Geochemical Trends in Weathering Profiles and Their Underlying Precambrian Basement Rocks in Akure, Southwestern Nigeria
Keywords:
Akure
Nigeria
Geochemical trends
In-situ weathering profile
Kaolinitic
ABSTRACT
Akure area in southwestern Nigeria falls within the basement complex
underlain by migmatite, quartzite granite and charnockite. Geochemical
features of these crystalline rocks and their overlying in-situ weathering
profiles are investigated and reported. Analytical result from ICP-MS
facility at the University of Malaya reveals average SiO2 content in
quartzite (91.1%), granite (73.8%), migmatite (67.4%) and charnockite
(58.6%) categorize the rocks as siliceous. SiO2 contents in the weathering
profiles above these rocks are 61.9%, 60.2%, 52.2% and 54.6%
respectively. Alumina contents in the weathering profiles overlying
quartzite (23.8%), granite (19.9%), migmatite (26.3%) and charnockite
(24.3%) are substantially higher than the precursor rocks. In the same
order, average alkali (Na2O+K2O) contents in the profiles are 3.38%, 3.42%,
3.48% and 2.68%. Chemical features of the profiles reflect that there exists
some correlation between the chemistry of crystalline basement and their
in-situ weathering profiles. The residual soils contain low plastic clays with
kaolinitic characteristics and compare well with other clays reported from
other parts of Nigeria basement complex.
Conclusions
From the study, the following conclusions are made.
The weathering profiles are formed in-situ and vary in col-
our, texture, and thickness. The composition is siliceous
and there exist some correlations between the chemistries
of weathering profile and their underlying crystalline
basement rocks. The geochemical features of the profiles
portray high alumina and alkali contents but with slight
variations that are related to the parent rock chemistry.
Field investigation shows the weathering profiles have
characteristic features comparable to kaolinitic and low
plastic clays and are like other industrial clay deposits in
southern Nigeria.
From Journal of Environmental & Earth Sciences
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