Coexistence of halloysite and kaolinite: a study on the genesis of kaolin clays of Campo Alegre Basin, Santa Catarina State, Brazil

Anais da Academia Brasileira de Ciências

Marisa T.g. De Oliveira²  Sandra M.a. Furtado¹  Milton L.l. Formoso¹  Richard A. Eggleton¹  Norberto Dani¹ 

[1],Universidade Federal do Rio Grande do Sul Instituto de Geociências Porto Alegre RS ,Brasil

关键词: kaolinite;    halloysite;    halloysite morphology;    kaolin;    weathering;    clay genesis;    caolinita;    haloisita;    morfologia da haloisita;    caolim;    intemperismo;    gênese de argilas;   

DOI  :  10.1590/S0001-37652007000400008

来源: SciELO

【 摘 要 】

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.

【 授权许可】

CC BY   
 All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License