First Finds of Native Gold and Platinum in the Ilmenite Placers of the Ariadnoye Basite–Ultrabasite Intrusion (Primorye)

Doklady Earth Sciences - The basic features of mineralogy and geochemistry of the gold-ilmenite placers, which are spatially and genetically associated with the Ariadnoye intrusion of ultrabasites...     

Tectonic and Geodynamic Settings of Formation of the Mesozoic Cumulative Dunite–Wehrlite–Olivine Clinopyroxenite—Gabbro Massif in Eastern Chukotka

Geotectonics - The dunite–wehrlite–clinopyroxenite–gabbro massif in Eastern Chukotka, a key object for geodynamic reconstructions of the Vel’may terrane, which represents...     

Factors of Localization and Forecasting of Ore Mineralization in the Dzhusa Pyrite–Polymetallic Deposit (Southern Urals)

An analysis of tectonic displacements along fractures and faults revealed changes in the character of tectonic deformations that resulted from tectonic evolution of the Magnitogorsk island arc. Structural conditions of localization of ore mineralization of various types were investigated in the open pit of the Dzhusa deposit. The block diagram of an ore shoot of the Dzhusa deposit, which is confined to intersection of NW-striking and sublongitudinal faults was constructed. Trends in the distribution of sites with enriched mineralization are slightly different for various metals. The obtained data make it possible to predict the localization of rich ore bodies at deeper levels of the deposit and to reveal new prospecting ore sites in the Terensai ore field.     

An Ordovician Age of the Dunite–Wehrlite–Clinopyroxenite Banded Complex of the Nurali Massif (Southern Urals,Russia): U–Pb (SHRIMP) Zircon Age Data

The data on the geochemistry and geochronology of zircons from wehrlites and clinopyroxenites of the dunite–wehrlite–clinopyroxenite banded complex that lies at the base of the crustal section of the ophiolite complex of the Nurali massif are presented. The obtained U–Pb age of the banded complex of 450 ± 4 Ma differs markedly from the previous age data. According to REE distribution patterns zircons from ultramafic rocks are attributed to the magmatic type and they indicate the age and supposed genetic similarity of the above rocks with lherzolites and dunites from the mantle section of the Nurali massif.     

Mineralogical–Geochemical Types and 190Pt–4He Age of Ferroan Platinum of Placers of the Anabar River Basin,Northeastern Part of the Siberian Platform

Doklady Earth Sciences - Typical features of platinum group minerals (PGMs) and the results of 190Pt–4He dating of the Fe–Pt solid solutions are presented for complex...     

First Determination of the Isotope Age of the Andesite–Dacite Complex of the Eastern Zone of the Middle Urals

Doklady Earth Sciences - This paper reports on the first U–Pb dating of zircons from dacites of the volcanic paleo-edifice of the andesite–dacite complex of the Eastern Zone of the...     

The Source of Ore Fluids and Sm–Nd Age of Siderite from the Largest Bakal Deposit,Southern Urals

Geology of Ore Deposits - Based on Sm–Nd data, a crustal source of iron-ore fluid was substantiated and the probability of age estimation for hydrothermal–metasomatic siderite of the...     

Finds of “Ancient” Zircons in Magmatic Rocks of the Shatak Complex (Southern Urals) and Their Petrogenic Implications

New data on the presence of “old” zircons in magmatic rocks of the Shatak Complex have been obtained. This suggests that the evolution of melts in intermediate magma chambers was controlled by the AFC process, in which the liquidus phases (olivine ± clinopyroxene) fractionated, the fluid phases accumulated in the apical part of the chamber, and the host rocks were partly assimilated. Hence, the “old” zircons were entrained from the Archaean–Paleoproterozoic granite–gneiss substrate and trapped by the melt during crustal contamination.     

Yixunite and Damiaoite—A Twin of New Native Alloys of Indium and Platinum from the Yanshan Mountains

Yixunite and damiaoite Were found in a cobalt- and copper-bearing platinum ore vein of a contact metasomatic deposit. The chief ore minerals are bornite, chalcopyrite, magnetite and carrollite. The platinum minerals include moncheite, sperrylite, daomanite, cobalt malanite and cooperite. Yixunite and damiaoite occur as immiscible globules, 1.0 to 2.0 mm in diameter. Yixunite is always in the central part of a globule. It is opaque with metallic lustre, bright white colour and black streak. HM = 5.8; VHN50 = 634 kg/mm2 (573-681 kg/ mm2); insoluble in HCl, HNO3, HF or H3PO4; no cleavage; no magnetism. Density is hard to measure because of small grain size. Calculated density = 18.21 g/cm3. Reflective colour is bright white with a yellowish tint. Isotropic. The mean analytical results (ranges) (%) are: Pt 82.8 (81.8-83.6), In 16.4(15.6-17.1) and total 99.2. The empirical formula (based on 4 atoms) is Pt2.993 In1.007 . The five strongest lines of X-ray diffraction (hkl, d,I) are 111, 2.30 (100); 200, 1.99 (     

Platinum group element mineralization of the Svetly Bor and Veresovy Bor clinopyroxenite–dunite massifs,Middle Urals,Russia

The new data for the geology and mineralogy of the platinum group element (PGE) mineralization related to the chromite–platinum ore zones within the dunite of the Svetly Bor and Veresovy Bor massifs in the Middle Urals are discussed. The geological setting of the chromite–platinum ore zones, their platinum content, compositional and morphological features of the platinum group minerals (PGM) are compared to those within the Nizhny Tagil massif, the world standard of the zonal complexes in the Platinum Ural belt. The chromite–platinum orebodies are spatially related to the contacts between differently granular dunites. Majority of PGM are formed by Pt–Fe alloys that are close in terms of stoichiometry to isoferroplatinum (Pt₃Fe), and associated with Os–Ir alloys, Ru–Os and Ir–Rh sulfides, and Ir–Rh thiospinels of the cuproiridsite–cuprorhodsite–ferrorhodsite solid solution. The tetraferroplatinum (PtFe)–tulameenite (PtFe_0.5Cu_0.5) solid solution and Pt–Cu alloys belong to the later PGM assemblage. The established features of the chromite–platinum ore zones testify to the highly probable identification of the PGE mineralization within the dunite of the Svetly Bor and Vesesovy Bor massifs and could be used in prospecting and exploration for platinum.     

Rare Th–Sc Minerals in Picrites of the Southern Urals and Their Genetic Value

Doklady Earth Sciences - The first data on the discovery of Th–Sc mineralization in the pyritic complexes of the Southern Urals are presented. The minerals of Th (thorite) and Sc-containing...     

First Results of U–Pb Dating of Detrital Zircons from the Upper Precambrian Basal Deposits of the Subpolar Urals

Doklady Earth Sciences - Based on the first results of massive U–Pb dating of detrital zircons from the basal deposits of the Upper Precambrian section in the Subpolar Urals, their age is...     

Minerals of the Fe–Ni–Co–Cu–S System in Picrite Intrusions of the Southern Urals: Signatures of Liquation and Differentiation of the Sulfide Melt

Doklady Earth Sciences - New data on the minerals of the Fe–Ni–Co–Cu–S system in the differentiated intrusions of the Southern Urals are presented. Based on a detailed study...     

Indicator Isotope–Geochemical Characteristics of Sulfides from the Satka Magnesite Ore Field (South Urals Province)

The stable enrichment of pyrite from magnesite ores in δ³⁴S isotope (from 5.4 to 6.9‰) compared with pyrite from the host (sedimentary and igneous) rocks was established in the classical Satka sparry magnesite ore field. Concretionary segregations of fine-grained pyrite in dolomite are depleted in the heavy sulfur isotope (δ³⁴S, from–9.1 to–5.8‰). Pyrite from dolerite is characterized by δ³⁴S values (–1.1 and 1.7‰) close to the meteorite sulfur. The δ³⁴S values in barite from the underlying dolomite horizon vary in the range of 32.3–41.4‰. The high degree of homogeneity of the sulfur isotope composition in pyrite from magnesite is a result of thermochemical sulfate reduction during the syngenetic crystallization of pyrite and magnesite from epigenetic brines, formed during dissolution of evaporite sulfate minerals at the stage of early catagenesis of the Riphean deposits.

     

Genesis,Features of Mineral Composition,and Problems of the Development of Rare Metal–Titanium Placers in the West Siberian Megaprovince

Lithology and Mineral Resources - The coastal-marine rare metal–titanium placers of the West Siberian megaprovince were formed in a relatively short Eocene–Late Oligocene interval. A...     

First data on Early Carboniferous intrusive magmatism of the eastern margin of the Middle Urals: Geodynamic conditions and U–Pb isotope constraints

U–Pb LA ICP–MS dating of zircon from rocks of the Nekrasov gabbro–granitoid complex within the eastern margin of the Middle Urals was performed. The average U–Pb age calculated from three concordant measurements (326 ± 8 Ma) shows that their intrusion occurred at the Serpukhov Stage of the Early Carboniferous. According to the ideas on periodization of magmatic processes within the eastern sector of the Middle Urals, the formation of this complex corresponds to the final episodes of the continental marginal (supersubduction) magmatism.     

Timing of Back–Arc Spreading of the Paleozoic Island Arc of the Urals: Implication of Sm–Nd and U–Pb Dating of Dolerites and the Composition of Inclusions in Zircon

Doklady Earth Sciences - Dolerites of the parallel dikes formed in a back-arc spreading setting have been dated by Sm–Nd to the Silurian (426 ± 34 Ma) for Mount Azov in the Central...     

190Pt–4He Age of Native Platinum Minerals of the Baimka Gold Placer Cluster,Western Chukotka

Doklady Earth Sciences - The results of 190Pt–4He dating of placer-forming minerals of platinum (PMP) from the Baimka gold placer cluster (Western Chukotka, Russia) are reported. PMPs are...     

Assessment of the Role of Carbonate–Bicarbonate Fluids in the Transport and Deposition of REEs in the Process of Ore Formation (Thermodynamic Modeling)

Doklady Earth Sciences - Thermodynamic calculations on the impact of carbonate–bicarbonate fluids cooling from 500 to 100°C on a monazite + calcite association with a simultaneous...