Inclusions Of Galena Research Articles

MINERALOGICAL DATA ON ANGELAITE, Cu2AgPbBiS4, FROM THE LOS MANANTIALES DISTRICT, CHUBUT, ARGENTINA

Angelaite, ideally Cu2AgPbBiS4, occurs as a hypogene mineral in polymetallic ores at the Angela groups of veins in the mining district of Los Manantiales, in the province of Chubut, Argentina. The new mineral species is predominantly associated with pyrite, sphalerite, chalcopyrite, hematite, native gold and galena; less common associates are aikinite, wittichenite, miharaite and cervelleite. Angelaite forms subhedral, commonly oriented inclusions in galena; these may attain a size of up to 200 x 50 mm. The mineral is grey in color with a brownish tint, opaque, and lacks internal reflections. It has a metallic luster and a dark grey streak. The VHN10 ranges between 245 and 263 kg/mm(3) (mean 253), corresponding to a Mohs hardness of 3 1/2. In plane-polarized light, it is strongly bireflectant and pleochroic from light grey with a brownish tint to light cream with a greenish tint. Angelaite is strongly anisotropic, with rotation tints in shades of pale grey, deep green and deep blue. We provide the measured values of reflectance in air and oil. The average of 23 electron-microprobe analyses is: Cu 16.7(3), Ag 13.4(2), Pb 27.8(6), Bi 26.6(5), S 16.0(2), total 100.5(5) wt.%, equivalent to Cu2.07Ag0.97Pb1.05Bi1.00S3.91. The ideal formula (on the basis of nine atoms) is Cu2AgPbBiS4, which requires Cu 16.31, Ag 13.84, Pb 26.58, Bi 26.81, S 16.45, total 100 wt.%. Angelaite is orthorhombic, with a 12.734(5), b 4.032(1), c 14.633(5) angstrom, V 751.8(5) angstrom(3), space group Pnma and Z = 4. The calculated density is 6.934 g/cm(3). It is a homeotype of galenobismutite, with Cu and Ag replacing one of the Bi positions in a complicated way. The strongest eight lines in the calculated powder-diffraction pattern [d in angstrom(I)(hkl)] are 3.672(100)(032), 3.660(64)(004), 3.407(60)(120), 3.319(62) ((1) over bar 21), 3.317(62)(121), 3.111(69)(041), 3.022(72)((1) over bar 13) and 3.017(72)(113). The mineral is named after the location. Both the mineral and its name were approved by the CNMNC (IMA #2003-064).

Daliranite, PbHgAs2S6, a new sulphosalt from the Zarshouran Au-As deposit, Takab region, Iran

AbstractDaliranite, ideally PbHgAs2S6, a new sulphosalt from the Zarshouran Au-As deposit, Takab region, Iran, occurs as a rare sulphosalt species at the Carlin-type Zarshouran Au-As deposit North of the town of Takab in the Province of West Azarbaijan, Iran. The new species is associated with orpiment, rarely with galkhaite, hutchinsonite and cinnabar. The strongly silicified matrix of the specimens has veinlets of sphalerite, with rare inclusions of galena and various (Cu)-Pb-As(Sb) sulphosalts. Daliranite occurs as matted nests of acicular and flexible fibres up to 200 μm in length and a width less than a few μm. The colour is orange-red with a pale orange-red streak and the lustre is adamantine. The mineral is transparent and does not fluoresce. The Mohs hardness is <2. Electron microprobe analyses give the empirical formula Pb0.95Tl0.01Hg1.04As2.10S5.91, ideally PbHgAs2S6, a new sulphosalt from the Zarshouran Au-As deposit, Takab region, Iran; the calculated density is 5.93 g cm–3. Unit-cell parameters were determined by an electron-diffraction study and refined from X-ray powder data. Daliranite is monoclinic primitive with a = 19.113(5) Å, b = 4.233(2) Å, c = 22.958(8) Å, β = 114.78(5)°, V = 1686.4 Å3 and Z = 8, a:b:c = 4.515:1:5.424, space group P2, Pm or P2/m. The strongest X-ray powder-diffraction lines [d in Å, (I), (hkl)] are: 8.676, (80), (200); 4.654, (50), (401); 3.870, (40), (211); 3.394, (50), (113); 3.148, (40b), (602); 2.892, (50), (600); 2.724, (100), (703); 2.185, (50), (319). The formula shows a sulphur excess which may correspond to S—S bonding (persulphide). The new sulphosalt is a late phase in the crystallization sequence, and was formed after orpiment, contemporaneously with quartz II, at a temperature between 157 and 193°C. The name honours Dr Farahnaz Daliran (University of Karlsruhe, Germany) in recognition of her outstanding contributions to research on ore deposits, especially Au, Zn and Fe, in Iran.

COMPOSITIONAL DATA FOR Bi-Pb TELLUROSULFIDES

Compounds containing essential Bi, Pb, Te and S are rare in nature. Aleksite, PbBi2Te2S2, is known from less than ten localities worldwide, and the single other recognized mineral, saddlebackite, Pb2Bi2Te2S3, is known only from the type locality, the Boddington Au deposit, Western Australia. Another phase, unnamed PbBi4Te4S3, had earlier been recognized as homogeneous grains and lamellar intergrowths within an assemblage consisting of aleksite, tellurobismuthite and tetradymite from St. David’s mine, Clogau, Wales, U.K. Re-investigation of this assemblage, including careful micro-analysis to avoid obvious intergrowths of phases, reveals an almost continuous range of compositions between tetradymite and aleksite. Investigations of complex sulfosalt–telluride assemblages from Iilijarvi, a satellite deposit within the Orijarvi orefi eld, southwest Finland, have revealed compositions approximating to the range Pb5Bi4Te4S7 – Pb7Bi4Te4S9. These occur as fi ne intergrowths, rarely as larger single lamellae, also with aleksite, within a matrix of giessenite, galena and cosalite. The samples contain abundant gold, seen also as symplectite intergrowths with rutile. Investigation of the microparagenesis of precious-metal-bearing galena – chalcopyrite – pyrite mineralization in quartz veins at Fragant (“Langenleiten”), Carinthia Province of Austria, revealed the presence of several compositionally different Bi–Pb tellurosulfi des. Aleksite is the most abundant, followed by unnamed phases with compositions close to Pb3Bi4Te4S5, Pb5Bi4Te4S7 and Pb6Bi4Te4S8. They occur as inclusions in galena and are variably associated with sulfosalts such as lillianite, cosalite, felbertalite and aikinite. The compositional dataset from the above occurrences is diffi cult to interpret

Textural, Compositional, and Sulfur Isotope Variations of Sulfide Minerals in the Red Dog Zn-Pb-Ag Deposits, Brooks Range, Alaska: Implications for Ore Formation

The Red Dog Zn-Pb deposits are hosted in organic-rich mudstone and shale of the Mississippian Kuna Formation. A complex mineralization history is defined by four sphalerite types or stages: (1) early brown sphalerite, (2) yellow-brown sphalerite, (3) red-brown sphalerite, and (4) late tan sphalerite. Stages 2 and 3 constitute the main ore-forming event and are volumetrically the most important. Sulfides in stages 1 and 2 were deposited with barite, whereas stage 3 largely replaces barite. Distinct chemical differences exist among the different stages of sphalerite. From early brown sphalerite to later yellow-brown sphalerite and red-brown sphalerite, Fe and Co content generally increase and Mn and Tl content generally decrease. Early brown sphalerite contains no more than 1.9 wt percent Fe and 63 ppm Co, with high Mn (up to 37 ppm) and Tl (126 ppm), whereas yellow-brown sphalerite and red-brown sphalerite contain high Fe (up to 7.3 wt %) and Co (up to 382 ppm), and low Mn (<27 ppm) and Tl (<37 ppm). Late tan sphalerite has distinctly lower Fe (< 0.9 wt %) and higher Tl (up to 355 ppm), Mn (up to 177 ppm), and Ge (426 ppm), relative to earlier sphalerite. Wide ranges in concentrations of Ag, Cu, Pb, and Sb characterize all sphalerite types, particularly yellow-brown sphalerite and red-brown sphalerite, and most likely reflect submicroscopic inclusions of galena, chalcopyrite and/or tetrahedrite in the sphalerite. In situ ion microprobe sulfur isotope analyses show a progression from extremely low δ 34S values for stage 1 (as low as –37.2‰) to much higher values for yellow-brown sphalerite (mean of 3.3‰; n = 30) and red-brown sphalerite (mean of 3.4; n = 20). Late tan sphalerite is isotopically light (–16.4 to –27.2‰). The textural, chemical, and isotopic data indicate the following paragenesis: (1) deposition of early brown sphalerite with abundant barite, minor pyrite, and trace galena immediately beneath the sea floor in unconsolidated mud; (2) deposition of yellow-brown sphalerite during subsea-floor hydrothermal recrystallization and coarsening of preexisting barite; (3) open-space deposition of barite, red-brown sphalerite and other sulfides in veins and coeval replacement of barite; and (4) postore sulfide deposition, including the formation of late tan sphalerite breccias. Stage 1 mineralization took place in a low-temperature environment where fluids rich in Ba mixed with pore water or water-column sulfate to form barite, and metals combined with H2S derived from bacterial sulfate reduction to form sulfides. Higher temperatures and salinities and relatively oxidized ore-stage fluids (stages 2 and 3) compared with stage 1 were probably important controls on the abundances and relative amounts of metals in the fluids and the resulting sulfide chemistry. Textural observations and isotopic data show that preexisting barite was reductively dissolved, providing a source of H2S for sulfide mineral formation. In stage 3, the continued flow of hydrothermal fluids caused thermal alteration of organic-rich mudstones and a build-up of methane that led to fluid overpressuring, hydrofracturing, and vein formation. Barite, red-brown sphalerite, and other sulfides were deposited in the veins, and preexisting barite was pervasively replaced by red-brown sphalerite. Hydrothermal activity ceased until Jurassic time when thrusting and large-scale fluid flow related to the Brookian orogeny remobilized and formed late tan sphalerite in tectonic breccias.

The Jacobina Paleoproterozoic gold-bearing conglomerates, Bahia, Brazil: a “hydrothermal shear-reservoir” model

The N–S Jacobina foreland basin is a Paleoproterozoic basin (2080 to 1900 Ma) of stacked detrital and schist formations developed along a sinistral wrench–overthrust fault of the Transamazonian orogeny. At least five successive stages are identified in the westward progradation of the basin, wherein bedding-parallel strike–slip thrusts and prograde metamorphism indicate progressive involvement in the Transamazonian collision. Shearing and associated metamorphic recrystallization indicate a high geothermal gradient and a gradual loading of the underthrust units, with those to the east being deeper seated than those to the west. Basic–ultrabasic dykes and granite stocks cross-cut the lithologies and contributed to the thermal evolution. Conglomerates and chaotic breccia layers found in several formations mark periods of tectonic instability accompanied by erosion of the earlier stages of basin development. Multistage hydrothermal activity is indicated by a widespread alteration with gold-bearing quartz lodes, conglomerates showing a sulphide–gold–Cr–mineral association, leaching of ultrabasic rocks, and emerald mineralization related to late-tectonic granite emplacement. The economic gold-bearing clastic sediments (conglomerates and minor quartzites deposited during the fourth unit/stage of basin development) have generally been interpreted according to the “modified paleoplacer” model. Such a model, which implies the existence of a gold preconcentration within the quartz–pebble conglomerates, is supported by the lithological controls, reworked pebbles (e.g. cataclastic quartz, quartz–pyrite mylonite and rare fuchsite-bearing rocks) that had been hydrothermally altered during an earlier hydrothermal stage, and lead isotopic compositions revealing an Archean inheritance that is partly preserved in galena inclusions. New basin-scale structural and metallogenic data obtained by the authors, suggest a basin model characterized by successive cycles of sedimentation–faulting/thrusting–erosion (“cannibalism” model) that favours both a “paleoplacer” model and a “mesothermal shear-zone-related epigenetic” model. Heterochronous shear zones, formed between 1988 and 1912 Ma during the development of the basin, acted as feeder zones for postsedimentary mesothermal quartz–tourmaline–muscovite/fuchsite lodes, which constitute a possible source of the reworked hydrothermally altered pebbles. These shear zones controlled (a) an acid leaching of the sediments and the subsequent development of Al-rich assemblages interpreted as advanced argillic alteration zones, and (b) a sulphidation process affecting detrital ilmenite and magnetite and responsible for the high concentration of gold within shear veins containing assemblages of Cr–Ni-bearing minerals (euhedral chromite, Cr–rutile, linnaeite, Cr–tourmaline and fuchsite) and euhedral pyrite that crystallized over andalusite. The conglomerates, with their pore and fissure permeability, acted as a “reservoir and trap” for the mineralizing fluids to give a “hydrothermal shear-reservoir” model. The homogeneous sulphur isotopic composition of the sulphides (between −0.5‰ and 1.3‰) and the δ 18O–δD values of the hydrothermal fluid (+8±1‰ and −36±3‰, respectively) suggest a magmatic source for the fluids. Moreover, the high thermal regime that characterizes the Jacobina basin could reflect a contribution from both the regional granitic magmatism and the basic–ultrabasic dyke network responsible for the Cr–(Ni–Co) mineralogical signature of the mineralization. Under the oxidation conditions of the Paleoproterozoic, the sulphidation of the gold-bearing conglomerates would depend largely on the extent of the hydrothermal–magmatic processes.

Alteration of monazite and zircon and lead migration as geochemical tracers of fluid paleocirculations around the Oklo–Okélobondo and Bangombé natural nuclear reaction zones (Franceville basin, Gabon)

Large-scale light rare earth element (LREE), uranium, lead and phosphorus migration has been evidenced in the FA Lower Proterozoic sandstones of the Franceville basin (Gabon) hosting Oklo natural nuclear reaction zones (RZ) in relation with extensive accessory mineral alteration by highly saline diagenetic brines (28.7 wt.% NaCl eq. to 30 wt.% CaCl 2 eq.) at about 140°C and 1 kbar. Monazite is the most severely altered accessory mineral in the coarse-grained sandstones of the basal FA formation. Detrital monazite crystals are altered to Th–OH silicate microcrystalline phase with very low concentrations of U and LREE. The Th/La ratio increase from non-altered (Th/La∼0.27) to altered sandstones (Th/La∼1.14) shows that about 76% of the LREE was leached. This corresponds to the leaching of 2.01×10 9 metric tons at the scale of the FA formation in the Franceville basin. Similarly, the Th/U increase from monazite (Th/U=18.6) to the Th-silicate phase (Th/U=88.7) is interpreted as a result of an alteration by oxidizing brines with leaching of U together with LREE and P. It corresponds to the leaching of 9.06×10 6 metric tons of uranium. This amount of uranium largely exceeds the known uranium reserves from the Franceville basin. In zircon crystals, the cores are generally homogeneous, weakly fractured and well preserved as attested by the Archean ages (2867±24 and 2865±51 Ma) obtained by ionic microprobe analysis on zircon of the FA Formation, respectively, from the marginal and central parts of the basin. Their composition corresponds to the pure end-member (Zr,Hf)(SiO 4), poor in Th and U (Th/U∼1). At the contrary, their rims, which present several growth zones with cracks fillings, are enriched in REE, P, Th and U with higher Th/U ratios (5–10). Both altered monazite and altered zircon contain galena as numerous inclusions in the outer growth zones and as crack fillings. For example, in zircon, the Pb of galena crystals (3–23 wt.%) largely exceeds the amount of Pb (maximum 0.1 wt.%) that would have been produced in situ by radioactive decay in this mineral. Nearly all the lead were introduced into altered zones of accessories. Dissolution of accessory minerals occurred at 2000 Ma, producing a porous and distorted crystal structure which has allowed a later incorporation of Pb. Galena inclusions in altered zircons located in the vicinity of reactor zones have radiogenic lead compositions. Altered zircon rims and galena inclusions in altered zircon located far from reactor zones have non-radiogenic Pb isotopic compositions, confirming the external origin of lead. Pb isotopic evolution models indicate a crystallization age sometime after 1000 Ma, both for galena located close to and far from U mineralizations and reactor zones, which may be synchronous with a regional extension event contemporaneous with intrusion of dolerite dyke swarms, between 1000 and 750 Ma, at the scale of the Franceville basin. The present study also illustrates the different retention capacities of accessory mineral for elements representing analogs of the radiotoxic nuclides in the relatively extreme natural conditions created by the circulation of moderately hot and chloride-rich fluids during the diagenesis of a sedimentary basin.

Solubility and behavior of lead in green orthoclase (amazonite) from Broken Hill, New South Wales, Australia.

The solubility and behavior of lead in feldspar are elucidated by EPMA and X-ray photoelectron spectroscopy (XPS; also known as ESCA) analyses for green orthoclase (amazonite) from Broken Hill, New South Wales, Australia. The role in the crystal structure establishes Pb cation as PbAl2Si2O8 endmember for the orthoclase solid solution, and the maximum quantity of PbAl2Si2O8 is 3.8 mol% in the green orthoclase. The lead cations, except the one existing in the orthoclase lattice, namely structurally bound Pb, occur in the green orthoclase by the following two ways; 1) as galena inclusions, and 2) as unidentified Pb-bearing micro-inclusions. The chemical shift for Pb atom in the green orthoclase was investigated by XPS, and compared with those in a Pb-metal, Pb-oxides, and a galena. Differences in the binding energy between Pb in the green orthoclase and other Pb-substances show distinctly that most of the Pb is not present as impurities like micro-minerals, but as structural components in green orthoclase. Crystal chemical consideration of Pb affords us infallible discrimination of solubility of PbAl2Si2O8 endmember rather than PbAlSi3O8. The existence of PbAl2Si2O8 as the main endmember in green orthoclase exhibits the charge-coupled substitution in the extra framework and the tetrahedral site; K++Si4+ ↔ Pb2++Al3+. Inhomogeneous distribution of Pb cation within the single crystal shows that the condition of Pb cation in green orthoclase structure is unstable.

Laforêtite, AgInS2, a new mineral of the chalcopyrite group from the Montgros mine, Haute-Loire, France

Laforetite, AgInS 2 , is a new mineral from the Montgros Pb-Zn mine, Haute-Loire, France. It occurs as very small, less than 30 mu m, anhedral inclusions in galena, which is associated with sphalerite, barite, carbonates and quartz. The new species is brownish grey with abundant red internal reflections in plane polarized light; under crossed nicols in oil immersion, it presents a strong anisotropy with red brick orange to bluish-grey purplish tints and polysynthetic twins. Electron-microprobe analysis yields (mean of 8 analyses): Ag 37.68, Cu 0.04, In 40.22, Fe 0.02, S 22.42, Se 0.01, total 100.39 wt.%. The simplified formula is AgInS 2 . Because of the material paucity, X-ray powder patterns were obtained from a very small inclusion (20X30 mu m) with a microdiffractometer using the reflection geometry. Parameters refined from a tetragonal cell (by comparison with the synthetic low-temperature from of AgInS 2 ) are: a = 5.880 (2), c = 11.21 (1) Aa, V = 387.57 (1) Aa 3 ; space group I 42d (no. 122) and Z = 4. Laforetite is the silver analogue of roquesite and belongs to the chalcopyrite group. The name honours Claude Laforet (BRGM, Orleans), a metallographer who first identified this mineral in the Montgros mine.

Petrology, mineral chemistry, and exploration significance of Fe-sulfides from the metal dispersion halo surrounding the Cadjebut Zn [sbnd]Pb MVT deposit, Western Australia

The Cadjebut MVT mineralization is hosted by carbonate-evaporite units in the Givetian lower dolomite sequence of the Pillara platform, northern Western Australia, and occurs as 2 ore types: (1) An early Zn-rich, stratiform and rhythmically banded ore and its laterally equivalent halo of banded marcasite, barite ± calcite; and (2) a later cross-cutting, breccia-fill, Pb-rich ore. The 2 ore types are exploited through 2 mining lenses; an upper lens 1 and lower lens 2. The orebody is sited N of the normal, basin-side down, Cadjebut Fault. Rhythmically banded marcasite completely envelopes the orebody in both lenses, whereas banded barite occurs N of the lower lens 2 only where the barite is partially to completely replaced by late cloudy calcite + marcasite. Barite replacement by marcasite and cloudy calcite increases northwards. Petrographic and trace element data indicate 3 types of Fe-sulfides: (1) low-Pb Fe-sulfides with Pb contents <5300 ppm; high-Pb Fe-sulfides with Pb contents <30 000 ppm and, extremely high-Pb Fe-sulfides with > 30 000 ppm Pb. Only the ‘colloform’ pyrites exhibit Pb contents above 30 000 ppm, and SEM images show these elevated Pb contents are due to micron-scale galena inclusions. Mineral chemical data from sulfides in the stratiform Fe-sulfide and barite halos indicate that main ore-stage fluids of the rhythmically banded ore event were enriched in Zn, Pb, Cd, As and, to a minor extent Ni and Cu. Late-stage fluids of the rhythmically banded ore event were not saturated with respect to galena, precipitating low-Pb marcasites along the very outer fringes of the orebody, and replacing rhythmically banded barite in lens 2. Only the low-Pb marcasites show various stages of pyrite inversion. Petrographic and trace element mineral chemistry of the 2 stratiform halos are best explained by a model in which main ore stage fluids of the early rhythmically banded ore event emanated from below the Cadjebut orebody along an inferred antithetic reverse fault. The presence of a laterally zoned alteration halo with a pattern of proximal higher Pb and trace element-bearing Fe-sulfides provides a vector towards the ore zone, and has important exploration significance for this style of base-metal mineralization.

Florencite-(La) with fissiogenic REEs from a natural fission reactor at Bangombe, Gabon

Florecite-(La) (La/Ce = 1.09) with fissiogenic REEs and florecite-(Ce) (La/Ce = 0.62) have been identified in illite from the clay mantle surrounding a natural, 2 Ga fission reactor at Bangombre and in sandstone beneath the reactor zone, respectively. Florencite-(Ce) is apparently unrelated to nuclear processes and occurs with monazite-(Ce), apatite, TiO{sub 2} (probably anatase), zircon, and illite. Grains of florencite-(Ce) contain inclusions of thorite, chalcopyrite, and galena. Florencite-(La) was found 5 cm from the {open_quotes}core{close_quotes} of the reactor and contains inclusions of galena and U-Ti-bearing phases. Secondary uraninite and coffinite have precipitated on some of the florencite grains. The chemical composition of florencite-(La) as determined by electron microprobe analysis is (La{sub 0.38}Ce{sub 0.35}Nd{sub 0.06}Sm{sub 0.01}-Ca{sub 0.03}Sr{sub 0.17})(Al{sub 2.98}Fe{sub 0.02}{sup 3+})(PO{sub 4})[PO{sub 3.80}(OH){sub 0.20}](OH){sub 6}. Secondary ion mass spectrometry revealed that between 27 and 30% of Nd and 67 and 71% of Sm in florencite-(La) is fissiogenic. The presence of fissiogenic REEs in {open_quotes}florencite{close_quotes} from the reactor zone in Bangombe and their preferential concentration in florencite relative to the bulk sample of clay demonstrate that aluminous phosphates may have played a more significant role in the fixation of fissiogenic REES released from uraninite after the sustained fission reactions than sorption ontomore » clays. 30 refs., 3 figs., 2 tabs.« less

Uraninite: a 2 Ga Spent Nuclear Fuel from the Natural Fission Reactor at Bangombé in Gabon, West Africa

ABSTRACTUraninites from the Bangombé natural fission reactor (RZB) and “normal” uranium-ore occur as fine veins in the sandstone host-rock as well as altered, broken, and slightly displaced grains in an illitic matrix, and in nodules and veins of solid bitumen. Inclusions of galena, (Y,Gd)-rich phosphates, a Pb-oxide and a Ti-oxide? were observed. Uraninites just below RZB were partially altered to a uranyl-sulfate. Three generations of uraninite were identified based on their PbO-contents of 8–11.06 wt%, 6 wt% (the largest population), and a younger generation with 3 wt%. The high Pb-uraninites may be the precursor to the low Pb-uraninites. Diffusional loss of Pb is indicated by the presence of a Pb-oxide at the interface to the uraninites. The behaviour of the metallic fission products, incompatible with the uraninite structure, may mimic the behaviour of Pb in these uraninites. The averaged impurity-content ranges from 4.29 to 6.89 wt%, and consists mainly of SiO2, TiO2, ZrO2, FeO, CaO, Al2O3 and P2O5. The averaged content of Y2O3 and the Ln's is less than 0.78 wt% and there is a scattered positive correlation with P2O5. The content of Y + Ln's is generally highest in the uraninites from RZB. Uraninite hydration and the formation of “uranopelite/zippeite” have caused complete loss of Y and the Ln's. These elements seems also to be partially lost by weak phosphatian coffinitization. The analytical results indicate that Y and the Ln's, which are high yield fission products, may be released from uraninite during alteration in the presence of P.

Boviksgruvan, a Au-Bi-bearing sulphide deposit in the Bergslagen Province, south central Sweden

Abstract The Boviksgruvan deposit, situated 18 km northeast of Falun, is a gold-bearing magnesian skarn deposit which was mined for iron and zinc during the 18th and 19th centuries. Magnetite, sphalerite, galena, chalcopyrite, pyrite, and pyrrhotite dominate the ore mineral assemblage. In addition, gold, native bismuth, galenobismutitc, cosalite, joseite A, and joseite B are specific constituents recognized in the Boviksgruvan deposit. The ore can be divided into two mineralogical types. Ore type 1 consists of a biotite-magnetite assemblage with disseminated galena and Pb-Bi-sulphosalts. Ore type 2 consists mainly of iron sulphides, base metal sulphides, and anthophyllite. Gold is often intergrown with native bismuth, as inclusions in galena or as cavity fillings in magnetite. According to the cross-cutting relations recognized between magnetite and Pb-Bi-sulphosalts in ore type 1, these sulphosalts, as well as gold, are considered to represent a younger ore forming epoch in relation to the magnetite. Fur...

Barstowite, 3PbCl2.PbCO3.H2O, a new mineral from Bounds Cliff, St Endellion, Cornwall

AbstractBarstowite, ideally 3PbCl2.PbCO3.H2O is a new mineral from a lead-antimony vein at the south-western end of Bounds Cliff, St Endellion, Cornwall. It occurs as very small (0.2–0.5 mm) subparallel elongate intergrown crystals which form aggregates (up to 3 mm) containing minor inclusions of galena and jamesonite. Other associated minerals are quartz, dolomite, phosgenite, cerussite, sphalerite, pyrite and chalcopyrite. Barstowite is colourless to white and is transparent with an adamantine lustre and white streak. It is brittle, has an imperfect prismatic cleavage, and an uneven fracture. Low reflecting, barstowite has a moderate bireflectance from grey to dark grey in hue and weak to moderate anisotropy. Internal reflections (colourless) are abundant. Measured reflectance values in air and oil are tabulated. Colour values relative to the CIE illuminant C for R1 and R2 in air respectively are: Y% 12.9, 13.3; λd 477, 476; Pe% 3.5, 3.7. VHN100 111 (range 108–117); calculated Mohs hardness is 3. Infrared spectra of barstowite, phosgenite and cerussite are compared.X-ray studies show that barstowite is monoclinic with space group P21/m and a 4.218(2), b 9.180(2), c 16.673(4) Å, β 91.49(3)°. It has a cell volume of 645.38 Å3 with Z = 2. Dcalc. is 5.76 g/cm3, Dmeas. is 5.71 g/cm3. The strongest six lines of the X-ray powder pattern are [d in Å (I) (hkl)] 4.02 (10) (022); 2.296(8) (040; ; 106); 2.377(6) (007; 026); 4.16(5) (004); 2.108(4) (200); 3.79(3) (014). The name is for the late Richard William Barstow, the Cornish mineral dealer.

Uranium-lead and lead-lead investigations of minerals from the Broken Hill lodes and mine sequence rocks

A regression analysis of combined rock and lode apatite data for the 207 Pb/ 206 Pb vs. 204 Pb/ 206 Pb plot gives an age of 1,565 + or - 20 m.y. (2sigma ) which is similar, within the experimental error limits, to the minimum U-Pb ages for monazite and Pb-Pb age for sphene from the mine sequence rocks of about 1,595 m.y. The possible differences in apparent age of the monazite-sphene and apatite may reflect the different blocking temperatures of the U-Pb systems in the two minerals. Cooling ages indicate that the Broken Hill Block remained at temperatures in excess of 600 degrees C for over 60 to 70 m.y. and would have allowed extensive concentration and/or recrystallization of the sulfide orebodies. On a concordia plot, the U-Pb data for zircons from two samples of upper granite gneiss and two of Potosi gneiss lie on an array with an apparent age of 1,663 (super +9) (sub -8) m.y. (2sigma ) and with a mean square of weighted deviates of 24.6. This age is interpreted as the time of granulite facies metamorphism. The least magnetic zircon fractions of samples close to mineralization contain from 2.2 to 16 ppm of common Pb. The abundant common lead in the zircons indicates that the sulfides were already in existence by 1,660 m.y., even if only in a disseminated form. An alternative explanation of the isotopic data is that there have been two major metamorphic events at Broken Hill during the middle Proterozoic: the granulite facies at approximately 1,660 m.y. and another at approximately 1,595 m.y. Thirty-five analyses of 21 sphalerites and pyrrhotites show uniform lead isotope ratios throughout the orebody because of the presence of galena inclusions.--Modified journal abstract.

Mercury in the Broken Hill (N.S.W., Australia) lead-zinc-silver lodes

In the Pb-Zn-Ag lodes at Broken Hill, significant Hg remains located in sphalerite and in tetrahedrite inclusions in galena, despite prograde granulite facies regional metamorphism that has resulted in recrystallization of the ore. The stratigraphically uppermost No. 3 lens has the highest Hg content, with sphalerite and galena concentrates containing up to 149,000 ppb and 198,000 ppb Hg, respectively, in Ag-Sb-rich parts of the lode. The No. 2 and 1 lenses and A lode have generally low Hg contents, but narrow tetrahedrite-rich sections contain up to 83,000 ppb Hg in sphalerite concentrates and 82,000 ppb in galena concentrates. The stratigraphically lowermost B lode has a moderately high Hg content with sphalerite concentrates containing from 4400 to 41,000 ppb Hg and galena concentrates from 30 to 21,000 ppb Hg. Programmed heating determinations showed Hg in sphalerite concentrates to be contained principally in the sphalerite structure, with subordinate amounts in tetrahedrite inclusions. Mercury in galena concentrates is almost wholly contained in tetrahedrite inclusions, with lesser amounts in dyscrasite and pyrargyrite. Piercement bodies show increased Pb, Ag, Sb, As and Hg contents due to preferential migration of galena and tetrahedrite. The Hg content of sphalerite in these bodies is approximately doubled relative to the source lode, and the Hg content of galena concentrates is increased sevenfold, due to an increase of tetrahedrite inclusions. Coarse-grained sulfide-gangue pods and pegmatites, which reflect partial melting and remobilization of parts of the lode, have a mean Hg content less than the same volume of host lode. Within these bodies Hg is strongly partitioned into sphalerite, which contains from 14,000 to 33,000 ppb Hg, whereas galena contains only from 10 to 570 ppb Hg, due to the absence of Hg-bearing tetrahedrite inclusions. Within the lode environment, trace amounts of Hg in veins formed during retrograde metamorphism are located in sphalerite which contains up to 29,000 ppb Hg. The presence of significant amounts of Hg in Ag-Sb-As minerals in a siderite-rich vein within the main lode and in the Consols lode (located 700 m from the main lode) indicates that Hg remains associated with these elements over a wide range of conditions. In the wall rocks, there is no Hg halo which is exclusive of disseminated sulfide minerals. Under high-grade regional metamorphism, trace amounts of Hg in the Broken Hill lode are retained within pre-metamorphism host minerals. However, mobilization of Hg does take place in veins associated with retrograde metamorphism after localized breakdown of tetrahedrite.

Franklinite from Långban, Sweden: a new occurrence

Franklinite showing exsolution lameilae of magnetite occurs as inclusions in galena from Långban, Sweden. Electron microprobe analyses indicate a composition (Zn 0.88Fe 0.12)(Fe 1.90Al 0.06Mn 0.02Ti 0.02) 2.00O 4. The unit-cell dimension is a = 8.43 ± 0.01 A ̊ . Spectral curves of reflectance and quantitative colour values are given for franklinite and magnetite.