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Article
Author(s)
H. Garba Saley, A. Soumaila and M. Konaté
Full-Text PDF XML 558 Views
DOI:10.17265/2328-2193/2018.05.001
Affiliation(s)
Abdou Moumouni University of Niamey, Department of Geology, Faculty of Sciences and Technology, Groundwater and Georesources Laboratory, POBox 10662, Niamey, Niger
ABSTRACT
The manganese deposit of North Téra is located in the western side of
the Diagorou-Darbani greenstone belt in the Niger Liptako Province
(Northeastern part of Man Schield, West African Craton). Manganese mineralization
bearing rocks are mainly gondites (a kind of garnet-rich quartzite of the
spessartine type) whose borders consist of a high concentration of Mn oxide
concretions. The methodological
approach implemented consisted of a field study followed by a polarizing
microscopic analysis in transmitted and reflected light and a geochimical
analysis. North Téra gondites
originate from Birimian manganese-rich sediments metamorphism in amphibolite
facies. The supergene
alteration, more or less important, has developed on the protore of gondites, a
saprolitic profile whose setting up conditions were recently described in our
previous work. The macroscopic analysis
of the manganese deposits samples combined with the metallographic microscopic
and geochemical analysis confirms that manganese mineralization originated from
weathering processes. The first oxide that
forms around the garnets is nsutite, while the mesostasis is invaded by
pyrolusite with lenses of lithiophorite destabilizing in favor of pyrolusite.
In the botryoidal concretions, the latter forms an alternation with the
psilomelane rich in Ba (8,101ppm) in the uppermost levels. The abundance diagram
shows that the normalize Rare Earths compared to PAAS derived from a
plagioclase-rich quartzitic source. This observation is corroborated by a
positive anomaly in Eu. Otherwise, the high levels of transition elements (Ni,
V, Co and Cr) highlight the involvement of a basic source. The contents of major
elements show a significant leaching, with an increase in those of Mn and Al
during the increasing weathering. The CIA and PIA indices move in the same
direction towards high values leading to the Al2O3 pole on the Al2O3-CaO * + Na2O-K2O diagram. This indicates an increasing alteration
along the profile, according to an alteration path comprising
plagioclase-smectite-kaolinite and illite to kaolinite.
KEYWORDS
Gondite, manganese, North Téra, supergene alteration, protore, Birimian.
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