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—We studied the mineralogical and geochemical features and formation conditions of productive mineral assemblages of the Tardan gold–sulfide–quartz deposit located in the endo-/exocontact zone of the Kopto–Bai-Syut gabbro-diorite–plagiogranite pluton of the Early Ordovician Tannu-Ola complex (O1tn). Postskarn mineralization of vein–dissemination type in skarns, quartz diorites, and carbonate rocks is limited by tectonic crushing zones and conjugated with beresitization and listwanitization of the ore-bearing rocks. Mineralogical and geochemical research has shown the formation of ultrahigh-fineness (986–952‰) and high-fineness (947–918‰) gold at the first productive gold–quartz–calcite substage, of high-fineness gold (918–904‰) → medium-fineness gold (896–809‰) → low-fineness gold (798–756‰) ± hessite Ag2Te ± volynskite AgBiTe2 at the second productive gold–telluride–sulfide–quartz–carbonate substage, and of medium-fineness gold (897–802‰) → low-fineness gold (799–717‰) → electrum (691–612‰) → mercurian electrum (471–451‰) ± hessite Ag2Te ± acanthite Ag2S ± matildite AgBiS2 at the third productive gold–sulfosalt–sulfide–quartz substage. High- and medium-fineness gold prevails in the ores, ultrahigh- and low-fineness gold is subordinate, and electrum and mercurian electrum are scarce. The fineness of native gold in the ores varies from 451 to 986‰, averaging 858‰. The productive mineral assemblages of the Tardan deposit formed from aqueous fluids containing Mg, Na, and K chlorides (salinity of 6.1–12.9 wt.% NaCl eq.), with a decrease in the mineral formation temperature from 380 to 150 ºC and variations in fO2, fS2, fSe2, and fTe2.

—The Inagli zoned ring massif is located in the Central Aldan ore district. The close localization of ultrabasic and alkaline potassic rocks, magmatism, and mineralization (platinum, gems Cr-diopside, and vermiculite) make this object unique from both geological and economic perspectives. Formation of alkaline rocks in the Inagli massif was related to the Mesozoic tectonomagmatic activation of the Aldan Shield and occurred in several stages. Intrusion of clinopyroxenites took place no later than 145.8 ± 3.2 Ma, whereas most of alkaline rocks of the ring framing formed at 133–128 Ma. The feldspar-Cr-diopside-mica veins in the dunite core are dated at 133.4 ± 1 Ma.

Based on study of fluid and melt inclusions in minerals from igneous rocks and associated ore-metasomatic objects, we consider the formation conditions of oxidized fluids produced at the final stages of differentiation of alkali-basic, alkaline, lamproitic, and some granitoid melts. These fluids are characterized by wide variations in composition, concentrations, and physicochemical parameters (P, T, Eh, pH, etc.) and are of sulfate-chloride, sulfate-carbonate, sulfate-fluoride, fluoride-sulfate, essentially sulfate, and other types. The specific composition of these magmatogene fluids showing a high extractive power favors the effective removal of ore-forming elements (Fe, Mn, Co, N, Ag, Cu, Pb, Zn, Mo, W, Bi, U, REE, etc.) from melt and their trapping from the host rocks. The set of these elements is determined by P-T-X-parameters, conditions of fluid separation from melts, composition of fluid-generating magmas, and geochemical composition and metal-bearing capacity of rocks through which the fluids migrate. These factors significantly determine the metallogeny of alkaline, alkali-basic, and some granitoid complexes and associated mineralization.