Bi Minerals Research Articles

Lazerckerite, Ag3.75Pb4.5(Sb7.75Bi4)S24, from Kutná Hora, Czech Republic: a new Sb–Bi member of the andorite branch of the lillianite homologous series

Abstract. Lazerckerite, ideally Ag3.75Pb4.5(Sb7.75Bi4)S24, is a new mineral species found in medieval mine dumps of the historic Ag–Pb–Zn Kutná Hora ore district, Czech Republic. The mineral is associated with other Sb–Bi lillianite homologues (terrywallaceite, gustavite, holubite) and Ag,Bi-bearing galena, most frequently as grain aggregates and replacement rims of earlier Ag–Pb–Bi minerals, growing together in aggregates of up to 0.6×0.3 mm. Lazerckerite is opaque, is steel grey in colour, and has a metallic lustre; the calculated density is 5.920 g cm−3. In reflected light lazerckerite is greyish white, and bireflectance and pleochroism are weak with grey tints. Anisotropy is weak to moderate with grey to bluish-grey rotation tints. Internal reflections are not observed. Electron microprobe analyses yielded the empirical formula, based on 44 apfu, (Ag3.61Cu0.04)Σ3.65(Pb4.55Fe0.01Cd0.01)Σ4.57(Sb7.87Bi3.75)Σ11.62(S24.15Se0.01)Σ24.16. Its unit cell parameters are a=13.2083(9), b=19.4595(8), c=8.4048(13), β=90.032(7)°, V=2160.3(4) Å3, space group P21/c, and Z=2. The structure of lazerckerite contains two Pb sites (Pb1 and Pb2) in bicapped trigonal prismatic coordination, 8 independent octahedral sites, and 13 distinct sulfur positions. Four of the octahedral sites are mixed (Sb,Bi) and (Bi,Sb) sites, one is a mixed (Ag,Bi) site, and one is a mixed (Sb,Pb) site. The new mineral belongs to the andorite branch of the lillianite homologous series with N=4 and is a new addition to the group of Sb–Bi mixed members of the series. Lazerckerite is defined as a lillianite homologue with the three following requirements: N=4, L (Ag++ (Bi3+, Sb3+) ↔ 2 Pb2+ substitution) ≈ 90 %–95 %, and approximately one-third of atom percentage of antimony is replaced by bismuth (Bi/(Bi+Sb) ≈ 0.30–0.38). The new mineral has been approved by the Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association (IMA 2022-113) and named after Lazarus Ercker, the supreme Royal Bergmeister of the Kingdom of Bohemia and the Master of Prague Mint.

Timing and Evolution of Gold Mineralization in the Maljavr Occurrence (NW Russia), NE Part of the Fennoscandian Shield

Gold occurrence Maljavr is the first Archean conglomerate-hosted gold mineralization found in the Fennoscandian Shield. Gold-mineralized metasomatic rocks form a set of lenses within a 10 m thick linear zone, conformable to the bedding of host conglomerates. The lenses are up to 10 m long and up to 1 m thick and they clearly exhibit three alteration envelopes: the rock in the central part consists of garnet and quartz or garnet-only; biotite, garnet, and quartz make the intermediate biotite–garnet envelope; hornblende, hedenbergite, and quartz are the principal rock-forming minerals in the outer zone of the lenses. All metasomatic rocks contain sulfide mineralization up to 15–20 vol.% and up to 0.6 g/t Au. The main ore mineral is pyrrhotite, and the minor minerals are arsenopyrite, chalcopyrite, pentlandite, löllingite, and troilite. The age of zircon from biotite gneiss in the zone of alteration is 2664 ± 18 Ma, this is considered as the time of formation of lenses of metasomatic rocks. Biotite gneiss-conglomerate and metasomatic rocks were later intruded by tourmaline granite pegmatite 2508 ± 7 Ma. The injection of pegmatite caused re-crystallization of sulfides (mainly arsenopyrite and löllingite) and redistribution of gold. Visible gold in association with Bi minerals native bismuth, ehrigite, maldonite, bismuthinite, joseite-B, and hedleyite was found in inclusions in recrystallized arsenopyrite and löllingite. Au content in the rocks with recrystallized arsenopyrite and löllingite is >1 g/t, up to 30 g/t in hand samples. The 2508 Ma pegmatite is interpreted as synchronous with formation of gold mineralization in its present form. The linkage of gold mineralization with pegmatite and geochemical association Au-As-Se-Te-Bi in the mineralized rocks agree with characteristics of intrusion-related gold deposits worldwide. Biotite gneiss–metaconglomerate, hosting the mineralized altered rocks, was the probable primary source of arsenic and gold for mineralization.

Overview of early cretaceous gold mineralization in the orogenic belt of the eastern margin of the Siberian craton: geological and genetic features

The giant Verkhoyansk-Kolyma gold province, producing more than∼ 3700 t of gold, is one of the most important metallogenic provinces for orogenic gold deposits in the world. The province is located on the eastern margin of the Siberian craton. The main types here are multistage orogenic Au-As and orogenic-like Au-Sb types of mineralization, related to the Late Jurassic-Early Cretaceous metallogeny and the evolution of the convergent margin. These deposits were formed in the environment of late orogeny during two metallogenic stages—the Late Jurassic-Early Cretaceous collision-related (early stage/stage one, 135–150 Ma) and the Early Cretaceous subduction-related (late stage/stage two 114–130 Ma). The common features, differences and genetic nature of the deposits of these two metallogenic stages have been debated for a long time. To improve the understanding of these problematic issues and the genesis of deposits, and control over them by the mantle lithosphere, we consider here the Early Cretaceous orogenic belts of the eastern margin of the Siberian craton. Orogenic belts are related to the development of the paleo-Arctic and paleo-Pacific margins of Siberia. The tectonic, geochronological, mineralogical and geochemical specificity of the deposits of the orogenic belts are shown. A regional metallogenic overview of gold deposits is performed using data on the age of mineralization and the isotopic composition of sulfur sulfides. A preliminary model of the origin of late stage mineralization is proposed in connection with the processes of the Okhotsk-Koryak orogenic belt formation. Increased concentrations of siderophilic and chalcophilic elements, the Ni, Bi minerals presence in the ores, relatively high fineness of gold, predominance of juvenile sulfur in the isotopic composition of sulfide sulfur, аnd the control by large trans-crustal faults as well as spatial and chronological association with initial (dike) magmatism indicate mantle sources of ore fluids. This mineralization within the orogenic belts of the eastern margin of the Siberian craton assumingly appeared due to dehydration of the submerged slab and local upwelling in the mantle in the rear of the active continental margin. The possibility of the gold-bearing fluids existence in such conditions is estimated. The metallogenic specific nature of collision-related and subduction-related orogenic Au is defined. The proposed model can be useful for the analysis of polychronous orogenic Au-As and orogenic-like Au-Sb metallogeny of orogenic belts on craton margins globally.

НОВЫЕ ДАННЫЕ О МИНЕРАЛОГИИ, ГЕОХИМИИ И ГЕНЕТИЧЕСКИХ ОСОБЕННОСТЯХ БЕЛОГОРСКОГО МАГНЕТИТОВОГО МЕСТОРОЖДЕНИЯ (СИХОТЭ-АЛИНЬ)

New data are in favor of the view previously substantiated by geological, geochemical and isotopic data that orebodies of the Belogorskoe deposit are metamorphosed and partially regenerated in the Late Cretaceous-Paleogene products of erosion (in the Triassic) of laterite weathering crust of gabbroids. The source for the formation of the Belogorskoe deposit was shown to be products of exogenous destruction of rocks, which by their isotopic and geochemical characteristics are close to the Cambrian gabbroids of the Vladimiro-Alexandrovsky massif (the southern part of the Okrainsko-Sergeevsky terrane). It has been found that the Belogorskoe deposit is composed of rocks and ores, the primary (magmatic) distribution of REE in which was changed to varying degrees as a result of interaction between sediments (protoliths) and seawater (presumably during the Late Jurassic-Early Cretaceous accretion), as well as their metamorphosed analogues and hydrothermal solutions (in the Late Cretaceous-Paleogene). The influence of gabbroids (as a source of matter) on the chemical and mineral composition of the Belogorskoe deposit is consistent with the data reported in the article concerning the enrichment of orebodies in such elements as Fe and Mn that are characteristic of ultrabasic rocks and the presence of Au-Ag-Pd-Pt, Ni-Co and Bi mineralization in them. The orebodies of the Belogorskoe deposit contain accessory minerals and mineral varieties that are rarity in nature and little-studied. These include an unusually rich Th variety of zircon, baddeleyite, gudmundite, a large group of bismuth compounds, including Bi2Te, (Ag,Pb)BiS2, as well as coloradoite, lafossaite, sanbornite, perovskite, and the compound InPO4. There is also a large group of rare and unusual compounds of noble metals: copper gold, platinum gold, jonassonite, disordered solid solutions of Cu, Ag and Au (Au-based), Pt-Pd, Pt-Ag intermetallics, and other rare minerals and mineral varieties.

Gersdorffit, tyrolit a Bi-minerály z žilné Cu mineralizace z lomu Smrčník u Lipové-lázní u Jeseníku (Česká republika)

A previously unknown primary Ni-As-Bi and supergene As-Bi mineralization was found in the active marble quarry Smrčník located 2 km WNW of the village of Lipová-Lázně, 7 km WNW of Jeseník, Rychlebské hory Mountains, Czech Republic. An electron-microprobe study of newly collected samples from a weakly Cu-mineralized quartz-carbonate vein cutting the marbles showed the presence of gersdorffite, bismuthinite, an unidentified Cu-Bi sulphide, bismite, and tyrolite, which were not known from the wider area. The microscopic grains of gersdorffite are part of primary ore mineralization of the studied vein with prevailing chalcopyrite, which is in places rimmed by chalcocite and djurleite. Nickel is partly replaced especially by Co (0.002 - 0.246 apfu) and Fe (0.030 - 0.158 apfu), less by Cu (0.008 - 0.038 apfu), whereas arsenic is weakly substituted by Sb (0.008 - 0.083 apfu) and in part of collected analyses by Bi (0.001 - 0.033 apfu) in the studied gersdorffite. All mentioned Bi minerals hosted by chalcopyrite were recorded in a single aggregate only. The blue-green tyrolite is a rare compound of supergene mineral assemblage of the same vein. Its chemical composition is characterized by small contents of S (0.050 - 0.248 apfu), P (0.052 - 0.104 apfu), and mostly also Cl (0.022 - 0.070 apfu). The new findings suggest much richer mineralogical and chemical variability of primary (hypogene) mineralization of hydrothermal veins, than was indicated by previous studies in the wider area.

Micro- to nanoscale textures of gold in arsenopyrite and scorodite from the As-Au-Bi assemblage of Drenjak locality (Serbia)

Arsenopyrite and pyrite are important carriers of Au that is present in the form of microscopic and “invisible” gold. Such gold can be expected to be released upon the process of oxidation of these sulfides. In studied gold mineralization at Drenjak, related to the granitoids of the Oligocene-Miocene Kopaonik Ore District, the main arsenopyrite-pyrite-(bismuthinite) sulfide assemblage was formed in the quartz bodies and partly replaced by scorodite (FeAsO4·2H2O) and Bi-arsenate. With only up to 5 ppm of gold recorded by LA-ICP-MS, aforementioned sulfide minerals are here practically free from lattice-bound gold. Native gold is present in the mineralization, generally ranging in grain size from 20 µm down to the nanoparticles, as revealed by TEM. It is mainly hosted by arsenopyrite and scorodite. In arsenopyrite, gold is polycrystalline and consists of nanocrystallites 20–30 nm in size. It was deposited after arsenopyrite, healing its cavities and microcracks, often associated with native bismuth and bismuthinite. The abundance of gold and Bi minerals correlates with the presence of scorodite. Two types of gold are present in scorodite and Bi arsenate: i) prevailing relict Au grains retained after arsenopyrite oxidation, ii) colloidal-like gold co-precipitated with the arsenates. Based on our observations, we additionally present and discuss indications of low-temperature hydrothermal origin of scorodite, formerly known only as a weathering product

Bismuth minerals from Yugo-Konevo and Porokhovskoe tungsten deposits (South Urals)

A mineral assemblage including sulfosalts of the bismuthinite-aikinite (aikinite, bismuthinite, gladite, salzburgite, krupkaite, lindstromite, pekoite, friedrichite, hammarite), pavonite (makovickyite, cupromakovickyite, pavonite, dantopaite, mummeite), cupropavonite (cupromakopavonite, cupropavonite) and lillianite (lillianite s.s.) homologous series, as well as angelaite, berryite, matildite, baksanite, ikunolite, tetradymite, hedleyite and native bismuth is identifed in veinlet ores of the Yugo-Konevo and Porokhovskoe tungsten deposits (Chelyabinsk oblast, South Urals). The Bi minerals occur as individual grains or intergrowths in fuorite-muscovite-quartz veins with hubnerite and scheelite , inclusions in quartz and intersticial aggregates between pyrite, sphalerite and galena. Angelaite, dantopaite, cupromakovickyite and cupromakopavonite are frst found at the territory of Russian Federation and salzburgite, cupropavonite, makovickyite and mummeite are found for the frst time in the South Urals.

Petrochemistry, rare metals-bearing minerals and spectrometric exploration in Khour Abalea, Abu Rusheid area, Eastern Desert, Egypt

On the Red Sea coast, Abu Rusheid area is located south Marsa Alam City (90 km) in the south Eastern Desert. Khour Abalea as a part of the Abu Rusheid area extends for about 1.0 km in E-W direction. It is subdivided into two main branches; the first one (the longest) extends about 0.7 km in E-W direction with 10–30 m in passing through mylonites, whereas the second branch extends about 0.5 km in ENE-WSW with about 5–20 m in width and passing through mylonites and ultra-mylonites. Microscopically, this rock is composed mainly of k-feldspars, plagioclases, biotite, and quartz as the main minerals, while the accessories include fluorite, allanite, secondary uranium (kasolite), and zircon. The hydrothermal alteration that occurs during the interaction of hydrothermal fluid and rock results in an M-W type tetrad effect range of 1.72–3.66 in the normalized REE chondrite patterns of the Khour Abalea mylonite rocks. The identified heavy minerals associated with Khour Abalea mylonite rocks can be categorized as a) radioactive minerals (soddyite, kasolite, thorite and uranothorite), b) rare earth minerals (monazite, xenotime and rare earth silicate), c) Nb–Ta minerals (columbite, fergusonite, ishikawaite and aeschynite), d) precious metals (gold, silver minerals (argentite, arcubisite and matildit), e) base metals (cassiterite, wolframite, chalcocite, galena, sphalerite pyrite and Bi minerals (bismite, bismuthinite and perite) and f) accessory mineral (zircon). According to the uranium mobilization equations, there are uranium enrichment in Khour Abalea mylonite.

The Volyn biota (Ukraine) – indications of 1.5 Gyr old eukaryotes in 3D preservation, a spotlight on the “boring billion”

Abstract. The Volyn biota, fossilized organisms with a minimum age of 1.5 Ga, were found in cavities in granitic pegmatites from the Korosten Pluton, NW Ukrainian shield. Fossilization was due to an influx of hydrothermal fluorine-rich waters, which silicified the outermost part of the organisms, thus preserving the 3D morphology. Details of the morphology (investigated by scanning electron microscopy) show that the majority of the specimens are filamentous, of a large variety with diameters ranging from ∼ 10 to ∼ 200 µm, thin filaments with typical branching and thick filaments with ball-shaped outgrowths and dented surface. Filaments can be straight or conical, curvilinear, or strongly curved, up to millimeters in length, some with a central channel. Some filaments show indications of segmentation and are grown as sessile organisms onto substrate; others show both intact ends, indicating a non-sessile, free-living lifestyle. Objects with flaky morphology and agglutinating filaments are interpreted as fossil biofilms. Other objects are hollow and show a large variety of forms; spherical objects are scarce. Infrared spectroscopy indicates the presence of chitosan in one filament type, electron microprobe analysis of nanometer-sized inclusions in filaments identified the presence of Bi(Te,S) minerals, and both observations are compatible with the interpretation as fungi-like organisms. Stable C- and N-isotope data of bulk samples are in the range of −31 ‰ to −47 ‰ δ13C and of +3 ‰ to +10 ‰ δ15N, indicating possible methanogens as part of the subsurface microecosystem. The Volyn biota indicate that at 1.5 Ga complex forms of life existed in the continental deep biosphere, well above the microscopic level, including fungi-like organisms resembling eukaryotes.

Holubite, Ag3Pb6(Sb8Bi3)Σ11S24, from Kutná Hora, Czech Republic, a new member of the andorite branch of the lillianite homologous series

AbstractA new mineral species, holubite, ideally Ag3Pb6(Sb8Bi3)Σ11S24, has been found at Kutná Hora ore district, Czech Republic. The mineral is associated with other lillianite homologues (gustavite, terrywallaceite, vikingite and treasurite) most frequently as grain aggregates and replacement rims of earlier Ag–Pb–Bi minerals, growing together in aggregates up to 200 × 50 μm. It typically occurs in a close association with Ag,Bi-bearing galena and terrywallaceite. Holubite is opaque, steel-grey in colour and has a metallic lustre, the calculated density is 5.899 g/cm3. In reflected light holubite is greyish white and bireflectance and pleochroism are weak with grey tints. Anisotropy is weak to medium with grey to bluish-grey rotation tints. Internal reflections were not observed. Electron microprobe analyses yielded an empirical formula, based on 44 atoms per formula unit (apfu) of (Ag3.03Cu0.03)Σ3.06(Pb6.19Fe0.02Cd0.01)Σ6.22(Sb7.71Bi2.90)Σ10.61S24.12. Its unit-cell parameters are: a = 19.374(4), b = 13.201(3), c = 8.651(2) Å, β = 90.112(18)°, V = 2212.5(9) Å3, space group P21/n and Z = 2. Holubite is a new member of the andorite branch of the lillianite homologous series with N = 4. The structure of holubite contains two Pb sites with a trigonal prismatic coordination, eight distinct octahedral sites, of which one is a mixed (Bi,Ag) site and one is a mixed (Sb,Pb) site, and twelve anion sites. Holubite is defined as a lillianite homologue with the three following requirements: N = 4, L% [Ag+ + (Bi3+,Sb3+) ↔ 2 Pb2+ substitution] ≈ 70% and approximately one quarter to one third at.% of antimony is replaced by bismuth [Bi/(Bi+Sb) ≈ 0.26–34]. The new mineral has been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2022-112) and named after Milan Holub, a key Czech geologist and specialist in the Kutná Hora ore district.

Role of metasomatized mantle lithosphere in the formation of giant lode gold deposits: Insights from sulfur isotope and geochemistry of sulfides

The Wulong deposit is one of the largest quartz vein-type gold deposits with at least 80 tons of identified gold reserves in the eastern part of the Liaodong Peninsula. Gold orebodies are mainly hosted in the Late Jurassic gneissic two-mica granite and Early Cretaceous diorite dykes, and are structurally controlled by the NNE- and NW-trending faults. Gold mineralization mainly occurs as veins with lenticular shapes and is closely associated with sulfides and Bi minerals. Previous studies on the deposit mainly focused on its geological characteristics, fluid inclusions and the timing of gold mineralization. However, the extreme enrichment mechanism of gold, the geodynamic setting and ore source of the gold deposit remain equivocal. Here we present results from geochemical studies of pyrite and pyrrhotite at Wulong to address these issues. Pyrrhotite can be grouped into euhedral (Po1) and anhedral (Po2) varieties based on the textures. Four generations of pyrite were identified based on petrographic studies: Py1 is coarse-grained subhedral to euhedral crystal coexisting with milky quartz, and Au-depleted in composition; Py2 is represented by medium-grained, subhedral to anhedral pyrite coexisting with euhedral Po1, smoky quartz and minor chalcopyrite; Py3 occurs as fined-grained anhedral grains in the quartz-polymetallic sulfide veins; Py4 occurs as veinlets or aggregates in the quartz-calcite veins and contains the lowest Au concentrations. The time-resolved LA-ICP-MS ablation depth profiles of sulfides combined with detailed petrological observations indicate that gold mainly occurs either as invisible solid solution within the crystal lattice of sulfides, to some extent, or as small blebs of native gold and electrum. The close temporal and spatial relationships among native bismuth, native gold and Bi-Te-S minerals suggest that Bi-rich melts may have significantly sequestered gold from the hydrothermal fluids in the Wulong gold deposit. Sulfides from auriferous quartz veins have a restricted Δ33S range (−0.2‰ to +0.2‰) and a mean δ34S value of +1.25‰ with a feature of the mass-dependent fractionation (MDF) of sulfur isotopes, implying that the ore-forming materials were potentially derived from the mantle lithosphere that was metasomatized and fertilized by subduction-related fluids released from slab during the Early Cretaceous. This study demonstrates the Bi-rich melts as significant gold scavengers in As-deficient ore-forming fluid, and highlights the fundamental role of the metasomatized and fertilized mantle lithosphere in the formation of giant lode gold deposits in the eastern North China Craton at ca. 120 Ma.

Mineralogy and geochemistry of Cu-Ni±Co±Ag±Bi polymetallic ores from the Hintermühlergang vein in the Chełmiec deposit, Sudetes Mountains, Poland

Chełmiec is a hydrothermal vein-type carbonate-sulphide deposit in the Kaczawa Mountains, where polymetallic Cu-Ni±Co±Ag±Bi mineralization occurs. Samples, collected from an old dump of the Hintermühlergang vein, were studied by reflected light microscopy and electron microprobe. Two mineral parageneses, Ni-Co±Bi and Cu-Zn-Pb±Sb±Ag, associated with two stages of precipitation, were discovered in samples from the Chełmiec deposit. The first stage is associated with quartz, and is represented by pyrite, arsenopyrite, gersdorffite, cobaltite, bismuth minerals (native Bi, bismuthinite, and matildite), pyrrhotite, marcasite and chalcopyrite. The second stage associated with siderite and quartz is represented by sulphides (sphalerite, chalcopyrite, galena, pyrite), tetrahedrite group minerals [tetrahedrite-(Fe), tetrahedrite-(Zn), tennantite-(Zn), and argentotetrahedrite-(Fe)], gersdorffite and bournonite. Two generations of sulpharsenides were discovered in the samples studied. The first is represented by massive gersdorffite-cobaltite aggregates, the second generation occurs as tiny zoned gersdorffite crystals. Sulpharsenides are characterized locally by presence of high amounts of As (up to 1.55 apfu). Silver in the Chełmiec ores is hosted mainly in tetrahedrite group minerals [from 0.07 to 2.07 apfu in tetrahedrite – (Zn) and -(Fe), and from 4.37 to 4.90 apfu in argentotetrahedrite-(Fe)], less in matildite. In the Sudetes, the presence of massive sulpharsenides is rare, whereas freibergite is much more common.

Precious metal mineralization in gabbroids of the Kumba intrusive, the uralian platinum belt (North Urals)

The paper presents the frst data on the distribution and composition of copper-noble metal mineralization in gabbroids of the Kumba intrusive (North Urals). The noble metal mineralization is associated with digenite-bornite, bornite-chalcopyrite, and pyrite-chalcopyrite ores and mainly occur minerals of precious metals. Nine noble metal mineral species are found for the frst time in amphibole and amphibole-olivine gabbro of the Kumba intrusive: native gold, Au-Ag alloys, Au, Ag, and Pd tellurides (hessite, merenskiite), Bi tellurides (kotulskite), antimonide-arsenides (isomertieite), arsenides (arsenopalladinite, sperrilite), and stannides (atokite) of Pt and Pd. Noble metal minerals from all sulfde assemblages in heavy concentrates are often accompanied by antimonides (stibnite) and Bi mineralization represented mainly by native bismuth and bismuthinite and less common sulfotellurides (baksanite) and tellurides (tsumoite). Our results make it possible to estimate the prospects of the discovery of new copper-noble metal deposits hosted in gabbro of the Uralian Platinum Belt. Taking into account the principles of occurrence of noble metal and copper mineralization, most gabbro intrusives of the Uralian Platinum Belt can be considered the promising objects for large-tonnage copper deposits with associated ore Au and Pd grades.

The Baogutu gold deposit in west Junggar, NW China: An epizonal intrusion-related gold deposit

The Baogutu gold deposit (∼4 Mt ore @ 5.5 g/t Au) in West Junggar, is hosted by Early Carboniferous volcano-sedimentary rocks and Late Carboniferous dioritic dikes. Both the dikes and gold mineralization are controlled by NE-trending faults. Two diorite dikes in direct spatial association with gold-bearing quartz veins have LA–ICP–MS zircon U–Pb ages of 316 ± 5 Ma and 314 ± 3 Ma, respectively. The emplacement ages of the dikes are a little older than reported gold mineralization ages (312–311 Ma), which is consistent with their crosscutting relationships. Gold mineralization occurs in quartz veins and stockworks in altered tuff, tuffaceous siltstone, silty mudstone, and dikes. Three gold-bearing vein stages have been identified: (I) pyrite–quartz veins in the deep part of the system; (II) stibnite–quartz veins and (III) native arsenic–quartz veins at shallower-level. Fluid inclusion study shows that the pyrite–quartz veins of stage I formed at temperatures between 345 and 265 °C from fluids with salinities of 5.1–9.1 wt% NaCl equiv, whereas the native arsenic–quartz veins of stage III formed at ∼200 °C from fluids with salinities of 1.4–3.9 wt% NaCl equiv. The ore-forming pressure is estimated to be ∼50–62 MPa, corresponding to mineralization depth of ∼3.3–4.0 km. Oxygen and hydrogen isotope compositions of the fluids (δ18OH2O = 7.9 to 11.2 ‰, δD = -88 to −96 ‰) indicate that the initial hydrothermal fluids have a magmatic source, with involvement of meteoric water in the late stage. The in-situ lead isotopic compositions of pyrite in stage I pyrite–quartz veins are similar to those of bulk sulfide minerals in the Baogutu porphyry Cu deposit, and close to the porphyry stocks, whereas the stibnite and native arsenic in stage II and III quartz veins have more radiogenic lead isotopic signatures due to water–rock exchange with the wall rocks. The Baogutu gold deposit shows affinities to epizonal gold deposits in intrusion-related gold systems (IRGS). The IRGS model suggests that, sheeted, disseminated and vein-type Au–As–Bi mineralization might be found hosted in dioritic to granitic stocks and proximal strata, and vein-type Au–As–Sb mineralization in distal faults.

Geology, mineralization, igneous geochemistry, and zircon U-Pb geochronology of the early Paleozoic shoshonite-related Julia skarn deposit, SW Siberia, Russia: Toward a diversity of Cu-Au-Mo skarn to porphyry mineralization in the Altai-Sayan orogenic system

The small but high-grade (average 1.29% to 2.04% Cu and 0.09–0.12% Mo for different orebodies, with also significant Au contents) Julia skarn Cu-Au-Mo deposit is situated some 30 km northeast from the Sorskoe porphyry Mo-Cu deposit in the Kuznetsk Alatau, a Paleozoic terrane in the northernmost part of the Altai-Sayan orogenic system, part of the Central Asian Orogenic Belt. The deposit comprises prograde calcic skarns and later retrograde skarn characterized by abundant andradite-rich garnet defining their oxidized type. These alteration assemblages bear abundant Cu sulfides (chalcopyrite and bornite), which are associated with magnetite and are partially overprinted by weak propylitic and stronger phyllic (carbonate-phyllic) alteration assemblages. Molybdenite is present in these assemblages, and various sulfides and sulfosalts, tellurides, and Bi minerals, as well as native Au are associated with phyllic alteration.The deposit is related to a magnetite-series, I-type, multiphase monzonite-syenite(-quartz syenite)-quartz monzonite-monzogranite igneous complex. Isotopic U-Pb zircon data indicate a Late Cambrian age (∼505 to 485 Ma) of the igneous rocks, whereas their geochemical signatures correspond to high-K calc-alkaline to shoshonitic intrusions emplaced in a post-collisional environment, with possible relationships to a subducted slab break-off. Magmatic evolution included a generation of shoshonitic magma by a low-degree partial melting of the metasomatically-enriched upper mantle, followed by amphibole fractionation in a deep (lower crustal?) magma chamber and then by magma fractionation and emplacement at shallower crustal levels. Although the overall magmatic evolution of the parental intrusions was long-lasting (ca. 20 m.y.), the mineralization is associated with a relatively rapid (ca. 5 m.y.) emplacement of more differentiated granitoid intrusions as well as late mafic dikes.The deposit represents an early Paleozoic (Late Cambrian) Cu-Au(-Mo) mineralization in the Altai-Sayan orogenic system and the broader Central Asian Orogenic Belt, thus confirming the Late Cambrian (to Early Ordovician) Cu-Au-Mo metallogenic event in the region. This, together with the broad regional occurrence of the Cambrian-Early Ordovician igneous complexes and related porphyry/skarn Cu-Au(-Mo) mineralization, emphasizes the early Paleozoic porphyries/skarns as a major regional event prior to much better known late Paleozoic porphyries/skarns in the Central Asian Orogenic Belt. There is a potential of the early Paleozoic terranes to host much more significant Cu-Au(-Mo) mineralization including that of skarn, porphyry and associated types.

The Glafirinskoe and related skarn Cu-Au-W-Mo deposits in the Northern Altai, SW Siberia, Russia: Geology, igneous geochemistry, zircon U-Pb geochronology, mineralization, and fluid inclusion characteristics

The Glafirinskoe and related skarn Cu-Au (+Mo, W) deposits represent an Early Paleozoic (Late Cambrian to very early Ordovician) mineralization in the Altaid Belt, also known as the Central Asian Orogenic Belt. They are associated with multiphase plutons of high-K calc-alkaline to shoshonitic rocks that are related to a low-degree partial melting of metasomatically-enriched upper mantle, followed by amphibole fractionation in a deep (lower crustal ?) magma chamber and then by magma fractionation and emplacement at shallower crustal levels. Isotopic U-Pb zircon dating of the igneous rocks yields early Ordovician (ca. 480–478 Ma and 483 Ma) age. These rocks were emplaced in a continental magmatic arc after the Late Cambrian collision, in a post-collisional setting involving the stall and break-off of the subducting slab during the Late Cambrian to Early Ordovician.The deposits comprise prograde and retrograde skarns that are characterized by abundant andradite-rich garnet, which defines their oxidized type. Wider zones of potassic (quartz-K-feldspar) and calc-potassic (quartz-K-feldspar-calcite-garnet) alteration occur in the igneous rocks, with their further overprint by propylitic (with abundant scapolite) and phyllic (carbonate-phyllic) alteration. All these alteration assemblages bear abundant chalcopyrite and minor bornite. Phyllic alteration assemblages also contain various As, Sb, Pb, Zn, Co, Ni sulfides and sulfosalts, tellurides, Bi minerals, and native Au. Scheelite and/or molybdenite are locally present in some mineralized zones. The Cu-Au-Mo(-W) mineralization occurs as skarn orebodies that are spatially associated with porphyry-style alteration assemblages reflecting the high exploration potential for additional, but concealed, skarn-porphyry Cu-Au-Mo deposits in the vicinity.The retrograde skarn and potassic (calc-potassic) alteration assemblages were formed from high temperature (570–580 °C), high salinity, aqueous chloride magmatic-hydrothermal fluid, with its boiling and phase separation indicating hydrostatic conditions at a relatively deep (~6 km) skarn-porphyry environment. Propylitic alteration assemblages were formed at lower temperatures (~380–420 °C) from a Ca-Na-chloride, low salinity (~8 wt% NaCl-eq.) magmatic-hydrothermal fluid. Fluid inclusions in minerals from phyllic alteration assemblages indicate the influx of a CO2-rich fluid at about 270–290 °C and 1400 ± 50 bars and subsequent mixing with more saline (20 wt% NaCl-eq.) and cooler (~240 °C) hydrothermal fluids.

Estimation of Formation Temperature of the Noble Metal Mineralization of the Kovdor Alkaline-Ultrabasic Massif (Kola Peninsula)

In this work, mineralogical and geochemical data are presented for sulfide-rich phoscorites and carbonatites in the Kovdor massif. The PGE and Ag-bearing mineralization of bornite–chalcopyrite and Ag‑bearing mineralization of pyrrhotite–chalcopyrite associations were investigated. In carbonatite stage formation of massif, the noble metal minerals occurred during evolution of alkaline–ultrabasic melt and after separation of primary sulfide melt enriched in PGE, Au and Ag. According to the observed relationships, the minerals of PGE, Au, and Ag in bornite–chalcopyrite association are crystallized sequentially from magmatic to hydrothermal stages. Crystallization of Os, Ir, Pt and Pd minerals (erlichmanite, rustenburgite, isoferroplatinum, mertieite–II, etc.) occurred at temperature close to 480°С, while further decrease in the temperature and an increase in the Cu and Fe activity in the melt leads to the crystallization of Sb, Pb, As, Bi and Te-bearing minerals (sperrylite, tatyanaite, moncheite, stumpflite, etc.). Formation of Au and Ag-bearing minerals (electrum, silver, stromeyerite, lenaite, etc.) occurred at temperatures below 300 °C with relatively low sulfur activity. In carbonatites and phoscorites of the middle and late magmatic stages enriched with magnetite, pyrrhotite–chalcopyrite association with silver-bearing minerals was formed at temperatures below 300°C. Ag-bearing minerals were produced during hydrothermal recrystallization of Cu–Fe–Ni sulfides at temperature close to 150°C.

Bismuth minerals from the intragranitic La Elsa NYF pegmatite, Potrerillos granite, Argentina: Monitors of fluid evolution from magmatic to hydrothermal stage

ABSTRACTThe NYF La Elsa pegmatite forms a subcircular, ∼30 m long, ∼20 m wide body enclosed in the parental Potrerillos granite, Las Chacras-Potrerillos batholith, Argentina. The pegmatite has a typical zonal internal structure with a volumetrically significant quartz core and pods of magmatic fluorite. Along with biotite, mostly in the outer units, tourmaline (schorl, fluor-schorl) is common to abundant in most pegmatite units. Accessory minerals include common strongly hematitized ilmenite and rare euhedral crystals of bismuthinite, up to 2 cm long, occurring at the transition between the blocky zone and the quartz core. The bismuthinite was significantly replaced by bismutite I according to the reaction Bi2S3(s) + CO2(aq) + 6O2(aq) + 3H2O(l) = Bi2CO3O2(s) + 3H2SO4(aq). Subsequently, bismutite I was replaced by bismutite II and kettnerite. The former requires an influx of Ca and F and its formation can be characterized by the reaction Bi2CO3O2(s) + 2Ca2+(aq) + 2F–(aq) + CO32–(aq) = 2CaBiCO3OF(s). At the late hydrothermal stages bismutite was replaced by clinobisvanite/pucherite during influx of V according to the reaction Bi2CO3O2s + 2H3VO4(aq) = 2BiVO4(s)+ CO2(aq) + 3H2O(l). All Bi minerals are close to the ideal formulae with only minor Pb and ±Cu in bismuthinite and its secondary products. The crystallization sequence of Bi minerals is magmatic bismuthinite (S2–) → early hydrothermal bismutite I (CO32–) → medium stage bismutite II + kettnerite (CO32–, F–) → late stage clinobisvanite, pucherite (VO43–). Pegmatite-derived early subsolidus fluids were enriched in CO2, which was confirmed by confocal Raman microspectroscopy of fluid inclusions in quartz and caused breakdown of bismuthinite to bismutite. Calcium and F, necessary for kettnerite formation, were released during alteration of magmatic fluorite at acidic conditions. Vanadium was supplied by meteoritic H2O enriched in elements from altered magmatic minerals (biotite, ilmenite), either from the pegmatite or from the host granite.

Gossan mineralogy, textures, and gold enrichment over the Au (As, Bi, Ag) deposit in the Buracão Area (Brasília Fold Belt, Brazil): Implications for gold prospecting in weathering profiles

The orogenic pyrite–rich Au (As, Bi, Ag) mineralization (up to 31 g/t) of the Buracão area is one of several orogenic deposits in the Brasilia Fold Belt (BFB; Central Brazil), exposed to tropical weathering that shows extensive oxidized profiles. The distribution and thickness of these gossan profiles lead to variable gold enrichments and uncertainties to gold prospecting in this region. In order to investigate physicochemical processes related to the evolution of the gossan cover and the supergene gold enrichment, we present mineralogical, textural and geochemical data from each zone of twenty gossan profiles in the Buracão area. These results show that the mineralogy and textures along the gossan profile reflect oxidation, hydrolysis, dissolution and precipitation processes controlled by different Eh–pH conditions, which are controlled by supergene conditions and hypogene ore composition. The geometry, distribution, and thickness of gossan profiles, as well as the style of gold occurrence, reflects textures of the hypogene orebodies, while the weathering has an important role in the gold chemical refining (i.e., increasing ca. 25% in gold fineness) and the distribution of gold grades along the profile.These points allowed us to identify that the leached spongy hematite–rich zone in the upper indigenous profile contains the higher fineness gold grades (i.e., the “bonanza level”), and Bi–minerals such as waylandite and bismutite that may be important pathfinders for high gold grades in these gossan profiles. Our results demonstrate that ore prospection in gossans over Au–As–Bi–Ag deposits should be done focusing on leached zones, different to that traditionally conducted in gossans related to base metal sulfide deposits that have focused on precipitation zones. The similarities between the hypogene mineralization of the Buracão area and many deposits in the BFB and worldwide encourage the application of this approach elsewhere, which improve gold prospecting in weathering profiles over orogenic deposits.

The Tumannoe Gold–Antimony Occurrence (East Sayan, Russia): Mineralogy, Fluid Inclusions, S and O Isotopes, and U–Pb and 40Ar/39Ar Age

The article discusses the features of the composition, age, and genesis of gold–antimony mineralization of the East Sayan based on the example of the largest Tumannoe ore occurrence. It is shown that objects of this type are rare in the considered region. In the course of studies, it was found that stibnite, pyrite, and arsenopyrite predominate in ores; Bi minerals (tetradymite, cobaltite, native Bi), antimonides and sulfosalts (zinkenite, chalcostibite, aurostibite, tetrahedrite, and andorite), and three generations of native gold are also present. The mineralization contains gold–bismuth and gold–antimony ore assemblages, which are the evolutionary products of a single ore-forming system, during which a sequential decrease in the PTX parameters of ore deposition occurred, where temperatures decreased from more than 380 to 180°С. Sulfur activity decreased during ore deposition, which led to the deposition of alternating ore assemblages from simple sulfides to sulfosalts, in the direction of increasing deposited components, and to the formation of different generations of native gold with a gradual increase in fineness from early to late assemblages. The results of mineralogical–genetic and isotope–geochemical studies evidence the magmatogenic nature of gold–antimony mineralization. The isotopic age of parent granitoids, obtained by LA-ICP-MS zircon dating, is Early Ordovician; age values are 491–486 Ma. 40Ar/39Ar dating of muscovite from ore veins shows a relatively young age value (439 Ma), which is due to the influence of late tectonic and thermal events associated with the Early Paleozoic orogeny occurred at that time throughout the territory of the present-day East Sayan.