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.