GEOCHEMICAL AND GEOTECHNICAL CHARACTERIZATION OF BARYTE MINERALISATION IN LESSEL AND IHUGH AREAS, LOWER BENUE TROUGH, NIGERIA
GEOCHEMICAL AND GEOTECHNICAL CHARACTERIZATION OF BARYTE MINERALISATION IN LESSEL AND IHUGH AREAS, LOWER BENUE TROUGH, NIGERIA
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Date
2015-11
Authors
LABE, NGUKPOSU AHEN
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Abstract
The Lessel-Ihugh area lies within the Lower Benue Trough, southeastern Nigeria. The area, which was mapped on the scale of 1:10,000 is underlain by Precambrian rocks comprising of gneiss, medium-grained muscovite granite, coarse-grained biotite muscovite granite, and Turonian arenaceous Lessel Sandstone. Baryte mineralization occurs generally as vein and cavity type deposits in Lessel Sandstone at Lessel-Mbagwa and Mbaakase (southwest of Ihugh) and also in banded gneiss at Bunde (northeast of Lessel Town). Baryte veins mapped in the area trending mainly in the NE-SW direction with minor NW-SE trends. The veins at Lessel area contain minor amounts of quartz, galena and sphalerite as associated minerals. Petrographic studies on the granitic and vein rocks collected from the area were carried out using transmitted light microscope. Whole rock geochemical analysis of granitic rocks, sandstones and baryte veins were carried out using ICP-AES and ICP-MS to chemically characterize baryte mineralization in the Lessel-Ihugh area. In addition, baryte minerals were subjected to density, moisture content and uniaxial compressive strength tests to establish their geotechnical attributes, variety and quality. Cross-cutting relationship of baryte veins suggests that opaque minerals (galena, sphalerite, iron-oxides), quartz was first deposited followed by early baryte, late baryte and lastly again by the opaque minerals. Geochemical data indicate that the granitic rocks are generally peraluminous calc-alkaline granites believed to have been emplaced during the compressional tectonism resulting from the Pan-African orogeny. Geochemical classification constrained the Lessel Sandstones as wacke, litharenite, sub-litharenite and quartz-arenite sandstones derived from granite and gneiss terrane. Barytes from the Lessel-
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Ihugh area is characterized by enrichment in Ba, Sr, depletion in major oxides and trace elements, low ΣREE (7.2 – 39.4 ppm), negative Eu anomalies (0.02 – 0.05), positive Ce and negative Ce anomalies (0.06 – 1.3) in addition to positive Gd anomalies (17.1 – 21.4). Trace element data indicates Ba was leached from Ba-rich magmatic rocks. CeN/SmN versus CeN/YbN plot suggests that the mineralizing fluid was derived from seawater dominated hydrothermal fluid. The interaction of Ba-rich fluid with sulphate-rich fluid led to precipitation of baryte under oxic and anoxic conditions in fractures during the Santonian to Campanian. Geotechnical investigations reveal that the Lessel-Ihugh barytes have low uniaxial compressive strength (2.02 – 5.36 N/mm2), moderate moisture content (0.42 – 1.18%) and specific gravity (3.65 – 4.01). Based on the geochemical and geotechnical characteristics of barytes in this study, the Lessel-Ihugh baryte fall below international standard specifications, and are therefore of relatively moderate quality or Grade II barytes.
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Keywords
GEOCHEMICAL,, GEOTECHNICAL CHARACTERIZATION,, BARYTE MINERALISATION,, LESSEL,, IHUGH AREAS,, LOWER BENUE,, NIGERIA