Mobility of gold and silver in lateritic weathering profiles; some observations from Western Australia

Mann, A.

doi:10.2113/gsecongeo.79.1.38

Cited by 284 publications

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“…Le garimpo de Serra Pelada (1980-1984 a été le site de la ruée vers l'or la plus spectaculaire en temps modernes, mais la minéralogie de cette minéralisation de style bonanza n'a pas encore fait l'objet d'une étude détaillée. La redécouverte d'une carotte forée en 1982 d'un profil latéritique du garimpo nous a permis d'échantillonner des aggrégats d'or à grains grossiers.…”

Section: Sommaireunclassified

“…The weathering of gold particles under lateritic conditions leads to the development of an Au-rich, Ag-depleted halo (e.g., Mann 1984, Colin & Vieillard 1991, Freyssinet et al 1989, Minko et al 1992, Colin et al 1997, and ultimately, to the formation of grains of com-positionally pure, supergene gold (e.g., Boyle 1979, Mann 1984, Oliveira & Campos 1991, Santosh & Omana 1991, Lawrance & Griffin 1994. Like silver, palladium also is leached from gold alloy during weathering (Varajão et al 2000).…”

Section: Dendrites Of Palladian Goldmentioning

confidence: 99%

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PALLADIUM AND PLATINUM MINERALS FROM THE SERRA PELADA Au-Pd-Pt DEPOSIT, CARAJAS MINERAL PROVINCE, NORTHERN BRAZIL

Cabral

Lehmann

Kwitko-Ribeiro

et al. 2002

The Canadian Mineralogist

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The Serra Pelada garimpo (1980)(1981)(1982)(1983)(1984) was the site of the most spectacular gold rush in recent history, but the mineralogy of the bonanza-style mineralization has not so far been documented in detail. Rediscovery of an early drill-core, recovered in 1982 from the near-surface lateritic portion of the garimpo area, has provided coarse-grained gold aggregates for this study. The centimeter-long aggregates of gold occur in powdery, earthy material. They exhibit a delicate arborescent fabric and are coated by goethite. Four compositional types of gold are recognized: palladian gold with an atomic ratio Au:Pd of 7:1 ("Au 7 Pd"), Hgbearing palladian gold (Au-Pd-Hg), Pd-bearing gold with up to 3 wt.% Pd (Pd-poor gold) and pure gold. A number of platinumgroup minerals (PGM) are included in, or attached to the surface of, palladian gold: "guanglinite", Sb-bearing "guanglinite", atheneite and isomertieite, including the noteworthy presence of Se-bearing PGM (Pd-Pt-Se, Pd-Se, Pd-Hg-Se and Pd-Bi-Se phases, and sudovikovite and palladseite). They define an As-Sb-Hg-Se mineral assemblage typical of hydrothermal vein-type deposits formed at relatively low temperatures. Native palladium, characteristically situated in the goethite coating, is intimately associated with a Pd-O phase. The remarkable occurrence of native platinum associated with Pd-bearing gold, PGM (compositionally close to mertieite-II and isomertieite) and berzelianite from a nearby prospect (Elefante prospect) is also recorded.

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Section: Sommaireunclassified

Section: Dendrites Of Palladian Goldmentioning

confidence: 99%

PALLADIUM AND PLATINUM MINERALS FROM THE SERRA PELADA Au-Pd-Pt DEPOSIT, CARAJAS MINERAL PROVINCE, NORTHERN BRAZIL

Cabral

Lehmann

Kwitko-Ribeiro

et al. 2002

The Canadian Mineralogist

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“…La baisse de l'humidité relative de l'air ou du niveau de la nappe phréatique force l'eau capillaire à migrer dans les pores de petite taille, entraînant ainsi une diminution de l'activité de l'eau à l'intérieur du système poral, et subséquemment une tendance à la déshydratation du milieu. En outre, l'oxydation du fer dans les profils latéritiques conduit inévitablement à la production des ions H + , d'où la tendance à l'acidification du profil (Mann 1984;Brimhall et al 1988 réduction de la surface adsorbante (Walker et al 1982). Le pouvoir adsorbant des produits d'altération peut être plus important, si les particules adsorbent à leur tour la matière organique (Davis 1984;Van Geen et al 1994).…”

Section: -Le Gaz Carboniqueunclassified

“…Les complexes chlorurés sont souvent mis en avant comme responsables de la mise en solution des EGP et de l'Au sous les conditions oxydantes et acides (Mann 1984;Jaireth 1988;Tait et al 1991;Mountain and Wood 1988a;Plimerand William 1988;Wood et al 1989;Wood et al 1992;Gammons et al 1992;Jaireth 1992). Il ressort de toutes ces études que sous les conditions de basse température, la formation des complexes chlorurés du Pt et du Pd reste limitée aux milieux acides (pH < 4) et extrêmement oxydants (hématite stable), que l'on peut retrouver dans la CU.…”

Section: Rôle Des Complexes Chlorurésunclassified

“…Il ressort de toutes ces études que sous les conditions de basse température, la formation des complexes chlorurés du Pt et du Pd reste limitée aux milieux acides (pH < 4) et extrêmement oxydants (hématite stable), que l'on peut retrouver dans la CU. En effet, on pense qu'au niveau de la CU, les pH sont les plus bas du profil latéritique, à cause de l'acidification des fluides latéritisants due à l'oxydation du fer ferreux ("ferrolysis") (Mann 1984;Webster 1986). …”

Section: Rôle Des Complexes Chlorurésunclassified

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Formation des latérites nickélifères et mode de distribution des éléments du groupe du platine dans les profils latéritiques du complexe de Musongati, Burundi /

Bandyayera¹

1997

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Laterite and Ferricrete

Widdowson¹

2007

Geochemical Sediments and Landscapes

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The term laterite, in its general sense, is given to a range of iron-rich, subaerial weathering products that develop as a result of intense, substrate alteration under tropical or sub-tropical climates. Physically, many laterites are rock-like, yet they cannot be easily placed into any of the major petrological groupings. Neither do they lend themselves readily to description as 'soils', other from the fact that they are the products of processes operating at the atmosphere -substrate interface. They are perhaps best considered to be metasomatic rock materials; i.e. rocks with chemical, mineralogical and physical characteristics that have been substantially changed by lowtemperature and pressure alteration processes such as those operating under subaerial conditions. The conditions under which lateritic profi les form are primarily:• a favourable climate, typifi ed by seasonal, high annual rainfall (e.g. a monsoon-like climate) -high humidity and high mean annual temperatures further promote chemical weathering and mineral alteration; • a favourable geomorphological environment, characterised by limited runoff and lack of aggressive erosion -the ingress of rainfall and/or the establishment of a water table may promote element enrichment and depletion processes; • relative tectonic stability, characterised by minimal uplift and crustal deformation.The manner in which ferricrete alteration profi les evolve differs from laterite weathering profi les in a number of ways: a genetic distinction between laterite and ferricrete is adopted here (Figure 3.1).

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Mobility of gold and silver in lateritic weathering profiles; some observations from Western Australia

Cited by 284 publications

References 0 publications

PALLADIUM AND PLATINUM MINERALS FROM THE SERRA PELADA Au-Pd-Pt DEPOSIT, CARAJAS MINERAL PROVINCE, NORTHERN BRAZIL

PALLADIUM AND PLATINUM MINERALS FROM THE SERRA PELADA Au-Pd-Pt DEPOSIT, CARAJAS MINERAL PROVINCE, NORTHERN BRAZIL

Formation des latérites nickélifères et mode de distribution des éléments du groupe du platine dans les profils latéritiques du complexe de Musongati, Burundi /

Laterite and Ferricrete

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