Литосфера (Jun 2018)
Bismuth-nickel mineralization in chromitites of Mariinskii deposit (Urals emerald mines)
Abstract
The unusual Bi-Ni mineralization, represented by parkerite, millerite, bismutohauchecornite, bismuthinite, nickeline and, possibly nickel analogue of smythite (?), found in the metasomatically altered chromite rocks of the Mariinsky emerald-beryllium deposit is described. Chromitites with Bi-Ni mineralization are found in the mica complexes in direct connection with serpentinite bodies., Polished sections from the selected chromite samples were examined with the CAMECA SX 100 electron probe microanalyzer (IGG UrB RAS). In the study of sulfide and arsenide mineralization, the accelerating voltage was 15 kV, the electron beam current - 30 nA, the duration of intensity measured at a peak was 10 sec, at the background was 5 seconds, the diameter of the analysis point was 2 μ. For microprobe analyzes, the following standard samples were used: pure metals (Bi, Ni, Co), alloys (GaSb) and sulphides with arsenides (pyrrhotite, sphalerite, InAs). The formation of the studied unusual Bi-Ni mineralization in metasomatically altered micaceous chromite ores of the Ural Emerald Mines is directly related to the formation of rare-metal pegmatites of the nearby Aduiskiy granite massif. The acidic fluid flow associated with the introduction of pegmatite veins transformed not only the chromite bodies, but also the serpentinites, which containing them, with the formation of talc-carbonate and talc-anthophyllite rocks, mica rocks and other high-temperature apohyperbasite metasomatites. This fluid, enriched in Be and F, which superimposed on the chromite matrix, that formed such unusual metasomatic mineral paragenesis as chromite, muscovite-aluminoseladonite, fluorophlogopite, tourmaline (fluorodravit-dravite), mariniskite-chrysoberyl, fluorapatite, eskolaite, zircon, sulphide, chromferide and native metals. The source of bismuth certainly was acidic fluids, nickel is contained in the hyperbasites themselves, sulfur and arsenic could be from hyperbasitic intrusions (they often contain impregnations of millerite, hizlewoodite and mauherite) and from granitoid ones. Such mineralization is typical for sulfide copper-nickel ores and hydrothermal veins of a five-element formation, in ophiolite bodies and associated chromite rocks such mineral association was not observed. The discovery of bismutohauchecornite is the first, and parkerite - the third in the Urals. Formation of Bi-Ni-mineralization took place in the temperature range from 300oC to 200oC.
