Geochemistry of coarse quartz sinter overlying an Early Cretaceous Serra Geral quartz andesite flow, Fronteira Oeste Rift, Rio Grande do Sul, Brazil

Sinter overlying the first quartz andesite flow at base of Serra Geral Group is a surface manifestation intense hydrothermal processes operating in Paraná Basin during Early Cretaceous. The coarse sinter from western Rio Grande do Sul state was studied satellite images, field surveying, optical petrography, scanning electron microscopy, and probe microanalyses, including backscattered images chemical analyses rocks. Quartz forms large crystals (10 cm) because it either deposited dilute aqueous solution or recrystallized fine-grained sinter. Well-crystallized chamosite — an iron aluminosilicate (Fe-chlorite) occurs crystals, partly associated with fractures. composition akin to that ore deposit associations. Noble metals two samples are present concentrations 0.1 ppm Ag 15 ppb Au. contents Ba, Bi, Cu, Mo, S, W low but significant. description signals presence major paleo-hotspring Fronteira Oeste Rift, Sul, Brazil, mertis further study fully characterize extent metallogenetic endowment (Au-Ag-Cu) epithermal province.