Pb-Sb Sulfosalts Research Articles

Distribution of In, Sn, Ga, Ge, and other critical metals in sulfide ores from epithermal listvenite-associated Badovc Pb–Zn–Sb–Ni deposit (Kosovo): Insights from mineralogy and geochemistry

This work presents a mineralogical and geochemical study of sulfide ores from the epithermal listvenite-associated Badovc Pb–Zn–Sb–Ni deposit, which is located in the central part of the Kizhnica-Hajvalia-Badovc ore field, in the Trepça Mineral Belt (TMB) in Kosovo. Badovc is an example of one of many base-metal Pb–Zn–Ag deposits associated with the Serbo-Macedonian metallogenic province. There are three types of ores, the first two associated with polymetallic epithermal IS veins (massive-banded Pb–Zn–Sb and rhodochrosite-stibnite breccia) and disseminated ores associated with listvenites, which are hydrothermally altered mafic and ultramafic rocks. The mineralogy of these ores was described using EPMA in combination with reflected and transmitted light microscopy. The mineralogy of massive-banded Pb–Zn–Sb and rhodochrosite-stibnite breccia ores is relatively limited: sphalerite + rhodochrosite-siderite + pyrite/marcasite ± Pb–Sb sulfosalts ± stibnite. Listvenite Pb–Zn–Sb–Ni ores are more mineralogically variable due to the multi-stage formation of these rocks and the overprint of polymetallic mineralization. Apart from typical base-metal sulfides such as sphalerite, pyrite, galena, and chalcopyrite, the listvenite ores contain Fe–Mn carbonates, quartz, and Ni–Fe ± As ± Sb association (gersdorffite, ullmannite, millerite, and Ni–Fe thiospinels), Sn minerals (stannite and cassiterite). The LA-ICP-MS technique was used to determine critical metals occurring as minor and trace elements and substitution mechanisms in sphalerite, pyrite, stibnite, chalcopyrite and stibnite. The main critical metals, such as In, Sn, Ga, and Ge, are hosted by sphalerite in all types of ores. The highest concentrations of tin in sphalerite are observed in massive-banded Pb–Zn–Sb ores, which substitutes within the 3Zn2+ ↔ 2(Cu, Ag)+ + Sn4+ mechanism. The highest concentrations of indium are observed in sphalerites from listvenites, indicating the 2Zn2+ ↔ Cu+ + In3+ substitution. Low-temperature sphalerites from rhodochrosite-stibnite breccia exhibit elevated concentrations of Ga, Ge, and Ag, which incorporate into the structure through 2Zn2+ ↔ (Ag, Cu)+ + Ga3+, and 3Zn2+ ↔ 2(Cu, Ag)+ + Ge4+ mechanisms. The specific crystallization temperatures using GGIMFis for sphalerite are: 248–332 °C for massive-banded Pb–Zn–Sb ores, 208 °C for rhodochrosite-stibnite breccia, and 2112–344 °C for listvenite Pb–Zn–Sb–Ni ores. Additionally, stibnite from Badovc exhibits substitutions such as As3+ ↔ Sb3+ and (Cu+ + Ag+) + Pb2+ ↔ Sb3+ + □, and can incorporate various monovalent elements other than copper, including Ag+ and Tl+. Studies of epithermal listvenite-associated Badovc Pb–Zn–Sb–Ni deposits suggest that similar deposits spread across the Balkans may hold considerable prospectivity.

Ag-Pb-Sb Sulfosalts and Se-rich Mineralization of Anthony of Padua Mine near Poličany—Model Example of the Mineralization of Silver Lodes in the Historic Kutná Hora Ag-Pb Ore District, Czech Republic

Significant selenium enrichment associated with selenides and previously unknown Ag-Pb-Sb, Ag-Sb and Pb-Sb sulfosalts has been discovered in hydrothermal ore veins in the Anthony of Padua mine near Poličany, Kutná Hora ore district, central Bohemia, Czech Republic. The ore mineralogy and crystal chemistry of more than twenty silver minerals are studied here. Selenium mineralization is evidenced by a) the occurrence of selenium minerals, and b) significantly increased selenium contents in sulfosalts. Identified selenium minerals include aguilarite and selenides naumannite and clausthalite. The previously unknown sulfosalts from Kutná Hora are identified: Ag-excess fizélyite, fizélyite, andorite IV, andorite VI, unnamed Ag-poor Ag-Pb-Sb sulfosalts, semseyite, stephanite, polybasite, unnamed Ag-Cu-S mineral phases and uytenbogaardtite. Among the newly identified sulfides is argyrodite; germanium is a new chemical element in geochemistry of Kutná Hora. Three types of ore were recognized in the vein assemblage: the Pb-rich black ore (i) in quartz; the Ag-rich red ore (ii) in kutnohorite-quartz gangue; and the Ag-rich ore (iii) in milky quartz without sulfides. The general succession scheme runs for the Pb-rich black ore (i) as follows: galena – boulangerite (– jamesonite) – owyheeite – fizélyite – Ag-exces fizélyite – andorite IV – andorite VI – freieslebenite – diaphorite – miargyrite – freibergite. For the Ag-rich red ore (ii) and ore (iii) the most prominent pattern is: galena – diaphorite – freibergite – miargyrite – pyragyrite – stephanite – polybasite – acanthite. The parallel succession scheme progresses from Se-poor to Se-rich phases, i.e., galena – members of galena – clausthalite solid solution – clausthalite; miargyrite – Se-rich miargyrite; acanthite – aguilarite – naumannite. A likely source of selenium is in the serpentinized ultrabasic bodies, known in the area of “silver” lodes in the South of the ore district, which may enable to pre-concentrate selenium, released into hydrothermal fluids during tectonic events. The origin of the studied ore mineralization is primarily bound to the youngest stage of mineralization of the whole ore district, corresponding to the Ag-Sb sequence of the ‘eb’ ore type of the Freiberg ore district in Saxony (Germany) and shows mineralogical and geochemical similarities to low-sulfidation epithermal-style Ag-Au mineralization.

Trace element distributions in (Cu)-Pb-Sb sulfosalts from the Gutaishan Au-Sb deposit, South China: Implications for formation of high fineness native gold

Trace element distributions in (Cu)-Pb-Sb sulfosalts from the Gutaishan Au-Sb deposit, South China: Implications for formation of high fineness native gold

Quartz veins with associated Sb-Pb-Ag±Au mineralization in the Schwarzwald, SW Germany: a record of metamorphic cooling, tectonic rifting, and element remobilization processes in the Variscan belt

A combination of textural observations from 38 Permian Sb-Pb-Ag±Au-bearing quartz veins in the Schwarzwald (SW Germany) with isotopic, fluid inclusion, and geochemical data allows to refine genetic models for this common type of mineralization, to understand the origin of mineralogical diversity and the correlation with large scale tectonic events. Textures record four main mineralization stages: (I) Fe-As(-Sb±Au), (II) Pb-Zn-Cu, (III) Pb-Sb, and (IV) Ag-Sb. Stage I sulfides, dominated by pyrite and arsenopyrite, formed due to cooling of low-salinity metamorphic fluids during the Permian with maximum homogenization temperatures of 400 °C. Invisible gold in arsenopyrite, pyrite, marcasite, and stibnite was remobilized and locally precipitated as electrum at the end of stage I. Minerals of stages II and III comprise a rich diversity of Sb-bearing sulfosalts including, e.g., bournonite, zinkenite, and jamesonite. This assemblage formed during Jurassic times due to mixing of high-salinity, mid- and upper-crustal fluids (up to 27 wt% NaCl+CaCl2) with homogenization temperatures between 50 and 250 °C. Stage III is marked by a rich variety of Pb-Sb sulfosalts. Its local abundance is directly related to the presence of stage I mineralization and its extent of remobilization during a significant influx of Pb in the Jurassic-Cretaceous. The formation of the Upper Rhine Graben during the Tertiary reactivated especially NE-SW-oriented veins. Percolating Ag-rich fluids reacted with earlier stage III Pb-Sb sulfosalts forming Ag-rich minerals (stage IV) such as miargyrite, pyrargyrite, and stephanite. The transition from metamorphic fluids to basinal, saline (e.g., Pb-bearing) brines over hundreds of millions of years as is shown in this study and present in other Variscan occurrences indicates a possibly typical poly-stage characteristic of Sb deposits worldwide, which has, however, not been investigated in detail so far.

Origin of the intrusion-related Lang Vai gold-antimony district (Northeastern Vietnam): Constraints from fluid inclusions study and C[sbnd]O[sbnd]S[sbnd]Pb isotope systematics

The Lang Vai ore district, located in the central part of the Lo Gam domain in the Northeast Vietnam, contains at least three deposits: Khoun Puc, Lang Vai, and Lung Luong. The general paragenetic sequences for these deposits may be represented by the following mineral associations (from early to late): (i) arsenopyrite, pyrite, native gold, sphalerite; (ii) Bi-rich Pb-Sb sulfosalts; (iii) Bi-poor Pb-Sb sulfosalts; (iv) Sb sulfosalts; (v) Sb-rich minerals, native antimony; and (vi) Pb-rich Sb sulfosalts (as a distal mineral association). Three major types were recognized within the primary fluid inclusions based on the phases present at room temperature, including: V-type, vapor-rich inclusions; L-type, liquid-rich inclusions; and C-type, CO2-rich inclusions. The early Au-As stage quartz crystals contain the V- and L-type fluid inclusions. The results indicate that the initial ore-forming fluid belonged to a (CO2-CH4)–H2O–NaCl system characterized by high temperatures (290–352 °C) and variable to moderate salinities (3.16–13.89 wt% NaCl), which are analogous to reduced intrusion-related ore-forming fluids that exhibit high homogenization temperatures and moderate salinities. The quartz crystals from the Bi-Pb-Sb mineral paragenesis (occurred only at the Khoun Puc deposit) contain both V- and L-type fluid inclusions and characterized by high temperatures (mainly 304–340 °C) and moderate salinities (6.28–8.22 wt% NaCl equiv.). The quartz crystals from the middle hydrothermal stage contain the V- and L-type fluid inclusions that yield moderate homogenization temperatures (240–290 °C) and variable salinities (3.3–8.2 wt% NaCl equiv.). These features indicate that the fluid evolved into an (CO2 ± CH4)–H2O–NaCl system at moderate temperatures, lower CH4 concentrations, and variable salinities, thus indicating changing physicochemical conditions. In the last Sb stage (the Lang Vai deposit) and Pb-Sb stage (the Lung Luong deposit), the ore-forming fluid belongs to CO2–H2O–NaCl system, which is characterized by low temperature (180–240 °C), enrichment of CO2, and medium-low salinity (1.12–9.5 wt% NaCl equiv.), that corresponded to typical fluids which formed the Sb-, and distal AgPbZn veins of the IRGS deposits in the Tintina Gold Province of Alaska USA and Yukon Canada. The fluid inclusion studies and laser Raman spectroscopy suggest that the early fluids were dominated by CH4, whereas the late fluids, by CO2. Our study suggests that the fluid boiling and accompanying decrease in the solubility of gold-bisulfide complex played an important role in gold deposition at the Khoun Puc and Lang Vai deposits. The trapping pressures estimated from the boiling fluid inclusions were 123–343 MPa during the ore-forming process. This suggests an alternating lithostatic–hydrostatic fluid system controlled by a fault-valve activity at a depth of 12.9–15.2 km. The characteristics of the S isotopes and fluid inclusions suggest that the ore-forming fluids were of magmatic origin. During mineralization process, the fluid–rock interaction between the fluids and host rocks resulted in the increase of δ34S values of the fluids as reflected in the range of sulfur isotope from the different deposits. On a plumbotectonic diagram, the sulfides show correlations between 206Pb/204Pb and both 207Pb/204Pb and 208Pb/204Pb, which suggest a two-component mixing between a high radiogenic end-member and another low radiogenic end-member. The δ13CPDB vs. δ18OSMOW study clear show that C and O in the Khoun Puc ore-forming fluids were most likely to be derived from the magma with limited contribution from the carbonate host rocks (predominantly magmatic origin of hydrothermal fluids). Wherein, the calcite separates from the Lang Vai and Lung Luong deposits have δ18OSMOW values higher than those of the Khoun Puc, suggesting that the carbonate host rocks may have provided more C and O for ore-forming fluids in these deposits. The results, combined with existing data on the regional geology, ore geology, ore geochemistry, age of mineralization, and tectonic setting, indicate that the Lang Vai ore district is an intrusion-related gold system.

Intrusion-related Lang Vai gold-antimony district (Northeastern Vietnam): Geology, mineralogy, geochemistry and 40Ar/39Ar age

The Lo Gam domain is one of the most important areas for metallogenic studies in northeastern Vietnam. The Lo Gam domain comprises numerous Pb-Zn deposits and occurrences, which account for >80% of the Pb and Zn resources in Vietnam. Furthermore, within the Lo Gam domain, there are several gold, antimony, and base metal deposits. The largest of these are the Lang Vai, Khoun Puc, and Lung Luong deposits, which are included in the Lang Vai ore district. Each of the deposits includes several ore zones and ore bodies with peculiar mineral compositions and geochemical features. The geological and structural settings show that the Khoun Puc, Lang Vai, and Lung Luong deposits represent a uniform ore system. The metal zoning in the Lang Vai district occurs laterally away from a granitic intrusion. A general paragenetic sequence for the three deposits may be represented by the following mineral associations (from early to late): (i) arsenopyrite, pyrite, native gold, sphalerite; (ii) Bi-rich Pb-Sb sulfosalts; (iii) Bi-poor Pb-Sb sulfosalts; (iv) Sb sulfosalts; (v) Sb-rich minerals, native antimony; and (vi) Pb-rich Sb sulfosalts (as a distal mineral association). Among the different types of mineralizations, there is exists a transient mineralization that is characterized by a complex mineral composition. Bi-bearing minerals have been found only in the Khoun Puc deposit, which is located near a granite stock, whereas Bi mineralization is absent away from the deposit. The general outward sequence of zoning is from Au-As-Bi to Au-As-(Sb) to Sb-(Au-As) to Pb-Sb at the periphery. The ages of mineralization at the Lang Vai and Lung Luong deposits have been estimated to be ca. 240 Ma and ca. 236 Ma, respectively, and are slightly younger than the earlier reported ages (ca. 254–245 Ma) of the Phia Bioc granite complex, indicating a possible genetic relationship between the mineralization and the intrusions. The geological characteristics, metal zoning patterns and new geochronological data suggest that the gold-antimony ores in the Lang Vai district are genetically related to the nearby granitic intrusions.

Mineralogical evolution of the Las Cruces gossan cap (Iberian Pyrite Belt): From subaerial to underground conditions

The Las Cruces VMS deposit is located at the eastern corner of the Iberian Pyrite Belt (SW Spain) and is overlain by the Neogene–Quaternary sediments of the Guadalquivir foreland Basin. The deposit is currently exploited from an open pit by Cobre Las Cruces S.A., being the supergene Cu-enriched zone the present mined resource. The Las Cruces orebody is composed of a polymetallic massive sulfide orebody, a Cu-rich stockwork and an overlying supergene profile that includes a Cu-rich secondary ore (initial reserves of 17.6 Mt @ 6.2% Cu) and a gossan cap (initial reserves of 3.6 Mt @ 3.3% Pb, 2.5g/t Au, and 56.3g/t Ag).The mineralogy of the Las Cruces weathering profile has been studied in this work. Textural relationships, mineral chemistry, deposition order of the minerals and genesis of the Las Cruces gossan are described and discussed in detail. A complex mineral assemblage composed by the following minerals has been determined: carbonates such as siderite, calcite and cerussite; Fe-sulfides including pyrite, marcasite, greigite and pyrrhotite; Pb–Sb sulfides and sulfosalts like galena, stibnite, fulöppite, plagionite, boulangerite, plumosite, and the jordanite–geocronite series, Ag–Hg–Sb sulfides and sulfosalts including miargyrite, pyrargyrite, sternbergite, acanthite, freibergite, cinnabar, Ag–Au–Hg amalgams; and Bi–Pb–Bi sulfides and sulfosalts such as bismuthinite, galenobismutite, others unidentified Bi–Pb-sulfosalts, native Bi and unidentified Fe–Pb–Sb-sulfosalts. Remains of the former oxidized assemblage appear as relicts comprised of hematite and goethite.Combining paragenetic information, textures and mineral chemistry it has been possible to derive a sequence of events for the Las Cruces gossan generation and subsequent evolution. In that sense, the small amount of Fe-oxyhydroxides and their relict textures replaced by carbonates and sulfides suggest that the gossan was generated under changing physico-chemical conditions. It is proposed that the Las Cruces current gossan represents the modified residue of a former gossan mineralization where prolonged weathering led to dissolution and leaching out of highly mobile elements and oxidation of the primary sulfides. Later, the gossan was subject to seawater-gossan interaction and then buried beneath a carbonated-rich cover. The basinal fluids-gossan interaction and the equilibration of fluids with the carbonated sediments brought to the carbonatization and sulfidation of the gossan, and thus to the generation of Fe-carbonates and Pb–Sb-sulfides.The Las Cruces mineral system likely represents a new category within the weathering class of ore deposits.

(Pb–Sb)-bearing sphalerite from the Čumavići polymetallic ore deposit, Podrinje Metallogenic District, East Bosnia and Herzegovina

Čumavići is a medium– to low–temperature hydrothermal Sb–Zn–Pb–Ag polymetallic vein–type ore deposit in the Srebrenica orefield, part of the Podrinje Metallogenic District, Eastern Bosnia and Herzegovina. The ore deposit occurs in the form of simple and complex veins along faults and fractures, as well as stockworks and disseminations hosted within Neogene volcanic rocks (pyroclastics and andesite lavas of calc–alkaline affinity). The deposit comprises sulfides (sphalerite, galena, stibnite, pyrite, marcasite, chalcopyrite, arsenopyrite, gudmundite, safflorite, löllingite, gersdorffite and acanthite), sulfosalts (berthierite, geocronite, boulangerite, semseyite, plagionite, jamesonite, bournonite, twinnite, andorite, fizéliyte, Ag–bearing tetrahedrite, stephanite, polybasite, pyrargyrite and argyrodite), native gold and silver, tungstates (hübnerite), oxides, and gangue quartz, chalcedony, Mn–siderite, anglesite, smithsonite, fluorite, gypsum and ludlamite. Three generations of sphalerite are recognized in the Čumavići deposit, evolving from Fe–rich to Fe–poor. The most common are yellowish to colorless Fe–poor varieties. Electron Probe Microanalyses of sphalerite free of micro–inclusions of galena and Pb–Sb-sulfosalts revealed wide compositional variations in minor- and trace–element contents (e.g., Fe, Cd, Mn, Cu, Sn, As, and In). Of particular interest are the lead and antimony content of sphalerite, which vary from 0.10 to 3.08, and 0.02 to 1.62wt.%, respectively. Lead– and Pb–Sb-rich zones are the most common in sphalerite, while individual Sb–bearing zones are rare. These zones have fan–like forms with circular to wave-like, micron–scale bands, filled with galena or Pb–Sb sulfosalts. In the Pb–Sb zones, the Sb/Pb atomic ratio ranges between 0.3 and 1.5, similar to ratios between geocronite and jamesonite, thus suggesting the presence of micro– to nano–scale inclusion of sulfosalts within the sphalerite. The mean composition of all sphalerite samples is (Zn0.78–0.99,Fe<0.01–0.21,Cu0.00–0.02,Pb<0.01–0.01,Cd<0.01–0.01,Sb<0.01–0.01,Mn<0.01–0.01)∑0.97–1.03S0.97–1.08 (Sn and As atomic proportions are <0.01 apfu). In all sphalerite samples, excellent negative correlations have been determined between Fe and Zn, and ∑(Fe+Sb) and Zn. The studied mineralization shares many mineralogical and geological characteristics in common to polymetallic Sn–Ag–Sb deposits in Bolivia and elsewhere.

The Au–As (Ag–Pb–Zn–Cu–Sb) vein-disseminated deposit of Arcos (Lugo, NW Spain): Mineral paragenesis, hydrothermal alteration and implications in invisible gold deposition

The Arcos deposit is located in the NW of the Iberian Variscan Massif, and consists of a pollymetallic Au–As (Ag–Pb–Zn–Cu–Sb) vein-disseminated mineralization. It is temporally and spatially related to post-Variscan rhyolite dikes and structurally controlled by Late-Variscan and Variscan structures. The mineralization in Arcos is divided into two stages. The first (Au–As) consists of fine-grained Au-bearing pyrite and arsenopyrite, with Au occurring as invisible gold. Sulfides occur filling veins as well as disseminated in hydrothermally altered (silicification, dolomitization, phyllic alteration and sulfidation) rhyolites and impure limestones and calcareous slates, Lower Cambrian in age. Several types of pyrite and arsenopyrite are defined according to their chemical and textural characteristics. Among these, the Py-II and Apy-II types are Au-bearing. Py-II is As-rich (up to 5wt.%) and is the main Au-bearing mineral (up to 0.2wt.% of Au) in Arcos, while Au content in Apy-II is local and low (up to 0.03wt.% of Au). The Py-II occurs as fine-grained pyritohedra and overgrowth rims of previous pyrite crystals, showing oscillatory As-zoning. The highest Au-contents are in the As-richer zones. The Au/As ratios of Py-II and Apy-II indicate that Au was mainly deposited as solid solution, suggesting that they precipitated from fluids undersaturated in Au. Sulfidation of iron derived from the alteration of ferroan silicates (mainly biotite) was the most important depositional mechanism of invisible gold in Arcos. The second stage of mineralization shows an Ag–Pb–Zn–Cu–Sb metallic signature. It replaces the first stage and consists of sphalerite, Ag-bearing tetrahedrite, bournonite, chalcopyrite and galena with Bi–Pb–Sb sulfosalts, pyrrhotite, Ni–Co–Fe sulfides and electrum as accessory minerals. The gangue minerals of this stage include Ca–Mg–Fe carbonates, quartz with minor fluorite and chlorite. In the most superficial levels of the area, secondary native Au, covellite and Fe oxide and hydroxide developed due to oxidation of the ore. The vein-disseminated mineralization of Arcos represents a distal deposit of an intrusion-related gold system developed around an unexposed, post-Variscan, calc-alkaline granitoid in the NW Iberian Massif.

Crankshaft chains of LEP cations as a solution to the cation size misfit

In Pb-As and Pb-Sb sulfosalts, columns of large coordination prisms of Pb combine with intervening slabs of As- or/and Sb coordination polyhedra. The LEP of these elements dictate the configurations resembling SnS (especially for As) or inflated PbS (especially for Sb). The size misfit of cation polyhedra forces the short As-S and Sb-S bonds to form crankshaft chains. In the homologues with thicker slabs, parallel crankshaft chains and incorporation of Pb in the slabs compensate for the misfit. In the low homologues, N = 3 for sartorite series and N = 4 for andorites, the misfit becomes critical and requires special arrangements. In sartorite (~PbAs2S4), two subsets of parallel short crankshaft chains in a slab are (approximately) mirror-related via two contacts. One contact has a missing S atom with valence compensation by Tl; the other one differs between the two structurally analyzed varieties, sartorite (9a) [1] and sartorite (11a) [new], which are type structures for two homologous subseries: (13a; 9a;5a) and (15a;11a;7a;3a). Structures of andorites VI and IV(~PbAgSb3S6) [2,3], and arsenquatrandorite [new] allow to construct a predictive scheme of zig-zag crankshaft chain arrangement. The 4c superstructure of andorite (IV) contains simple zig-zag sequences of As3S7 chains; in 6c andorite (VI) parallel and perpendicular chains alternate. Andorite (VI) unites, in one slab, two different stackings of perpendicular chains which are present, as separate 3c intervals, in two adjacent slabs in andorite (IV). An additional 1c interval gives the 4c structure. Further varieties, such as 10c roshchinite, are derived from these unit sequences. The fourfold varieties either have slight surplus of Pb or As replaces a part of Sb (arsenquatrandorite).

Rujevac Sb-Pb-Zn-As polymetallic deposit, Boranja orefield, Western Serbia: native arsenic and arsenic mineralization

Rujevac is a low-temperature hydrothermal polymetallic Sb-Pb-Zn-As vein-type ore deposit, hosted within a volcanogenic-sedimentary zone situated in the Rujevac-Crvene Stene-Brezovica Diabase-Chert Formation (DCF) of the Podrinje Metallogenic District (PMD), Serbia. It is located several kilometers SE from the Boranja contact aureole, which is an integral part of the PMD in Western Serbia. Genetically related to the Tertiary granodioritic magma, the mineral assemblages are characterized by specific features. The mineral association of this deposit consists of sulfides, Pb-Sb(As) sulfosalts, native metals, oxides, hydroxides and gangue minerals. Chemical composition of the ore is very complex, where contents of valuable metals range as follows: Sb (0.17–24.31 wt.%), Zn (0.21–6.29 wt.%), Pb (0.15–6.33 wt.%), As (0.06–1.28 wt.%), Cd (25–747 ppm), Ag (7–408 ppm), Hg (13–473 ppm), and Tl (<1–29 ppm). Electron Probe Microanalyses (EPMA) of native arsenic from both the Rujevac and Stragari deposits showed contents of As up to 98.8 and 97.1 wt.%, with impurity contents of Sb up to 1.3 and 6.6 wt.%, and Tl up to 2 and 1.3 wt.%, respectively. Rhombohedral unit-cell parameters for native arsenic from Rujevac and Stragari deposits amount to: a = 3.760(2), c = 10.555(3) A, V = 129.23(7) A3 and a = 3.763(1), c = 10.560(5) A, V = 129.48(8) A3, respectively. Mineral assemblages, deposition order and genesis of the Rujevac polymetallic deposit were also discussed in detail. Native arsenic mineralization here has been additionally compared with similar well-known global deposits.

THE CRYSTAL STRUCTURE OF SULFOSALTS WITH THE BOXWORK ARCHITECTURE AND THEIR NEW REPRESENTATIVE, Pb15-2xSb14+2xS36Ox

The new monoclinic phase with a structure-determined formula Pb 15−2 x Sb 14+2 x S 36 O x (Z = 4) was found only as a single grain in a micro-intergrowth of sulfosalts in the Klacianka Sb deposit, Low Tatra Mountains, Slovakia. Unit-cell dimensions are a 48.293(15), b 4.1107(13), c 34.223(11) A, β 106.168(5)°, space group C 2 /m. There are 11 independent lead sites, 13 antimony sites, and five mixed (Pb, Sb) sites, 36 sulfur positions, and a single, approximately half-occupied oxygen site. Some coordination polyhedra of antimony exhibit split Sb sites, with positional parameters refined independently. Because of the intergrowth, the final R 1 value remained at 23.5%. It does not reflect visibly upon positional parameters, but has an adverse influence on the occupancy of mixed positions. Until further occurrences are documented, it remains an unnamed mineral. It is a typical sulfosalt representative of the category of boxwork structures. Other structures of this category comprise pellouxite, marrucciite, vurroite, neyite, and several synthetic sulfosalts. Sulfosalts with a boxwork structure are formed by a combination of three types of structural modules: continuous walls with a complex structure of rod-layer type; these walls are interconnected by partitions, and the resulting boxlike channels are filled by another type of structure rods. In its entirety, this group demonstrates a number of types for each of these kinds of module. The “core” group of Pb–Sb sulfosalts, scainiite, pillaite, pellouxite, rouxelite, a synthetic Mn–Pb sulfosalt, and Pb 15−2 x Sb 14+2 x S 36 O x described in this study, depend on the presence of minor amounts of oxygen in the structures. Oxygen forms a part of a kermesite-like configuration that generates a pronounced change of the local structural arrangement and, in this way, makes the boxwork framework possible. Several REE sulfides form boxwork structures as well.

Lead-antimony sulfosalts from Tuscany (Italy). III. Pillaite, Pb9Sb10S23ClO0.5, a new Pb-Sb oxy-chloro-sulfosalt, from Buca della Vena mine

The new mineral pillaite, Pb9Sb10S23ClO0.5, an oxy-chloro-sulfosalt, has been found at Buca della Vena mine in the Apuan Alps, northern Tuscany, Italy. It crystallized in small fractures of dolomitic lenses in massive Fe- Ba ore, together with many Pb-Sb sulfosalts, among which the oxy-sulfosalt scainiite. Pillaite occurs as black acicu- lar crystals with metallic lustre, elongated // (010), up to 1 cm long and less than 0.1 mm thick. The mineral is brittle, opaque; VHN50 = 175 kg/mm2, dcalc = 5.77 g/cm3. In reflected light it shows a weak anisotropy and bireflectance, and

Origin and evolution of the calcic and magnesian skarns hosting the El Valle-Boinás copper–gold deposit, Asturias (Spain)

The El Valle-Boinás copper–gold deposit is located in the southern part of the Rio Narcea Gold Belt 65km west of Oviedo (NW Spain), within the Cantabrian Zone (Iberian Hercynian Massif). The deposit is related to the Boinás stock, which ranges from quartz-monzonite to monzogranite and intruded (303Ma) the carbonated Láncara Formation (early Cambrian) and the siliciclastic Oville Formation (middle-late Cambrian).A copper–gold skarn was developed along the contact between the igneous rock and the carbonated sedimentary rocks. The skarn distribution and mineralogy reflects both structural and lithologic controls. Two types of skarn exists: a calcic skarn mainly developed in the upper calcic member of the Láncara Formation, and a magnesian skarn developed in the lower dolomitic and organic-rich member. The former mainly consists of garnet, pyroxene and wollastonite. Retrograde alteration consists of K-feldspar, epidote, quartz, calcite, magnetite, ferroactinolite, titanite, apatite, chlorite and sulfides. Magnesian skarn mainly consists of diopside with interbedded forsterite zones. Pyroxene skarn is mainly altered to tremolite, with minor phlogopite and serpentine. Olivine skarn is pervasively altered to serpentine and magnetite, and is commonly accompanied by high sulfide and gold concentrations. This altered skarn results in a very dark rock, referred to as “black skarn”, which has great importance in gold reserves. Sulfide mineralization mainly consists of chalcopyrite, bornite, arsenopyrite, pyrrhotite and pyrite, while wittichenite, sphalerite, digenite, bismuthinite, native bismuth and electrum occur as accessory minerals.After extensive erosion, reactivation of the northeast-trending fracture zone provided conduits for the subsequent emplacement of porphyritic dikes (285±4Ma) and diabasic dikes (255±5Ma). Alteration, characterized by sericitization, silicification, carbonatization and hypogene oxidation took place, as did sulfide mineralization (pyrite, arsenopyrite, sphalerite, chalcopyrite, galena, bournonite, and Fe–Pb–Sb sulfosalts). Veins with quartz, carbonate, adularia and sulfide minerals crosscut all previous lithologies. Jasper and jasperoid breccias developed at the upper parts of the deposits.The fluid inclusion and stable isotope studies suggest a predominantly magmatic prograde-skarn fluid characterized by high-salinity (26–28wt.% KCl and 32–36wt.% NaCl) and high temperature, above 580°C. This fluid evolved into two immiscible fluids: a CO2- and/or CH4-rich, high-salinity aqueous fluid. Temperatures for the first retrograde-stage are between 350 and 425°C. A second stage is related to a more diluted aqueous fluid (3–6.2wt.% NaCl eq.) and temperatures from 280 to 325°C. The fluid inclusion study performed on quartz from low-temperature mineralization indicates a very low salinity (0.2–6.2wt.% NaCl eq.), low-temperature aqueous fluid (from 150 to 250°C), and trapping pressure conditions less than 0.2kbar. In addition, the stable isotope study suggests that an influx of metamorphic waters derived from the country rocks produced these lower temperature fluids. The last control for the Au mineralization is the Alpine tectonism, which developed fault breccias (cataclasites to, locally, protomylonites) and gold remobilization from previous mineralization.

Late-Variscan antimony mineralisation in the Rheinisches Schiefergebirge, NW Germany: evidence for stibnite precipitation by drastic cooling of high-temperature fluid systems

Antimony-rich vein mineralisation is widespread in the German part of the Variscan orogenic belt. Mineralogical investigation of a representative suite of these deposits, coupled with fluid inclusion characterisation and microthermometry, permits a reconstruction of their genetic evolution. Two structural settings host antimony mineralisation: the cores or flanks of anticlinal zones and major lithological contrasts. Channelled migration of geothermal fluids through permeable rock sequences and later stagnation of fluids in cap-rock situations inside the anticlinal zones led to mineral deposition. The mineralising event is interpreted as relating to input of deep-sourced fluids during late-orogenic exhumation at the transitional stage between collision tectonics and the late-Variscan extensional regime. Fluid inclusion data, chlorite geothermometry and the presence of meneghinite as a characteristic Pb-Sb-sulfosalt mineral in a number of vein systems allows constraints on model P-T conditions at the onset of mineralisation to be made. These are as high as 390 to 440 °C at 0.6–1.0 kbar for the Saarsegen, Apollo and Schone Freundschaft deposits, with lower temperatures of 320–340 °C being obtained for the Spes deposit. The fluid inclusion data indicate drastic fluid cooling during the mineralising event; minimum temperatures of approximately 150–220 °C are obtained for all deposits at the end of vein quartz formation, which coincided with deposition of stibnite and most of the Pb-Sb sulfosalts. Besides the formation of extensional quartz-stibnite-Pb-sulfosalt veins, the mineralising, low-salinity NaCl-KCl-rich high-temperature tectonic brines have overprinted sulfide assemblages within earlier siderite-(Cu)-Pb-Zn veins. This has led to replacement reaction textures and remobilisation of sulfide components within the vein systems. In contrast with the earlier siderite-(Cu)-Pb-Zn veins, neither the quartz-stibnite-sulfosalt nor the (Cu)-Pb-Sb sulfosalt assemblages were affected by Variscan deformation. Rather, they display characteristic extensional features crosscutting all earlier structures and can thus be assigned to a later phase of mineralisation. Fluid composition characteristics and structural criteria indicate formation in the latest part of the Variscan mineralisation cycle; a post-Variscan genesis being rejected on grounds of conspicuously diverging fluid characteristics. A comparison of antimony deposits in the Rheinisches Schiefergebirge with other late-orogenic deposits elsewhere in the European Variscan belt indicates a significant number of shared features, enabling them to be placed into a common model related to the onset of late-Variscan brittle extensional tectonics.

Lead-antimony sulfosalts from Tuscany (Italy). I. Scainiite, Pb14Sb30S54O5, the first Pb-Sb oxy-sulfosalt, from Buca della Vena mine

The new mineral scainiite, Pb 14 Sb 30 S 54 O 5 , the first lead oxy-sulfosalt, has been found at Buca della Vena mine in the Apuan Alpes, northern Tuscany, Italy. Scainiite occurs as black acicular crystals with bluish metallic lustre, elongated [010], up to 2 mm long and 0.2 mm thick. The mineral is brittle, opaque; VHN 20 = 192 kg/mm 2 , d calc = 5.56 g/cm 3 . In reflected light it shows a low anisotropy and bireflectance, and rare red internal reflections. Its ideal chemical formula, derived from electron-microprobe data and from crystal structure refinement, is Pb 14 Sb 30 S 54 O 5 . Scainiite is monoclinic, space group C2/m, a = 52.00(2), b = 8.148(2), c = 24.31(6) Aa, beta = 104.09(4) degrees , Z = 4. The strongest five lines of the X-ray powder diffraction pattern are [d in Aa(I)(hkl)]: 3.472(100)(14 0 4), 2.956(54) (6 2 4, 12 2 1), 2.052(46)(14 0 8, 24 0 1), 3.041(35)(4 0 8), 2.228(22)(22 0 1, 22 0 6, 8 2 9). Scainiite is a structural derivative of synthetic hexagonal Ba (sub approximately 12) Bi (sub approximately 24) S 48 , a member of cyclically twinned sulfosalt structures (zinkenite group). Scainiite crystallized in small fractures of dolomitic lenses in massive Fe-Ba ore, together with many Pb-Sb sulfosalts. The formation of this unique lead oxy-sulfosalt is related to narrow fO 2 -fS 2 conditions, corresponding to the magnetite-hematite-pyrite buffer at relatively high temperature (>300 degrees C).

Phase equilibrium study in the system Cu2S-PbS-Sb2S3: non-stoichiometry in sulfosalts and isothermal variation in sulfur fugacity

Evacuated silica tube experiments (+halide flux) were conducted in portions of the system Cu2S-PbS-Sb2S3 at 440°C, using two-pyrrhotite indicator method to measure the sulfur fugacity. Product phases were identified by optical and X-ray powder diffraction methods supplemented with microprobe analyses. In addition to the previously reported mineral phases, famatinite (Cu3SbS4) appears to be a stable phase in the Sb2S3-rich portion of the system. Microprobe data indicate that almost all the sulfosalts depart from stoichiometry. Copper in Pb-Sb sulfosalts and Pb in chalcostibite and skinnerite are indicative of the coupled substitution 2Pb2+=Cu++Sb3+. Pb-solubility in skinnerite and Cu-solubility in zinkenite are dependent on the initial bulk composition of the charges. The compositions of meneghinite and boulangerite compare well with their natural analogues. The maximum isothermal variation of logfs2 falls in the range of-6.36 (1.06)≤logfs2≤11.12 (0.30). The experimentally derived logfs2 values for some two phase assemblages, compare reasonably well with the respective minimum logfs2 values calculated by the method of Craig and Barton (1973). The stable coexistence of famatinite with zinkenite plus stibnite instead of chalcostibite may be described by the sulfidation reaction: 3CuSbS2+1/2 S2=Cu3SbS4+Sb2S3.

Gold in the volcanogenic mercury-rich sulfide deposit L�ngsele, Skellefte ore district, northern Sweden

The mineralogy of gold from a volcanogenic sulfide deposit in northern Sweden (Langsele) was studied. The enrichment of gold and silver in massive ore occurs associated with an intrusive metadolerite vein which can be traced across the ore. The emplacement of this vein mobilized the precious metals together with galena and Pb-Sb sulfosalts into fractures and low pressure zones. A high mercury content at L»ngsele (average 250 ppm) has influenced the gold mineralogy. Thus, gold occurs as Au-Ag amalgam, native gold and rarely as aurostibite (AuSb2). The results of microprobe analyses of amalgam cluster around Au0.45Ag0.45Hg0.10. The composition of ternary amalgam is discussed in connection with the synthetic Au-Ag-Hg system. Furthermore, native gold was found myrmekitically integrown with stibnite which has been interpreted as a breakdown product of aurostibite at low temperature.