Mineralogical, micromorphological and geochemical evolution of the kaolin facies deposit from the Capim region (northern Brazil)

Abstract

The Capim Kaolin District (eastern Brazilian Amazon), is one of the largest kaolin deposits in the world; with the kaolin used mainly for paper coating. The kaolin developed at the expense of Cretaceous sandy-clayey sediments of the Ipixuna formation, through intense lateritization from the Mesozoic to Cenozoic times.This work describes the morphological, mineralogical, crystallochemical and geochemical evolution of the Capim kaolin facies. Based on the profile analysis in the open pit fronts, it encompasses X-ray diffraction, thin-section optical analysis, EDS-assisted scanning electron microscopy and transmission electron microscopy, chemical analysis, infrared and Mössbauer spectroscopies.Six facies were defined as different stages of the supergene process. Ferruginization led to a thick duricrust on the soft kaolin, which in turn evolved from sandy-clayey sediments of the Ipixuna Formation. A subsequent deferruginization event degraded the duricrust, resulting in the flint kaolin facies.

The contribution of lateritization processes to the formation of the kaolin deposits from eastern Amazon

“…When considering the controversial genetic aspects; the excellent ore, rock exhibitions and geological and geochemical data at the IRCC mine; the geological experience obtained at other deposits; and results from published data (Hurst and Bosio, 1975;Murray and Partridge, 1981;Moraes, 1994;Costa and Moraes, 1998;Sousa et al, 1999a,b;Kotschoubey et al, 1999;Sousa, 2000 andSousa et al, 2007b); there is strong evidence which demonstrates the close relationship between kaolin and lateritic profiles.…”

“…In the PCKBD and surrounding area, the terrain is formed by sediments of the Ipixuna (and/or Itapecuru formation) and Barreiras IBGE (1990), Rossetti and Santos (2006) and Sousa et al (2007b). Formation and their correspondent lateritic profiles (Fig. 1c), which will be described later.…”

“…1c), which will be described later. The two most important kaolin mines (IRCC and PPSA) are located in the sub-basin Cametá at the eastern margin of the Marajó basin (Costa et al, 2002;Sousa et al, 2007b;Santos et al, 2007), although other nearby small mines and deposits are positioned along the Belém-Brasilia highway, which is far removed from the basin. The Itapecuru formation is comprised of: red loamy sandstones of medium to coarse size and conglomeratic, with incipient parallel plane bedding and crossed bedding; intercalation of clayey siltstones and sandstones displaying variegated coloration; and red and whitish kaolinic sandstones with large crossed bedding, which are locally feldspar bearing (Francisco et al, 1971;Petri, 1977;Lima et al, 1979;Góes, 1981;Santos et al, 1984;Cunha and Del'arco, 1988).…”

“…The kaolin mining at PCKBD began in 1996 with the following companies: Sumitomo Some authors consider that the Capim kaolin is typically of sedimentary origin (Krebs and Arantes, 1973;Monteiro, 1977;Coura et al, 1986;Santos and Rossetti, 2003;Rossetti and Santos, 2006;Wilson et al, 2006;Murray et al, 2007;Góes et al, 2007), while others point to weathering originating from Miocene Barreiras sediments (Hurst and Bosio, 1975;Murray and Partridge, 1981), or from cretaceous sediments of Itapecuru or Ipixuna formations (Costa, 1991;Costa and Moraes, 1992;Moraes, 1994;Moraes et al, 1994;Costa, 1997;Kotschoubey et al, 1996;Costa and Moraes, 1998;Sousa et al, 1999a,b;Kotschoubey et al, 1999;Sousa, 2000;Sousa et al, 2007b). Santos et al (2007) conducted d 18 O and d D analyzes on kaolinites originating from soft and hard (semi-flint) kaolin from Rio Capim deposits and concluded that kaolinites were not in equilibrium with modern weathering processes.…”

“…These authors concluded that kaolinites must have been formed during different phases of paleoweathering (Santos et al, 2007), which is in contradiction to Santos and Rossetti (2003), Rossetti and Santos (2006) for flint kaolin and Góes et al (2007), who have all supported the argument of sedimentary deposition. Recently, Sousa et al (2007b) offered new insights regarding the chemical, mineralogical and micromorphological characteristics and origins of kaolin deposits. Sousa et al (2007a) using geochronological data from several zircon grains extracted from both soft and flint kaolin found two distinct source areas for the kaolin-bearing sediments, which confirmed the lateritic origin of kaolin.…”