U-Pb zircon age of a sheeted dike complex in ophiolites in the structure of the Revdinsky massif, Ural Рlatinum Belt

Research subject. A tectonic block of ophiolites, corresponding to the root zone of a sheeted dike complex, in the eastern part of the Revdinsky massif of the Platinum-bearing belt of the Urals (UPB).Materials and methods. Zircons for dating were collected in the first-generation dolerite dikes of the sheeted dike complex under study, which had been previously considered as Ordovician. U-Pb dating of zircons was performed by LA-ICP-MS on a NexION 300S quadrupole mass spectrometer with a laser ablation attachment NWR 213.Results. Zircons with an age of 425.6 ± 2.9 Ma are characterized by primary magmatic zoning and apparently correspond to the time of intrusion of the sheeted dike complex. In zircons with an age of 404.0 ± 2.9 Ma, inclusions of metamorphogenic minerals (amphibole, chamosite, quartz, clinozoisite) were discovered. This age reflects rock recrystallization or metamorphism, for example, during the intrusion of later vein rocks of the diorite-tonalite series or dolerite dikes of the second generation. Three points of determination showed a younger age of 362 ± 5.6 Ma, probably reflecting the time of metamorphism at the beginning of collisional processes. Conclusions. For the first time, the Silurian U-Pb age of zircons (LA-ICP-MS) was obtained for the ophiolite block (root zone of the sheeted dike complex) in the structure of the Revdinsky massif UPB. The obtained age of intrusion of the sheeted dike complex (425.6 ± 2.9 Ma) coincides with the age of zircons (428.5 ± 3.7 Ma) from gabbro screens in sheeted dikes of the East Ural zone determined earlier (Smirnov, Ivanov, 2010) and corresponds to the time of spreading over the subduction zone in the Middle Urals.

Ore-controlling dike complexes of the gold-rare metal deposit Vladimirskoe (Eastern Sayan)

<p>Vladimirskoe gold-rare metal deposits are located in the Urik-Kitoiskaya gold zone, at the edges of the Neoarchean age Gargan microcontinent, in the southeastern part of the Eastern Sayan. Gold mineralization is localized in sheared, beresitised mineralized zones among granite gneiss of the Gargan Group (NARg). The width of the zones is 3-10 m and the length is up to 800 m. The material composition of the ores is sulfide-carbonate-quartz. The main ore minerals are pyrite, chalcopyrite, pyrrhotite, galena, sphalerite, as well as tellurides and sulfosalts of silver, lead, and bismuth. The main minerals at the deposit are gold, associated - silver, and bismuth, associated with sulfide mineralization. Average gold grades in ores are 7-12 g / t.</p><p>Mineralized ore zones are associated with faults, and are often localized at their intersection with dike complexes. Several fault systems are identified in the deposit. The first-order fault system is a right-lateral dip-slip with a submeridional strike. The second-order system has a northwest strike and represents zones of viscous faults, expressed by zones of cleavage, beresitisation, silicification, and sulfidization, which are associated with gold mineralization.</p><p>There are two types of dike complexes within the region. The first dike complex of the barun-holba subvolcanic complex (O-S) has basic composition. Dikes are widespread throughout the entire area and are characterized by diabase porphyrites, metabasalts, and more rarely, basaltic andesite porphyrites. The rocks have a porphyry structure with phenocrysts (1-3 cm) characterized by plagioclase, altered to form epidote and muscovite. Large porphyry segregations up to 10 cm, bearing traces of deformation processes are observed in some cases. The groundmass has a fine-grained, microlepidogranoblastic structure and is composed of a secondary epidote-chlorite-albite aggregate.</p><p>The second dike complex is less pronounced and is characterized by felsic dikes belonging to the Early Paleozoic Holba complex. It is located in the southeastern part of the region and is characterized by granite-porphyries, leucocratic pegmatoid granites, and dacites. Dikes of felsic composition have a felsic structure caused by microliths of albitised plagioclase, biotite, and secondary minerals (chlorite, epidote, amphibole, calcite).</p><p>Dikes and dike belts are the ore-controlling structures of gold mineralization. In intersecting zones of a northwestern strike, gold mineralization is concentrated near dikes and gradually fades away as we move from them. The greatest development of mineralized zones and the associated quartz-vein ore mineralization can be observed at the intersection of fault zones with dikes. In this case, ore columns with a thickness of 20-50 m formed, extending to a depth of 3 km. Vladimirskoe deposits belong to vein-dike ore-magmatic systems, their source of ore matter is of deep origin.</p><p>This work is supported by RFBR grants: No. 19-05-00764 and the Russian Ministry of Education and Science. </p><p>References:</p><p>Gordienko I.V. et al., // Geology Ore Deposits. 2016. V. 58, № 5, P. 405-429.</p><p>Seminsky Zh. V. et al. // Proceedings of the Siberian Branch of the Section of Earth Sciences of the Russian Academy of Sciences. T. 45, N. 2. 2014. P. 19-34.</p>

Study and Diagnostics of Convergent Rocks on the Example of Carbonated Fluid-Explosive Ultramaphic Dyke Complex (Middle Timan)

Fluid-explosive rocks of the dike complex are identified in the Middle Timan. The rocks have convergent properties due to a combination of explosive and metasomatic processes. The study of the petrographic features of the rocks revealed their explosive nature. Further study of the chemical composition of rock-forming minerals established the source of the mantle material and the paragenetic relationship with carbonatite magmatism. The fluid-explosive rocks of the dyke complex have a long-term multistage formation history. The fluids caused fenitization of the host strata and its disintegration. Solid-gas material of the mantle-crustal compound fills the cracks. At the last stage of formation of fluid-explosive rocks, the rare-metal, rare-earth, and sulfide mineralization took place.

Sources of matter for Neoarchaean subalkaline magmatic rocks of the Keivy structure (Kola Peninsula)

The Neoarchaean subalkaline magmatism of Keivy structure is expressed in formation of the volcano-plutonic association of latite-monzonite-granite (ALMG). The quantity of the measured relation 143Nd/144Nd in rocks is determined in 0.511061-0.511365, and values of model age are located in an interval from 3.14 to 3.21 billion years at εNd (2670) from 2.2 to -1.3. The initial relations 176Hf/177Hf in zircon are in limits 0.280950-0.281069, and figurative points of composition form the field around a trend of the CHUR. According to the isotope and geochemical data for all rocks the basic composition of protholits is supposed. In quantity εHf(T) points of zircon are localized in the field of the development of the crust with 176Lu/177Hf = 0.015 and 3.0-3.3 billion years age. It probably demonstrates the formation of initial melts mainly at the expense of matrix with a long time of stay in crust. The formation of ALMG magmas is assumed to appear due to the melting of metasomatically altered rocks of the lower crust during intrusion of basaltic melts initial for the rocks of the dike complex and the gabbro-labradorite massifs into the upper crust.

A New Porphyry Mo Mineralization at Aisymi-Leptokarya, South-Eastern Rhodope, North-East Greece: Geological and Mineralogical Constraints

A new porphyry Mo prospect has been discovered in the Aisymi-Leptokarya area, along the southern margin of the Byala Reka–Kechros metamorphic dome, south-eastern (SE) Rhodope metallogenic zone. The study area is dominated by an Oligocene felsic dike complex, which hosts the porphyry Mo mineralization and intrudes into upper Eocene sandstones-marls and the Leptokarya monzodiorite pluton. The Aisymi-Leptokarya felsic dike complex displays a rhyodacitic to dacitic composition with post-collisional affinities. The porphyry Mo mineralization occurs in the form of porphyry-style quartz stockworks in the felsic dike complex associated with potassic alteration characterized by hydrothermal K-feldspar. The ore minerals consist mainly of pyrite, molybdenite, kesterite, bismuthinite and galena within both the stockwork and the rock matrix. Bulk ore analyses indicate enrichment in Mo (up to 215 ppm), Se (up to 29 ppm), Bi (up to 8 ppm) and Sn (up to 14 ppm) in the porphyry quartz veins. Late-stage, north-east (NE-) and north-west (NW-)trending milky quartz intermediate-sulfidation epithermal veins with base metals, crosscut previous vein generations and are characterized by Ag, Sn and Te anomalies. The Aisymi-Leptokarya porphyry Mo prospect is set in a back-arc geotectonic regime and shares similarities to other post-subduction porphyry molybdenum deposits elsewhere.