Geoelectrical Signatures and their Relationships with the Lateritic Horizons: A Case Study of the N4EN Mine’s Iron Cave, Carajás Complex, Brazil

Abstract

The Brazilian speleological heritage is protected by laws, and every region where caves are present requires scientific studies to assist in environmental licensing. In the context of mining in iron formations, the near-surface geophysical studies using electroresistivity survey were performed in the cave N4E-0022, located at the N4EN iron mine, Carajás Complex, northern Brazil. The near-surface geophysical surveys generated continuous images that enhanced the lithostructural mapping of the lateritic profile, especially in places to which access by conventional methods was difficult. The electrical resistivity profiles were acquired with the dipole-dipole arrangement in the upper portion of the cave. Three sections were performed in SW-NE direction and two in SE-NW direction, totaling 435 meters of acquisition. The geoelectrical signatures were correlated with the lithologic logs of drillholes, the geophysical well logging and with the typical lateritic profile in the cave N4E-0022 surroundings. The results showed a satisfactory interpretation for the near-surface geoelectrical profiles and evolved to a comparison with the lateritic profile (lateritic crust, transition horizon, and saprolite horizon), providing inherent resistivity signatures for each modeled material.Keywords: applied geophysics, iron cave, Carajás.RESUMO O patrimônio espeleológico brasileiro é protegido por leis, e qualquer região com a presença de cavidades precisa de estudos científicos para auxiliar o licenciamento de empreendimentos. No contexto da mineração em terrenos ferríferos, estudos geofísicos rasos utilizando eletrorresistividade foram executados na cavidade N4E-0022, localizada no extremo norte da Mina de N4EN, Complexo Carajás. A geofísica rasa gerou imagens contínuas que potencializaram o mapeamento lito-estrutural do substrato rochoso, principalmente em locais de difícil acesso aos métodos convencionais. Os perfis de eletrorresistividade foram adquiridos com arranjo dipolo-dipolo na porção superior da cavidade. de modo paralelo entre si na porção superior da cavidade. Três seções foram executadas na direção SW-NE e duas na direção SE-NW, totalizando 435 metros de aquisição. As assinaturas geoelétricas das seções foram correlacionadas com as descrições litológicas de furos de sondagem, perfilagens geofísicas de furos de sonda e o mapeamento de detalhe do perfil laterítico no entorno da cavidade N4E-0022, evidenciando um resultado satisfatório para as interpretações realizadas. Os resultados evoluíram para uma comparação com o perfil de alteração típico de rochas ferruginosas (crosta laterítica, horizonte de transição e saprolito), e forneceram assinaturas de resistividades inerentes à cada material modelado. Palavras-chave: geofísica aplicada, caverna ferrífera, Carajás.

Electrical resistivity tomography technique coupled with numerical modelling: A case study for stability analysis

“…The literature published in the past revealed that various researchers used the ERT technique very effectively to delineate sinkholes, potholes, old abandoned goaves, cavities, voids, underground galleries/workings and so on (Abu‐Shariah, 2009; Das & Mohanty, 2016; Das et al., 2017; Ortega et al., 2010; Van Schoor, 2002; Zhou et al., 2004; Bharti, Pal, Priam, Kumar, et al., 2016; Bharti, Pal, Priam, Pathak, et al., 2016; Bharti et al., 2016c; Arjwech et al., 2021; Barbosa et al., 2020; Bharti et al. 2021; Bhattacharya & Shalivahan, 2016; Fargier et al., 2017; Nthaba et al., 2020; Prakash & Bharti, 2022; Prakash et al., 2022; Prosdocimi et al., 2019; Samanlangi, 2018; Bharti, Singh, et al., 2022; Bharti, Prakash, et al., 2022). A recent study by Saurabh et al.…”

“…ERT is a versatile tool for mapping of subsurface features like voids, cavities, underground galleries/tunnels (air‐or water‐filled) and so on, where high contrast in resistivity is leveraged to delineate the features very easily. In ERT study, high‐resolution information on subsurface resistivity variation depends on the data quality, data density, choices of electrode configuration and electrode spacing (Aizebeokhai, 2010; Barbosa et al., 2020; Bharti, Pal, Saurabh, Kumar, et al., 2019; Bharti, Pal, Saurabh, Singh, et al., 2019; Cardarelli et al., 2010, 2014; Chandra et al., 2008; Fargier et al., 2017; Giao et al., 2003; Horo et al., 2020; Kumar, 2012; Kumar et al., 2021; Leucci, 2006; Loke, 2000; Nthaba et al., 2020; Prosdocimi et al., 2019; Samanlangi, 2018; Singh, 2013; Singh et al., 2004; Ward, 1989).…”