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Russian Geology and Geophysics

2008 year, number 10

Gold-brannerite nuggets in placers of the Ozernoe ore cluster ( Buryatia )

A.G. Mironov, N.S. Karmanov *, A.A. Mironov, E.V. Khodyreva
Geological Institute, Siberian Branch of the RAS, 6a ul. Sakh'yanovoi, Ulan Ude, 670043, Russia
Keywords: Native gold; uranium mineralization; brannerite
Pages: 743-748


Large gold-brannerite aggregates (nuggets up to 50 g in weight) were found in placers of the Ozernoe ore cluster, western Transbaikalia. Brannerite occurs as large crystals and crystal aggregates and has the near-stoichiometric composition UTi2O6. It lacks REE, contains little, if any, Th, and has admixtures of FeO (2.0-3.7 wt.%), CaO (up to 2.7 wt.%), and SiO2 (up to 2.14 wt.%). It also bears fine (<1 μm) inclusions of Au-Ag- and Bi-containing tellurium minerals and bismuth minerals. Gold occurs in cracks of brannerite or aggregates with it on coprecipitation from solutions. Gold was also found as fine (1-3 μm) segregations in muscovite. Accessory minerals are hematite, barite, rutile (containing 0.36-3.61 wt.% FeO and up to 7.5 wt.% WO3), dolomite, siderite, and muscovite. High contents of Te and Bi were detected in Fe, Ti, and U hydroxides. A specific relationship between gold and rutile has been revealed both in large aggregates and in gold microinclusions (<1 μm) in rutile grains. In composition and paragenesis the studied gold-brannerite association is similar to ores of the El'kon type (Central Aldan) related to the Mesozoic magmatism.