Unusual, high grade iodide mineralization comprising marshite, miersite, and iodargyrite has been discovered in the oxidation zone of the Rubtsovskoe VHMS base metal deposit, Northwest Altai, Rus sia. The distribution of iodides reveals distinct zoning. Iodargyrite is widespread in the upper part of the oxi dized orebody at the hypsometric level of +156 to 163 masl. The iodargyrite zone extends for more than 150 m. The content of iodargyrite in gossan occasionally reaches 1-5 vol %. Marshite is localized at the lower level (+146 to +151 masl); the zone enriched in marshite is about 50 m in extent. The marshite content in the high grade oxidized ore with native copper and in the zone of wall rock argillic alteration is typically close to 1 vol %, occasionally reaching 7-10 vol %. Miersite occurs sporadically in association with both iodargyrite and low Ag marshite, which are antagonistic mineral species. Iodargyrite is stoichiometric AgI (2H polytype with a = 4.574 and c = 7.519 Å). Isostructural cubic marshite CuI and miersite (Ag,Cu)I make up an isomor phic series within compositional limits Mar 100 Mie 0 -Mar 9 Mie 91 and a break between Mar 82.5 Mie 17.5 and Mar 57 -Mie 43 ; the a parameter of their unit cells varies from 6.050 to 6.424 Å. The crystal morphology, prop erties, and mode of iodide occurrence are described in the paper. According to the suggested genetic model, the source of iodine was related to exhalations of seafloor fumaroles accompanying volcanic-hydrothermalsedimentary ore formation. Iodine is absorbed by clay in the wide zone of wall rock argillic alteration. During the early stages of sulfide ore oxidation, sulfuric acid oxidized iodine to (I 5+ O 3 ) -, and it was subsequently reduced and fixed in poorly soluble Ag + and Cu + iodides.

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