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Apport d'Une Prospection Systématique à l'Étude de l'Origine de l'Or et du Platine Alluviaux du Córrego Bom Sucesso (Serro - Minas Gerais)

par Cassedanne, Jacques J.P.;Jedwab, Jacques ;Alves, Jeanete J.N.
Référence Anais da Academia Brasileira de Ciências, 68, 4, page (569-582)
Publication Publié, 1996

Article révisé par les pairs

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Résumé :

This work deals with the search for the source of gold and platinum (associated to diamond) which are worked for more than two hundreds years in the Córrego Bom Sucesso, in the neighbourhood of the town of Serro (Minas Gerais State). A preliminary panning prospecting supported by the collect of 50 samples, allowed to determine the source of diamond: it proceeds from conglomeratic lenses embedded in quartzites, as to the source of the main associated minerals as: magnetite, ilmenite, hematite, pyrite, rutile and zircon. However, gold and platinum source remained hypothetical because no typical association or correlation with the above-mentioned minerals were detected. A complementary prospecting was realized in creek deposits ("lit vif"), old alluvium and soils. The usual alluvium study routine was also applied to crushed rocks. HF dissolution, geochemical analysis, gold nuggets analysis were also performed as done MEB examination of gold and platinum nuggets. Gold proceeds from two independent and no synchronous sources. Parte of it is included in quartzites of varied facies and colours. This gold was eroded from old rocks, transported and deposited among sands in a shallow sea. Then metamorphism, which little affected the gold, transformed the sands into quartzites. The second source of gold is from basic rocks transformed into amphibolites. These rocks occur as a long, almost NS running, rosary-shaped, intrusion that crosses and outcrops in the medium Córrego Bom Sucesso valley. Platinum also proceeds from the same intrusion, but from a northern and smaller lense. The composition of nuggets, which are unique in the world, with Pt-Pd-Hg alloys, without arsenides, tellurium or selenium, as the commonly botryoidal texture point out to a low temperature hydrothermal processus of metal deposition. A sample location map, analyses tables and a platinum nugget MEB microphotography complete the text.