On the Rosettes of "Native Palladium" From Minas Gerais, Brazil: Evidence From Gongo Soco

Cabral, Alexandre Raphael; Kwitko-Ribeiro, Rogerio

doi:10.2113/gscanmin.42.2.683

Cited by 6 publications

(4 citation statements)

References 17 publications

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“…Serra Pelada and Minas Gerais (Brazil), and Gold Ridge and Alligator River (Australia), the concentrations of the metals follow the sequence Pt,Pd,,Au. 2,25,31 The Waterberg deposit comprises two quartz veins that occupy a fault between northwest dipping Rooiberg volcano-sedimentary rocks and horizontally bedded Mesozoic sandstones. The deposit has enormous historical as well as genetic significance, as its discovery by the prospector Adolph Erasmus in June 1923 marked the first find of platinum as a primary metal in South Africa.…”

Section: Introductionmentioning

confidence: 99%

A geological investigation of the Waterberg hydrothermal platinum deposit, Mookgophong, Limpopo Province, South Africa

Armitage¹,

McDonald²,

Tredoux³

2007

Applied Earth Science

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The geology around the unusual quartz-vein hosted Waterberg platinum deposit was mapped using aerial photographs at a scale of 1 : 1000 to establish possible controls on this unique style of mineralisation. The study area is located in the Mookgophong (Naboomspruit) District of the Limpopo Province in South Africa and is dominated by a gently to moderately, NNW-dipping irregular sequence of bimodal (rhyolite-basalt) volcanics, interbedded with many sedimentary rocks, that form part of the extensive 2?06 Ga Rooiberg Group, that are cut by variably striking, steep to subvertical quartz veins. The regional geology of the area was mapped at various scales in the 1920s and 1940s, but much of this work remains inaccessible and mapping during this study has uncovered more detail. The major platiniferous quartz vein (known as the 'Main Lode') juxtaposes volcanic rocks of Rooiberg age against Triassic sandstones and therefore occupies a fault. There is no textural evidence that quartz veining was syntectonic and may be much younger. The well-exposed vein fabrics show many features typical of low pressure epithermal quartz veins and probably formed near the present-day surface beneath a highly eroded Karoo cover, suggesting a recent age for veining and Pt mineralisation. The Main Lode can be followed for at least 3 km along strike, but Pt mineralisation is concentrated in a short section of the vein around 500 m in length. A major regional fault (the Welgevonden Fault) occurs about 2 km to the northwest of, and parallel to, the Main Lode. The Welgevonden Fault zone is suggested to extend to the northeast and merge with the Planknek-Ysterberg Fault system, south of Mokopane (Potgietersrus). The Welgevonden Fault is presently geothermally active, but this fluid system does not carry significant concentrations of Pt and may represent a younger Pt-depleted stage of hydrothermal activity related to the event that formed the Main Lode. It is unlikely that the Rooiberg volcanics and younger rocks supplied the platinum-group elements in the deposit and the source for these metals must lie elsewhere. It is suggested that shearing along the Welgevonden-Plankneck Fault system transposed PGE-bearing mafic rocks of the northern Bushveld Complex to a position at unknown depth beneath the Waterberg deposit, or provided a network of shear zones which could be exploited by a recent hydrothermal event that transported platinum and other metals westwards along the fault system and redeposited them near the surface.

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Section: Introductionmentioning

confidence: 99%

A geological investigation of the Waterberg hydrothermal platinum deposit, Mookgophong, Limpopo Province, South Africa

Armitage¹,

McDonald²,

Tredoux³

2007

Applied Earth Science

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“…These Pd-Cu rosettes formed in supergene oxidizing conditions possibly at the expense of the Pd-Cu grains replacing the preexisting merenskyite, as they mainly coat the goethite crusts in situ or right around the grains. The rosettes located in areas lacking a precursor PGM may reflect either a complete dissolution of the Pd-PGM or, more likely, further mobility and reprecipitation of Pd away from its main source.Similar rosette-like crystals, between 1 and 5 µm diameter, with an orthogonal-disclike framework have been documented previously in Au-Pd-Pt veins (locally known as jacutinga type mineralization), at Itabira,Brazil (Kwitko et al, 2002;Cabral & Lehmann, 2003;Cabral & Kwitko-Ribeiro, 2004). These authors observed that the rosettes have a compositional range from PdO-like stoichiometry to native Pd.…”

supporting

confidence: 78%

“…PGE in gossans can occur in platinum-group minerals (PGM) inherited from fresh ores or in new minerals formed in the supergene environment. The latter involves remobilization of PGE at low temperatures, has been disputed in the past, but several studies have shown conclusive evidence of this process (e.g., Bowles 1986;Kwitko et al, 2002;Oberthür et al 2003;Cabral and Kwitko-Ribeiro, 2004). Alloys, such as Os-Ir-Ru and Pt-Fe, are among the most common types of PGM argued to have formed in surface zones either by weathering or later precipitation in streams, where they commonly form PGE placer deposits (Tolstykh et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

O depósito sulfetado Ni-Cu-(pge) de Limoeiro : metalogênese, magmatismo máfico e metamorfismo no leste da Província Borborema

Silva¹

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Obrigado à banca de defesa desta tese. Excelentes contribuições de todos: Elton Dantas (UnB), Massimo Matteini (UnB), Haroldo Sá (UFBA) e Elson Oliveira (UNICAMP). E é claro, obrigado àqueles dois para quem este trabalho é inteiramente dedicado; a base das bases: Julia e Tito. Nada mais nada menos que parceiros de vida... Enfrentaram comigo o desconforto de uma mudança atropelada para a porção mais chuvosa da terra da rainha. Viveram por entre ratos e mofos e foram de bicicleta na chuva para creche inúmeras vezes. O que falar deles? Amo vocês! v "The noble science of Geology loses glory from the extreme imperfection of the record. The crust of the earth with its embedded remains must not be looked at as a well-filled museum, but as a poor collection made at hazard and at rare intervals."

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“…One example are the internally zoned Au–Pd arborescent grains from Hope's Nose, UK (Leake et al ., 1991) and Serra do Espinhaço, Minas Gerais (Cabral et al , 2008). Another example are the rosettes of native Pd on the surface of gold nuggets from Gongo Soco Fe-ores, Minas Gerais (Cabral and Kwitko-Ribeiro, 2004) and the Pd–Cu rosettes coating goethite in the Limoeiro Ni–Cu–(PGE) deposit (Mota-e-Silva et al ., 2016). Neoformed Pt–Ir–Fe–Ni alloys and layers of Ir-rich alloys on multistage PGE-grains are reported from Ni-laterites in the Falcondo mining area, Dominican Republic (Aiglsperger et al ., 2016).…”

Section: Discussionmentioning

confidence: 99%

Placer platinum-group minerals in the Shetland ophiolite complex derived from anomalously enriched podiform chromitites

et al. 2018

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Highly anomalous platinum-group element (PGE) concentrations in the podiform chromitites at the Cliff and Harold's Grave localities in the Shetland ophiolite complex have been well documented previously. The focus of this study is alluvial platinum-group minerals (PGM) located in small streams that drain from the PGE-rich chromitites. The placer PGM assemblage at Cliff is dominated by Pt-arsenides (64%) and Pd-antimonides (17%), with less irarsite–hollingworthite (11%) and minor Pd-sulfides, Pt–Pd–Cu and Pt–Fe alloys and laurite. Gold also occurs with the PGM. Alluvial PGM have average sizes of 20 µm × 60 µm, with sperrylite the largest grain identified at 110 µm in diameter, matching the range reported for the primary PGM in the source rocks. The placer assemblage contains more Pt-bearing and less Pd-bearing PGM compared with the rocks. The more resistant sperrylite and irarsite–hollingworthite grains which are often euhedral become more rounded further downstream whereas the less resistant Pd-antimonides which are commonly subhedral may become striated and etched. Less stable phases such as Pt- and Pd-oxides and other Ni-Cu-bearing phases located in the rocks (i.e. Ru-pentlandite, PtCu, Pd–Cu alloy) are absent in the placer assemblage. Also the scarce PGM (PdHg, Rh- and Ir-Sb) and Os in the rocks are absent. At Harold's Grave only three alluvial PGM (laurite, Ir, Os) and Au were recovered reflecting the limited release of IPGM from chromite grains in the rocks. In this cold climate with high rainfall, where erosion dominates over weathering, the PGM appear to have been derived directly from the erosion of the adjacent PGE-rich source rocks and there is little evidence of in situ growth of any newly formed PGM. Only the presence of dendritic pure Au and Pd-, Cu-bearing Au covers on the surface of primary minerals may indicate some local reprecipitation of these metals in the surficial conditions.

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On the Rosettes of "Native Palladium" From Minas Gerais, Brazil: Evidence From Gongo Soco

Cited by 6 publications

References 17 publications

A geological investigation of the Waterberg hydrothermal platinum deposit, Mookgophong, Limpopo Province, South Africa

A geological investigation of the Waterberg hydrothermal platinum deposit, Mookgophong, Limpopo Province, South Africa

O depósito sulfetado Ni-Cu-(pge) de Limoeiro : metalogênese, magmatismo máfico e metamorfismo no leste da Província Borborema

Placer platinum-group minerals in the Shetland ophiolite complex derived from anomalously enriched podiform chromitites

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