Abstract

Ferromagnesian carbonate metasomatites in limestones of the Lower Riphean Suran Formation in the Avzyan ore region (Bashkir meganticlinorium) are represented by large Fe-magnesite deposits (e.g., Ismakaevo deposit) and breunnerite stocks (Bogryashka ore occurrence). Metasomatic zonation is manifested as alterations in the series: limestone → dolomite → Fe-magnesite (breunnerite). Fe-magnesite contains up to 8 mol % FeCO₃; breunnerite, from 10 to 40 mol % FeCO₃. Metasomatic fluid represented the Ca–Na–Mg chloride brine with Fe admixture and was linked with processes of the remobilization of evaporite brines buried in Lower Riphean rocks. Salinity and homogenization temperature of fluid inclusions are: 20–26 wt % equiv NaCl and 200–240°C, respectively, in magnesites; 10–15 wt % equiv NaCl and 140–190°C, respectively, in breunnerites. Interaction of the fluid with terrigenous rocks in a tectonically active zone of the Mashak riftogenic graben ensured the enrichment of brine with different ligands and the accumulation of MREE and HREE in metasomatic products. Upon the migration of fluid across the limestone sequence and its cooling, Fe-magnesite was formed in the frontal zone (Ismakaevo deposit); breunnerite, in the rear zone adjacent to the terrigenous shales (Bogryashka ore occurrence).

中文翻译：

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乌拉尔南部下里菲安陆生碳酸盐岩中铁磁交代碳酸盐的形成条件

摘要

Avzyan矿区（Bashkir meganticlinorium）下里菲安苏兰组的石灰岩中的铁镁碳酸盐交代岩由大量的铁菱镁矿床（例如Ismakaevo矿床）和褐铁矿床（Bogryashka矿床）代表。交代带化表现为一系列变化：石灰岩→白云岩→铁菱镁矿（褐铁矿）。铁菱镁矿包含高达8 mol％的FeCO ₃；breunnerite，从10至40％（摩尔）的FeCo ₃。交代液代表含铁的Ca-Na-Mg氯化物盐水，并且与掩埋在下Riphean岩石中的蒸发盐盐水的迁移过程有关。镁铝矿中流体包裹体的盐度和均质温度分别为：当量氯化钠20–26 wt％和200–240°C。在褐铁矿中分别含10-15 wt％当量的NaCl和140-190°C。Mashak裂谷ift构造活动区内流体与陆源岩石的相互作用确保了具有不同配体的盐水的富集以及交代产物中MREE和HREE的积累。随着流体在整个石灰岩层中的迁移和冷却，在锋区（Ismakaevo矿床）形成了菱镁矿。褐铁矿，在与陆源页岩相邻的后部（Bogryashka矿石的发生）。