Native Bismuth Research Articles

Native gold from alluvial deposits of the Kyvvozhsky district and its probable primary sources (Volsko-Vymskoe rise, Middle Timan)

Based on the study of typomorphic features of gold from alluvial deposits of the Kyvvozh region of Middle Timan, including industrial placers, the most probable genetic types of primary sources were determined. The size of gold particles varies widely, reaching the size of small nuggets; along with rounded ones, there are weakly rounded and unrounded particles. Many of them have undergone repeated deformations in the form of envelope-shaped bends, dents and tears. Most gold coins have high-fineness rims. Gold always contains Ag, sometimes Cu, Pd and Cu. Gold particles with a block structure with high-silver vein zones are often found. In intergrowths with gold and in the form of inclusions are noted in it pyrite, galena, and occasionally minerals of the cobaltine-gersdorfite series, ankerite, galenobismutite, native bismuth, aurostibite, and also sudovikovite (PtSe2), which was first identified in the region. Three types of gold have been identified: 1 – homogeneous silver-containing, 2 – block with highly silvery vein-like zones, 3 – rare silver-containing with impurities of Cu, Pd. The morphology, composition and structure of placer gold indicate its entry into placers from various sources, including nearby sources. Of greatest interest are the zones of development in Riphean rocks of hydrothermal veinlet-disseminated sulfide mineralization, oriented in the northwest direction, partially exposed during the development of placers. Gold with Cu and Pd impurities is most likely associated with derivatives of mafic magmatism. The Volsko-Vymskoe, as well as the Tsilemskoe and Chetlasskoe uplifts of Middle Timan can be considered promising in terms of primary gold content and deserve further study and prospecting.

Contribution of bismuth melts to gold endowment in the Baolun gold deposit, Hainan Island, South China

Bismuth (Bi) melts and related polymetallic alloys can efficiently scavenge gold (Au) from Au-unsaturated aqueous solutions, contributing to the Au endowment in many hydrothermal deposits. However, original evidence for Au–Bi melts is often poorly preserved due to post-precipitation alteration. This complicates investigation of the liquid bismuth collector model in hydrothermal Au deposits. Here we present primary evidence for the occurrence of Au–Bi melt in hydrothermal systems through an examination of the Au–Bi phases and textures in the Baolun Au deposit (Hainan Island). This study found that maldonite, native bismuth, Au–Bi symplectite and Au–Bi melt blebs appeared successively following the precipitation of native gold. Notably, large Au–Bi melt blebs were well preserved in natural systems due to the rapid cooling of fluids. The mineral assemblages and their corresponding fluid physiochemical conditions suggest that the evolution of the ore fluids at Baolun was characterized by a continuous reduction in Au and Bi concentrations and Au/Bi ratios alongside decreasing fluid temperatures and sulfur fugacity (fS2). These observations offer direct evidence for Au scavenging by Bi melts in a mesothermal (275–450 °C), low-fS2 and reduced hydrothermal system, aligning well with the Au–Bi binary phase evolution established in metallurgy. As the fluid cooled further, the Au–Bi phases were subsequently overprinted by later Te–S-rich fluids, as evidenced by the formation of bismuthinite, jonassonite, and joséite-A around the Au–Bi phases. Importantly, our study reveals that the Baolun Au deposit ischaracterizedby a Au–Bi–Te hydrothermal system and that the metamorphic country rocks at Baolun are the major source of Au, Bi, and Te.

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.

Paragenetic and geological setting of the Starra iron oxide copper–gold deposits, Mount Isa Inlier, Queensland, Australia: constraints on IOCG deposit models

The five Starra iron oxide copper–gold (IOCG) deposits, which are located in the Cloncurry district of the Mount Isa Inlier, NW Queensland, are hosted in a N-trending zone of deformed iron-rich metasedimentary rocks that are underlain by two mineralogically distinct mafic–intermediate meta-igneous rocks. Copper–Au mineralisation is subdivided into two stages—an early main stage that transitioned from a magnetite-dominated Cu substage comprising chalcopyrite, pyrite, biotite and chlorite, to a hematite–muscovite-bearing Cu–Au substage with chalcopyrite, bornite and rare chalcocite, as well as Au–Ag-tellurides and native Au. This second stage was followed by a subordinate but nonetheless important carbonate–quartz–barite vein stage with minor but locally high-grade Cu–Au mineralisation characterised by abundant chalcocite and bornite, minor native bismuth and wittichenite (Cu3BiS3), together with minor Au–Ag telluride minerals. Bornite in these carbonate–quartz–barite veins contains considerable amounts of Au (>10 ppm), which appears to be deported either as lattice substitution in the bornite crystal structure or as homogeneously distributed Au0 nanoparticles. An earlier, coarse-grained mafic intrusion was affected by early Na–Ca alteration, whereas a second mafic intrusion lacks evidence of Na–Ca alteration but was exposed to K–Fe alteration and subsequent mineralisation at Starra 222. Mushketovite (magnetite after specular hematite) is only observed in ironstone lodes proximal to the mafic–intermediate rocks. The close spatial and mineralogical associations of the mafic–intermediate bodies and the ironstone lodes point to a stronger link between magmatic activity and IOCG mineralisation than has previously been recognised at Starra. Remobilisation of gold by late-stage hydrothermal fluids aided by the relatively low fluid temperatures during the main pulse of Cu–Au mineralisation refined gold grades at Starra, making it a relatively gold-rich IOCG deposit. We show that the Cu–Au deposits of the Starra trend feature mineralogical and geochemical elements common to both Cloncurry IOCG deposits (e.g. abundant magnetite) and IOCG deposits of the Tennant Creek district (e.g. Au–Cu–Bi mineralisation; hematite–bornite–chalcocite assemblages), making them a unique and important member of this complex family of deposits.

Two episodes of mineralization in the Baolun high-grade lode gold deposit, Hainan Island, South China: Insight from LA-ICP-MS analysis of hydrothermal rutile

The Baolun is the largest gold deposit on Hainan Island, South China, with proven reserves of over 80 t Au at an average grade of 10.3 g/t. Two economic types of gold mineralization coexist in the long-lived fault system: 1) Au-bearing sulfide quartz veins (Va), dominated by pyrite, pyrrhotite, and arsenopyrite; and 2) Au-Bi assemblage quartz veins (Vb), dominated by bismuthinite, maldonite, and native bismuth. The Baolun district has a long history of tectonic reactivation, involving crustal compression and extension, magmatic activity, multiple episodes of fluid flow, and hydrothermal mineralization. Consequently, there exists no generally accepted model for the precise timing and source of the Baolun gold deposits. In this study, two different rutile grains (Rt-1 and Rt-2) were recognized separately in the Va veins and Vb veins based on paragenetic sequence. In situ U-Pb dating indicates that Rt-1 and Rt-2 yielded two group ages of 248.3 ± 2.8 Ma (MSWD = 0.8) and 78.2 ± 8.4 Ma (MSWD = 1.4), respectively. The Rt-1 contains 632.0–6051.2 ppm W, 459.1–2169.1 ppm Zr, 1215.0–8267.5 ppm Nb, 107.3–1229.6 ppm Ta, 19.0–79.2 ppm Hf, 160.2–311.8 ppm Sn, 1371.6–3500.7 ppm V, 325.3–3813.9 ppm Cr, 0.6–22.7 ppm Sb, 0.1–38.8 ppm Y, with Ca below the detection limit. The Rt-2 contains 704.9–4390.2 ppm W, 1.8–168.5 ppm Zr, 1264.6–4062.9 ppm Nb, 108.1–453.2 ppm Ta, 0.3–6.9 ppm Hf, 6.5–32.1 ppm Sn, 14.3–311.0 ppm V, 29.4–167.1 ppm Cr, 0.6–27.3 ppm Sb, 56.3–38.8 ppm Y, and 548.7–2750.3 ppm Ca. Obviously, LA-ICP-MS trace element analysis revealed significant discrepancies in composition between Rt-1 and Rt-2, suggesting that they precipitated from distinct fluid systems. Combining mineral studies, field observations, structural analysis, and geologic evolution, the results of this study indicate that the Baolun gold deposit formed during two episodes of mineralization. The Early Triassic gold mineralization is clearly classified as an orogenic type. The ore-forming materials were liberated by the deformation and metamorphism during the Indosinian orogeny of South China, which was triggered by the closure of the Paleotethys Ocean. The Late Cretaceous Au-Bi mineralization belongs to a magmatic-hydrothermal origin, which was deposited under an extension setting associated with the post-subduction of the paleo-Pacific plate. The new mineralization model proposed provides significant implications for future exploration strategies.

Metallogenic model of the Amensif Zn-Pb-Cu-Ag±Au-Bi carbonate replacement deposit (Western High Atlas, Morocco): New litho-structural and mineralogical data

Purpose. In this paper, we discuss the genetic model and emphasize many pending issues on the carbonate replacement textures of the Amensif Zn-Pb-Cu-Ag±Au-Bi deposit (the Western High Atlas, Morocco), the source of metal and the possible contribution of the Azegour granite to this ore genesis. Methods. This study is based on geological mapping, drill core and petrography analysis in combination with ICP-AES, XRD, and SEM data. Findings. The detailed mineralogy consists mainly of sulfides and sulfosalts. The main ore minerals include arsenopyrite, pyrite, sphalerite, chalcopyrite, galena and bismuthinite. Mineral inclusions related to isomorphic sulfosalts are found in galena and/or chalcopyrite. They include matildite, galenobismutite, pavonite, cosalite, schirmerite, krupkaite, ramdohrite, wittichenite, emplectite, luzonite, gustavite, hedleyite, krennerite, wittite, freibergite, tetrahedrite, tennantite and native bismuth. The supergene minerals are anglesite, covellite, malachite, azurite and goethite. In addition, specific replacements are observed between dolomites and sulfides, indicating an interaction between hydrothermal fluid and host rocks. Four ore stages have been identified based on the relationship between mineral phases and ore-forming conditions. The results of this study indicate that Ag and Au precipitation is controlled by the Bi-Te-Pb-S system, while enrichment in Bi, Te and Se sulfosalts and Bi-telluride indicates a magmatic source of the ore-forming fluid. Originality. The study delves into the genetic model of the Amensif Zn-Pb-Cu-Ag±Au-Bi deposit in the Western High Atlas, Moroc-co, with a focus on carbonate replacement textures, while also exploring its classification as either a carbonate replacement deposit or a skarn deposit. Practical implications.Mineral textures are indicators of the replacement process in the Amensif Zn-Pb-Cu-Bi-Ag±Au carbonate replacement deposit (the Western High Atlas, Morocco). The results obtained from this research paper can be used as a powerful tool in mineral exploration of the Western High Atlas.

Algama Gold Ore Cluster (Aldan–Stanovoi Shield): Mineralogy, Formation Conditions, Sources of Ore Matter, and Age of Mineralization

Abstract —The paper presents results of research into the conditions of formation of ores in the poorly studied Algama ore cluster (Bodorono deposit and Dyvok ore occurrence) located at the junction of the Aldan Shield and the Stanovoi area. We have established that Bi and Se minerals (bismuthinite, lillianite, native bismuth, tellurobismuthite, tetradymite, hedleyite, pilsenite, and laitakarite) are present in the ores of the Bodorono deposit. Two successive productive stages of mineral formation have been distinguished: Au–polymetallic and Au–Bi–Te. The corresponding minerals are products of the evolution of a hydrothermal system, during which a gradual decrease in fluid temperature (from 300 to 145 °C) and salinity (from 5 to 1.9 wt.% NaCl equiv.) took place. The fineness of native gold gradually increases from early (~840‰) to late (~940‰) stages and changes in passing from simple sulfides to sulfosalts. The evolution of the ore system is accompanied by a change in the composition of the vapor phase of fluid inclusions from CH4–CO2 to CO2 with an impurity of N2 and CH4. The results of 40Ar/39Ar dating of pre-ore metasomatites point to ore-forming processes at the Bodorono deposit ca. 150 ± 1.8 Ma. Analysis of the isotopic composition of lead in galena shows the leading role of the ancient crustal source of ore matter. The calculated isotopic composition of oxygen (δ18OH2O) in ore-bearing quartz varies from 1.0 to 7.3‰, which corresponds to an aqueous fluid of a mixed source. The Dyvok ore occurrence differs from the Bodorono deposit in the mineral composition of ores and the physicochemical parameters of ore formation. Four mineral stages have been established within the ore occurrence: gold–arsenopyrite–pyrite–quartz, pyrite–chalcopyrite–sphalerite, quartz–boulangerite, and telluride. The telluride stage is represented by hessite, altaite, volynskite, merenskyite, melonite, and rucklidgeite. Gold-bearing mineralization formed from a fluid of medium salinity (0.9–9.2 wt.% NaCl equiv.) with a predominance of CO2 and an impurity of CH4 in the vapor phase at moderate temperatures (310–360 °C). The calculated values of δ34S and δ18O varied from 2.2 to 3.0‰ and from 0.6 to 12.0‰, respectively. The 40Ar/39Ar age of gold mineralization is 124.0 ± 1.5 Ma, which corresponds to the stage of tectonomagmatic activity in the Aldan Shield.

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

Polygenic gold mineralization in quartz-pebble formations on the Takyr-Kaljir site of the Southern Altai, East Kazakhstan Region

Purpose. The research purpose is to study the forms of gold occurrence in the Takyr graben alluvial-proluvial deposits in order to develop a low-waste resource-saving processing technology. Methods. At the first stage, in the course of field studies, the geological structure of the site is specified, samples are taken for mineralogical-technological analysis, which includes the following procedures: studying granulometric and mineral composition of detrital material; fractional gravitational beneficiation of the source material; fractional beneficiation of material pre-processed in the autogenous mill (AG mill); studying free (native) and bound gold in beneficiation products, their quantitative assessment. The samples are processed under the three-stage scheme using an autogenous mill for sample preparation. Findings. For the first time, the geological structure of the site has been specified with the identification of the deposits in the Turangi and Tuzkabak suites within its boundaries, as well as granulometric and petrographic composition of gold-bearing deposits, and the specifics of gold bearing. The detrital material, represented by quartz with a sharply subordinate amount of quartzite, quartz diorites and jasperoids, is practically identical in all fractions. Originality. For the first time, various types of gold mineralization have been identified in placer sands: clastogenic, newly-formed hypergene, newly-formed hydrothermal and residual. Fractional beneficiation makes it possible to estimate the gold content in each fraction and gravitational beneficiation products, as well as the ratio of free and bound native gold in different fractions. The largest amount of free native gold has been revealed in fractions of -0.25 + 0.1 mm (60%) and -0.074 + 0.044 mm (~40%). Gold is high-grade (96.5%) with an admixture of silver and iron. Together with gold, ilmenite, zircon, scheelite, native bismuth, as well as barite, galena, sphalerite, and dolomite have been identified. Practical implications. The research results make it possible to reassess the prospects of similar objects, to adjust the scheme and methodology for processing stream-sediment samples, to solve the issues of productive sand processing technology, as well as to improve the efficiency of geological exploration and eliminate the “underestimation” of gold deposits. The results obtained can be recommended for implementation by both domestic and foreign organizations specializing in the exploration and mining of gold deposits.

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.

PLATINUM-PALLADIUM OCCURRENCE VASILINOVSKOE: A NEW TYPE OF NOBLE-METAL MINERALIZATION IN THE URALS

For the first time, a new noble-metal (Pt–Au–Pd) Vasilinovskoe ore occurrence discovered near the village of Kharp in the Yamalo-Nenets Autonomous Okrug is described. It is associated with amphibolized gabbroids and subordinate pyroxenites of the Kershor complex, dated mainly to the Late Ordovician. In these rocks, mineralization zones with an apparent thickness from 0.5 to 50 m (sulfides 3–5 vol.%, occasionally more) are developed. In areas with scattered or finely nested sulfide inclusions, feldspar-quartz, epidote and other veins are often present. According to assay data, in substantially sulfide 0.5–1 kg samples of these, in general, low–sulfide zones, the Pd content reaches 1.4 g/t, Au – 0.8 g/t, and Pt – 0.2 g/t. PGE minerals are represented by abundant secretions of micron–sized palladium tellurides – merenskite PdTe2, temagamite Pd3HgTe3, kotulskite PdTe, as well as other noble metal compounds – sadberite PdSb, arsenopalladinite Pd8(As,Sb)3 and others. In addition to these palladium minerals, the magnetite–chalcopyrite–pyrite association contains microinclusions of native silver, native bismuth and native tin. In the later polysulfide–feldspar–carbonate–quartz association, Au and Ag tellurides, native gold (including Hg-bearing), Se-containing argentite, greenockite are found. The formation of parageneses of precious metals is associated with late magmatic processes, as well as with redistribution by subsequent magmatogenic hydrothermal fluids, up to a temperature of ~250°C; pressure decreased from ~0.9–1.3 to ~0.4–0.5 kbar.

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.

Mechanisms of ore formation in Silurian (Caledonian) scheelite deposits of the Nanling Range, South China: A case study from the Pingtan W deposit

The Pingtan scheelite deposit is a newly-discovered Caledonian W deposit situated in the northwestern portion of the Miao’ershan granitic batholith in the Nanling Range. The W mineralization can be divided into three stages, the altered granite-scheelite stage (I), the quartz-scheelite stage (II) and the quartz-sulfide stage (III). This contribution characterizes the mechanisms of ore formation of the deposit using fluid inclusion microthermometry, H-O isotopes, and in situ S isotopes. Fluid inclusion microthermometry demonstrates that the scheelite mainly formed at moderate to high temperatures (∼260–380 °C for stage I and ∼ 240–300 °C for stage II). The inclusions were trapped at maximum pressures of ∼ 140 MPa, which corresponds to a maximum depth of ∼ 5.3 km. Homogenization temperatures of the inclusions decrease slightly from stage I to stage II mineralization, and more drastically from stage II to stage III, whereas their salinity decreases gradually during the entire mineralization process. Raman spectroscopy indicates that fluid inclusions in stages I and II contain CO2, CH4, and N2, whereas those in stage III mainly contain H2O. The presence of native bismuth, pyrrhotite, and marcasite, and the presence of CH4-bearing fluid inclusions suggest reduced ore-forming conditions during Stages I and II. The δ34SCDT value (+0.8 to + 5.3 ‰, average 3.2 ‰) of sulfides and the δ18Ovsmow value of ore-bearing quartz, which decreases from Stage I (δ18Ovsmow = +5.1 to + 6.3 ‰) to Stage III (δ18Ovsmow = − 1.5 ‰ to + 0.6 ‰), as well as the presence of abundant fluid inclusions with daughter minerals in the first two stages, supports a magmatic origin for the ore-forming material, with exogenic fluid input after the tungsten mineralization stage. Based on the results of this contribution, boiling may be the dominant mechanism for the formation of W deposits in the Nanling Range.

ГЕОЛОГИЧЕСКАЯ ПОЗИЦИЯ И ЗОЛОТО-ВИСМУТОВАЯ МИНЕРАЛИЗАЦИЯ МЕСТОРОЖДЕНИЯ НАМОВСКОЕ (ЮЖНЫЙ СИХОТЭ-АЛИНЬ, ДВ РОССИИ)

Based on the results of a comprehensive geological and mineralogical-geochemical study of the ores of the Namovskoye deposit, new data have been obtained that reflect the specifics of mineralization. The ores of the deposit were formed in close connection with the manifestation of Early Cretaceous monzonitoid magmatism against the background of active left-hand movements along the Central Sikhote-Alin fault. U-Pb dating of the ore-bearing dike yielded an age of 103 Ma. The ores of the deposit, in addition to native gold, contain high concentrations of Ag, Bi, and Cu. A variety of bismuth minerals were found in the ores: sulfide (bismuthinite), telluride (hedleyite), sulfotellurides (tetradymite, joseite-А and joseite-В), Ag sulfobismuthite (matildite), Pb-Bi sulfosalts (aschamalmite, cannizzarite, cosalite, lillianite, nuffieldite, galenobismuthite), an intermetallic compound of gold (maldonite), and native bismuth. Silver minerals were also found: chloride (cerargyrite), sulfide (acanthite), and telluride (hessite). The typomorphic features of ore minerals and the geological structure of the Namovskoye deposit assign it to the gold deposits formed in a transform continental margin setting. A mantle source of ore mineralization is suggested.

Bi-Ag-Sulfosalts and Sulfoarsenides in the Ruwai Zn-Pb-Ag Skarn Deposit, Central Borneo, Indonesia

The Ruwai skarn deposit is located in the Schwaner Mountain complex within the central Borneo gold belt and is currently considered the largest Zn skarn deposit in Indonesia. The deposit has been known to host Zn-Pb-Ag mineralization in the form of massive sulfide ore bodies; however, the occurrence of Ag-bearing minerals has not been identified yet. This study documents the mineralogical characteristics of several Bi-Ag sulfosalts and sulfoarsenides, as well as their chemical compositions. Ten Bi-Ag sulfosalts were identified, including native bismuth, tetrahedrite, cossalite, tsumoite, bismuthinite, joseite-B, Bi6Te2S, Bi-Pb-Te-S, Bi-Ag-S, and Bi-Te-Ag. Three sulfoarsenides were identified, including arsenopyrite, glaucodot, and alloclasite. The occurrence of Bi-Ag sulfosalts is typically associated with massive sulfide mineralization, although tsumoite can also be found associated with massive magnetite. In terms of sulfoarsenides, both arsenopyrite and glaucodot are associated with massive sulfide mineralization, whereas alloclasite is associated with massive magnetite mineralization. The Bi-bearing minerals are characterized by irregular, bleb-like texture or patch morphology, and occur either as free grains or inclusions within sulfides, such as galena or pyrite. Tetrahedrite typically has an anhedral shape with a rim or atoll texture surrounding sphalerite or galena. In contrast, sulfoarsenides are typically found as euhedral–subhedral grains where glaucodot typically is rimmed by arsenopyrite. Both Bi-Ag sulfosalt and sulfoarsenides were formed during the retrograde stage under high oxidation and a low sulfidation state condition. The ore-forming temperature based on arsenopyrite geothermometry ranges from 428 °C to 493 °C.

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.

Mineral composition of Albazinskoe deposit ores as an indicator of its belonging to the gold-rare metallic ore-formational type

The paper presents new data on mineral composition and geochemical peculiarities of ores from the Albazinskoe gold-bearing deposit (Khabarovsk region, Far East of Russia). Excepting earlier known ore minerals represented by sulfides of iron, arsenic, lead, zinc, and copper, authors have established about two tens of ore minerals, new for this deposit. Among them are sulfides of antimony, bismuth and molybdenum, native bismuth, copper, nickel, silver, tellurides of bismuth, cobalt sulphoarsenite, nickel sulphoantimonite, silver sulphobismuthites, lead-antimony-bismuth sulphosalts, oxides of tin, titanium, tungsten and some others. The revealed specificity of the ores' material composition indicates this deposit belongs to the gold-rare metallic ore-formational type. The sets of geological and structural data show that gold-bearing deposits of this ore-formational type are spatially and genetically associated with the granitoid magmatism, which is exhibited within transform continental margin and related to the geodynamic mode of sliding of the continental and oceanic lithospheric plates.

Timing of Magmatism and Skarn Formation at the Limon, Guajes, and Media Luna Gold ± Copper Skarn Deposits at Morelos, Guerrero State, Mexico

Abstract The Morelos district, located in the center of the Guerrero gold belt, Guerrero State, southern Mexico, has been the site of several recent gold ± copper skarn discoveries (total of ~8.5 Moz Au) associated with Upper Cretaceous-Paleocene granodiorite intrusions. The Limon, Guajes, and Media Luna skarn deposits developed along the contact of the El Limon granodiorite and the sedimentary host rocks. Native gold is associated with retrograde alteration of garnet-pyroxene skarn and is accompanied by native bismuth as well as telluride and sulfide minerals. The Media Luna deposit is characterized by a distinct magnesium-rich skarn mineralogy and contains an average of ~1 wt % Cu, in addition to gold and silver. This distinguishes it from the other gold-only skarn deposits in the Guerrero gold belt. This observation suggests that skarns in the Guerrero gold belt, which replaced magnesium-rich sedimentary protoliths, may host significant copper resources in addition to gold. Uranium-lead laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon ages of the El Limon granodiorite range from 66.86 ± 0.40 to 65.88 ± 0.79 Ma. Preskarn molybdenite-quartz veins cut through the El Limon granodiorite and yield Re-Os molybdenite ages between 66.63 ± 0.22 and 65.55 ± 0.25 Ma. A series of pre-, syn-, and postskarn porphyritic dikes intruded the El Limon granodiorite, having zircon ages ranging from 65.9 ± 1.1 to 64.68 ± 0.38 Ma. The timing of skarn formation at Limon and Media Luna was constrained to 64.6 ± 1.2 to 63.2 ± 1.0 Ma, applying U-Pb LA-ICP-MS to garnet. The ubiquitous presence of garnet in skarn deposits and the time- and cost-efficiency of in situ geochronology are striking advantages of this method to constrain the timing of mineralization.

Geology, molybdenite Re-Os age, H-O-S-Pb isotopes, and fluid inclusion features of the Maodeng Mo-Bi-Sn-Cu deposit, Inner Mongolia

Maodeng deposit is a large-sized Mo-Bi-Sn-Cu deposit located in the Xinlinhot of Inner Mongolia in the southern segment of the Great Xing’an Range. The ore-forming elements in the deposit are found in the volcanic breccia of Lower–Middle Permian Dashizhai Formation and granite porphyry of the Alubaogeshan complex, constituting distinct regional mineralization zones such as hydrothermal vein-type of Sn-Cu orebodies in the upper parts and stockworks, veinlets and disseminated-type of Mo-Bi orebodies in the lower parts. This paper has conducted an integrated study using a comprehensive field survey, molybdenite Re-Os age, fluid inclusion, and isotopic (O, H, S, and Pb) analyses. The mineralization in the deposit can be divided into four stages, which are molybdenite-native bismuth-quartz (stage I), cassiterite-wolframite-topaz-quartz (stage II), chalcopyrite-sphalerite-galena-fluorite-sericite-quartz (stage III) and stibnite-pyrite-quartz-fluorite (stage IV). The Re-Os isochron age of four molybdenite samples was estimated as 139.2 ± 3.9 Ma, indicating the deposit was formed during the Early Cretaceous. The Maodeng deposit is characterized by three kinds of fluid inclusions (FIs): liquid-rich two-phase, vapor-rich two-phase, and daughter mineral-bearing three-phase FIs. The homogenization temperatures for the FIs of stages I through IV are 292–387 °C, 222–333 °C, 172–252 °C, and 122–197 °C, with calculated salinities of 4.2–43.6 wt%, 2.1–38.9 wt%, 1.9–33.6 wt% and 0.7–5.1 wt% NaCl equiv., respectively, showing the gradual reduction in temperature and salinity of hydrothermal fluids. Hydrogen and oxygen isotopic data of quartz indicate that the dominant origin of the ore-forming solutions from deep granitic intrusions followed by their dilution by limited meteoric water. The sulfides have δ34S values ranging from − 6 ‰ to − 0.49 ‰, and have 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios similar to those of K-feldspars from the Alubaogeshan pluton, suggesting the primary origin of ore-forming materials of the Maodeng deposit are magmatic. Molybdenite and native bismuth may precipitate primarily by fluid boiling, chalcopyrite could deposit mainly by fluid mixing, and cassiterite precipitate mainly through fluid boiling and mixing.

Jonassonite from the Belogorskoe iron deposit (Sikhote-Alin)

The paper describes a rare Au–Bi sulfde (jonassonite) from the Belogorskoe iron deposit (Sikhote-Alin), the ore bodies of which are composed of metalliferous sediments that underwent contact metamorphism (T ~550 °С, Plithostatic ~1.5 kbar) and late hydrothermal processes (T 350–415 and 271 °С or slightly lower). Jonassonite is found in products of hydrothermal alteration of metamorphic bustamite-andradite (with a low amount of Mn-bearing hedenbergite, scheelite, lollingite and baryte) rocks composed of calcite, fuorite, native bismuth, bismuthinite, joseite A, an unnamed AgBiS2 phase, cosalite, Mo-bearing scheelite, povellite-molybdenite and other minerals. Jonassonite is intergrown with anhedral calcite aggregates in andradite and forms grains with sections (~5 ? 7 µm) close to ellipsoid shape. The mineral contains up to 2.29 wt. % Te, which most likely isomorphically substitutes S. Jonassonite formed at a temperature not exceeding 271 °C during hydrothermal alteration of metamorphic mineral assemblages.