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Mineralogy and genesis of the Pugu Hill kaolin deposit, Tanzania

Published online by Cambridge University Press:  09 July 2018

B. Schwaighofer  and
H. W. Müller
B. Schwaighofer
Affiliation:
Engineering Geology Department, Vienna University of Agriculture, Gregor Mendel-Straße 33, A-1180 Vienna, Austria
H. W. Müller
Affiliation:
Engineering Geology Department, Vienna University of Agriculture, Gregor Mendel-Straße 33, A-1180 Vienna, Austria
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Abstract

According to field studies of the Pugu Hill kaolin deposit and mineralogical investigations (X-ray, SEM), two main types of Miocene sandstones are distinguished: (i) clayey-silty kaolinitic sandstones with stacks of idiomorphic pseudohexagonal kaolinite crystals; (ii) massive clayey-silty kaolinitic sandstones with irregular fabric of isolated kaolinite plates. The Precambrian metamorphic rocks of the Uluguru Mountains are a probable source for the kaolinitic sediments of the Pugu Hill Formation. Decomposition products of weathering profiles on meta-anorthosites are mainly 7Å- and 10Å-halloysite and gibbsite. It is suggested that the kaolinitic sandstones were deposited in a former delta. The first sandstone type is considered to have developed in situ from weathered arkosic sandstone, and the second represents channel deposits in an old river system (probably a Miocene predecessor of the Ruvu River) with kaolin transported from a hinterland and redeposited. The variable formation and fabric of the kaolinites in the Pugu Hill Formation are due to in situ weathering of transported primary minerals (fedspar), and to transported weathered material (with secondary halloysite).

Type
Research Article
Information
Clay Minerals , Volume 22 , Issue 4 , December 1987 , pp. 401 - 409
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1987

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