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Abstract:We present a physicochemical model for the formation of magnetite-chlorite-carbonate rocks with copper gold in the Karabash ultramafic massif in the Southern Urals, Russia. The model was constructed based on the formation geotectonics of the Karabash massif, features of spatial distribution of metasomatically altered rocks in their central part, geochemical characteristics and mineral composition of altered ultramafic rocks, data on the pressure and temperature conditions of formation, and composition of the ore-forming fluids. Magnetite-chlorite-carbonate rocks were formed by the hydrothermal filling of the free space, whereas chloritolites were formed by the metasomatism of the serpentinites. As the source of the petrogenic and ore components, we considered rocks (serpentinites, gabbro, and limestones), deep magmatogenic fluids, probably mixed with metamorphogenic fluids released during dehydration and deserpentinization of rocks in the lower crust, and meteoric waters. The model supports the involvement of sodium chloride-carbon dioxide fluids extracting ore components (Au, Ag, and Cu) from deep-seated rocks and characterized by the ratio of ore elements corresponding to Clarke values in ultramafic rocks. The model calculations show that copper gold can also be deposited during serpentinization of deep-seated olivine-rich rocks and ore fluids raised by the tectonic flow to a higher hypsometric level. The results of our research allow predicting copper gold-rich ore occurrences in ultramafic massifs.

Реферат. На основе обширного архивного материала и новой геологической информации обсуждается природа газо-геотермальных явлений горы Янгантау (Башкирия), на которой располагается известный курорт. Несмотря на длительную историю изучения, феномен Янгантау все еще является предметом дискуссии. Помимо наиболее популярной гипотезы подземного горения высказывались предположения о том, что это результат разогрева при шарьировании, проявление окисления сульфидов, следствие внедрения молодой интрузии и даже реакции радиоактивного распада. Впервые обнаруженные здесь «черные блоки» (участки, обогащенные сажистым веществом) позво-лили провести аналогию между горой Янгантау и горящими угольными терриконами, а особенности состава термальных газов и их вариации - однозначно поддержать гипотезу горения углеводородов в качестве причины их выделения. Изучение находки самородного чугуна, найденного при стро-ительных работах на курорте «Янган-Тау», позволило подкрепить этот вывод и получить дополнитель-ные сведения о температурах и составе термальных газов на начальной стадии горения. Хроматогра-фия чугуна и стекла с его поверхности в интервале температур 600-1000 °С показала в составе выделившихся газов высокие содержания монооксида углерода. Сделан вывод, что на горе Янгантау имел место природный доменный процесс. Очаг горения расположен в осадочных отложениях на небольшой глубине. Рудой послужили, вероятно, поверхностные скопления бурого железняка. Предложена модель процесса в очаге как многофазной системы, в которой взаимодействуют горные породы, метеорные осадки, воздух, проникающий по трещинам, битумы, содержащиеся в янгантауской свите и (предположительно) газообразные углеводороды. В настоящее время тем-пература очага быстро снижается, что ставит перед администрацией курорта непростые вопросы о путях его дальнейшего развития. Notwithstanding a long history of study, the phenomenon of Yangantau is still a topic of a discussion. Apart of the most popular hypothesis of an underground fire, assumptions that it is a result of frictional heating at a tectonic thrust, of sulfide burning, heat of a young igneous intrusion or even a result of a radioactive decay were suggested. The «black blocks», discovered here for the first time (places, enriched by a carbonaceous substance) permitted to find an analogy between the mountain and burning coal refuse heaps, and a specifics of compositions of geothermal gases and their variations - to support the hypothesis of burning of hydrocarbons as the reason of their discharge. The study of a find of a native cast iron, discovered during constructional works in the resort, permitted to support this conclusion and acquire additional information оn a temperature and composition of thermal gases at an early stage of burning. Chromatography of the iron and glass from its surface in the temperature interval of 600-1000 °С have shown high concentrations of CO. A conclusion was made that it was a natural blast-furnace proce s that was taking place in the Yangantau mountain. The center of burning is s...

Research subject. The results of studying the geology and mineralogy of the Poldnevskoye deposit of demantoid are presented. Material and methods. The factual material was collected during feld research. Demantoid samples were pro vided by mine owners. Rock and vein minerals were studied in hand specimens, polished specimens and thin sections; the chemical composition was determined by X-ray fluorescence spectroscopy, scanning electron microscopy, electron probe X-ray spectral microanalysis, inductively coupled plasma mass spectrometry with laser sampling (LA-ICP-MS).Results. The Korkodinsky ultrabasic massif containing the deposit experienced strong decompression and syndecompression mineral formation during the ascent. At an early stage, veins of clinopyroxenite formed in dunite, which also experienced decompression cracking. Then the rocks underwent antigoritization and the appearance of vein antigorite, which was replaced by veins of clinochrysotile (+ magnetite ± carbonate ± demantoid). This was followed by the formation of lizardite (+ magnetite ± carbonate ± demantoid), which also developed along the earlier vein serpentines. Demantoid is represented by rounded grains and rounded grain aggregates with the signs of growth under the conditions of allround extension. The predominant color is brownish-green, yellow-green, rarely green and dark green. Green and dark green demantoids contain Cr2O3 0.52–2.3 wt %. In the central part of some grains and demantoid aggregates, a brown color is observed, which binds to TiO2, the content of which reaches 1 wt %. The demantoids of the Poldnevskoye deposit bear typomorphic features of the Ural-type demantoids (inclusions of the “horse’s tail” type). The distribution of demantoid is nested. The length of the veins with demantoid is frst meters. Their pillar-like shape is assumed. Conclusion.Demantoids from nests in serpentinized massive or brecciform dunites are more intact; demantoid nests in strongly serpentinized rocks were tectonic crushed and contain little gemstone.

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