| Abstrakt: |
Gold nuggets, loose in talus material, triggered an ongoing gold rush in the southern Serra do Espinhaço, Minas Gerais, Brazil. The talus material has abundant fragments of vein quartz in a clay-rich matrix, resting on metagreywacke of the Neoproterozoic Macaúbas Group. Quartz lodes, which truncate the metamorphic foliation of the bedrock metagreywacke, are the source of the gold nuggets, which formed after the main tectonic and metamorphic overprint of the Ediacaran–Cambrian Brasiliano orogeny. The gold nuggets are hypogene in origin, but they have a minor component of supergene gold, which occurs as dendrites of bud-like gold particles, mostly <1 µm across. Amongst the latter, apically branched hyphae of essentially pure gold are noteworthy and suggest pseudomorphism after fungi. [ABSTRACT FROM AUTHOR] |
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