ΔH^‡ = 82 (±2) kJ · mol⁻¹, and ΔS^‡ = −29 (±7) J · mol⁻¹ · K⁻¹, corresponding to exchanges ≈40 and ≈1550 times, respectively, more rapid than the less labile μ₂-OH sites in the Al₁₃ and GaAl₁₂ molecules. We find evidence of nearly first-order pH dependence on the rate of exchange of this μ₂-OH site with bulk solution for the GeAl₁₂ molecule, which contrasts with Al₁₃ and GaAl₁₂ molecules.     

Germanium-bearing Colusite in Siliceous Black Ore from the Ezuri Kuroko Deposit, Hokuroku District, Japan

Abstract. Germanium‐bearing colusite occurs with sphalerite, galena, tetrahedrite‐tennantite, chalcopyrite and pyrite in microdruses and veinlets in the siliceous black ore from the Ezuri Kuroko deposit in the Hokuroku district of Japan. X‐ray microdiffractometry of this mineral gives strongest lines at 1.60, 1.32 and 1.09 Å, which are consistent with the known powder diffraction data of colusite. On the basis of 32 S atoms per formula unit, electron microprobe analyses yield empirical chemical formulae of (Cu_{24 0}Fe_0.3Zn_1.0)_σ25.3V_1.9(A_s4.8Sb_0.2)_σ5.0Ge _1.3S₃₂ for Ge‐bearing colusite in close association with sphalerite, and (Cu_24.6Fe_0.9)_σ25.4V_1.8(A_s4.1 Sb_0.2)_σ4.3Ge_1.7S₃₂ for that coexisting with chalcopyrite, consistent with the ideal formula of Cu_24+xV₂(As, Sb)_6‐x(Sn, Ge)_xS₃₂ (x = 0 to 2) proposed by Spry et al. (1994) for this mineral species. The Ge‐bearing colusite mineralization is suggested to have occurred concurrently with consolidation of the siliceous black ore, possibly during hydrothermal modification in association with the igneous activity of the Ohtaki quartz diorite of the later Onnagawa stage. It is likely that biogenic siliceous ooze, a possible precursor of the siliceous black ore, may have served as an in situ source of Ge as well as other essential rare elements, leading to the formation of Ge‐bearing colusite during transformation or recrystallization of biogenic opal into a‐quartz.     

Two Se-bearing Ag–Bi Sulphosalts, Benjaminite and Matildite from the Ikuno Deposits, Hyogo Prefecture, Japan –Au–Ag Mineralization in Polymetallic Zone

Abstract: Se-bearing benjaminite and matildite are described from the polymetallic zone of the Ikuno deposits, Japan. The former is the first occurrence in Japan, and is from two separate veins, the Nanten and Daimaru, while the locality of the latter could not be specified. The empirical formulae of two benjaminites based on 22 atoms are (Ag_{2. 74}Cu_{0. 24})_{Σ2. 98}(Bi_{7. 00}Sb_{0. 01})_{Σ7. 01}(S_{10. 89}Se_{1. 12})_{Σ12. 01} (Nanten) and (Ag_{2. 90}Cu_{0. 10})_{Σ3. 00}(Bi_{6. 74}Pb_{0. 18}Sb_{0. 07})_{Σ6. 99}(S_{11. 68}Se_{0.33)Σ12. 01} (Daimaru), leading to the validation of the formula Ag₃Bi₇S₁₂ as the ideal one for benjaminite, and that of matildite based on 4 atoms is Ag_{1. 00}Bi_{1. 00}(S_{1. 78}Se_{0. 22})Σ_{2. 00}. These designate the substitution of Se for S in all of them, where Se is preferentially incorporated into these Ag-Bi sulphosalts. The unit-cell parameters of them and matildite are: a 13. 272, b 4. 037, c 20. 185 Å, and β 103. 16° (Daimaru), a 13. 270, b 4. 040, c 20. 273 Å, and β103. 17° (Nanten); and a 4. 0670, c 18. 996 Å, respectively. The products of Au-Ag mineralization in the Ikuno polymetallic vein-type deposits also occur as such Ag-Bi sulfosalts as benjaminite and matildite, in addition to pavonite, “treasurite derivative” and “electrum” with cassiterite in the polymetallic zone, and also do as “electrum”, acanthite, and pyrargyrite-proustite in the Au-Ag zone. The significant quantity of the Ag-Bi sulfosalts does not violate the zoning occupying the outermost part of the zonal distribution of ores in the deposits.     

Chemistry of some Pb-(Cu,Fe)-(Sb,Bi sulfosalts from France and Portugal. Implications for the crystal chemistry of lead sulfosalts in the Cu-poor part of the Pb2S2-Cu2S-Sb2S3-Bi2-Bi2S3 system

Electron microprobe analysis of Pb-Cu(Fe)-Sb-Bi sulfosalts from Bazoges and Les Chalanches (France), and Pedra Luz (Portugal), give new data about (Bi, Sb) solid-solution and incorporation of the minor elements Cu, Fe or Ag in jaskolskiite, and in izoklakeite-giessenite and kobellite-tintinaite series. Jaskolskiite from Pedra Luz has high Sb contents (from 17.9 to 20.7 wt.%), leading to the extended general formula: Cu _x Pb_2+x (Sb_1–y Bi _y )_2–x S₅, with 0.10 x 0.22 and 0.19 y 0.41. Fe-free, Bi-rich izoklakeite from Bazoges has high Ag contents (up to 2.2 wt. %), leading to the simplified formula Cu₂Pb₂₂Ag₂(Bi, Sb)₂₂S₅₇; in Les Chalanches it contains less Ag content (1.2 wt.%), but has an excess of Cu that gives the formula: Cu_2.00 (Cu_0.49Ag_1.18)_=1.67Pb_22.70(Bi_12.63Sb_8.99)_=21.62S_57.27.In tintinaite from Pedra Luz, the variation of the Fe/Cu ratio can be explained by the substitution: Cu + (Bi, Sb) Fe + Pb; Fe-free kobellite from Les Chalanches has a Cu-excess, corresponding to the formula Cu_2.81Ag_0.54Pb_9.88(Bi_10.37Sb_5.21)_=15.38S_35.09. Eclarite from the type locality, structurally related to kobellite, shows a Cu excess too. In natural samples of the kobellite homologous series, Fe is positively correlated with Pb, and its contents never exceed that of Cu. Ag substitutes for Pb, together with (Bi, Sb). Taking into account the possibility of Cu excess, but excluding formal Cu²⁺ and Fe³⁺, general formulae can be written:     

A note on the bonding,optical spectrum and composition of tetrahedrite

Tetrahedrites of composition (Cu, Ag)₁₀(Cu₂, Fe, Zn)₂(Sb, As)₄S₁₃ or Cu₁₂Sb_14/3S₁₃ have 208 valence electrons per unit cell and are expected to be semiconductors. The bands are full in these cases, whereas compositions towards the classical formula Cu₁₂Sb₄S₁₃ (204 valence electrons per unit cell) have only partially filled bands and are therefore expected to be metallic. These predictions are supported by new optical absorption spectra of tetrahedrites with 205 and 208 valence electrons per unit cell. The gap between valence and conduction bands of the semiconductor is about 1.7 (±0.2) eV. A further prediction based on a nearly-free electron model is that 208 valence electrons per unit cell represent a compositional limit for tetrahedrites, and that the stability increases as compositions approach this limit. Existing data indicate an exponential increase in the number of occurrences as the limit is approached.     

Phase relations in the systems Cu2S-PbS-Bi2S3 and Ag2S-PbS-Bi2S3 and their mineral assemblages

The phase diagrams of the systems Cu₂S-PbS-Bi₂S₃ and Ag₂S-PbS-Bi₂S₃ have been investigated in the present study. The paper is concerned with the complete solid solution between bismuthtite and aikinite above 300°C in the system Cu₂S-PbS-Bi₂S₃. The synthetic phases CuBi₃S₅ and Cu₃Bi₅S₉ have their solid solution ranges in the ternary system with 9 and 26 mole% PbS at maximum, respectively. A complete solid solution between PbS and AgBiS₂ divides the phase diagram of the system Ag₂S-PbS-Bi₂S₃ into two parts: Bi-rich and Ag-rich. All sulfosalt minerals and solid solutions, including pavonite ss, lillianite ss, heyovskyite and benjaminite are on the Bi-rich side. And divarant relations were found between pavonite ss -lillianite ss, benjaminite and bismuthtite as well as between lillianite ss -bismuthtite and galenobismutite. Synthetic experiments using LiCl-KCl flux technique show that when a minor amount of copper (less lwt.%) is added in, many of Ag-and Pb-bismuth sulfosalt minerals, for example, vikingite (Ag₅Pb₈Bi₁₃S₃₀), are synthesized successively, particularly at 400°C. So is heyrovskyite, which has a solid solution range with 3.7 mole% Cu₂S at maximum in the system Cu₂S-PbS-Bi₂S₃.     

Structure cristalline d'une ménéghinite naturelle pauvre en cuivre,Cu0,58Pb12,72(Sb7,04Bi0,24)S24Crystal structure of a Cu-poor natural meneghinite,Cu0.58Pb12.72(Sb7.04Bi0.24)S24

Cu-poor meneghinite from La Lauzière Massif (Savoy, France) has the composition (electron microprobe) (in wt%): Pb 59.50, Sb 20.33, Bi 1.19, Cu 0.87, Ag 0.05, Fe 0.03, S 17.62, Se 0.05, Total 99.64. Its crystal structure (X-ray on a single crystal) was solved with R1=0.0506, wR2=0.1026, with an orthorhombic symmetry, space group Pnma, and a=24.080(5) Å, b=4.1276(8) Å, c=11.369(2) Å, V=1130.0(4) Å³, Z=4. Relatively to the model of Euler and Hellner (1960), this structure shows a significantly lower site occupancy factor for the tetrahedral Cu site (0.146 against 0.25). Among the five other metallic sites, Bi appears in the one with predominant Sb. Developed structural formula: Cu_0.15Pb₂(Pb_0.53Sb_0.47)(Pb_0.46Sb_0.54)(Sb_0.75Pb_0.19Bi_0.06)S₆; the reduced one: Cu_0.58Pb_12.72(Sb_7.04Bi_0.24)S₂₄. The formation of such a Cu-poor variety seems to be related to specific paragenetic conditions (absence of coexisting galena), or to crystallochemical constraints (minor Bi). To cite this article: Y. Moëlo et al., C. R. Geoscience 334 (2002) 529–536.     

Trace elements of Indium-bearing sphalerite from tin-polymetallic deposits in Bolivia,China and Japan: A femto-second LA-ICPMS study

Indium-bearing tin-polymetallic base metal deposits in Japan (Toyoha, Ashio and Akenobe), China (Dulong and Dachang), and Bolivia (Potosi, Huari Huari, Bolivar and Porco), were studied using femto-second Laser Ablation ICPMS (fsLA-ICPMS) and EPMA analyses for major and minor elements in sphalerite, paying special attention to In concentrations.Sphalerite is a principal mineral in these tin-polymetallic deposits and a broad range of In concentration is measured in the ores. There are distinct differences in mode of occurrence of the sphalerite and the distribution of In. The highest In concentration (up to 18 wt.%) occur as a Zn–In mineral within black sphalerite zones in an oscillatory-zoned sphalerite from the Huari Huari deposits. Additionally, jamesonite from the Huari Huari deposit also contains anomalous In values, ranging from several hundreds to thousands μg/g. Sphalerite from the Toyoha and the other Bolivian deposits are characterized by oscillatory and chemical zoning, whereas those from Akenobe and the Chinese deposits are represented by homogeneous distribution of In. The 1000In/Zn values of sphalerite are in good agreement with those of the ore grade for each of the selected tin polymetallic deposits indicating that sphalerite is the principal host of In.The In-bearing sphalerite principally involves the combined coupled substitutions (2Zn^2 +) ↔ (Cu⁺, In^3 +), (3Zn^2 +) ↔ (Cu⁺, Ag⁺, Sn^4 +) and (3Zn^2 +) ↔ (2Cu⁺, Sn^4 +). The first of these is apparent in sphalerite from Huari Huari and Bolivar, whereas the second is prominent in sphalerite from Toyoha, Ashio, Potosi, Porco and Dachang. Akenobe and Dulong sphalerite features the dominant coupled substitution of (2Zn^2 +) ↔ (Cu⁺ or Ag⁺, In^3 +), owing to their poor Sn content. Occasionally, sub-micron inclusions of minerals such as stannite and Pb–Sb-bearing sulfides can occur in sphalerite, contributing to high Cu–Sn and high-Ag contents, respectively. The observed correlations of each element in the In–Cu–Ag–Sn-bearing sphalerite can be proposed as a fundamental reason for the indium enrichment related to sulfur-rich oxidized magmatism. In addition, the Ag content in sphalerite is considered a possible indicator of formation depth, which ranges from plutonic to subvolcanic environments.     

Synthesis, characterization, and thermochemistry of K-Na-H3O jarosites

The thermochemistry of well-characterized synthetic K-H₃O, Na-H₃O and K-Na-H₃O jarosites was investigated. These phases are solid solutions that obey Vegard’s law. Electron probe microanalyses indicated lower alkali and iron contents than predicted from the theoretical end-member compositions, in agreement with thermal analyses, suggesting the presence of hydronium and “additional” water. The standard enthalpies of formation (ΔH°_f) of K-H₃O, Na-H₃O and K-Na-H₃O jarosites were determined by high-temperature oxide melt solution calorimetry. These enthalpies vary linearly with the K/H₃O, Na/H₃O and K/Na ratio, respectively. The enthalpy of formation of pure hydronium jarosite was also determined experimentally (ΔH°_f = −3741.6 ± 8.3 kJ.mol⁻¹), and it was used to evaluate ΔH°_f for the end-members KFe₃(SO₄)₂(OH)₆ (ΔH°_f = −3829.6 ± 8.3 kJ.mol⁻¹) and NaFe₃(SO₄)₂(OH)₆ (ΔH°_f = −3783.4 ± 8.3 kJ.mol⁻¹). Finally, enthalpies of dehydration (loss of the “additional” water) of some jarosites were determined and found to be near the enthalpy of vaporization of water, suggesting that the “additional” water is weakly bonded in the structure.     

Solid solutions in the system acanthite (Ag<Subscript>2</Subscript>S)–naumannite (Ag<Subscript>2</Subscript>Se) and the relationships between Ag-sulfoselenides and Se-bearing polybasite from the Kongsberg silver district,Norway, with implications for sulfur–selenium fractionation

Sulfoselenides [Ag₂(S,Se)] and Se-bearing polybasite have been discovered at the Kongsberg silver district. The selenium-bearing minerals occur in two samples from the northern part of the district, forming either single or polyphase inclusions together with chalcopyrite within native silver. The Ag-sulfoselenides show large chemical variations, covering nearly the complete compositional range between acanthite (Ag₂S) and naumannite (Ag₂Se). For the data presented here, there is no local maximum at the composition Ag₄SSe attributed to the distinct phase called aguilarite, suggesting that this composition can be considered as one of many possible along the monoclinic Ag₂S–Ag₂S_0.4Se_0.6 solid solution series rather than a specific mineral phase. We present a model explaining the variations in the Se-content of Ag₂(S,Se) as a result of gradual de-sulfidization of the rock under oxidizing conditions. During this process, sulfur from the Ag₂S-component of Ag₂(S,Se) oxidized and dissolved in the fluid phase as SO₄^2?, resulting in the formation of native silver. The activity ratio \({a_{{{\text{S}}^{2 - }}}}/{a_{{\text{S}}{{\text{e}}^{2 - }}}}\) of the system gradually decreased due to the removal of SO₄^2?, which resulted in the stabilization of a sulfoselenide with higher selenium content. As a result of reaction progress, grains of Ag₂(S,Se) became gradually enclosed in newly formed native silver, and therefore isolated from further reactions with the grain-boundary fluid. Grains isolated early during the process show low content of Se reflecting high \({a_{{{\text{S}}^{2 - }}}}/{a_{{\text{S}}{{\text{e}}^{2 - }}}}\) of the equilibrium fluid, while grains showing high Se reflect the composition of late low \({a_{{{\text{S}}^{2 - }}}}/{a_{{\text{S}}{{\text{e}}^{2 - }}}}\) fluids. Analyses of Se-bearing polybasite show that selenium is preferentially partitioned into Ag₂(S,Se) compared to polybasite. The model presented here demonstrates how oxidation of sulfoselenides leads to fractionation of sulfur and selenium.     

Calculation of the energetics for the oxidation of Sb(III) sulfides by elemental S and polysulfides in aqueous solution

Recent experimental studies have reported the existence of two new Sb sulfide species, Sb₂S₅²⁻ and Sb₂S₆²⁻, in alkaline sulfidic solutions in equilibrium with stibnite, Sb₂S₃, and orthorhombic S. These species contain Sb(V), which has also recently been identified in similar solutions using EXAFS by other researchers. This represents a significant change from the consensus a decade ago that sulfidic solutions of Sb contained only Sb(III) species. I have calculated from first principles of quantum mechanics the energetics for the oxidation of the Sb(III) sulfide dimer Sb₂S₄²⁻ to the mixed Sb(III,V) dimer Sb₂S₅²⁻ and then to the all Sb(V) dimer, Sb₂S₆²⁻. Gas-phase reaction energies have been evaluated using polarized valence double zeta effective core potential basis sets and Moller-Plesset second order treatments of electron correlation. All translational, rotational and vibrational contributions to the gas-phase reaction free energy have been calculated. Hydration energies have been obtained using the COSMO version of the self-consistent reaction field polarizable continuum method. Negative free energy changes are calculated for the oxidation of the dianion of the III,III dimer to the III,V dimer by both small polysulfides, like S₄H⁻, and elemental S, modeled as S₈. For the further oxidation of the III,V dimer to the V,V dimer the reaction free energies are calculated to be close to zero. The partially protonated Sb III,III dimer monoanion HSb₂S₄⁻ can also be oxidized, but the reaction is not so favorable as for the dianion. Comparison of the calculated aqueous deprotonation energies of H₂Sb₂S₄, H₂Sb₂S₅ and H₂Sb₂S₆ and their dianions with values calculated for various oxyacids indicates that the III,V and V,V dimers will have pK_a2 values <5, so that their dianions will be the dominant species in alkaline solutions. These results are thus consistent with the recent identification of Sb₂S₅²⁻ and Sb₂S₆²⁻ species. I have also calculated the Raman spectra of Sb₂S₅²⁻ and Sb₂S₆²⁻ to assist in their identification. The calculated vibrational frequencies of the III,V and V,V dimers are characteristically higher than those of the III,III dimer I previously studied. The III,V dimer may contribute shoulders to the Raman spectrum.     

Cuprokalininite, CuCr2S4, a new sulfospinel from metamorphic rocks of the Sludyanka Complex, South Baikal region

Cuprokalininite as an accessory mineral has been found in Cr-V-bearing quartz-diopside metamorphic rock of the Sludyanka Complex, South Baikal region, Russia. This mineral is named as Cu analogue of kalininite (ZnCr₂S₄), is associated with quartz, Cr-V-bearing tremolite and mica, calcite, diopside-kosmochlor, goldmanite-uvarovite, dravite-chromdravite, Cr-V spinellide, karelianite-eskolaite, V-bearing titanite, pyrite, and plagioclase. Cuprokalininite forms euhedral microcrystals up to 0.05–0.20 mm in size, of octahedral and cuboctahedral habit with faces o {111} and a {100}, and polysynthetic and simple twinning along the {111}. Cleavage and parting were not observed. The mineral is black with a dark bronze tint, black streak, and metallic luster. The microhardness (VHN) is 356–458 (loadings are 20 and 30 g), 396 kgf/mm², on average. The Mohs hardness is 4.5–5.0, d _calc = 4.16(2). In reflected light, the mineral is pale-cream-colored, without anisotropy; reflectance values (λ, nm-R, %): 400-34.3, 420-34.1, 440-33.9, 460-33.7, 480-33.5, 500-33.2, 520-33.0, 540-32.8, 560-32.3, 580-32.2, 600-31.9, 620-31.6, 640-31.2, 660-30.9, 680-30.6, 700-30.4. Cubic, space group Fd [`3]\bar 3 m, Z = 8; unit cell parameter a = 9.814(2) ?, V = 945.2(4) ?³. The strongest lines of the X-ray powder diffraction pattern [d, ? (I) (hkl)]: 3.44 (6)(220), 2.94 (10)(311), 2.44 (6)(400), 1.884 (9)(511, 333), 1.731 (10)(440), 1.133 (6)(751, 555), 1.098 (6)(840), 1.030 (6)(931), 1.002 (10)(844). Chemical composition (mean of 202 microprobe analyses of 11 grains, wt %): Cu 21.03, Fe 0.47, Zn 0.17, Cr 29.01, V 5.85, As 0.21, Sb 0.08, S 43.25; the total is 100.07. The empirical formula calculated on the basis of seven ions is (Cu_0.98Fe_0.02Zn_0.01)_1.01(Cr_1.65V_0.34As_0.01)_2.00S_3.99. The type material has been deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia.     

Raman spectra and unit cell parameters of sphalerite solid solutions (FexZn1−xS)

Synthesized sphalerite solid solutions (Fe_xZn_1−xS) in the range 0 < x < 0.5 have been studied with the use of Raman spectroscopy. The main objective of these experiments was to learn how the iron content of sphalerite affects the Raman spectra. Raman intensities over the whole range of concentrations suggest a structure change in the rather narrow region of mole fractions of FeS between 0.15 and 0.25. Analysis of literature data as well as our own results on Raman scattering and X-ray powder diffraction suggests the observed phenomena might be due to a change in the percolation state of the crystal lattice. The ratio of intensities of some Raman lines can be, in principle, used for the compositional analysis of sphalerite.