A hydrogeological conceptual model for the groundwater dynamics in the ferricretes of Capão Xavier, Iron Quadrangle, Southeastern Brazil

Enhanced terrestrial Fe(II) mobilization identified through a novel mechanism of microbially driven cave formation in Fe(III)-rich rocks

“…In recent years, there has been increasing evidence that microbial Fe-cycling may be responsible for the maintenance of canga, with Fe(III) reduction releasing Fe(II) that is then oxidized as it moves toward the surface 9 , 12 , 13 , 19 , 20 . The abundance of consolidated Fe(III) (hydr)oxide cements at the surface make it resistant to weathering and limits water infiltration; however, discontinuities in the surface of the canga, such as tension joints, fractures and penetration by plant roots allow water to enter the subsurface, where the crust-like surface give ways to a high-porosity matrix in the canga, with an internal porosity up to 29% 1 , 11 , 21 – 23 . The routes for water into the subsurface and relatively high internal porosity of canga results in the formation of regionally significant aquifers, and water flow can reach 2.80 × 10 –4 m s −1 , comparable to highly fractured rocks and even karst aquifers, with primary porosity occurring at the canga-BIF interface 1 , 11 , 24 .…”

“…The abundance of consolidated Fe(III) (hydr)oxide cements at the surface make it resistant to weathering and limits water infiltration; however, discontinuities in the surface of the canga, such as tension joints, fractures and penetration by plant roots allow water to enter the subsurface, where the crust-like surface give ways to a high-porosity matrix in the canga, with an internal porosity up to 29% 1 , 11 , 21 – 23 . The routes for water into the subsurface and relatively high internal porosity of canga results in the formation of regionally significant aquifers, and water flow can reach 2.80 × 10 –4 m s −1 , comparable to highly fractured rocks and even karst aquifers, with primary porosity occurring at the canga-BIF interface 1 , 11 , 24 . Despite this porosity, the weathering-resistant nature of canga would suggest that karstification is limited; however, these iron landscapes represent some of the most cave-dense regions of Brazil, containing over 3,000 documented iron formation caves (IFCs), representing ~ 20% of all the known caves in Brazil 1 , 21 , 22 , 25 , 26 .…”

Relações entre Mineração e Recursos Hídricos Subterrâneos

“…sedimentares, Formação Cata Preta (Castro et al, 1998 apud Endo et al, 2020, envolvem horizontes saprolitizados de coloração avermelhada com presença seixos sub angulosos à arredondados de filitos, quartzitos ferruginosos e quartzo de veio envolvidos por uma matriz argilosa. Cangas estruturadas recobrem os platôs enquanto detríticas ocorrem em encostas e fundos de vales(Dias & Bacellar, 2021). Os perfis de solo predominantes são cambissolos, e neossolos litólicos, com presenças locais de plintossolos, os quais integram regiões de encostas e vales, com regiões planas elevadas recobertas por latossolos de baixa a moderada estruturação(Shinzato & Carvalho Filho, 2005) (Figura 5).…”