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a comparatively large mass of native metal (gold, silver, platinum) in ores and placer deposits. Nuggets are rare and are usually distinctly larger than the great majority of particles of the native metals. Their weight, as a rule, exceeds 1 g. The largest gold nuggets, which were found in Australia, include the Holtermann nugget (285 kg with quartz, 83.3 kg of pure gold) and the Welcome Stranger nugget (70.9 kg with quartz, 69.6 kg of pure gold). The Diamond Fund of the USSR contains such gold nuggets as the Bol’shoi Treugol’nik (36.2 kg) and the Verbliud (9.29 kg). Large platinum nuggets have been found in the dunites (0.427 kg) and placers (9.639 kg) of the Nizhnii Tagil massif of the Central Urals.
The morphological characteristics of the nuggets of noble metals derive from the shapes of the enclosing cavities; only rarely does the development of the metals’ own crystalline forms play a part. Distinctions are made between nugget crystals, nugget concretions, nugget dendrites, fissured and cemented accumulations, included quartz fragments, “casts” of drusy cavities, and nuggets with mixed shapes. The liquids passing over nuggets in placers cause the nuggets to acquire rounded shapes. It is commonly believed that most nuggets were formed in the process of ore formation from hydrothermal solutions. Nuggets from the “head” of ore shoots and from the zone of oxidation of certain ore deposits are the richest. Special devices—electronic nugget-catchers—are mounted on scrubbers to remove nuggets from placers.
REFERENCESBetekhtin, A. G. “Mineraly gruppy samorodnoi platiny.” In Mineralogiia Urala, vol. 2. Moscow-Leningrad, 1941.
Soboevskii, V. I. Zamechatel’nye mineraly. Moscow, 1971.
Petrovskaia, N. V. Samorodnoe zoloto. Moscow, 1973.
N. V. PETROVSKAIA