Abstract
Kaolin at Campo Alegre Basin, Santa Catarina State, Brazil was formed from alteration of volcanic acid rocks. Halloysite clays dominate the clay fraction of the matrix of the kaolin body, whereas a poorly crystalline kaolinite is abundant in veins. Some primary blocky structures have high amounts of illite, in one mine, but in general, only low contents of illite-smectite, illite, chlorite-vermiculite, vermiculite and quartz were identified in the clay fraction of the samples. Toward the top of the mines, hematite and lepidocrocite appear in horizontal red and ochre colored levels and the amount of kaolinite increases compared to halloysite. The vertical zoning of alteration levels, the changes in mineralogy, the positive correlation between depth and Cation Exchange Capacity of the clays, the preservation of different types of rock textures in the kaolin bodies, the dominant tube morphology of the halloysite clays indicate a supergene genesis for the deposits. Criteria to distinguish between supergene and hypogene kaolin are discussed. Transmission Electron Microscopy of the cross sections of halloysite tubes showed polygonal forms that are ascribed to be transitional between kaolinite and halloysite. It is proposed that some of the kaolinite of these deposits be inherited from the dehydration of halloysite tubes.
Highlights
Campo Alegre Basin is an important source of clays for the ceramic market of the Mercosul and a place of a welldeveloped ceramic industry; these clays have been little studied
Kaolin deposits of Campo Alegre Basin resulted from the alteration of acid rocks of the upper volcanic unit of Campo Alegre Formation (Neoproterozoic)
Kaolin was formed from the alteration of volcanic acid rocks, near São Bento do Sul, Santa Catarina State, Brazil (Fig. 1)
Summary
Campo Alegre Basin is an important source of clays for the ceramic market of the Mercosul and a place of a welldeveloped ceramic industry; these clays have been little studied. Kaolin deposits of Campo Alegre Basin resulted from the alteration of acid rocks of the upper volcanic unit of Campo Alegre Formation (Neoproterozoic). Kaolin was formed from the alteration of volcanic acid rocks, near São Bento do Sul, Santa Catarina State, Brazil (Fig. 1). These rocks are components of Campo Alegre volcanic-sedimentary basin (Citroni et al 2001) of almost 400 km. These rocks are components of Campo Alegre volcanic-sedimentary basin (Citroni et al 2001) of almost 400 km2 It is a Neoproterozoic sequence (595 ± 16 Ma, Cordani et al 1999) lying on older Archean granulite terranes. The Upper Volcanic Sequence (80% of the exposed area) of late Proterozoic age consists of trachytes and rhyolites. Three kaolin mines in Campo Alegre Basin were studied: Oxford (or Floresta) Mine, Incepa (or Cambuí) Mine and Ceramarte Mine (Table I)
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