Gossan - from a mafl 'upload'25 Aug 2017 20:25
2.1. Gossan
The gossan from Lagoa Salgada consists mainly of goethite, hematite and silica with substantial amounts of gold and lead.
In general, petrographic observations of the gossans confirm the predominance of goethite over the rest of the minerals and the main textures include: massive, boxwork, colloform and
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open space fillings. The final result is a heterogeneous assemblage of residual fragments of early goethite, accompanied by quartz, hematite, and fragments of gossanized rocks cemented by late Fe-oxyhydroxides and siliceous particles. The precious metals mainly occur as Au–Ag– Hg and Ag–Hg amalgam particles. Gold usually occurs as very fine-grained particles.
The high content in lead is explained by the presence of beudantite and mimetite crystals.