Geological characteristics of the Serra do Navio Formation, Guiana Shield, Brazil, and its manganiferous ores: queluzite as a source rock of oxide and carbonate manganese ores

Abstract

Article InformationPublication type: Review article

The arsenic contamination event of Santana, Amapá State, Brazil, and the high values of arsenic in the brownish Amazon waters

“…2). The oxide ores were mined from 1957 to 1998, and the larger resources of manganese carbonates, which occur below the water table, remain practically untouched (Scarpelli 2022).…”

“…Figure 2 -Geological section of the Serra do Navio manganese deposit, showing the manganese oxide ore replacing a weathered portion of a layer of queluzite protore, which is flanked by layers of quartzites and schists. Mining was done until the contact of the oxide ore with the fresh queluzite (adapted from Scarpelli and Horikava 2017;Scarpelli 2022).…”

“…Conditioned by the high rainwater, high temperature, and by the action of the acid decay of the Amazon rainforest, which brings the pH of the groundwater to 4.5-5.5, the chemical weathering is quite intense, and the rocks are decomposed below the water table. Some of the solubilized components, like manganese, iron, aluminum, and silicon, reprecipitate soon after the rock decomposition, forming supergene oxides and hydroxides of manganese (cryptomelane, lithiophorite and pyrolusite), of iron (limonite, goethite and hematite), aluminum (gibbsite), and silica (Scarpelli 2022). Some of the dissolved elements, such as potassium, cobalt and arsenic, have chemical affinities with manganese and iron, and stay in the crystalline structure of some of the supergene manganese and iron minerals, not representing a health problem for the mine workers and for the inhabitants of Serra do Navio.…”

“…Initiated in 1957, the mining production ceased in 1998, in response to the exhaustion of the economically minable oxide ores. Serra do Navio still has resources of carbonate and low-grade oxide ores to be explored (Costa 1997, Scarpelli 2022.…”