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| Mexias,André S.; Berger,Gilles; Gomes,Márcia E.B.; Formoso,Milton L.L.; Dani,Norberto; Frantz,José C.; Bongiolo,Everton M.. |
| A geochemical modeling of gold deposition was performed using the EQ3/EQ6 software package using conditions inferred from geological, petrographic, geochemical and fluid inclusion data from the Bloco do Butiá gold mine, Lavras do Sul, RS. Gold in the mine occurs only in the pyrite structure (invisible gold). The pyrite occurs associated with white mica (phengite) in the zone of phyllic alteration. The process of gold deposition showed to be related to temperature and pH decrease. The pH decrease was fundamental to gold deposition by destabilization of sulfur species [Au(HS)2- , HAu(HS)2(0) and Au(HS)0] dissolved in the aqueous solution, being Au(HS)0 the main gold transporting complex. The addition of KCl is hard to accept as cause of gold precipitation... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Geochemical modeling; Gold; Pyrite; Sulfur; Fluid-rock interaction. |
| Ano: 2005 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652005000400010 |
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| Bongiolo,Everton M.; Bongiolo,Daniela E.; Sardini,Paul; Mexias,André S.; Siitari-Kauppi,Marja; Gomes,Márcia E.B.; Formoso,Milton L.L.. |
| This work is an application of the 14C-Polymethylmethacrylate method to compare the porosity evolution between unaltered and propylitic-altered granites, using samples from Lavras do Sul region, Brazil. This method, when coupled with optical and electronic petrography has the advantage over other methods to provide the quantification and identification of total and local porosity of rocks. From petrographic observations, different kinds of porous zones were identified and quantified (microfractures, grain boundaries, alteration of minerals, etc). Results show that unaltered granites have 0.5 to 0.6% porosity and propylitic-altered ones have 1.7 to 1.8% porosity, even between samples with different textures. Porosity of altered rocks increases mainly due to... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Porosity quantification; 14C-PMMA method; Granite porosity; Hydrothermal alteration; Propylitic alteration; Lavras do Sul. |
| Ano: 2007 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652007000300011 |
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