In weakly metamorphosed massive sulfide deposits of the Urals (Dergamysh, Yubileynoe, Yaman-Kasy, Molodezhnoe, Valentorskoe, Aleksandrinskoe, Saf’yanovskoe), banded sulfides (ore diagenites) are recognized as the products of seafloor supergene alteration (halmyrolysis) of fine-clastic sulfide sediments and further diagenesis leading to the formation of authigenic mineralization. The ore diagenites are subdivided into pyrrhotite-, chalcopyrite-, bornite-, sphalerite-, barite- and hematite-rich types. The relative contents of sphalerite-, bornite- and barite-rich facies increases in the progression from ultramafic (=Atlantic) to bimodal mafic (=Uralian) and bimodal felsic (=Baymak and Rudny Altay) types of massive sulfide deposits. The ore diagenites have lost primary features within the ore clasts and dominantly exhibit replacement and neo-formed nodular microtextures. The evolution of the mineralogy is dependent on the original primary composition, sizes and proportions of the hydrothermal ore clasts mixed with lithic serpentinite and hyaloclastic volcanic fragments together with carbonaceous and calcareous fragments. Each type of ore diagenite is characterized by specific rare mineral assemblages: Cu–Co–Ni sulfides are common in pyrrhotite-rich diagenites; tellurides and selenides in chalcopyrite-rich diagenites; minerals of the germanite group and Cu–Ag and Cu–Sn sulfides in bornite-rich diagenites; abundant galena and sulfosalts in barite- and sphalerite-rich diagenites and diverse tellurides characterize hematite-rich diagenites. Native gold in variable amounts is typical of all types of diagenites.

The aim of this paper is the investigation of the role of diagenesis in the transformation of clastic sulfide sediments such as sulfide breccias from the Semenov-3 hydrothermal field (Mid-Atlantic Ridge). The breccias are composed of marcasite–pyrite clasts enclosed in a barite–sulfide–quartz matrix. Primary hydrothermal sulfides occur as colloform, fine-crystalline, porous and radial marcasite–pyrite clasts with inclusions or individual clasts of chalcopyrite, sphalerite, pyrrhotite, bornite, barite and rock-forming minerals. Diagenetic processes are responsible for the formation of more diverse authigenic mineralization including framboidal, ovoidal and nodular pyrite, coarse-crystalline pyrite and marcasite, anhedral and reniform chalcopyrite, inclusions of HgS phase and pyrrhotite–sphalerite–chalcopyrite aggregates in coarse-crystalline pyrite, zoned bornite–chalcopyrite grains, specular and globular hematite, tabular barite and quartz. The early diagenetic ovoid pyrite is enriched in most trace elements in contrast to late diagenetic varieties. Authigenic lower-temperature chalcopyrite is depleted in trace elements relative to high-temperature hydrothermal ones. Trace elements have different modes of occurrence: Se is hosted in pyrite and chalcopyrite; Tl is related to sphalerite and galena nanoinclusions; Au is associated with galena; As in pyrite is lattice-bound, whereas in chalcopyrite it is related to tetrahedrite–tennantite nanoinclusions; Cd in pyrite is hosted in sphalerite inclusions; Cd in chalcopyrite forms its own mineral; Co and Ni are hosted in chalcopyrite.

The pyrite nodules from ore diagenites of the Urals massive sulfide deposits associated with various background sedimentary rocks are studied using optical and electron microscopy and LA-ICP-MS analysis. The nodules are found in sulfide–black shale, sulfide–carbonate–hyaloclastite, and sulfide–serpentinite diagenites of the Saf’yanovskoe, Talgan, and Dergamysh deposits, respectively. The nodules consist of the core made up of early diagenetic fine-crystalline (grained) pyrite and the rim (±intermediate zone) composed of late diagenetic coarse-crystalline pyrite. The nodules are replaced by authigenic sphalerite, chalcopyrite, galena, and fahlores (Saf’yanovskoe), sphalerite, chalcopyrite and galena (Talgan), and pyrrhotite and chalcopyrite (Dergamysh). They exhibit specific accessory mineral assemblages with dominant galena and fahlores, various tellurides and Co–Ni sulfoarsenides in sulfide-black shale, sulfide–hyaloclastite–carbonate, and sulfide-serpentinite diagenites, respectively. The core of nodules is enriched in trace elements in contrast to the rim. The nodules from sulfide–black shale diagenites are enriched in most trace elements due to their effective sorption by associated organic-rich sediments. The nodules from sulfide–carbonate–hyaloclastite diagenites are rich in elements sourced from seawater, hyaloclastites and copper–zinc ore clasts. The nodules from sulfide–serpentinite diagenites are rich in Co and Ni, which are typical trace elements of ultramafic rocks and primary ores from the deposit.

Gallium-containing chlorite, mica, and magnetite (up to 14, 13, and 5–7 wt % of Ga) along with Ga hydroxides (oxyhydroxides?) were found for the first time in massive sulfide deposit in the Urals....

The article presents the results of a comparative analysis of fluorite from various mineralization types of the Saf’yanovka massive sulfide deposit in the Central Urals. The predominant green fluorite is intergrown with barite, quartz, and carbonates in hydrothermal colloform and massive pyrite, veinlet–disseminated chalcopyrite–pyrite–sphalerite and pyrite–chalcopyrite ores, as well as in hydrothermally altered rhyolite. In colloform pyrite ore, fluorite together with galena, sphalerite, chalcopyrite, fahlore, and barite fills interstices between crystals. In altered rhyolite, yellow-green fluorite occurs as veins of 1 cm thick, 2–3 cm pockets, and intergrowths with quartz, carbonate, and barite. The rare-earth element (REE) and yttrium concentrations have been determined by ICP-MS. The highest Y content (160 ppm) is measured in fluorite from metasomatic rock; the intermediate Y content (40–130 ppm) is determined in fluorite from pyrite ore, and the lowest one (4–9 ppm) is typical of fluorite from chalcopyrite–pyrite–sphalerite and chalcopyrite ore. The total REE content in fluorite is 70–150 ppm (chalcopyrite–pyrite–sphalerite and chalcopyrite ore), 100–280 ppm in pyrite ore, and reaches 180 ppm in altered rhyolites. The highest REE concentration is caused by the presence of xenotime, goyazite, monazite, barite or apatite inclusions in fluorite. The Tb/La and Tb/Ca ratios suggest that fluorite resulted from hydrothermal processes. The REE distribution patterns with an evident Eu anomaly (Eu/Eu* > 1) show enrichment in LREE. Positive Eu anomalies reflect the high-temperature conditions (≥250°C) during fluorite crystallization. The pressure-corrected (~100–150 bar) temperature of fluorite formation is 190–260°С.

The paper describes the findings of minerals of the alunite supergroup (crandallite, hinsdalite, and alunite) in hematite-bearing fine-bedded massive sulfide ores with a higher total rare-earth-element (REE) content (up to 110 ppm). Crandallite forms elongated aggregates up to 120 µm in size with a rhythmically zoned structure and uneven REE distribution. Rare spherulitic aggregates up to 120 µm in size occur in assemblage with alunite, quartz, chlorite, and hematite. The high PbO content (7–19 wt %) is the main feature of crandallite. Some crandallite grains contain (wt %) up to 1.84 La₂O₃ and 1.03 Ce₂O₃, 0.85–1.73 Nd₂O₃, 0.39–0.54 Pr₂O₃, 0.52–2.70 BaO, 0.99–2.50 SrO, 0.34–0.55 UO₂, 0.30–0.69 ThO_2, and 0.32–0.57 CuO. Hinsdalite and alunite in the form of interstitial spherulites up to 30 µm in size and platy aggregates up to 20–30 µm long occur between chalcopyrite and barite. Alunite and hinsdalite contain V₂O₅ (up to 0.3 and 0.1 wt %, respectively). The formation of minerals is considered a result of mobilization of components from hyaloclasts and ore clasts in the presence of phosphorus, which was sourced from biogenic matter during the formation of late quartz–hematite assemblage.