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.     

Pressure induced phase transition in Pb<Subscript>6</Subscript>Bi<Subscript>2</Subscript>S<Subscript>9</Subscript>

The crystal structure of Pb₆Bi₂S₉ is investigated at pressures between 0 and 5.6 GPa with X-ray diffraction on single-crystals. The pressure is applied using diamond anvil cells. Heyrovskyite (Bbmm, a = 13.719(4) Å, b = 31.393(9) Å, c = 4.1319(10) Å, Z = 4) is the stable phase of Pb₆Bi₂S₉ at ambient conditions and is built from distorted moduli of PbS-archetype structure with a low stereochemical activity of the Pb²⁺ and Bi³⁺ lone electron pairs. Heyrovskyite is stable until at least 3.9 GPa and a first-order phase transition occurs between 3.9 and 4.8 GPa. A single-crystal is retained after the reversible phase transition despite an anisotropic contraction of the unit cell and a volume decrease of 4.2%. The crystal structure of the high pressure phase, β-Pb₆Bi₂S₉, is solved in Pna2 ₁ (a = 25.302(7) Å, b = 30.819(9) Å, c = 4.0640(13) Å, Z = 8) from synchrotron data at 5.06 GPa. This structure consists of two types of moduli with SnS/TlI-archetype structure in which the Pb and Bi lone pairs are strongly expressed. The mechanism of the phase transition is described in detail and the results are compared to the closely related phase transition in Pb₃Bi₂S₆ (lillianite).     

Pb−Bi−(Cu)-sulfosalts in Paleozoic gneisses and schists from Oberpinzgau,Salzgurg province,Austria

Summary Pb–Bi–(Cu)-sulfosalts occur as minor minerals widely distributed in rocks of the Penninic unit (gneisses, schists, metavolcanics, etc.), Oberpinzgau, Salzburg. The sulfosalts have been investigated by ore microscopy, X-ray diffraction and electron microprobe analysis. The phases identified are: heyrovskyite, cosalite (Moaralm, Sedl, and Wiesbachrinne in the Habach Valley), lillianite (Moaralm, Sedl; Modereck near the Fuscher Valley), galenobismutite (Bärenbad in the Hollersbach Valley) and Bi-bearing galena. Heyrovskyite (Moaralm) has a composition close to Pb₆Bi₂S₉, with Ag contents between 0.2 (Sedl) and 0.6 (Moaralm) wt.%. Lillianite has the composition Pb_2.86–2.91 Bi_2.08–2.17Ag_0.04–0.08 S₆, and cosalite, Pb_1.81–2.04 Bi_1.92–2.02 Ag_0.02–0.06 Cu_0.11–0.18S₅. The average chemical composition of galenobismutite is Pb_1.25Bi_1.6Sb_0.1Cu_0.1Ag_0.02Fe_0.1S₄. Needle-like inclusions of a joseite-type mineral, joseite-A (Bi,Pb)_4.01 Te_0.9S_2.08, and irregular to needle-like grains of native bismuth usually occur along the elongation direction of the lath-like galenobismutite crystals.The occurrences can be divided into two types: 1) stratiform Pb–Bi sulfosalts which occur only in the quartzite intercalations of the Paleozoic Habach unit (Frasl, 1958), and 2) alpidic vein type Pb–Bi sulfosalts which occur in quartz veins intersecting gneisses and are considered to be the remobilization products of the first type. Temperature of formation for heyrovskyite in this region is estimated at between 400±25°C and 500°C. Most probably, the assemblage heyrovskyite-lillianite-galena (Moaralm) was formed at or below 473°C.

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Pb–Bi–(Cu)-Sulfosalze in paläozoischen Gesteinen des Oberpinzgau, Salzburg, Österreich

Zusammenfassung Pb–Bi-Sulfosalze verschiedener Vorkommen des Oberpinzgau, Salzburg, wurden mittels Erzmikroskopie, röntgenographischer Methoden und Mikrosonde untersucht. Folgende Phasen wurden identifiziert: Heyrovskyit, Cosalit (Moaralm, Sedl und Wiesbachrinne; alle Habachtal), Lillianit (Moaralm, Sedl; Modereck nahe des Fuschertales), Galenobismutit (Bärenbad, Hollersbachtal) und Bi-hältiger Bleiglanz. Heyrovskyit (Moaralm) ist nahezu Pb₆Bi₂S₉, mit Ag-Gehalten zwischen 0,2 (Sedl) und 0.6 (Moaralm) Gew.%, Lillianit Pb_2,86–2,91Bi_2,08–2,17Ag_0,04–0,08S₆, und Cosalit Pb_1,81–2,04Bi_1,92–2,02Ag_0,02–0,06 Cu_0,11–0,18S₅. Galenobismutit ist Pb_1,25Bi_1,6Sb_0,1Cu_0,1Ag_0,02Fe_0,1S₄. Nadelige Einschlüsse von Joseit-A, (Bi, Pb)_4,01Te_0,9S_2,08, und unregelmäßige bis nadelige Körner von ged. Wismut treten entlang der Längsrichtung der Galenobismutit-Kristalle auf. Die Mineralisationen sind an stratiforme, sulfidreiche Quarzlagen (Typus 1, z. B. Bärenbad) oder an diskordante Quarzgänge (Typus 2; alle anderen Vorkommen) gebunden. Typus 1 tritt innerhalb der altpaläzozischen Habachserie (Frasl, 1958), Typus 2 in Randbereichen dieser zu den Gneismassen der Habachzunge (z. T. auch in letzteren) auf. Die dem Typus 2 zugerechneten Vererzungen werden als Remobilisationsprodukte der altpaläozoischen Mineralisationen (Typus 1) angesehen.Die Bildungstemperatur des Heyrovskyit dürfte im betrachteten Bereich zwischen 400±25°C und 500°C gelegen haben; eine Bildungstemperatur von 473°C oder wening darunter wird für die Assoziation Heyrovskyit-Lillianit-Bleiglanz in Anlehnung an experimentelle Untersuchungen vonSalanci undMoh (1969) angenommen.

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With 4 Figures

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This investigation forms part of a wider study Genetic types of gold deposits in the Alps.     

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.     

Phase relations and mineral assemblages in the Ag-Bi-Pb-S system

Phase relations within the Ag-Bi-S, Bi-Pb-S, and Ag-Pb-S systems have been determined in evacuated silica tube experiments. Integration of experimental data from these systems has permitted examination and extrapolation of phase relations within the Ag-Bi-Pb-S quaternary system. — In the Ag-Bi-S system liquid immiscibility fields exist in the metal-rich portion above 597±3°C and in the sulfur-rich portion above 563±3°C. Ternary phases present correspond to matildite (AgBiS₂) and pavonite (AgBi₃S₅). Throughout the temperature range 802±2°C to 343±2°C the assemblage argentite (Ag₂S) + bismuth-rich liquid is stable; below 343°C this assemblage is replaced by the assemblage silver + matildite. — Five ternary phases are stable on the PbS-Bi₂S₃ join above 400°C — phase II (18 mol-% Bi₂S₃), phase III (27 mol-% Bi₂S₃), cosalite (33.3 mol-% Bi₂S₃), phase IV (51 mol-% Bi₂S₃), and phase V (65 mol-% Bi₂S₃). Phase IV corresponds to the mineral galenobismutite and is stable below 750±3°C. Phases II, III, and V do not occur as minerals, but typical lamellar and myrmekitic textures commonly observed among the Pb-Bi sulfosalts and galena evidence their previous existence in ores. Phase II and III are stable from 829±6°C and 816±6°C, respectively, to below 200°C; Phase V, stable only between 730±5°C and 680±5°C in the pure Bi-Pb-S system is stabilized to 625±5°C by the presence of 2% Ag₂S. Experiments conducted with natural cosalites suggest that this phase is stable only below 425±25°C in the presence of vapor. — In the Ag-Pb-S system the silver-galena assemblage is stable below 784±2°C, whereas the argentite + galena mineral pair is stable below 605±5°C. — Solid solution between matildite and galena is complete above 215±15°C; below this temperature characteristic Widmanstätten structure-like textures are formed through exsolution. Schematic phase relations within the quaternary system are presented at 1050°C, at 400°C, and at low temperature.

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Zusammenfassung Die Phasenbeziehungen in den Systemen Ag-Bi-S, Bi-Pb-S und Ag-Pb-S wurden durch Versuche in evakuierten Quarzglasröhrchen bestimmt. Die Auswertung aller experimentellen Daten gestattete eine Extrapolation der Phasenbeziehungen im quaternären System Ag-Bi-Pb-S. — Im System Ag-Bi-S besteht ein Zwei-Schemlzenfeld im metallreichen Teil über 597±3°C und im schwefelreichen Teil über 563±3°C. Die ternären Phasen entsprechen den Mineralien Schapbachit (AgBiS₂) und Pavonit (AgBi₃S₅). Zwischen 802±2°C und 343±2°C ist die Paragenese Silberglanz (Ag₂S) + Bi-reiche Schmelze stabil; unterhalb 343°C wird sie jedoch ersetzt durch die Paragenese Silber + Schapbachit. — Fünf ternäre Phasen sind stabil im Schnitt PbS-Bi₂S₃ oberhalb von 400°C: Phase II (18 Mol-% Bi₂S₃), Phase III (27 Mol-% Bi₂S₃), Cosalite (33.3 Mol-% Bi₂S₃), Phase IV (51 Mol-% Bi₂S₃) und Phase V (65 Mol-% Bi₂S₃). Phase IV entspricht dem Mineral Galenobismutit und ist stabil unterhalb 750±3°C. Die Phasen II, III und V kommen zwar nicht in der Natur vor, jedoch weisen typische myrmekitische und lamellare Gefüge, die man häufig in Pb-Bi-Sulfosalzen und deren Verwachsungen mit Bleiglanz beobachtet, auf die ehemalige Existenz solcher Phasen in diesen Erzen hin. Die Phasen II und III sind stabil von 829±6°C bzw. 816±6°C bis unter 200°C. Die Phase V, die im reinen System Bi-Pb-S zwischen 730±5°C und 680±5°C auftritt, wird in Gegenwart von 2% Ag₂S stabilisiert bis herab zu 625±5°C. Versuche mit natürlichen Cosaliten lassen darauf schließen, daß diese Phase nur unterhalb 425±25°C in Gegenwart einer Gasphase stabil ist. — Im System Ag-Pb-S ist die Paragenese Silber-Bleiglanz unterhalb von 784±2°C stabil, die Paragenese Silberglanz-Bleiglanz dagegen unterhalb 605±5°C. — Die Mischkristallreihe von Schapbachit und Bleiglanz ist vollständig oberhalb 215±15°C; unterhalb dieser Temperatur entstehen charakteristische Entmischungsgefüge ähnlich den Widmannstättenschen Figuren. Für das quaternäre System werden schematische Phasenbeziehungen für 1050°C, 400°C und eine noch tiefere Temperatur gegeben.

     

Heyrovskýite, 6(Pb0.86Bi0.08(Ag,Cu)0.04)S . Bi2S3 from Hůrky,Czechoslovakia, a new mineral of genetic interest

Heyrovskýite has a composition range from 6(Pb_0.83Bi_0.10(Ag, Cu)_0.07) S . Bi₂S₃ to 6(Pb_0.92Bi_0.05(Ag, Cu)_0.03) S . Bi₂S₃. It is orthorhombic. Crystal forms {100}, {010}, {120}, {140}, {250}, and {321} (?) were observed; {010} and {140} are dominant. Elongated c, flattened (010). a:b:c _morph=0.432:1:0.128. Cell parameters a=13.705±0.013 Å, b=31.194±0.033, c=4.121±0.003, a:b:c _X-ray=0.439:1:0.132. The diffraction symbol is Bb, compatible with Bbmm, Bb2₁ m, Bbm2. Morphology corresponds to point groups mmm or mm2, reducing the possible space groups to Bbmm and Bbm2. Density at 20 °C is 7.17 g/cm³, calculated, 7.18; Z=4. Micro-indentation hardness (VHN) (50 g load) is 166 to 234 kp/mm². Strongly anisotropic; reflectance strongly variable, roughly the same as of galena. Etch tests: HNO₃ (1:1) and HCl (1:1) positive, FeCl₃ 20%, HgCl₂ 5%, KCN 20%, and KOH 40% all negative. Powder data are identical with those for phase II of Otto and Strunz (1968). Heyrovskýite is associated with galena and cosalite at H?rky, Czechoslovakia.     

A quantum chemical investigation of the oxidation and dissolution mechanisms of Galena

The oxidation and dissolution mechanisms of galena (PbS) remain uncertain with a wide variety of possible mechanisms having been proposed in the literature. In this study, the thermodynamic viability of some possible mechanisms has been tested using semi-empirical quantum chemical calculations applied to a perfect (001) galena surface.The adsorption of O₂ and H₂O has been examined in both the gaseous and aqueous environments. In agreement with previous ab initio quantum chemical calculations, the surface induced dissociation of H₂O in either environment was found to be energetically unfavourable. However, the dissociative adsorption of O₂ was found to be possible and resulted in two O atoms bonded to diagonally adjacent S atoms with the O atoms oriented along the diagonal.The adsorption of H⁺ and possible subsequent dissolution mechanisms have been examined in the aqueous environment. An anaerobic mechanism leading to the dissolution of hydroxylated Pb²⁺ was identified. The mechanism involves the protonation of 3 surface S atoms surrounding a central surface Pb atom followed by substitution of this Pb by a further H⁺. The activation energy of this mechanism was estimated to be ≈100 kJ mol⁻¹. Pb²⁺ dissolution could only occur with vacancy stabilisation by a H⁺. The analogous mechanisms for systems comprising H⁺ adsorbed on either 2 or 4 of the S atoms surrounding a central surface Pb were not found to be energetically viable. Subsequent dissolution of one of the protonated S atoms to form H₂S_(g) was not found to be possible thus indicating the likely formation of a Pb-deficient S-rich surface under acidic anaerobic conditions.Acidic aerobic dissolution has also been examined. Congruent dissolution to form H₂SO₄ and Pb²⁺•6H₂O is energetically viable. The dissolution of one of the protonated S atoms neighbouring the Pb²⁺ vacancy, resulting from the anaerobic dissolution, to form H₂SO₄, is also possible.     

EPR study of coordination of Ag and Pb cations in BaB<Subscript>2</Subscript>O<Subscript>4</Subscript> crystals and barium borate glasses

It is shown the possibility to determine the coordination of paramagnetic ions in disordered solid structures, e.g., in barium borate glasses. For this purpose the electron paramagnetic resonance (EPR) method was used to study α-and β-BaB₂O₄ crystals and glasses of 45·BaO × 55·B₂O₃ and 40·BaO × 60·B₂O₃ (mol%) composition activated by Ag⁺ and Pb²⁺ ions. After the samples were exposed to X-rays at 77 K, different EPR centers were observed in them. In α-and β-BaB₂O₄ crystals and glasses the EPR centers Ag²⁺, Ag⁰, Pb⁺, Pb³⁺, and hole centers of O⁻ type were studied. The EPR parameters of these centers and their arrangement in crystal structure were determined. It is shown that Pb³⁺ ions in β-BaB₂O₄ crystals occupy Ba²⁺ position in an irregular polyhedron from the eight oxygen, whereas in α-BaB₂O₄ crystals they occupy Bа₂ position in a sixfold coordination. Pb⁺ ions in α-BaB₂O₄ crystals occupy Bа₁ position in a ninefold coordination from oxygen. In barium borate glasses, Pb³⁺ ions were studied in coordination polyhedron from six oxygen atoms and in a polyhedron from nine to ten oxygen atoms. It is assumed that the established difference in the structural position of Pb³⁺ ions in glasses is due to their previous incorporation in associative cation–anion complexes (AC) and “free” structure-forming cations (FC). Computer simulations have been performed to analyze the stability of specific associative complexes and to compare their bond lengths with experimental data.     

Ore mineralogy of the Waschgang gold-copper deposit,upper carinthia,Austria

Summary The gold-copper deposit at Waschgang (Southern Goldberg mountains, Upper Carinthia) belongs to a type of stratiform, dominantly pyritic deposit, which is hosted by greenschists (Alpine Kieslager;Friedrich, 1936). The ores occur as impregnations (ore type 1) and as massive ores (ore type 2) in prasinitic rocks of the Obere Schieferhülle of the Penninic unit. A N–S trending fault zone cuts the ore deposit to the W (Lettenkluft); the position of the displaced part is unknown.The mineralogical composition of type 1 ores is rather monotonous. Pyrite is the most important ore, minor components are chalcopyrite, bornite, sphalerite and magnetite. No visible native gold has been observed in this type of ore. Type 2 ores are dominated by chalcopyrite and are characterized by large amounts of visible native gold. The majority of these ores occur in the vicinity of the Lettenkluft.Type 2 ores carry a great variety of cogenetic mineral inclusions, of which several have been studied with the electron microprobe and investigated by X-ray methods. These include: tetradymite, Bi₂Te_1.81Se_0.13S; hessite, Ag₂Te; matildite, AgBiS₂; gladite, Cu_1.09Pb_1.14Bi_5.28S₉; krupkaite, CuPbBiS₆; pekoite, Cu_1.09Pb_0.97Bi_12.56S₁₈; (?) benjaminite, (Ag_2.72Cu_0.42)_3.14 (Bi_6.88Pb_0.12)₇(S_11.08Se_0.92)₁₂; pavonite, (Ag_0.74Cu_0.45)_1.19(Bi_2.86Pb_0.27)_3.13 (S_4.96Se_0.04)₅; (?) cupropavonite, (Cu_0.73Ag_0.4)_1.13(Bi_2.59Pb_0.83)_3.42S₅; and siegenite, (Ni_1.07Co_1.76Cu_0.19)_3.02S₄. Other components have been determined by qualitative and quantitative microscopy and include: bornite, idaite, mawsonite, sphalerite, millerite, magnetite, hematite, ilmenite, rutile and a variety of silicates.While the layered ore impregnations (type 1 ores) can be considered as being syngenetic with the associated volcanics of Jurassic age, a syn- to postkinematic (Alpidic) crystallization can be postulated for the type 2 ores. These ores are considered as remobilized and reconcentrated parts of the type 1 ores formed in tectonic stress zones. The crystallization of chalcopyrite and included ore minerals occurred during the cooling history of Alpidic metamorphism, for which in this region a maximum temperature of 500°C and pressures between 4–6 kb have been deduced from the mineral assemblage of the surrounding prasinites, consisting of albite with rims of oligoclase, epidote, chlorite, sphene and amphibole (Höck, 1980). Based onSpringer's limit of 300°C as approximately representing the maximum temperature at which natural members of the bismuthinite-aikinite mineral series have been formed, krupkaite and gladite with the intergrown pavonite type phases might have been deposited directly from solutions at or below 300°C. Unmixing of pekoite from gladite probably occurred at or below the same temperature.

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Zur Erzmineralogie der Gold-Kupfer-Lagerstätte Waschgang, Oberkärnten, Österreich

Zusammenfassung Die Gold-Kupfer-Lagerstätte Waschgang (südliche Goldberggruppe, Oberkärnten) ist dem Typus der stratiformen Kiesvererzungen in Grüngesteinen (Alpine Kieslager;Friedrich, 1936) zuzurechnen. Die Erzmineralisationen treten als stoffkonkordante Imprägnationen (Vererzungstypus 1) und als Derberze (Vererzungstypus 2) in Prasiniten der Oberen Schieferhülle des Penninikums auf. Das Erzlager wird im W an einer N–S streichenden Störung abgeschnitten; die Position des verworfenen W-Flügels ist nicht bekannt.Die Imprägnationserze sind in ihrer mineralogischen Zusammensetzung monoton; Pyrit als Haupterz überwiegt bei weitem die sporadischen Begleiter Kupferkies, Bornit, Sphalerit und Magnetit. Dieser Typus führt kein Freigold.Die von Kupferkies dominierten und an Freigold reichen Derberze treten vor allem im Bereich der Lettenkluft auf. Sie sind durch eine Vielfalt zum Teil komplex zusammengesetzter Einschlußminerale gekennzeichnet, von denen einige mittels Mikrosonde und röntgenographischer Methoden untersucht wurden: Tetradymit, Bi₂Te_1,81Se_0,13S; Hessit, Ag₂Te; Matildit, AgBiS₂; Gladit, Cu_1,09Pb_1,14Bi_5,28S₉; Krupkait, CuPbBiS₆; Pekoit, Cu_1,09Pb_0,97Bi_12,56S₁₈; (?) Benjaminit (Ag_2,72Cu_0,42)_3,14(Bi_6,88Pb_0,12)₇(S_11,08Se_0,92)₁₂; Pavonit, (Ag_0,74Cu_0,45)_1,19(Bi_2,86Pb_0,27)_3,13 (S_4,96Se_0,04)₅; (?) Cupropavonit, (Cu_0,73Ag_0,4)_1,13(Bi_2,59Pb_0,83)_3,42S₅; Siegenit, (Ni_1,07Co_1,76 Cu_0,19)_3,02S₄. Andere Mineralphasen wurden mittels qualitativer und quantitativer Mikroskopie bestimmt: Bornit, Idait, Mawsonit, Sphalerit, Millerit, Magnetit, Hämatit, Ilmenit, Rutil und Silikate.Während die stoffkonkordaten Imprägnationserze syngenetisch mit den assoziierten jurassischen Vulkaniten anzusehen sind, wird für die Derberze eine syn- bis postkinematische Kristallisation angenommen. Sie sind als remobilisierte und rekonzentrierte Teile der Imprägnationserze in tektonisch besonders beanspruchten Lagerstättenteilen anzusehen. Die Kristallisation des Kupferkieses und seiner Einschlußminerale erfolgte während der Abkühlungsphase der alpidischen Metamorphose, für die im betrachteten Gebiet eine Maximaltemperatur von ca. 500°C und Drucke zwischen 4–6 kb aufgrund der Petrologie der erzführenden Prasinite angenommen werden können. Die dafür maßgebende Paragenese besteht aus Albit mit Oligoklasrändern, Epidot, Chlorit, Sphen und Amphibol (Höck, 1980). Zieht man die vonSpringer (1971) ermittelte Stabilitätsgrenze von ±300°C für natürliche Mischkristalle der Bismuthinit-Aikinit-Reihe in Betracht, können für Krupkait und Gladit und den damit verwachsenen Pavonit-Phasen Bildungstemperaturen um oder unterhalb 300°C angenommen werden. Die Kristallisation dieser Minerale dürfte dabei direkt aus Lösungen erfolgt sein. Die als Entmischungsstrukturen interpretierten Gladit-Pekoit-Verwachsungen legen den Schluß einer primären Bildung beider Minerale als feste Lösung nahe, deren Zerfall vermutlich unterhalb von 300°C erfolgte.

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With 13 Figures

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Herrn em. Univ.-Prof. Dr.-Ing. O. M. Friedrich zum 80. Geburtstag in Dankbarkeit gewidmet

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This investigation forms part 2 of a major study on Genetic Types of Gold Deposits of the Alps.     

Mineralogical data on a sulphosalt from the Rhodope mountains,Bulgaria

Zusammenfassung Bei dem Versuch, die Kristallstruktur von Bonchevit zu bestimmen, stellte sich heraus, daß dieses Mineral—bis dahin PbBi₄S₇—aus zwei Phasen besteht. Der Hauptanteil wurde eindeutig als Galenobismutit identifiziert. Der Rest wies nach den Gitterkonstanten (a₀=13,58±0,02 Å, b₀=20,51±0,07 Å, c₀=4,09±0,07 Å) auf ein bisher unbekanntes Mineral hin. Die Raumgruppe ist Bbmm. Ein indiziertes Pulverdiagramm und die dazugehörigen d-Werte werden angegeben.Die Emissionsspektralanalyse zeigt Pb und Bi als Hauptkomponenten, Cu und Ag als Nebenkomponenten und Spuren von Zn und Sn. Die Strukturanalyse führte zu der Formel Me₅S₆, wobei die Me-Atome etwa gleich schwer sind, so daß als chemischo Formel nur Pb₃Bi₂S₆ mit Z=4 in Frage kommt.Strukturell gehört das Mineral in die Gruppe Andorit-Ramdohrit-Fizelyit. Die Verwandtschaft bzw. Identität des Minerals mit anderen Mineralen und synthetischen Verbindungen wird diskutiert.

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Mineralogical data on a sulphosalt from the Rhodope mountains, Bulgaria

Summary During an attempt to determine the crystal structure of bonchevite, this mineral was found to consist of two phases. Previously it was thought to have the composition PbBi₄S₇. The main constituent could unambiguously be identified as galenobismutite. For the rest the lattice constants (a₀=13.58±0,02 Å, b₀=20.51±0,07 Å, c₀=4.09±0.07 Å), indicated a new mineral. Space group is Bbmm. An indexed powder diagram (with d-values) is given.The emission spectrographic analysis shows Pb and Bi to be main components, Cu and Ag to be minor components, and traces only of Zn and Sn. The structure analysis has led to the formula Me₅S₆, with Me-atoms of approximately the same atomic number; therefore, the chemical formula has to be Pb₃Bi₂S₆, with Z=4.In a structural classification the mineral belongs to the andoriteramdohrite-fizelyite-group. The relationships to or the identity with other minerals and synthetic compounds are discussed.

     

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:     

Crystal structure and cation lone electron pair activity of Bi2S3 between 0 and 10 GPa

Crystal structure of Bi₂S₃ was refined at eight distinct hydrostatic pressures in the range 0–10 GPa using a CCD equipped 4-circle diffractometer and a diamond-anvil cell. Coefficients of the BM3 equation of state are as follows: zero-pressure volume 498.4(7) Å³, bulk modulus K ₀ 36.6(15) GPa and its pressure derivative 6.4(5). The bulk of compression takes place in the structural space between Bi₄S₆ ribbons, where lone-electron pairs are accommodated. Eccentricity of Bi in its coordination polyhedra decreases in the process, with long Bi–S distances decreasing, whereas the opposing short Bi–S distances stay constant or even increase in length. All these phenomena are compatible with the movement of lone-electron pairs of Bi closer to the parent atom at increasing pressure.     

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.     

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.     

Betekhtinite and bi-sulfosalts from the copper mine of „La Leona“ (Argentina)

The copper deposit La Leona consists of ore veins in a granite batholite which intruded into Permian sediments. In these veins the following minerals are observed: pyrite, sphalerite, chalcopyrite, galena, betekhtinite, two Bisulfosalts, electrum, bornite, chalcocite, enargite, tennantite, Zn-Fahlerz, cuprite, delafossite, molybdenite, hematite and iron hydroxides, and copper carbonates with quartz and iron carbonates as gangue. The betekhtinite, (CuFe)₁₀Pb S₆, found for the first time in Argentina, the Zn-Fahlerz and the sulfosalts (Cu_3.2Bi_1.2Pb_1.2S_8.5) and (Cu_9.3Bi_1.1S_6.8) were studied in detail under the microscope, by X-rays and by microprobe. Specifically, the paragenesis of these three minerals with galena, chalcocite and bornite is discussed.

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Résumé Le gisement de cuivre de la mine «La Leona» est formé de filons de minerais recoupant un batholite granitique qui a fait intrusion dans des sédiments permiens. Les minéraus suivants ont été observés: pyrite, blende, chalcopyrite, galène, bétekhtinite, deux sulfosels de Bi, électrum, bornite, chalcosine, énargite, tennantite, «Zn-Fahlerz», cuprite, delafossite, molybdénite, hématite et hydroxydes de fer, des carbonates de cuivre, dans une gangue de quartz et de carbonates de fer. La bétekhtinite (Cu Fe)₁₀Pb S₆, trouvée pour la première fois en Argentine, le «Zn-Fahlerz» et les sulfosels (Cu_3.2Bi_1.2Pb_1.2S_8.5) et (Cu_9.3Bi_1.1S_6.8) ont été spécialement étudiés à l'aide de la microscopie, de la diffraction des rayons-X et de la microsonde. La paragénèse formée par ces trois mineraux associés à la galène, la chalcosine et la bornite est discutée.

     

Laser-induced time-resolved luminescence of tugtupite,sodalite and hackmanite

We have interpreted a number of luminescence centers in natural tugtupite Na₈Al₂Be₂Si₈O₂₄Cl₂, sodalite Na₈Al₆Si₆O₂₄C₂ and hackmanite Na₈Al₆Si₆O₂₄(Cl₂,S) by use of laser-induced time-resolved luminescence spectroscopy. The main new results are the following: Fe³⁺, Mn²⁺, Eu²⁺, Ce³⁺, mercury type (potentially Pb²⁺, Tl⁺, Sn²⁺ and/or Sb³⁺), radiation induced luminescence centers; several types of S₂ ⁻ centers. Spectral shift connected with the presence of luminescence centers, which are detected together with S₂ ⁻ centers and impossible to resolve with continuous wave luminescence spectroscopy, is the possible reason for spectral diversity of S₂ ⁻ luminescence centers presented in different publications.     

Mineralogy and mineral chemistry of Bi-minerals: Constraints on ore genesis of the Beiya giant porphyry-skarn gold deposit,southwestern China

The Beiya deposit, located in the Sanjiang Tethyan tectonic domain (SW China), is the third largest Au deposit in China (323 t Au @ 2.47 g/t). As a porphyry-skarn deposit, Beiya is related to Cenozoic (Himalayan) alkaline porphyries. Abundant Bi-minerals have been recognized from both the porphyry- and skarn- ores, comprising bismuthinite, Bi–Cu sulfosalts (emplectite, wittichenite), Bi–Pb sulfosalts (galenobismutite, cosalite), Bi–Ag sulfosalt (matildite), Bi–Cu–Pb sulfosalts (bismuthinite derivatives), Bi–Pb–Ag sulfosalts (lillianite homologs, galena-matildite series), and Bi chalcogenides (tsumoite, the unnamed Bi₂Te, the unnamed Ag₄Bi₃Te₃, tetradymite, and the unnamed (Bi, Pb)₃(Te, S)₄). Native bismuth and maldonite are also found in the skarn ores. The arsenopyrite geothermometer reveals that the porphyry Au mineralization took place at temperatures in the range of 350–450 °C and at log fS₂ in the range of − 8.0 to − 5.5, respectively. In contrast, the Beiya Bi-mineral assemblages indicate that the skarn ore-forming fluids had minimum temperatures of 230–175 °C (prevailing temperatures exceeding 271 °C) and fluctuating fS₂–fTe₂ conditions. We also model a prolonged skarn Au mineralization history at Beiya, including at least two episodes of Bi melts scavenging Au. We thus suggest that this process was among the most effective Au-enrichment mechanisms at Beiya.     

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.     

The system Pb-As-S

Silica-tube quenching experiments and gold-tube pressure experiments were used to study phase relations in the PbS-rich portion of the system Pb-As-S. Emphasis was placed on determining the P-T-X stability relations of jordanite, the most Pb-rich of the synthetic Pb-As-S compounds. Jordanite, Pb₉As₄S₁₅, is stable below 549 ± 3° C, at which temperature it melts to galena, liquid, and a sulfur-rich vapor phase. Confining pressures of up to 2 Kb do not measurably change this reaction temperature. Density measurements on synthetic material show that the jordanite cell contains 3 (Pb₉As₄S₁₅); space group P2₁/m requires that the cell content be expressed as either Pb_28–xAs₁₂S_46–x or Pb_26+xAs₁₂S_44+x, with the former much more probable from a structural point of view. In both cases 0.8 < x < 1.4 and the situation is thus quite different from the usual case of defect structures, such as pyrrhotite, Fe_1–xS, which shows considerable range of solid solution. Heating experiments on natural gratonite (Pb₉As₄S₁₅) show that this mineral is most probably a low-temperature dimorph of jordanite, the inversion occurring below 250° C. Experiments have also confirmed the extensive substitution of Sb for As in jordanite, as suspected from chemical analyses of the isostructural mineral geocronite (Pb_28–x(As,Sb)₁₂S_46–x).

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Zusammenfassung Durch Abschreckversuche mit Hilfe von Quarz- und Gold-Druckampullen wurden die Phasenbeziehungen im PbS-reichen Teil des Pb-As-S-Systems studiert. Besonderer Wert wurde auf die Feststellung der P-T-X-Stabilitätsverhältnisse des Jordanits, des Pb-reichsten Phase der synthetischen Pb-As-S-Reihe, gelegt. Jordanit (Pb₉As₄S₁₅) ist unterhalb 549 ± 3° C stabil, wo er sich semikongruent zu PbS, einer Schmelze und einer schwefelreichen Dampfphase zersetzt. Drucke bis zu 2 kb ergaben keine meßbaren Änderungen dieser Reaktionstemperatur. Dichtemessungen am synthetischen Material weisen darauf hin, daß die Jordanitzelle 3 × (Pb₉As₄S₁₅) enthält. Die Raumgruppe P2₁/m fordert entweder die Formel Pb_28–xAs₁₂S_46–x oder Pb_26+xAs₁₂S_44+x, wobei die erstere Form strukturell wahrscheinlicher zu sein scheint. In beiden Fällen ist 0.8 < x < 1.4 und weicht vom gebräuchlichen Begriff der Defektstrukturen, wie z.B. beim Pyrrhotin (Fe_1–xS) ab, wie das bemerkenswerte Mischkristallfeld zeigt. Erhitzen von natürlichem Gratonit (Pb₉As₄S₁₅) zeigt, daß dieses Mineral sehr wahrscheinlich eine dimorphe Tieftemperaturphase des Jordanits ist. Die Umwandlung erfolgt unterhalb 250° C. Außerdem wurde eine umfangreichere Substitution von As durch Sb im Jordanit festgestellt, was nach den chemischen Analysen des isostrukturellen Geochronits Pb_28–x(As,Sb)₁₂S_46–x) zu erwarten war.

     

Modeling diagenesis of lead in sediments of a Canadian Shield lake

Triplicate porewater lead concentration profiles were determined on six occasions in a Canadian Shield lake. Total Pb concentrations were also measured in a dated core obtained at the same site. This information, as well as an extensive dataset comprising ancillary geochemical measurements on porewaters and sediment and the population densities of benthic animals, is used in a one-dimensional transport-reaction diagenetic model to investigate the transport and mobilization of Pb in these sediments. Application of the model consistently indicates the presence of a zone of Pb production to the porewaters that lies above a zone of Pb consumption. The profiles of various porewater constituents and thermodynamic calculations indicate that Pb is mobilized in the zone of production by the reductive dissolution of iron oxyhydroxides, whereas it is removed in the zone of consumption by precipitation as a solid sulfide. Rate constants are estimated for reductive iron dissolution (k_d^Fe(III) = 2.0 ± 0.5 × 10⁻¹ cm³ mol⁻¹ s⁻¹), Pb adsorption on iron oxyhydroxides (k_ads^Pb = 98 ± 55 cm³ mol⁻¹ s⁻¹), and Pb precipitation (k_ppt^Pb = 8 × 10⁻²⁰ mol cm⁻³ s⁻¹ to 16 ± 13 × 10⁻²² mol cm⁻³ s⁻¹, depending on the solubility product assumed for the precipitation of PbS). According to model calculations, diagenetic processes, such as remobilization, molecular diffusion, bioturbation, and bioirrigation have a negligible influence on the solid phase Pb profile. In agreement with this finding, the present-day fluxes of dissolved Pb by diffusion (J_D^Pb = −6.5 × 10⁻¹¹ mol cm⁻² yr⁻¹), bioturbation (J_B^Pb = −1.1 × 10⁻¹³ mol cm⁻² yr⁻¹), and bioirrigation (J_I^Pb = −1.5 × 10⁻¹¹ mol cm⁻² yr⁻¹) are small compared to the flux of Pb deposited with settling particles (J_S^Pb = 5.3 × 10⁻⁹ mol cm⁻² yr⁻¹).