Mineralogy, geochemistry and genesis of kaolins from the Amazon region

• Published in: Mineralium deposita Vol. 33; no. 3; pp. 283 - 297
• Main Authors: da Costa, M. L., Moraes, E. L.
• Format: Journal Article
• Language: English
• Published: Heidelberg Springer Nature B.V 1998
• Subjects: Aluminum; Cretaceous; Floodplains; Geochemistry; Illite; Kaolinite; Mineralogy; Quartz; Sedimentary geology; Sedimentary rocks; Trace elements; Volcanic rocks
• ISSN: 0026-4598; 1432-1866
• DOI: 10.1007/s001260050147

The kaolin deposits of the Amazon region of Brazil are of lateritic origin, modified by subsequent reduced lacustrine and/or swamp environment. They are contemporaneous with lateritic bauxites found in the same region, all formed from aluminium silicate rocks. These are principally sedimentary rocks from the Cretaceous period (Itapecuru and Alter do Chão), but also include metamorphic and felsic volcanic rocks. After erosion of the upper part of these profiles they became locally a substratum for swampy and/or lacustrine environments mostly developed over the clayey saprolitic horizon where kaolin occurs. The saprolitic horizon is made up mainly of iron-mottled kaolinite which has been subject to an intense deferrification, which has increased the kaolin brightness and thickness. The kaolins are basically made up of well-crystallized kaolinite, quartz, sometimes illite-muscovite, anatase and hematite. In certain locations, crandallite-goyazite is also present. The deposits studied differ from each other in the mineral content levels, concentration of principal elements and in trace element distribution. The greatest quantity of quartz and, consequently SiO^sub 2^, is intrinsically related to the type of parent rock. Small sedimentary deposits occur in alluvial flood plains located not very far from the lateritic source.[PUBLICATION ABSTRACT]