Sequential opening and filling of cavities forming vesicles, amygdales and giant amethyst geodes in lavas from the southern Paraná volcanic province, Brazil and Uruguay

Paralavas in the Cretaceous Paraná volcanic province, Brazil - A genetic interpretation of the volcanic rocks containing phenocrysts and glass

“…In the dark reaction rim, loss on ignition is 2.4 wt.% and in the light reaction rim 1.5 wt.%. This distribution shows that these rocks were affected by the H1, H2 and H3 hydrothermal events described in detail by Hartmann et al (2012aHartmann et al ( , b, 2013.…”

“…The study of paralavas in the Paraná volcanic province derived from several years of research of hydrothermal mineralization hosted in volcanic rocks (e.g., Duarte et al 2009, Hartmann et al 2012a, b, Rosenstengel and Hartmann 2012 and sand injectite structures . Field studies for the present study focused in two areas ( Figure 1) that provided significant evidence for the genetic interpretation.…”

“…The older generation was trapped at higher temperatures from a higher salinity fluid, which may contain a volatile of low-density, besides single-phase inclusions consisting only of this volatile species. Fluid inclusions of later generation were entrapped under low temperature conditions from low salinity solutions which may be related to the Cretaceous hydrothermal events described by Hartmann et al (2012a) and superimposed on these rocks. On the other hand, the presence of CH 4 in the fluid inclusions in the paralavas of Paraná volcanic province has not been definitively identified because of the small size of inclusions.…”

Discussion: "Volcanic stratigraphy of intermediate to acidic rocks in southern Paraná magmatic Province, Brazil" by polo and janasi (2014), geologia USP. série científica, 14(2), 83-100

“…But the intrusive nature of the sand is clear in the province. The authors are presently directed to the detailed studies on the origin of the fine-grained sandstones intercalated with the volcanic rocks, because overwhelming genetic evidence for intrusion is displayed by Hartmann et al (2012aHartmann et al ( , 2012bHartmann et al ( , 2012c, Duarte et al (2014) and other chapters in Hartmann and Baggio (2014). These studies covered the Paraná volcanic province from Uruguay to Mato Grosso do Sul, including the intervening Brazilian states.…”

Relation between the sedimentary organic record and the climatic oscilations in the Holocene attested by palynofacies and organic geochemical analyses from a pond of altitude in southern Brazil

“…This process also led to the formation of ponds identified as "gossans" (Hartmann 2008), which have been considered as important guides for mineral prospecting (Pertille et al 2013) due to their consistent relationship to the underground amethyst mines. Pools showing similar morphology are common in the studied area, and according to Hartmann et al (2010Hartmann et al ( , 2012, have the same origin; in other words, the formation of gossans is due to supergenic processes in which weathering is superimposed on the hydrothermal systems, constituting an anomaly coincident with the mineralization of amethyst geodes. According to Hartmann et al (2012), the formation of smectite in the altered and mineralized rocks leads to the concentration of similar minerals in the overlying soil and a decrease in mass, and consequently, to the longterm residence of water in the depression or pond.…”