RARE-EARTH ELEMENTS IN METASOMATITES AND ORES OF THE DUKAT GOLD-SILVER DEPOSIT (northeastern Russia)
R.G. Kravtsova, M.N. Zakharov, and O.I. Korkina†
Institute of Geochemistry, Siberian Branch of the RAS, 1a ul. Favorskogo, Irkutsk, 664033, Russia
Keywords: Geochemistry, rare-earth elements, igneous rocks, metasomatites, ores
Pages: 589-603
Abstract
The distribution of rare-earth elements (REE) in metasomatites and ores of the Dukat epithermal gold-silver deposit in northeastern Russia has been studied for the first time. The deposit occurs in the sequence of Lower Cretaceous acid effusive rocks intruded by a granite massif. Granites, acid effusive rocks, rhyodacitic ignimbrites, and felsites form a volcanoplutonic association; in leucogranites, ΣREE = 288 ppm. Rhyodacitic ignimbrites contain more REE (191-203 ppm) than felsitic lavas and dikes (105-127 ppm). The ignimbrites and leucogranites have similar proportions of major lanthanide groups - 78Ce 16Y6Sc and 77 Ce 16 Y 17 Sc , respectively. High REE contents have been found in hornfels (up to 254 ppm) and greisens (up to 410 ppm) developed after acid effusive rocks at their contact with the granite intrusion. Processes of pre-ore areal sericitization and hydromicatization in acid volcanics contribute to the REE accumulation in hydrothermally altered rocks of the roof of the Dukat intrusion, particularly in hydromicatized volcanics (up to 404 ppm). Near-ore propylites developed after andesites on the deposit flanks are enriched in REE (up to 174 ppm). Altered argillizites of the central part of the deposit, which host gold-silver mineralization, are depleted in REE (61 ppm). Despite the difference in ΣREE, all wallrocks, irrespective of their composition and spatial occurrence, are enriched in light lanthanides. The Ce/Yb values vary from 37 to 46 in the altered propylites and argillizites and do not exceed 21 in the other wallrocks. The proportion of lanthanide groups in the altered propylites (88 Ce 10 Y 2 Sc ) is nearly the same as in the altered argillizites (88 Ce 11 Y 1 Sc ). In polychronous ores of the Dukat deposit, ΣREE varies over a broad range of values (3.9-37 ppm). High REE contents (up to 37 ppm) have been found in tin-silver-polymetallic ores of deep horizons of the deposit, and low ones, in later formed gold-silver and silver ores of the upper and middle horizons of its central part. Rejuvenated gold-silver ores show a minor variation in ΣREE (5.1-5.7 ppm). Minimum concentrations have been found in the last produced predominantly silver ores (3.9-5.1 ppm). Hydrophile lanthanides of the cerium group prevail in these ores but to a lower degree than in the altered metasomatites. The Ce/Yb values in the ores do not exceed 22.
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