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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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| Formoso,Milton L.L.. |
| Weathering is a complex process comprising physical disaggregation, chemical and biological decomposition of rocks and minerals transforming complex structure minerals in simpler ones. Hydrolysis of silicates is perhaps the most important process but associated certainly to biological weathering. It is discussed the role ofwaters: activities/concentrations of chemical species, pH, Eh, importance of complexes. Weathering is not only a destructive process. It can concentrate chemical species and form mineral deposits (kaolin, bauxite, Fe, Mn, P, Nb, Au). Weathering studies are important in pedology, engineering geology, hydrogeology, paleoclimatology and ecology. The use of stonemeal is based upon the study of rock weathering. |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Chemical weathering; Hydrolysis of silicates; Biological weathering; Physicochemical parameters of weathering. |
| Ano: 2006 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652006000400014 |
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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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| Oliveira,Marisa T.G. de; Furtado,Sandra M.A.; Formoso,Milton L.L.; Eggleton,Richard A.; Dani,Norberto. |
| Kaolin at Campo Alegre Basin, Santa Catarina State, Brazil was formed from alteration of volcanic acid rocks. Halloysite clays dominate the clay fraction of the matrix of the kaolin body, whereas a poorly crystalline kaolinite is abundant in veins. Some primary blocky structures have high amounts of illite, in one mine, but in general, only low contents of illite-smectite, illite, chlorite-vermiculite, vermiculite and quartz were identified in the clay fraction of the samples. Toward the top of the mines, hematite and lepidocrocite appear in horizontal red and ochre colored levels and the amount of kaolinite increases compared to halloysite. The vertical zoning of alteration levels, the changes in mineralogy, the positive correlation between depth and... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Kaolinite; Halloysite; Halloysite morphology; Kaolin; Weathering; Clay genesis. |
| Ano: 2007 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652007000400008 |
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| Minuzzi,Orlando R.R.; Bastos Neto,Artur C.; Formoso,Milton L.L.; Andrade,Sandra; Janasi,Valcir A.; Flores,Juan A.. |
| This work aims at the geochemical study of Pitinga cryolite mineralization through REE and Y analyses in disseminated and massive cryolite ore deposits, as well as in fluorite occurrences. REE signatures in fluorite and cryolite are similar to those in the Madeira albite granite. The highest ΣREE values are found in magmatic cryolite (677 to 1345 ppm); ΣREE is lower in massive cryolite. Average values for the different cryolite types are 10.3 ppm, 6.66 ppm and 8.38 ppm (for nucleated, caramel and white types, respectively). Disseminated fluorite displays higher ΣREE values (1708 and 1526ppm) than fluorite in late veins(34.81ppm). Yttrium concentration is higher in disseminated fluorite and in magmatic cryolite. The evolution of several parameters... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Cryolite; REE; Y; Pitinga; Amazonia. |
| Ano: 2008 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652008000400012 |
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