Lead-antimony sulfosalts from Tuscany (Italy). XVIII. New data on the crystal-chemistry of boscardinite

Boscardinite, ideally TlPb4(Sb7As2)Σ9S18, has been described recently as a new homeotypic derivative of baumhauerite, found at Monte Arsiccio mine, Apuan Alps, Tuscany, Italy. New findings of boscardinite in different mineral associations of this deposit have allowed the collection of new crystal-chemical data. Electron-microprobe analysis of the crystal used for the single-crystal X-ray diffraction study gave (in wt.%): Ag 1.81(5), Tl 12.60(21), Pb 17.99(12), Hg 0.14(5), As 9.36(12), Sb 33.60(27), S 23.41(30), Cl 0.06(1), total 98.97(100). On the basis of ΣMe = 14 apfu, it corresponds to Ag0.42Tl1.52Pb2.14Hg0.02 (Sb6.82As3.08)Σ9.90S18.04Cl0.04. With respect to the type specimen, these new findings are characterized by a strong Pb depletion, coupled with higher Tl contents, and a significant As enrichment. The single crystal X-ray diffraction study of this (Tl,As)-enriched boscardinite confirms the structural features described for the type sample. The unit-cell parameters are a = 8.1017(4), b = 8.6597(4), c = 22.5574(10) Å, α = 90.666(2), β = 97.242(2), γ = 90.850(2)°, V = 1569.63(12) Å3, space group Pī. The crystal structure was refined down to R1 = 0.0285 on the basis of 6582 reflections with Fo > 4σ(Fo). Arsenic is dominant in three MeS3 sites, compared to one in type boscardinite. The main As-enrichment is observed in the sartorite-type sub-layer. Owing to this chemical peculiarity, (Tl,As)-rich boscardinite shows alternation, along b, of Sb-rich sites and As-rich sites; this feature represents the main factor controlling the 8 Å superstructure. The chemical variability of boscardinite is discussed; the Ag increase observed here gets closer to stoichiometric AgTl-Pb4(Sb14As6)Σ20S36 (Z = 1), against possible extension up to AgTl2Pb6(Sb15As4)Σ19S36 for type boscardinite

Lead-antimony sulfosalts from Tuscany (Italy). XVI. Carducciite, (AgSb)Pb6(As,Sb)8S20, a new Sb-rich derivative of rathite from the Pollone mine, Valdicastello Carducci: Occurrence and crystal structure

The new mineral species carducciite, (AgSb)Pb6(As,Sb)8S20, has been discovered in the baryte-pyrite-(Pb-Ag-Zn) deposit of the Pollone mine, near Valdicastello Carducci, Apuan Alps, Tuscany, Italy. It occurs as black metallic prismatic crystals, up to 0.5 mm long, associated with pyrite and sterryite. Its Vickers hardness (VHN10) is 61 kg/mm2 (range: 52-66), corresponding to a Mohs hardness of ∼2-3. In reflected light, carducciite is dark grey in colour, moderately bireflectant; internal reflections are very weak and deep red in colour. Reflectance percentages for the four COM wavelengths [R min, Rmax (%) (λ)] are: 35.8, 40.8 (471.1 nm), 33.7, 39.0 (548.3 nm), 32.7, 37.6 (586.6 nm) and 30.4, 35.1 (652.3 nm). Electron microprobe analysis gives (wt.%-mean of six analyses): Ag 3.55(12), Tl 0.13(3), Pb 41.90(42), Sb 17.79(19), As 12.41(14), S 22.10(17), total 97.9(6). On the basis of ∑Me = 16 a.p.f.u., the chemical formula is Ag0.96Tl0.02Pb5.91As4.84Sb4.27S20.14. The main diffraction lines, corresponding to multiple hkl indices, are (relative visual intensity): 3.689 (s), 3.416 (s), 3.125 (s), 2.989 (s), 2.894 (s), 2.753 (vs), 2.250 (s). The crystal-structure study gives a monoclinic unit cell, space group P21/c, with a 8.4909(3), b 8.0227(3), c 25.3957(9) Å, β 100.382(2)°, V 1701.63(11) Å3, Z = 2. The crystal structure has been solved and refined to a final R 1 = 0.063 on the basis of 4137 observed reflections. It can be described within the framework of the sartorite homologous series, as formed by chemically twinned layers of the dufrenoysite type. The simplified idealized structural formula, based on 20 sulfur atoms, can ideally be written as (AgSb)Pb6(As,Sb)∑=8S20. Carducciite is an (Ag,Sb)-rich homeotype of dufrenoysite, stabilized by the complete coupled substitution 2 Pb2+ = Ag+ + Sb3+ on a specific site of the crystal structure. Together with barikaite, it belongs to the rathite sub-group of P 21/c homeotypes of dufrenoysite, of which the crystal chemistry is discussed. The distribution of Ag, coupled with As or Sb on specific sites, appears to be the main criterion for the distinction between the three species of this sub-group

Could incommensurability in sulfosalts be more common than thought? the case of meneghinite, CuPb13Sb7S24

The structure of meneghinite (CuPb13Sb7S24), from the Bottino mine in the Apuan Alps (Italy), has been solved and refined as an incommensurate structure in four-dimensional superspace. The structure is orthorhombic, superspace group Pnma(0β0)00s, cell parameters a = 24.0549 (3), b = 4.1291 (6), c = 11.3361 (16) Ã\u85, modulation vector q = 0.5433 (4)bâ\u88\u97. The structure was refined from 6604 reflections to a final R = 0.0479. The model includes modulation of both atomic positions and displacement parameters, as well as occupational waves. The driving forces stabilizing the modulated structure of meneghinite are linked to the occupation modulation of Cu and some of the Pb atoms. As a consequence of the Cu/[] and Pb/Sb modulations, three-to sevenfold coordinations of the M cations (Pb/Sb) occur in different parts of the structure. The almost bimodal distribution of the occupation of Cu/[] and Pb/Sb at M5 conforms with the coupled substitution Sb3+ + [] â\u86\u92 Pb2+ + Cu+, thus corroborating the hypothesis deduced previously for the incorporation of copper in the meneghinite structure. The very small departure (~0.54 versus 0.50) from the commensurate value of the modulation raises the question of whether other sulfosalts considered superstructures have been properly described, and, in this light, if incommensurate modulation in sulfosalts could be much more common than thought.The crystal structure of the mineral meneghinite, CuPb13Sb7S24, has been solved and refined as an incommensurate structure from X-ray single-crystal diffraction data in four-dimensional superspace. The very small departure from the commensurate value of the modulation raises the question of whether incommensurability in sulfosalts could be much more frequent than previously thought

Lead-antimony sulfosalts from Tuscany (Italy). XVII. Meerschautite, (Ag,Cu)5.5Pb42.4(Sb,As)45.1S112O0.8, a new expanded derivative of owyheeite from the Pollone mine, Valdicastello Carducci: occurrence and crystal structure

The new mineral species meerschautite, ideally (Ag,Cu)5.5Pb42.4(Sb,As)45.1S112O0.8, has been discovered in the baryte + pyrite ± (Pb-Zn-Ag) deposit of the Pollone mine, near Valdicastello Carducci, Apuan Alps, Tuscany, Italy. It occurs as black prismatic crystals, striated along [100], up to 2 mm long and 0.5 mm thick, associated with baryte, boulangerite, pyrite, quartz and sphalerite. Meerschautite is opaque with a metallic lustre and shows a black streak. In reflected light, meerschautite is white in colour, weakly bireflectant and non pleochroic. With crossed polars, it is distinctly anisotropic with grey to dark grey rotation tints with brownish and greenish shades. Reflectance percentages for COM wavelengths [λ (nm), R air (%)] are: 470: 39.7/41.4; 546: 38.3/39.9; 589: 37.4/39.0; 650: 35.8/37.2. Electron-microprobe data collected on two different samples gave (wt.%): Cu 0.22, Ag 3.15, Tl 0.07, Pb 48.54, Sb 25.41, As 2.82, S 19.74, Se 0.14, Cl 0.03, sum 100.12 (# 1) and Cu 0.22, Ag 3.04, Tl 0.13, Pb 48.53, Sb 25.40, As 2.93, Bi 0.06, S 19.82, Se 0.13, Cl 0.05, sum 100.31 (# 2). On the basis of 112 anions (S+Se+Cl) per formula unit, the empirical formulae are (Ag5.29Cu0.63)∑5.92(Pb42.43Tl0.06)∑42.49(Sb37.80As6.82)∑44.62(S111.53Se0.32Cl0.15)∑112 (# 1) and (Ag5.08Cu0.62)∑5.70(Pb42.22Tl0.12)∑42.34(Sb37.61As7.07Bi0.05)∑44.73(S111.45Se0.30Cl0.25)∑112 (# 2). Main diffraction lines, corresponding to multiple hkl indices, are [d in Å (relative visual intensity)]: 3.762 (m), 3.663 (s), 3.334 (vs), 3.244 (s), 3.016 (m), 2.968 (m), 2.902 (m), 2.072 (ms). The crystal structure study gave a monoclinic unit cell, space group P21, with a = 8.2393(1), b = 43.6015(13), c = 28.3688(8) Å, β = 94.128(2)°, V = 10164.93(2) Å3, Z = 2. The crystal structure has been solved and refined to a final R 1 = 0.122 on the basis of 49,037 observed reflections. The structure is based on two building blocks, both formed by a complex column with a pseudotrigonal Pb6S12 core and two arms of unequal lengths (short and long arms, respectively). Two different kinds of short arms occur in meerschautite. One is an Ag-rich arm, whereas the other shows localized Sb–O–Sb bonds. Meerschautite is an expanded derivative of owyheeite and has quasi-homeotypic relationships with sterryite and parasterryite.© The Mineralogical Society of Great Britain and Ireland 2017. The attached document is the authors’ preproof accepted version of the journal article, which is made available under a Creative Commons CC-BY-NC-ND license: https://creativecommons.org/licenses/by-nc-nd/4.0/. You are advised to consult the publisher’s version if you wish to cite from it

Guides géologiques régionaux : Bretagne — Coordinateurs : S. Durand et H. Lardeux. Seconde édition révisée et complétée, 1985

Moëlo Yves. Guides géologiques régionaux : Bretagne — Coordinateurs : S. Durand et H. Lardeux. Seconde édition révisée et complétée, 1985. In: Bulletin de Minéralogie, volume 109, 3, 1986. p. 317

Guides géologiques régionaux : Bretagne — Coordinateurs : S. Durand et H. Lardeux. Seconde édition révisée et complétée, 1985

Moëlo Yves. Guides géologiques régionaux : Bretagne — Coordinateurs : S. Durand et H. Lardeux. Seconde édition révisée et complétée, 1985. In: Bulletin de Minéralogie, volume 109, 3, 1986. p. 317

Lead-antimony sulfosalts from Tuscany (Italy). XIX. Crystal chemistry of chovanite from two new occurrences in the Apuan Alps and its 8 Å crystal structure

Two new occurrences of the lead oxy-sulfosalt chovanite have been identified at the Monte Arsiccio and Pollone mines, Apuan Alps, Tuscany, Italy. Chovanite from Monte Arsiccio occurs as black acicular crystals, up to 5 mm long, associated with rouxelite, robinsonite, sphalerite, valentinite, baryte, dolomite, quartz and Ba-rich K-feldspar ('hyalophane') inmetadolostone vugs. Its unit-cell parameters are a = 48.38(5), b = 4.11(4), c = 34.18(4) Ã\u85, β = 106.26(2)°, V = 6521(64) Å3, space group C2/m. Very weak reflections indicate the doubling of the b parameter. Electron-microprobe data gave (wt.%): Ag 0.28, Tl 1.51, Pb 45.57, Sb 31.00, As 1.09, S 19.73, Se 0.05, Cl 0.02, sum 99.25. On the basis of ΣMe = 58 apfu, its formula is Ag0.30Tl0.86Pb25.56Sb29.59As1.69S71.52Se0.07Cl0.05. Adding one oxygen atom, it is close to the formula TlPb26(Sb,As)31S72O. Chovanite from Pollone occurs as thick black acicular crystals, up to 1 cm long, associated with baryte and quartz. The high-diffraction quality of the available material allowed the solution and refinement of the 8 Ã\u85 crystal structure in the space group P21/c, with unit-cell parameters a = 34.052(3), b = 8.2027(7), c = 48.078(4) Ã\u85, β = 106.258(4)°, V = 12891.9(19) Ã\u853. The refinement converged to R1 = 9.14% on the basis of 19,853 observed reflections with Fo > 4Ï\u83(Fo). Electron-microprobe data gave (wt.%): Ag 0.12, Tl 0.54, Pb 48.34, Bi 0.20, Sb 26.71, As 3.37, S 20.23, Cl 0.07, sum 99.57. It corresponds to the formula Ag0.13Tl0.30Pb26.94Bi0.10Sb25.33As5.20S72.85Cl0.20, close to the idealized formula Pb28(Sb, As)30S72O, with a single oxygen atom bound to two (Sb/As) atoms alternating with a vacancy along b as in scainiite and in other Pb oxy-sulfosalts. The crystal chemistry of this 8 Ã\u85 crystal structure is detailed, taking into account its modular description, the (Sb,As)mSn polymerization, its topological derivation from pellouxite, and the oxygen non-stoichiometry

L'indice à sulfoantimoniures de plomb des Cougnasses (commune d'Orpierre, Hautes-Alpes). Partie II. Étude paragénétique

Paragenetic analysis of ore from Cougnasses occurence has permitted to distinguish two principal phases : — phase I, with iron carbonates (initial), present a Pb/Sb ratio regularly increasing : • first stade : zinkenite + quartz, • second stade : plagionite → semseyite (+ bournonite) → geocronite → galena, with sphalerite terminal ; — phase II, with baryte (initial) and calcite (terminal), show as dominant succession : boulangérite first, then chalcopyrite (+ galena and sphalerite) → tetrahedrite → bournonite + andorite, and, for iron sulphides : arsenopyrite marcasite → pyrite. Two metallographic models are proposed : — for phase I, a process of ascending mixing, along a fault, of a familiar solution, source of antimony and sulphur, with a foreign solution, probably triassic, source of lead and zinc ; — for phase II, a process of alteration of the first mineralization by an oxydizing solution. Genetic antagonism observed between semseyite (phase I) and boulangerite (phase II) seem to be caused by variation of oxydizing power of sulphur between the two generating mediums : boulangerite would form for a more weak activity of sulphur in solution than semseyite.L'analyse paragénétique détaillée du minerai de l'indice des Cougnasses a permis, à partir de l'interprétation des modes de contact entre minéraux selon huit types de processus génétique, de distinguer deux phases principales : — une phase I à gangue de carbonates de fer dont la succession montre un rapport Pb/Sb régulièrement croissant : • premier stade : zinkénite + quartz, • deuxième stade : plagionite → semseyite (+ bournonite) → géocronite → galène, avec blende terminale ; — une phase II à gangue de barytine (initiale) et de calcite (terminale) avec, comme succession la plus fréquente : boulangérite initiale, puis chalcopyrite (+ galène et blende) → tétraédrite → bournonite + andorite˗ramdohrite, et, pour les sulfures de fer : mispickel → marcasite → pyrite. Deux modèles métallogéniques sont proposés : — pour la phase I, un processus de mélange ascendant le long d'une fracture, d'une solution familière, source de l'antimoine et du soufre, et d'une solution étrangère, probablement d'origine triasique, source du plomb et du zinc ; — pour la phase II, un processus de remaniement par une solution oxydante de la minéralisation primaire. L'antagonisme génétique observé entre la semseyite (phase I) et la boulangérite (phase II) semblerait déterminé par la variation du pouvoir oxydant du soufre entre les deux milieux générateurs, la boulangérite se formant pour une plus faible activité en soufre de la solution que la semseyite.Moëlo Yves, Lévy Claude. L'indice à sulfoantimoniures de plomb des Cougnasses (commune d'Orpierre, Hautes-Alpes). Partie II. Étude paragénétique. In: Bulletin de la Société française de Minéralogie et de Cristallographie, volume 99, 1, 1976. pp. 38-49

Étude paragénétique de la minéralisation sulfurée complexe (Sb-Pb-Zn...) de Bournac (Hérault, France)

Paragenetic study of complex sulfide ore from Bournac (Montagne Noire -France) has revealed, among common sulfides (principaly stibnite, galena, sphalerite and arsenopyrite) numerous rare species, essentially lead-antimony sulfosalts : boulangerite, semseyite, plagionite, zinkenite, fulöppite, geocronite, meneghinite, manganeous jamesonite, andorite˗fizelyite. Arsenopyrite (0 to 0.7 % Sb) shows variation of (As + Sb)/S ratio ; the silver content of tetraedrite˗freibergite series ranges from 3 to 32 %. The paragenetic sequence is divided into five stages. Fe-As stage (n°l), Zn stage (n°2) and Pb-Sb stage (n°3) belong to the same paragenesis, as in the neighbouring deposit of La Rabasse. This paragenesis closely refers to the "k-pol" type defined in the Bohemian Massif. The antimony stage (n°4) has induced formation of various lead-antimony sulfosalts through metasomatism of galena and other preexisting sulfosalts. The fifth stage indicates remobilization of the ore. Although ore controls are quite different, geochemical and paragenetic evolutions of Bournac deposit and Cap Sizun Pb-Sb district (Finistère, France) are very similar. This similarity, which shows the independence of paragenetic and deposits types, would essentially reflect the parental geochemistry of ores sources.L'étude paragénétique du minerai sulfuré complexe de Bournac (Montagne Noire ˗ France) a permis d'observer, aux côtés d'espèces courantes (principalement stibine, galène, blende et mispickel), la présence de nombreuses espèces assez rares, dont une majorité de sulfosels de Pb/Sb : boulangérite, semseyite, plagionite, zinkénite, fulöppite, géocronite, ménéghinite, jamesonite manganifère et andorite˗fizélyite. Le mispickel, parfois antimonifère, montre une forte facturation du rapport (As+Sb)/S ; les cuivres gris montrent une variation de la teneur en argent de 3 à 32 %. La succession paragénétique se subdivise en cinq stades, dont quatre ont été générateurs de sulfosels d'antimoine spécifiques. Les trois premiers (ferro˗arsénifère, zincifère, puis plombo˗antimonifère) forment une unité paragénétique qui se retrouve dans le gisement voisin de La Rabasse, et correspond fidèlement à l'un des types définis dans le massif de Bohême. Le quatrième, purement antimonifère, a induit la formation de divers sulfosels de plomb par métasomatose de la galène et de sulfosels préexistants. Le cinquième correspond à une faible remobilisation in situ, avec évacuation préférentielle de l'antimoine. Bien que les contextes gîtologiques soient très différents, l'évolution géochimique et paragénétique de la minéralisation de Bournac montre un parallélisme remarquable avec celle du district plombo˗antimonifère du Cap Sizun (Finistère - France). Cette similitude des paragenèses, qui souligne la possibilité de fortes distorsions entre type paragénétique et type gîtologique, traduirait directement la parenté géochimique des processus sources des métaux.Munoz Marguerite, Moëlo Yves. Étude paragénétique de la minéralisation sulfurée complexe (Sb-Pb-Zn...) de Bournac (Hérault, France). In: Bulletin de Minéralogie, volume 105, 6, 1982. pp. 625-632

Étude paragénétique de la minéralisation sulfurée complexe (Sb-Pb-Zn...) de Bournac (Hérault, France)

Paragenetic study of complex sulfide ore from Bournac (Montagne Noire -France) has revealed, among common sulfides (principaly stibnite, galena, sphalerite and arsenopyrite) numerous rare species, essentially lead-antimony sulfosalts : boulangerite, semseyite, plagionite, zinkenite, fulöppite, geocronite, meneghinite, manganeous jamesonite, andorite˗fizelyite. Arsenopyrite (0 to 0.7 % Sb) shows variation of (As + Sb)/S ratio ; the silver content of tetraedrite˗freibergite series ranges from 3 to 32 %. The paragenetic sequence is divided into five stages. Fe-As stage (n°l), Zn stage (n°2) and Pb-Sb stage (n°3) belong to the same paragenesis, as in the neighbouring deposit of La Rabasse. This paragenesis closely refers to the "k-pol" type defined in the Bohemian Massif. The antimony stage (n°4) has induced formation of various lead-antimony sulfosalts through metasomatism of galena and other preexisting sulfosalts. The fifth stage indicates remobilization of the ore. Although ore controls are quite different, geochemical and paragenetic evolutions of Bournac deposit and Cap Sizun Pb-Sb district (Finistère, France) are very similar. This similarity, which shows the independence of paragenetic and deposits types, would essentially reflect the parental geochemistry of ores sources.L'étude paragénétique du minerai sulfuré complexe de Bournac (Montagne Noire ˗ France) a permis d'observer, aux côtés d'espèces courantes (principalement stibine, galène, blende et mispickel), la présence de nombreuses espèces assez rares, dont une majorité de sulfosels de Pb/Sb : boulangérite, semseyite, plagionite, zinkénite, fulöppite, géocronite, ménéghinite, jamesonite manganifère et andorite˗fizélyite. Le mispickel, parfois antimonifère, montre une forte facturation du rapport (As+Sb)/S ; les cuivres gris montrent une variation de la teneur en argent de 3 à 32 %. La succession paragénétique se subdivise en cinq stades, dont quatre ont été générateurs de sulfosels d'antimoine spécifiques. Les trois premiers (ferro˗arsénifère, zincifère, puis plombo˗antimonifère) forment une unité paragénétique qui se retrouve dans le gisement voisin de La Rabasse, et correspond fidèlement à l'un des types définis dans le massif de Bohême. Le quatrième, purement antimonifère, a induit la formation de divers sulfosels de plomb par métasomatose de la galène et de sulfosels préexistants. Le cinquième correspond à une faible remobilisation in situ, avec évacuation préférentielle de l'antimoine. Bien que les contextes gîtologiques soient très différents, l'évolution géochimique et paragénétique de la minéralisation de Bournac montre un parallélisme remarquable avec celle du district plombo˗antimonifère du Cap Sizun (Finistère - France). Cette similitude des paragenèses, qui souligne la possibilité de fortes distorsions entre type paragénétique et type gîtologique, traduirait directement la parenté géochimique des processus sources des métaux.Munoz Marguerite, Moëlo Yves. Étude paragénétique de la minéralisation sulfurée complexe (Sb-Pb-Zn...) de Bournac (Hérault, France). In: Bulletin de Minéralogie, volume 105, 6, 1982. pp. 625-632