Gold and silver in polymetallic deposits of northwestern Rudny Altai

Studies of the contents and distribution of gold and silver and their compo sition and parageneses at the barite polymetallic and pyrite-polymetallic d eposits of northwestern Rudny Altai show that ore concentrations of these e lements formed during the generation of deposits of pyrite-polymetallic ore formation related to the Middle-Upper Devonian basalt-rhyolite volcanism. The concentrations of gold and silver in the deposits of different mineral types and their distribution in orebodies are extremely uneven. The barite- polymetallic deposits show the highest concentrations of gold and silver an d various mineral forms of their occurrence. The total contents of gold and silver at these deposits range from 4.3 to 6.3 ppm and from 43 to 82.8 ppm , respectively. Gold is characterized by a varying composition with fairly high contents of Ag (to 72%) and Hg (to 27%). A specific feature of these d eposits is a multistage development of ore formation processes and the pres ence of several generations of gold-silver minerals. The most productive we re the late stages, when barite and barite-polymetallic ores and veined ess entially copper ores of gold-bornite-chalcopyrite-pyrite association formed . The pyrite-polymetallic deposits are characterized by rather low contents o f gold (0.25-1.05 ppm) and silver (12-62.7 ppm). Gold-silver minerals are t ypically represented by one generation corresponding to the main stage of f ormation of pyrite-polymetallic ores and show an increased fineness of nati ve gold (Au - from 74.75 to 89.61%, Ag - from 25.58 to 8.32%). The most productive barite-polymetallic deposits occur at the bottom of the section of the Devonian volcanosedimentary series. Pyrite-polymetallic dep osits with elevated contents of gold are also localized at this level. This is especially typical of the deposits in the Zmeinogorsk ore region.