Geologicheskii Vestnik

The petrochemical and geochemical features of intrusive rocks occurring within the area of the gold deposits and ore occurrences of the Ismakaevo and Gornyi Priisk ore zones in the Avzyan ore region of the Southern Urals have been studied. The gabbro-dolerites from gold ore occurrences differ somewhat in geological and petrochemical parameters, that served the previous researchers as a basis for their isolation in different age groups — the Early Middle Riphean in the Ismakaevo ore zone and the Vendan zone in the Gornopriisk zone in the Bogryashka ore zone. In gabbro-dolerites of the Ismakaevo ore zone (UlyukBar, Kurgashlya), elevated concentrations of chromium (up to ~4000 g/t) have been established, which are probably due to the relatively high magnesia of the unchanged representatives of these igneous rocks. At the same time, gabbro-dolerites from gold ore occurrences have similar lanthanide distribution trends, similar to those in supposedly Late Riphean gabbro-dolerites, developed outside of ore gold occurrences, and also coincide with the graphs of normalized lanthanide contents of the Middle Riphean intrusive rocks of the Bashkir meganticlinorium. The similarity of the distribution of REEs in igneous rocks from the gold ores of the Avzyan ore region suggests that they are not uneven-age formations, but differentiates of a single magmatic source, probably formed in the Middle Riphean time.

Bashkir meganticlinorium, gold deposit, gabbro-dolerite, rare and rare-earth elements, Riphean

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