The large gold-telluride Svetlinsk deposit (~135 t Au) is considered to be a nontraditional one in the Urals and its origin is debated. A specific feature of the deposit is the abundance of various ...tellurides, such as tellurides of Fe, Ni, Pb, Sb, Bi, Ag, and Au. The new data of microthermometry, Raman spectroscopy, LA-ICP-MS, and crush-leach analysis (gas and ion chromatography, ICP-MS) for fluid inclusions as well as O-isotope data for quartz were obtained for the construction of PTX parameters of ore-formation and fluid sources in the deposit. Mineralisation was formed at a wide range of temperature and pressure (200–400 °C, 1–4 kbar) and from contrasting fluids with multiple sources. At the early stages, the magmatic fluid evolved during its ascent and phase separation and the fluid derived from the host rock decarbonation and dehydration were involved in the hydrothermal system. In addition, mantle-derived fluid might be involved in the ore-forming process during gold-telluride precipitation as well as heated meteoric waters during the late stages. Early fluids were rich in H2S, S0, and CH4, while the Au-Te mineralisation was formed from N2-rich fluid.
A significant part of the primary gold reserves in the world is contained in sulphide ores, many types of which are refractory in gold processing. The deposits of refractory sulphide ores will be the ...main potential source of gold production in the future. The refractory gold and silver in sulphide ores can be associated with micro- and nano-sized inclusions of Au and Ag minerals as well as isomorphous, adsorbed and other species of noble metals (NM) not thoroughly investigated. For gold and gold-bearing deposits of the Urals, distribution and forms of NM were studied in base metal sulphides by laser ablation-inductively coupled plasma mass spectrometry and by neutron activation analysis. Composition of arsenopyrite and As-pyrite, proper Au and Ag minerals were identified using electron probe microanalysis. The ratio of various forms of invisible gold—which includes nanoparticles and chemically bound gold—in sulphides is discussed. Observations were also performed on about 120 synthetic crystals of NM-doped sphalerite and greenockite. In VMS ores with increasing metamorphism, CAu and CAg in the major sulphides (sphalerite, chalcopyrite, pyrite) generally decrease. A portion of invisible gold also decreases —from ~65–85% to ~35–60% of the total Au. As a result of recrystallisation of ores, the invisible gold is enlarged and passes into the visible state as native gold, Au-Ag tellurides and sulphides. In the gold deposits of the Urals, the portion of invisible gold is usually <30% of the bulk Au.
A rare gold–telluride montbrayite from the large Svetlinsk gold–telluride deposit (South Urals, Russia) was comprehensively studied using optical microscopy, scanning electron microscopy, electron ...microprobe analysis, reflectance measurements, electron backscatter diffraction, and Raman spectroscopy. Significant variations in the composition of the mineral were revealed (in wt%): Au 36.98–48.66, Te 43.35–56.53, Sb 2.49–8.10, Ag up to 4.56, Pb up to 2.04, Bi up to 0.33, Cu up to 1.42. There are two distinct groups with much more-limited variation within the observed compositional interval (in wt%): (1) Au 36.98–41.22, Te 49.35–56.53, Sb 2.49–5.57; (2) Au 47.86–48.66, Te 43.35–44.92, Sb 7.15–8.10. The empirical formula calculated on the basis of 61 apfu is Au16.43–23.28Sb1.79–6.09Te32.01–38.89Ag0–3.69Bi0–0.14Pb0–0.90Cu0–1.96. Two substitution mechanisms for antimony are proposed in the studied montbrayite grains: Sb→Au (2.5–5.6 wt% Sb) and Sb→Te (7–8 wt% Sb). The dependence of the reflection spectra and Raman spectra on the antimony content and its substitution mechanism, respectively, was found in the mineral. The slope of the reflectance spectra decreases and the curve in the blue–green region of the spectrum disappears with increasing Sb content in montbrayite. Raman spectra are reported for the first time for this mineral. The average positions of the peak with high-intensity are ~64 cm−1 and ~90 cm−1 for montbrayite with Sb→Te and Sb→Au, respectively. Two grains of montbrayite demonstrate decomposition according to two schemes: (1) montbrayite (7 wt% Sb) → native gold + calaverite ± altaite, and (2) montbrayite (5 wt% Sb) → native gold + tellurantimony ± altaite. A combination of melting and dissolution–precipitation processes may be responsible for the formation of these decomposition textures.
Pampaloite AuSbTe, a rare gold-antimony telluride that was first described in 2019 from the Pampalo gold mine, Finland, was found in samples from the large Svetlinsk gold-telluride deposit, South ...Urals, Russia. Optical microscopy, scanning electron microscopy, electron microprobe analysis, reflectance measurements, electron backscatter diffraction and Raman spectroscopy were used to study eight grains of pampaloite. Pampaloite forms inclusions (5–30 μm) in quartz together with other tellurides (typically petzite), native gold and, less often, sulfides. In reflected light, pampaloite is white or creamy white in color with weak anisotropism and without internal reflections. The empirical formula calculated on the basis of 3 apfu is Au0.97–1.07Ag0–0.02Sb0.96–1.04Te0.96–1.04 (n = 18). The holotype pampaloite structure was used as a reference and provided the perfect match for an experimental EBSD pattern (12 bands out of 12, mean angle deviation 0.19°). Raman spectra are reported for the first time for this mineral. All studied pampaloite grains exhibit vibrational modes in the range 60–180 cm−1. Average peak positions are 71, 108, 125, 147 and 159 cm−1. According to experimental data for the Au-Sb-Te system, we estimate the upper temperature range of pampaloite crystallization at the Svetlinsk deposit to be 350–430 °C.
Display omitted
•PTX and stable isotope data for Au-Bi intrusion-related deposits of North-East Russia.•Au-Bi mineralisation was mainly formed at 400–250 °C and 0.1–1.9 kbar.•Brine and CO2-rich FIs ...coexist at shallow level, CO2-rich FIs occur at depth.•Magmatic fluid was enriched with light O, C and S isotopes due to fluid immiscibility.
Intrusion-related Au-Bi deposits of North-East Russia are related to Late Mesozoic orogenic S- and I-type granites of ilmenite series. The studied deposits differ in their position relatively to the plutons, alteration, ore body morphology and sulphide content in ores. Based on mineral composition of ores, studied deposits are divided into bismuth-sulphotelluride-quartz, bismuth-arsenide-sulpharsenide and bismuth-siderite-polysulphide types. Bismuth-sulphotelluride-quartz deposits (Levo-Dybinskoe, Kurum, Ergelyakh, Tuguchak, Basugunya) are characterised by low-sulphide (≤3 vol%) mineralisation. Native gold associates with bismuth minerals (bismuthinite, sulphotellurides and tellurides, maldonite, jonassonite, native bismuth). Bismuth-arsenide-sulpharsenide deposits (Myakit, Chepak, Dubach, Chistoe, Kandidatskoe) host As-rich mineralisation. Löllingite and arsenopyrite are main minerals, and their contents vary from 5 to 60 vol% (commonly ∼10%). The intergrowths of native gold with bismuth minerals (sulphotellurides, tellurides, native bismuth) occur mainly in arsenopyrite. Bismuth-siderite-polysulphide (Arkachan) type is characterised by high-sulphide (5–15 vol%) and high-carbonate (up to 35 vol%) ores. Native gold associates with bismuthinite and other sulphobismuthites. Minerals of tellurium are rare. Fluid inclusion and stable isotope study of samples from eighteen Au-Bi deposits constrains the fluid composition, formation temperatures, pressures, and fluid sources. Four types of fluid inclusions (FI) were revealed: (I) two-phase FI, consisting of H2O liquid and CO2 vapour, and three-phase FI with H2O liquid, CO2 vapour and CO2 liquid; (II) vapour-rich CO2 one- or two-phase FI with minor (rarely dominant) CH4 and N2, sometimes with a thin liquid rim; (III) two-phase liquid-vapour aqueous inclusions; (IV) three- or multiphase FI, consisting of H2O liquid, gas bubble and one or more daughter minerals. Au-Bi mineralisation formed at 437–200 °C (mainly from 400 to 250 °C) and 0.1–1.9 kbar from a H2O-CO2-NaCl fluid, which forms an immiscible brine and CO2-bearing vapour at low pressure (≤1.3 kbar) as well as low- to moderate salinity CO2-H2O mixtures without brines at higher pressure (≥1.3 kbar). The studied deposits formed at shallow (Ergelyakh, Tuguchak, Arbatskoe at 1–2 km, Kurum, Levo-Dybinskoe at 2–3 km) and deep (Chuguluk, Shkolnoe, Arkachan at ∼4 km, Dubach at >5 km) depth. Bismuth-sulphotelluride-quartz deposits commonly occur at shallow depth, whereas bismuth-arsenide-sulpharsenide and bismuth-siderite-polysulphide deposits are mainly formed in deeper environment. The stable isotope data suggest predominantly magmatic source of gold-bearing fluids, but magmatic fluid was enriched in light O, C and S isotopes as a result of fluid immiscibility. The magmatic source is consistent with the overlap in lead isotope compositions of ores and related intrusions, as well as synchronism of magmatism and hydrothermal activity according to geochronology data.
Inductively coupled plasma-mass spectrometry (ICP-MS) has been used to determine rare earth element concentrations in aqueous solutions extracted from fluid inclusions. Quartz has been sampled from ...ores of three major types of polygenic gold hydrothermal systems of North-Eastern Russia: (1) gold-quartz-sulphide (Au-Q, Nezhdaninsk); (2) gold-antimony (Au-Sb, Sarylakh) and (3) intrusion-related gold-bismuth-siderite-polysulphide (Au-Bi-Sid, Arkachan) large deposits located in terrigenous rocks of the Verkhoyansk fold belt. The total concentration of REE in the fluid inclusions is not high (up to 52 ppm). The contribution of LREE dominates in REE balance (ΣLREE/ΣHREE=7.4–112.1). The chondrite-normalized REE patterns of inclusion fluids for the Au-Q and Au-Bi-Sid deposits are characterized by LREE enrichment with a positive or negative Eu anomaly. REE patterns for the regenerated quartz from Au-Sb deposits are characterized by pronounced differentiation between light and heavy lanthanides in fluid inclusions. Significant total REE concentration decreasing (on 1–2 order) from early to late stages of Nezhdaninsk and Arkachan deposits is revealed. The positive correlations of total REE concentrations with Rb, Cs, Li and B contents in fluid inclusions are shown. The REE distribution in fluid inclusions can be used as indicators of the contribution of magmatic fluid in the hydrothermal system.
Display omitted
•The Berezovsk deposit is the oldest gold mine in the Urals and in Russia and is still in production.•Mineral and metal zoning occurs in the roof of the Shartash granite massif.•Gold ...ores were formed at 300–230°C and 0.3–2.3kbar (mostly 0.5–1.2) from the H2O-CO2-CH4-NaCl fluid with salinity 7.3–18.2wt% NaCl equiv.•Magmatic fluid evolved as a result of phase separation and mixing with fluid derived from decarbonation and dehydration of host rock and with meteoric water.
The Berezovsk gold deposit in the Middle Urals has been mined for 270years. Its endowment (past production and gold reserves) is estimated to be 490t of gold. The deposit is located in the greenschist metamorphosed Silurian volcanogenic-sedimentary rocks intruded by granitoid dykes to the north-east of Late Carboniferous Shartash granite massif. Mineralisation is represented by sulphide-quartz veins in the granitoid dykes (“ladder” veins) and in the host rocks (“krassyk” veins) formed in the following four stages: ankerite-quartz, quartz-pyrite, gold-polymetallic and carbonate. Ore veins are accompanied by halos of gumbeite (quartz+orthoclase+carbonate), beresite (quartz+sericite+ankerite+pyrite) and listvenite (quartz+Fe-Mg carbonate+fuchsite+pyrite). The veins mainly consist of quartz with sulphide minerals (commonly 3–5vol%). About 180 minerals have been identified in ores, but the most abundant minerals are quartz, calcite, ankerite, pyrite, galena, tennantite, chalcopyrite, aikinite, native gold, and sphalerite. Native gold was deposited during quartz-pyrite (Au I) and gold-polymetallic (Au II) stages. Fineness of gold ranges from 863 to 984 and from 723 to 848 for Au I and Au II, respectively. The mineral and metal zoning was identified relative to the roof of the Shartash granite massif. The fluid inclusion study revealed that the gold mineralisation at the Berezovsk deposit was formed at 300–230°C and 0.3–2.3kbar (mostly 0.5–1.2kbar), from a H2O-CO2-NaCl fluid with salinity of 7.3–18.2wt% NaCl equiv. The fluid was separated into H2O-CO2-NaCl and CO2-rich fluids due to temperature and/or pressure drop at the deposition site. Calculated δ18O and δD values are 5.2–8.1‰ and −39 to −63‰, respectively, for the fluid in equilibrium with alteration assemblages. The average δ13C value for the fluid equilibrated with carbonates from the inner zones of metasomatic halos is −5.3‰. The calculated δ18O and δ13C values are 3.0–9.6‰ and −3 to −9‰, respectively, for ore-forming fluids. The δ34S values are 1.4–12.9‰ and −1.6 to 11.7‰ for the fluid in equilibrium with early and late sulphides, respectively. In addition to the isotopic data, the geological, mineralogical and fluid inclusion data confirmed the predominant contribution of the magmatic fluid to formation of the Berezovsk hydrothermal system. The light C, O, and S isotope enrichment of the fluid was mainly caused by fluid phase separation. Fluids generated by decarbonation and dehydration reactions due to the contact metamorphism of the host rocks during the Shartash massif emplacement were responsible for additional 34S input. The ore-forming fluid was enriched in the light 16O isotope on the deposit flanks indicating the mixing with heated meteoric water.
PDF
