Maldonite, Uytenbogaardtit and Varieties of Native Gold in Lodesof the Nizhne-Myakitsky Mineral District, North-East Russia
This paper contains diagnostic descriptions of ore minerals as maldonite, uytenbogaardtit, and sponge and “mustard” native gold from ore occurrences of the RIRGD class in the south-east of the Yana-Kolyma gold belt. Maldonite is identified from Front and Platsdarm lodes characterized by bismuth-sulfotelluride mineral type, and utenbogaardtit from sulfide-sulfoarsenide ores of Platsdarm. Maldonite is present both as microinclusions in native gold and very small individual grains. It is also found as fragmentary rims around high-fineness native gold and grains intergrown with very high-fineness sponge gold containing bismuth oxides. Early mineralization stages were characterized by a joint crystallization of maldonite, native gold, and bismuth minerals. Maldonite usually deposited in interstitial pores and cracks in recrystallized quartz and sulfide-sulfoarsenide grains. Due to the hypogene transformation, maldonite was in part substituted by sponge gold of very-high fineness in association with bismuth oxides. The decomposition of maldonite included its substitution into native gold and bismuthine and the subsequent oxidation of bismuthine to bismuth oxides. Besides maldonite, uytenbogaardtite associated with galena and acanthite is observed as microinclusions and rims around fine gold grains with low fineness. In most cases, “mustard” native gold is present in chemical weathering products associated with base metal mineralization at the Berental lode. Globular particles of “mustard” gold are particles of almost pure native gold of tenths and hundredths of a micrometer. Pore-hosted cerargyrite may be sometimes present. Presumably, “mustard” gold has been due to hypogene alterations of uytenbogaardtit.