E. V. Belogub

Chemical evolution of pyrite at the Kopylovsky and Kavkaz black shale-hosted gold deposits, Bodaybo district, Russia: Evidence from EPMA and LA-ICP-MS data

The Kopylovsky and Kavkaz gold deposits in the Artemovskiy ore cluster, Bodaybo district, hosted in terrigenous carbonaceous sequence of the Dogaldyn formation of the Upper Proterozoic Bodaybo group, are localized in cores of high-order anticlines. These deposits contain gold-sulfide and gold-sulfide-quartz ore types. Pyrite is the predominant ore mineral; copper, zinc, nickel, and cobalt sulfides are minor. Native gold is found as free grains, and inclusions and ultrafine stingers in pyrite. A few morphological varieties of pyrite are identified: (1) framboidal and fine-grained pyrite resulting from sedimentation and diagenesis; (2) fine-grained subhedral to euhedral pyrite corresponding to catagenesis, metamorphism, and dynamometamorphism; and (3) coarse-crystalline euhedral gold-free pyrite occurring in the host rocks beyond ore bodies and deposits. According to electron microprobe and LA-ICP-MS data, the contents of Au, Ag, Co, Pb, Sb, Bi, Ba, Mo, and Tl decrease from sedimentary-diagenetic to metamorphic pyrite, while Ni, Cu, As, Se and especially U contents increase in the same direction. Primary gold is suggested to have accumulated during sedimentation as species associated with carbonaceous matter and cogenetic pyrite and redeposited as a result of catagenesis and metamorphism as native species with crystallization of the latest pyrite and associated sulfides of base metals.

Age and sources of matter for the Kedrovskoe gold deposit, Northern Transbaikal tegion, Republic of Buryatia: Geochronological and isotopic geochemical constraints

The paper presents new geochronological and isotopic geochemical data on gold mineralization of the Kedrovskoe deposit. The deposit is located in the northeastern part of the Transbaikal metallogenic province, Russia’s largest. The Early Permian age (273 ± 4 Ma) of mineralization based on the results of Rb–Sr study of metasomatic rocks is correlated with the age of the final phases of Hercynian magmatism in the Baikal–Muya Foldbelt. The Sr, Nd, and Pb isotopic geochemical characteristics of mineralization show that the host rocks are involved in the formation of the latter. It has been established that ore lead was supplied to the hydrothermal system of the deposit mainly from a geochemical reservoir represented by the Neoproterozoic juvenile continental crust of the Baikal–Muya Foldbelt.

Florencite-(Sm)—(Sm,Nd)Al3(PO4)2(OH)6: A new mineral species of the alunite-jarosite group from the subpolar urals

Florencite-(Sm), a new mineral species of the florencite subgroup, was found in association with xenotime-(Y) in quartz veins of the Maldynyrd Range of the Subpolar Urals as thin zones within rhombohedral crystals of florencite-(Ce) with faceting by

Native bismuth, tsumoite, and Pb-bearing tsumoite from the Tarn’er copper-zinc massive sulfide deposit, northern Urals

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Mineralogy of alluvial sediments of Avzyan gold region (the Southern Urals)

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Mineralogical and Geochemical Features of Oolitic Ironstones from the Sinara–Techa Deposit, Kurgan District, Russia

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Mössbauer spectroscopy of Pb-bearing minerals from the jarosite group

. The thickness of particular florencite-(Sm) zones is 0.01–0.1 mm, and the total thickness of a series of such zones is 1–3 mm. Florencite-(Sm) is colorless and pale pink or pale yellow with white streaks; its Mohs hardness is 5.5–6.0. Its measured and calculated densities are 3.70 and 3.743 g/cm3, respectively. The mineral is transparent, nonpleochroic, and uniaxial (positive), and ω = 1.704(2) and ɛ = 1.713(2). The electron beam’s fluorescence spectrum was 592 nm (intense green luminescence of Sm3+) and 558 nm (yellow luminescence of Nd3+). The chemical composition was as follows (microprobe, average of 2 WDS, wt %): 0.62 La2O3, 3.29 Ce2O3, 1.05 Pr2O3, 10.31 Nd2O3, 12.62 Sm2O3, 0.41 Eu2O3, 2.30 Gd2O3, 0.13 Dy2O3, 0.71 SrO, 0.35 CaO, 29.89 Al2O3, 26.14 P2O5, 0.85 SO3, 0.09 SiO2, 88.76 in total; 10.74 H2O (meas.). The empirical formula based on 14 oxygen atoms is (Sm0.38Nd0.32Gd0.07Ce0.10Pr0.03La0.02Eu0.01Sr0.04Ca0.03)1.0Al3.04(P1.91S0.05Si0.01)1.97O14H5.92. The idealized formula is (Sm,Nd)Al3(PO4)2(OH)6. Mineral is trigonal, space group R3m, a = 6.972(4), c = 16.182(7) Å, V = 681.2 Å3, Z = 3. The XRD pattern is as follows: dln (I) (hkl): 2.925 (10) (113), 1.881 (6) (303), 2.161 (5) (107), 5.65 (4) (101), and 3.479 (4) (110). The IR spectrum: 466, 510, 621, 1036, 1105, 1223, 2957, and 3374 cm−1.

Silver sulfoselenide from ore of the Valunisty Au-Ag deposit, Chukchi Peninsula

Bismuth mineralization, including native bismuth, tsumoite (Bi1.99–2.03Te2.00), and Pb-bearing tsumoite (Bi1.56–1.88Pb0.45–0.14)2.00–2.03Te2.00, was identified in the Au-enriched disseminated ore at the Tarn’er massive sulfide deposit formed under the effect of a large diorite intrusion. Native bismuth associated with hessite forms idiomorphic inclusions in chalcopyrite. The assemblage of Pb-bearing tsumoite, hessite, and altaite occurs as angular allotriomorphic-granular inclusions in silicates or at the contact between silicate and sulfide aggregates. Tsumoite in allotriomorphic-granular aggregates with galena, hessite, and sphalerite is devoid of lead. Gold (Au0.65Ag0.35) was identified along with bismuth tellurides. The temperature of contact methamorphism (500–800°C) was estimated from the stability of andalusite, sillimanite, and cordierite. The morphology of the bismuth telluride aggregates in silicates and graphic intergrowth of tsumoite with galena suggest possible crystallization from anatectic melt. The positive correlation between Bi, Te, and Au confirms their probable joint transportation in the melt.

Mineralogy of oxidized ores at the Ik-Davlyat gold-base-metal deposit, the southern Urals

The Avzyan gold region is located within the Bashkirian anticlinorium and includes lode gold deposits and placers. The Gorny Priisk, Bogryashka and Ulyuk-Bar gold deposits are hosted in the Riphean metamorphosed carbonaceous sequence. The article describes the mineralogy of the heavy concentrates from alluvial sediments of the streams of Bolshoy Avzyan basin which drains the Gorny Priisk, Bogryashka and Ulyuk-Bar gold ore deposits. The comparison of mineralogical and chemical feature of the studied heavy concentrates is done. Samples and Methods. Samples from the streams were collected every 50-100 m. Hand specimens of ore and host rocks from the lode gold deposits were collected from outcrops and dumps. The content of metals in the heavy concentrates estimated using X-ray fluorescence analyzer Innov-X alfa. Chemical composition of the accessory minerals was studied using electron microscope Vega-3 Tescan with EDA X-Act Oxford. Discussion and Results. The source of the alluvial sediments was the lode gold deposits located in the immediate vicinity of placers. Heavy concentrates of the Kamenny stream are characterized by a high content of As and Cu while ones of the Bogryashka and Bolshoy Klyuch streams show a high content of Cr and Ba. Goethite is major ore mineral for all studied samples. Ilmenite, rutile, epidote and barite are also widespread in the samples from the Bogryashka and Bolshoy Klyuch streams. Native gold is present in the sediments of all studied stream. The greatest number of gold grains was found in the samples from the Bolshoy Klyuch stream. The weak roundness of the golds and the presence of unoxidized sulfides (pyrite, chalcopyrite and pyrrhotite) indicate a relatively small age of placers. Monazite and xenotime morphology suggests autigenic catagenetic and/or metamorphic origin. Monazite contains (apfu) Ce (0.27-0.56), Nd (0.10-0.37) and La (0.09-0.33), minor Pr, Sm, Gd, Eu and Dy; ThO 2 up to 9.78 wt. % (0.08 apfu). It is similar with monazite composition from other streams of the east part of the Bashkirian anticlinorium and can be evidence of their similar origin. Xenotime contains major Gd, Dy and Er and minor Tb and Ho. Xenotime from the Bogryashka stream is characterized by the increased concentration of (apfu) Gd (0.10-0.24), Nd (0.01-0.02), Sm (0.03-0.06), Eu (0.02-0.06) and absence of Ho and Yb. Xenotime composition from the Kamenny and Bolshoy Klyuch streams is similar with ones from east part of the Bashkirian anticlinorium. Galena inclusions in REE phosphates, monazite inclusions in goethite and xenotime inclusions in pyrite can be evidence about similar conditions and time of formation gold-sulfide and REE mineralization.

Supergene sulphides and related minerals in the supergene profiles of VHMS deposits from the South Urals

The paper discusses the mineralogical and geochemical features of oolitic ironstones from the Sinara–Techa deposit, Transural region, Kurgan district. The ore unit is localized in the lower part of a thick Mesozoic–Cenozoic sequence of sedimentary rocks that fill the West Siberian Basin beneath calcareous clay and overlying beds enriched in glauconite and clinoptilolite. The ironstone consists of goethite ooids in smectite–opal cement. Accessory minerals are pyrite, galena, sphalerite, and monazite. The texture and structure make it possible to suggest the formation of sediments enriched in iron as a result of colloid coagulation. The most probable source of iron is related to inland drift. Deposition of iron took place in the estuaries of subtropical rivers due to mixing of colloidal solution of river water with seawater electrolyte. The chemical features of rocks are controlled by the composition of the adsorbed iron oxi/hydroxide complex.