INDUSTRIAL MINERAL POTENTIAL OF PEGMATITES IN THE LOKOJA AREA (SHEETS 247NW AND 247SW), NORTH-CENTRAL NIGERIA

Field geological mapping and compositional (mineralogical and chemical) evaluation of the pegmatites in the Lokoja area (Longitudes 6º 37′ 00″ E and 6º 47′ 00″ E and Latitudes 7º 42′ 00″ N and 7º 51′ 00″ N) were carried out to evaluate the industrial mineral potential of the pegmatites. The pegmatites occur in tabular forms as dyke-like structure and veins of large interlocking crystals of quartz, feldspars and mica and distributed within two host rocks (migmatite and granite gneiss). Petrographic analysis (thin section) of eight of the pegmatite samples revealed that the pegmatite has a modal composition of plagioclase (26.25%), orthoclase (17.89%) and microcline (36.75%) which are raw materials used in glass and ceramics production, quartz (8.1%) and biotite (11%). twelve samples of the pegmatite were analysed using the X-ray Fluorescence spectrometry and the chemical composition obtained for silica (SiO 2 ) and alumina (Al 2 O 3 ) content of 67.47 wt % and 14.01 wt % respectively. The alumina (Al 2 O 3 ) is greater than the alkalis (Na 2 O + K 2 O + CaO) in the samples with an average value of 1.43% which indicates that the pegmatites are siliceous and peraluminous. The pegmatite is dominated by feldspars which are raw material used in ceramics and glass production and the chemical composition of the major element of the pegmatites of the study meets up with the Indian standard requirement suitable for use in various industries (glass, whiteware and pottery) and also meets the requirement for sanitary ware and ceramic-tiles industry as required by the British standard.


INTRODUCTION
Pegmatites are coarse-grained igneous rocks composed of large interlocking crystals of mostly quartz, feldspar and accessory micas.Pegmatite bodies vary in size and shape.They are found as vertical intrusions in the form of dykes and veins, and also near large masses of igneous rocks called batholiths.Pegmatites have been a known source of gem and precious minerals and rare earth metals (Cerny, 1991a;Morteani & Gaupp, 1989).Pegmatites have attracted remarkable interest all over the world, and particularly in Nigeria as it is the host to various gemstones (beryl, tourmaline, etc), and industrial minerals such as feldspars, muscovite and quartz.They have also been found as a source of broad spectrum of rare earth elements such as Lithium (Li), Rubidium (Rb), Caesium (Cs), Beryllium (Be), Gallium (Ga), Scandium (Sc), Yttrium (Y), Tin (Sn), Niobium (Nb), Tantalum (Ta), Uranium (U) and Thorium (Th) from which various economic ore minerals originated from (Jimoh, 2011).Nigeria is known to have an extensive belt of pegmatite environment, covering approximately 400 km (Figure 1) from Ilesha, south-west Nigeria to Wamba (near Jos, Plateau state) in North Central Nigeria (Jacobson & Webb, 1964).Ekwueme & Matheis (1995) reported that the NE-SW trending pegmatites veins are more productive and richer in rare metals while the NW-SE pegmatites in Oban-Obudu basement are relatively barren and unproductive.Matheis & Caen (1983) further studied the pegmatite of the Pan African reactivation zone covering Egbe, Ijero and Wamba in Southwestern Nigeria and were able to distinguish between the barren and mineralized pegmatite.Recently other researchers who studied the pegmatite in Southwestern Nigeria such as (Garba, 2003;Matheis, 1987) concentrated on the exploration of the Sn-Nb-Ta, also in the study area Daniel & Ebo, 2021;Omada et. al, 2015, analysed some pegmatite dykes around Lokoja area and concluded that they are moderately mineralized but emphasis was on the rare metals.Geologists, especially petrologists, mineralogists, and economic geologists have developed interest in the study of pegmatite.However, their emphasis has been on the rare metals associated with the pegmatites (including the study area) with little or no published work on the industrial mineral potential of pegmatites.The increase in the global demand for industrial minerals like feldspar, quartz and muscovite which are found in pegmatite for manufacturing of glass, ceramics and electrical insulator has led to a heightened quest for economically viable deposits that could possibly host these important minerals.Furthermore, as Nigeria is being positioned on the path of industrialization, these minerals are vital ingredients for ceramics, glass and allied industries.These industries, in turn, create a value chain platform for the growth of other smallscale industries thereby providing large quantum of employment for the teeming population of the country in addition to enhancing its Gross Domestic Product (GDP).This study aims at evaluating the industrial minerals occurrence in the pegmatite of the study area and their potential uses.The study area covers parts of Lokoja sheet 247 NW and 247 SW and lies between Longitudes 6º 37′ 00″ E and 6º 47′ 00″ E and Latitudes 7º 42′ 00″ N and 7º 51′ 00″ N (Figure 2).

Regional Geologic Setting
The Nigeria Basement Complex lies in the extensive region East of the West African Craton and North-west of Congo Craton which was affected by the Pan-African orogeny about 600my ago (Rahaman, 1976).The Pan-African belt evolved by plate tectonic processes which involved the collision between the passive continental margin of the West African Craton and the active continental margin (Pharusian belt) of the Tuareg shield about 600my ago (Black et. al., 1979;Burke & Dewey, 1972).The collision at the plate margin is believed to have led to the reactivation of the internal region of the belt.The Nigerian Basement Complex lies in the reactivated part of the belt (Rahaman, 1976).Three areas comprise the Basement Complex in Nigeria.These include: i. North Central Complex which covers Zaria, Abuja, Bauchi and Jos where we have the intrusions of Younger Granites.ii.The South-West Basement covering parts of Lokoja, Igarra, Ilesha, etc. iii.The South-East Basement Complex covering Jato-Aka, Obudu, Oban massive and Mambila hills.The South-West Basement Complex is made up of four major rock types (Igboama, et.al, 2024;Rahaman, 1976;Tijani, 2023), namely: i. Migmatite-Gneiss Complex ii.Metasedimentary rocks (Schist Belt) iii.The Older Granites iv.Undeformed acid and basic dykes which include pegmatites, quartz veins and dolerite dykes.

MATERIALS AND METHODS
Field mapping was carried out using Global Positioning System (GPS), a compass clinometer, and topographic map sheet on a scale of 1:25,000 prepared from Lokoja sheet 247 NW and 247 SW.Data were collected in form of rock samples, photographs and readings of attitudes of rocks and structures.The locations where the rocks were encountered within the mapped area were determined using Global Positioning System (GPS), This was used to produce the geological map of the area.The exposed rocks were carefully observed and the texture, grain size and composition of the various minerals that make up the rock were recorded in the field notebook.Samples were obtained to ensure they are fresh and representative using geological hammer and chisel which are properly labelled and put into sampling bags.The rock samples collected from the field were subjected to the following analyses: Petrographic analysis (thin section analysis) on eight (8) pegmatite samples were carried out in the thin section laboratory of the Department of Geology, Federal University Lokoja, Kogi State, Nigeria.Below is the procedure for the analysis.
i.The fresh rock samples were air-dried and impregnated using epoxy A and B. ii.The impregnated samples were trimmed using the GTS cut-off saw and making sure one surface of the sample is made very flat.The flat surface is lapped on a glass plate using carborundum of size 600 grit.iii.One surface of glass slide was also lapped on a glass slide.
The lapped surface of the sample and that of the slide is ettlemen t then bonded using epoxy, this was to dried and later trimmed to 50 microns on the slide using cut-off saw.iv.The slide is then transferred to the CL 50 lapping machine to reduce the size of the sample to 30 microns.v.The slide is then covered using Canada balsam and coverslid, ready for study under the petrographic microscope.vi.The representative thin sections were chosen and observed with polarising microscope under plane polarised light (PPL) and the cross polarised light (XPL).Geochemical analysis (X-ray Fluorescence analysis) of twelve ( 12) samples of the pegmatites was carried out using Thermo-Fisher Scientific Energy Dispersive X-Ray Fluorescence (ARL.QUANTX.EDXRF) done at the Central Laboratory of the Umaru Musa Yar'adua University, Katsina State, Nigeria.The instrument has three components of operation; i. Helium gas for liquid sample ii.Vacuum Pump for light Elements.iii.Air for heavy and light element excluding Sodium which can only be gotten in a vacuum.The samples were first grounded into fine powder with the aid of mortar and pistol.2g each of the samples were weighed and then poured into a sample holder and covered with cotton wool to prevent it from spraying.The bottom of the sample holder is made of polypropylene which is a thermoplastic.The sample holders containing the samples were ran in a vacuum or air for 10 minutes each and they were inserted into the XRF Spectrometer for the elemental analysis after which the results were obtained.The XRF Analyzer determine the elemental composition of a sample by measuring the fluorescent X-ray emitted from a sample when it is excited by primary X-ray source.Each of the elements in the sample produces a set of characteristic fluorescent X-rays that is unique for specific element.

RESULTS AND DISCUSSION
The study area is underlain by Basement Complex rocks (metamorphic and igneous rocks) and contacts between the various rock types are sharp and sometimes gradational.The geological map of the study area (Figure 3a) reveals the major rock types encountered in the study area which are host to the pegmatites are migmatite and granite gneiss.

Field and Petrographic Analysis of Pegmatites
The pegmatites in the study area occur in tabular form as dyke and veins of variable sizes within the basement complex rocks (migmatite and granitic gneiss) of the study area.They also occur as low-lying intrusions and as massive bodies in the hilly area along with their host rocks with majority having a strike trend of NW-SE.The pegmatites generally show sharp contacts with the host rocks.They range 15 centimetres to about 1m in width with a very coarse grain texture, with large interlocking crystals of feldspars and quartz that vary from 1

Geochemistry
The results of XRF analysis of pegmatite samples in the study area are presented in the table below.The data in table 2 shows a wide range in the composition of the pegmatites in the study area with silica SiO2 (67.47 wt %) and alumina Al2O3 (14.01 wt %) having higher value than other oxides.The data also reveals the composition of Na2O as 3.54wt %, K2O (5.80wt %), MgO (0.36 wt%), CaO (0.71 wt %), Fe2O3 (0.73 wt %) and TiO2 (0.08 wt%).Rocks that are characterized by low Mg, Ca, and Fe as well as low ratio of Na2O / K2O are peraluminous (Cerny, et al., 1981;Obasi & Madukwe, 2016;Longstaffe, 1982).These values are similar to the Ijero-Ekiti pegmatites which are rich in albite (NaAlSi3O8), potassium feldspar (KAl Si3O8) and quartz (SiO2).

Figure 2 :
Figure 2: Topographic map of study area

Figure 3 :
Figure 3: (a) Geological map of the study area.(b) Geological cross-section across the profile A-B of the study area . The pegmatites in the study area are made up of quartz, feldspars and mica (biotite) similar in composition to granite.The quartz is colourless, milky or smoky, while the feldspars are pinkish and blocky and the mica which are mainly biotite are brownish.Based on mineralogy, the pegmatite in the study area are simple pegmatites.Some clusters of quartz (milky quartz) of up to 40 cm was seen in the pegmatite.The pegmatites in some places are weathered due to erosion.