ENERO%2031-GEOCIENCIAS-VOL%2012-2%20DIC-EN%20BAJA[1].pdf EARTH SCIENCES RESEARCH JOURNAL Earth Sci. Res. J. Vol. 12, No. 2 (December 2008): 213-234 MINERALIZATION POTENTIALS OF PEGMATITES IN THE NASARAWA AREA OF CENTRAL NIGERIA Akintola, O. F.1 and *Adekeye, J. I. D.2 1 Raw Materials Research and Development Council, P. M. B.232, Garki, Abuja, Nigeria Fax: 234 9 4136034, E-mail: akintolaolatunde@yahoo.com, Phone: 2348055239304 2 Geology and Mineral Sciences Department, University of Ilorin, P. M. B. 1515, Ilorin, Nigeria. Email: adekeye2001@yahoo.com, Phone: 2348033795444. * Corresponding author ABSTRACT Pegmatites in Nasarawa area of Central Nigeria lie within a fracture-controlled east-north-east trending rare metal pegmatite belt closely associated with late PanAfrican peraluminous granites in Nigeria. Trace elements of feldspars andmuscovites of pegmatites in Nasarawa area of Central Nigeria were analyzed to determine the raremetals miner- alization potentials of the pegmatites. The minerals show fractionation even within units of complex mineralized pegmatites as indicated by the wide ranges of K/Rb in Na-feldspars (albites), muscovites and K-feldspars and the wide range of K/Tl in the latter two minerals. Cs, Rb and Tl and the rare earth elements (REEs) Ce, La, Pr and Y are enriched in the K-bearing muscovites and K-feldspars; K-feldspars have the highest average values of Tl, Ce, La, Pr and Y while the muscovites have the highest average values of Sn, Nb, Ga, F and Zn. Average values of Ta, Sr, Ba, W andZr are highest in the albites, which also have the lowest averageNb/Ta ratio. This is an indication that these el- ements are enriched along lateNa-rich raremetalmineralizing fluids. The rare alkalis Rb andCs and Tl are positively correlated with the rare lithophile elements (Ta, REEs, Pb, Bi and Y), in both the pegmatite K-feldspars and musco- vites, strongly positively correlated with Sn in the muscovites but negatively correlated with Nb in the minerals. In the pegmatitic albites, Nb has very strong positive correlations with Ta (0.868) and Zr (0.847), which is indicative of the incorporations/substitution of these elements in the crystal lattice of the ore minerals. There is a general enrich- ment of the rare elements towards themiddle and inner zones of the complexmineralized pegmatites. Fluorine, phos- phorus and boron-rich fluids played significant roles in the magmatic complexation/fractionation and concentration of Sn-Ta-Li-Cs-Be in the albitized zones of the highly evolved pagmatites. K/Rb versusCs in theK-feldspars classify the pegmatites into barren, Be-, Li-Be, and Li-Cs-Be-Ta types. Comparably low Nb/Ta ratios in the late albites and amblygonites indicate the paragenesis of these minerals with the tantalum ores in the middle/inner zones of the com- plex mineralized pegmatites. While the Be-, and Li-Be-types are highly prospective for gem tourmaline, beryl and 213 Manuscript receiver: October 22th, 2008. Accepted for publication: November 4th, 2008. columbite; the most evolved pegmatites in this area are good candidates for tantalite, amblygonite-montebrasite, and probably pollucite prospecting/mining. Key words: Rare metals, Pegmatites, Muscovites, Feldspars, Mineralization, Correlations. RESUMEN Pegmatitas en el área de Nasarawa, Nigeria central, se encuentran dentro de un cinturón de pegmatitas conmetales de tierras raras controlado por fracturas, con tendencia Este-Noreste, y estrechamente asociado con granitos peralumínicos del Pan Africano tardío en Nigeria. Elementos trazas en feldespatos ymuscovitas de las pegmatitas del area deNasarawa, Nigeria central, fueron analizados para determinar el potencial demineralización demetales de tierras raras en las pegmatitas. Los minerales muestran fraccionamiento aun dentro de unidades en las pegmatitas complejamente mineralizadas, como lo indica el amplio rago K/Rb en feldespatos sódicos (albitas), muscovitas y feldespatos potásicos y el amplio rango de K/TI en estos dos últimos minerales. Las muscovitas potásicas y los feldespatos potásicos están enriquecidos en Cs, Rb y TI y en los elementos de tierras raras (REEs) Ce, La, Pr e Y; los feldespatos potásicos poseen el mayor valor promedio de TI, Ce, La, Pr yY eYmientras que las muscovitas tienen losmayores valores promedios de Sn, Nb, Ga, la F y Zn. Los valores promedios de Ta, Sr, Ba, la W y Zr son más altos en las albitas, las cuales poseen también el promedio más bajo de Nb/Ta. Esto indica que estos elementos son enriquecidos por fluidos mineralizantes tardíos ricos en sodio y metales de tierras raras. Los elementos alcalinos raros Rb andCs y TI se correlacionan positivamente con los elementos litofilos (Ta, REEs, Pb, Bi y Y), en los feldespatos potásicos y las muscovitas de las pegmatitas, y tiene una fuerte correlacion positiva con Sn en la muscovita pero la correlacion es negativa con Nb en los minerales. En las albiticas pegmatiticas, Nb tiene una correlacion positiva muy fuerte con Ta (0.868) y Zr (0.847), lo que indica la incorporación o sustitución de estos elementos en la estructura cristalina de los minerales de mena. Hay un enriquecimiento general de los elementos de tierras raras hacia la mitad y las partes mas profundas del complejo pegmatitico mineralizado. Fluidos ricos en flúor, fósforo y boro juegaron un papel importante en la complejización y fraccionamiento magmatico y en la concentración de Sn- Ta-Li-Cs-Be en las zonas albitizadas de las pegmatitas altamente evolucionadas. K/Rb vs Cs en feldespatos potásicos clasifican las pegmatitas en tipos estériles, de Be, de Li-Be, y de Li-Cs-Be-Ta. Relaciones de Nb/Ta comparativamente bajas en las albitas y ambligonitas tardias indican la paragenesis de estos minerales con las menas de tantalio en las zonas medias e internas del complejo pegmatitico mineralizado. Mientras los tipos Be y Li-Be son altamente prospectivos para tourmalina, berilo y columbita como gemas; las pegmatitas mas evolucionadas en esta area son buenas candidatas para la prospección minera de tantalita, ambligonita- montebrasita, y probablemente polucita. Palabras clave:Metales raros, Pegmatitas, Moscovitas, Feldospastos, Mineralización Correlaciones. Introduction Nigeria possesses a very large pegmatite environment. The pegmatites are widely distributed with a marked concentration ofmineralized pegmatites in a broad belt, which extends from Ago-Iwoye in the southwest to Bauchi in the northeast, an air distance of more than 400kilometers. Thousands of pegmatites occur in this belt, most of which have never been mapped or sam- pled in a systematic, scientific manner. Potassium feld- spar, albitic plagioclase, quartz, and subordinate, if any muscovite and/or biotite constitute the major minerals while a wide spread spectrum of minerals including le- pidolite, tourmaline (green, pink, black and blue), beryl, chrysoberyl, apatite, amblygonite, monazite, lithiophyllite- triphyllite, ghanite, cassiterite, wodginite, nigerite, columbo-tantalite, tapiolite, microlite, bis- muthinite, bismuthite, scheelite, cholite, andalusite and 214 AKINTOLA, O. F. AND ADEKEYE, J. I. D. sillimanite occur as accessory minerals in the pegmatites, Bowden and Kinnaird (1984). The ages, mineralogy, and composition of these pegmatite units appear to be analogous to those of the pegmatites environment in Brazil, Canada and Australia. The pegmatitic belt and the orientation of the units within it appear to be re- lated to rotational stresses created by the Benue Trough. From a more global perspective, this trend is probably the northern extension of the Brazilian pegmatite belt, which runs from Rio Grande del Sul to Rio Grande del Norte. The pegmatite field of this study area is part of late Pan African, (Jacob- son and Webb, 1949; Wright, 1970), rare (spe- cialty) metals granitic pegmatites. The primary mineralization of tantalum, niobium, tin, beryllium and lithium is hosted in quartz-feldspar-muscovite pegmatites (Kinnaird, 1984). The Nasarawa area lies between latitudes 8o 18’ N and 8o 30’ N and longitudes 7o 35’ E and 7o 50’ E, west of the southern boundary of Afu com- plex- the southern most unit of the Younger Gran- ites complexes (Figure 1). Mining of tantalite from both pegmatites and the eluvials started in the area some years ago. The mining continues for the ma- jor periods of the year except during the very dry months of February to early April when lack of wa- ter makes it difficult to mine and concentrate the minerals. Columbite and cassiterite are recovered as by-products of the tantalite mining, while other pegmatite minerals like quartz, feldspar, amblygo- nite-montebrasite, cookeite and mica are still being discarded in waste dumps. Area description, methods and materials studied Regional Geology Central Nigeria is part of an Upper Proterozoic mobile belt extending from Algiers across the southern Sa- hara into Nigeria, Benin, and the Cameroun. This Pan-African belt continues into Northeast Brazil where analogous rare-metal mineralized pegmatites are also known (Schuiling, 1967). Bordered to the west by the West African Craton (stabilized around 2 Ga) the Pan-African belt itself is made up of gneiss-migmatites, metasediments, and metavolcanics that have been subjected to polycyclic metamorphism, and emplacement of igneous rocks. These rocks all constitute the Precambarian to Lower Paleozoic Base- ment Complex rocks. The gneiss-migmatites bears imprints of the Liberian (ca. 2500Ma), Eburnean (ca 2000Ma) and Pan African (ca. 600Ma) tectonic events (Oversby, 1975; Turner, 1983). Within the sequence are domains of metasediments and metavolcanics in- truded by igneous rocks, which constitute the north/south trending schist belts. The schist belt lithologies which consist of fine grained clastics, pelitic schists, phyllites, banded iron-formations, marble and amphibolites are consid- ered to be Upper Proterozoic assemblages (Turner, 1983). They host most of the economic minerals in the Basement Complex. During the Pan-African epi- sode, the Proterozoic gneiss-migmatite-schist com- plex were intruded by various granitoids resulting from oceanic closure, subduction, oblique collision between the West African craton and the Hoggar – Nigeria shields (Black, 1984) and crustal thickening. The Pan-African granitoids of Nigeria, which is col- lectively termed Older Granites, comprise gabbros, charnockites, diorites, granites, and syenites. Geochronological data from previous works (Rb – Sr whole-rock and U-Pb zircon) of Pan-African granitoids intruding the reactivated Archean to Lower Proterozoic crust of central and south-western Nigeria show that intrusive magmatite activity in these areas lasted from at least 630 to 530 Ma (van Breemen et al., 1977; Rahaman et al., 1983; Dada et al., 1987; Matheis and Caen-Vachette, 1983; Umeji and Caen-Vachette, 1984; Akande and Reynolds, 1990). Results of the rock ages also show that pegmatities’ emplacement in the southwestern Nige- ria occurred mainly after the peak of the Pan-African orogenic event in this area. The end of the Pan-African tectonic event is marked by a conjugate fracture system of the strike-slip faults (Ball, 1980). Fault directions have 215 MINERALIZATION POTENTIALS OF PEGMATITES IN THE NASARAWA AREA OF CENTRAL NIGERIA consistent trend and sense of displacement; i.e. a NE-SW (NNE-SSW) trending system having a dextral sense of movement and a NW-SE trending system a sinistral sense (McCurry, 1971; Wright, 1976; Holt et al., 1978; Ball, 1980). Both sets crosscut all the main Pan-African structures, including older N-S trending shear zones (mylonites) and late orogenic granites (Ball, 1980; Ajibade and Wright, 1989; Kuster, 1990; Garba, 1992). Gold and pegmatities’ rare mineraliza- tion are closely associated with the fractures in the Pan-African belt (Kuster, 1990; Ekueme and Matheis, 1995; Garba, 2002, 2003). About 100km north-east of the area of study at Wamba, rare metal pegmatites have also been geochemically linked to peraluminous late Pan-Afri- can tectonic granitoids, the emplacement of which have largely been controlled by the regional fractures (Kuster, 1990). Chemical data on granites, and gra- nitic and pegmatitic muscovites show that RB, Cs, Sn, Nb, and Ta are enriched during both magmatic and postmagmatic evolution, with the highest contents of these elements occurring in early muscovites of the albitized and mineralized pegmatities (Kuster, 1990). Albite, K-feldspar, and quartz are the main pegmatitie-forming mineral; white mica is a typical but minor component. From a geochemical point of view, quartz is of no particular interest since it diadochially (substitutionally) hosts trace elements to a negligible extent. Feldspars and white micas are the most informative minerals because their element distributions reflect the trace elements contents in ei- ther early pegmatite forming fluids or in the later metasomatizing solutions (Moller and Morteani, 1987). Feldspars and white micas of pegmatites in the Nasarawa area were sampled and analysed for trace elements to determine the mineralization poten- 216 AKINTOLA, O. F. AND ADEKEYE, J. I. D. Ilorin Ilesha Sokoto Gusau Kano Zaria Kaduna Abuja Study Area EnuguLagos Maiduguri Port-Harcourt Pan African Nigeria Belt 10°0° 10° 20° Atlantic Ocean Congo Craton0 5001000 50 100 150 Kilometres Kilometres Legend Faults Barren Pegmatites Newly metal pegmatites discovered rare- Known rare- pegmatites metal Major Cities / Towns Cretaceous- sedimentary cover Recent Mesozoic ring complexes [Younger Granites] Supracustal (Schist belts) Basement, Gneisses Migmatites and Pan - African (Older) Granites N Atlantic Ocean 6° 4° 8° 10° 12°N 6° 10° 16°E12°8°2° West African Craton 0° Figure 1: Geological Map of Nigeria Showing the Regional Fractures and Location of Areas of Rare-metal and Barren Pegmatites (after Garba, 2003) tials of the pegmatites. Data from this area is also compared with published data on well-studied pegmatities for comparison of the potentials. Analytical procedures are as stated in Akintola and Adekeye (2006). The chemical data on the peg- matite mica and feldspars were subjected to bivariate correlations after a lognormal transformation of the data. Bivariate correlation coefficient of the ele- ments, r, were interpreted to determine elemental geochemical associations and evolutionary trends in the pegmatites. Local Geology The geological setting of Nasarawa area is shown in Figure 2. From field evidence, the oldest rocks in the study area are micaceous pelitic schists. Variations in the schist composition for instance, the mica versus the quartz – feldspathic contents are observable in the field. This rock unit has undergone a polyphase meta- morphism and ductile deformations evidenced by lo- cal variations in the strike and dips of the foliation. Like the other schist belt rocks in the country, the schists have a general strike of north-south, and in the area, dips at gentle angle (10o – 30o) to the east. The schists were intruded by Older Granites, which out- crop as hills especially to the northwest, and west of the area. These Older Granites have a range of granodiorite to granite compositions. To the east of the area are rocks of the Afu com- plex of the Younger Granites. The Afu complex is made up of high-level anorogenic granites mainly biotic granites and minor quartz porphyry emplaced within Precambrian Paleozoic Basement gneisses and Older Granites but exposed beneath the Creta- ceous-Recent sedimentary cover of the lower Benue Valley to the South. The geochemistry of the gran- ites and the mica schists hosting the pegmatites in this area are discussed in Akintola and Adekeye (2006). Two groups of pegmatites are noticeable in the area with minor muscovite in the area: (1) sim- ple, usually barren massive quartz – microcline pegmatites with minor muscovite and accessory tourmalines and (2) complex, albitized musco- vite-quartz-microline pegmatites, bearing the rare-metals Ta, Nb, Sn, Li and Be mineralization. The simple, barren quartz-feldspar (with mi- nor mica) pegmatites occur at the north western and western parts of the area and are spatially closely associated with the main phase Older Gran- ites. On an outcrop scale, the pegmatites grade into patches of aplite. The complex rare-metal pegmatites are found far away from the granite plutons usually hosted by schists (exterior pegmatites). Wall-rock alteration in the simple pegmatites is negligible, but more pronounced in the complex pegmatites especially at contacts with the hanging walls (Jacobson and Webb, 1946). Al- though tourmalinization is by far the most common type of contact alteration, it is generally accompa- nied by silicification, albitization, greisenization and sometimes formation of apatites/fluorapatites which give rise to graded contacts. K-Feldspars Table 1 shows the trace element contents of the microcline, microperthites (K-feldspars) taken from different pegmatites in the study area. For example, one sample of K-feldspar has the highest Cs (3489ppm), Tl (73ppm), Bi (21ppm), REEs Ce (69ppm), La (166ppm), Pr (29ppm) and very high Rb (9474ppm). It has the lowest total Fe and Mn (Fe2O3, 0.13%; MnO, 0.002%), and K/Tl (1558), Rb/Tl (130), K/Cs (33) and K/Rb (12) ratios. These characteristic indicate that the feldspar crystallized from a highly fractionated melt and although this particular sample has low concentration of the ore elements, Sn-Ta-Nb, an eluvial concentrate from the mine had earlier yielded high values of Ta (1749ppm) with high Ta/Nb ratio of 5.45, NIMAMOP (1998). The average content of Ta in the K-feldspars is very low (2ppm). The K-feldspars have K/Rb range of 12-35 and a mean of 19. K/Rb has a very high neg- ative correlation (-0.938) with Cs in the K-feldspars, Figure 3. In Figure 3, the Cs content is plotted versus the K/Rb ratio for K-feldspar together with the boundaries discriminating, according to Trueman 217 MINERALIZATION POTENTIALS OF PEGMATITES IN THE NASARAWA AREA OF CENTRAL NIGERIA and Cerny (1982), between barren, Be-, Li-Be-, and Li-Cs-Be-Ta mineralized pegmatites. From the fig- ure, the following pegmatites in the study area of which the K-feldspars were analyzed belong to the corresponding classes (Table 2). It is important to note from this classification that some pegmatites from the same location have differ- ent degrees of evolution – some are more evolved be- longing to the lithium-beryllium class and some belong to the beryllium class. The pegmatites in the beryllium and lithium-beryllium classes have high prospects for gem tourmaline and beryl mineraliza- tion, especially in the albitized zones of the pegmatites (Preinfalk et al., 2000). The Liberia and Onyelow Wazobia pegmatites mainly belong to the lithium-cesium-beryllium-tantalum class. It is also important to note here that a sample of the Liberia pegmatites plots in the lithium-beryllium class show- ing that the pegmatites must at least have evolved from the lithium-beryllium class to the lithium-ce- sium-beryllium-tantalum class. The Liberia pegma- tite therefore has potentials for bearing ore mineral characteristics of both the lithium-beryllium and lith- ium-cesium-beryllium-tantalum classes in the differ- ent zones of the pegmatite. Active mining of Sn-Nb-Ta ores and analysis of mica and other min- eral samples such as amblygonite and fluorapatite, confirm the enrichment of the pegmatite in the ores of Li-Be-B-Sn-Nb-Ta. Na – Feldspars The framework silicate samples (feldspars and feldspathoids) with low silica (SiO2 < 55.95%) and Na/K greater than 1 (except cookeite) were grouped together for convenience as Na-feldspars (Table 2). The true Na-feldspars according to Deer et al (1966) have the following average contents of ore and lithophile elements: P2O5 (1.17%), F (bdl), Ga (27ppm), Nb (145ppm), Sn (221ppm), Ta (195ppm), Rb (175ppm) and Cs (31ppm). The ore elements are finely disseminated in the albites. The aplitic footwall albite is probably sec- ondary or at least late primary in crystallization.Most of the albite in the pegmatites is found in the al- bite-rich aplitic zone often occurring in the footwalls of pegmatites (Jahn and Tuttle, 1963; Jahn and Burnham, 1969). The secondary albite has very low Nb/Ta ratio of 0.26, which is comparable to the low Nb/Ta ratio of 218 AKINTOLA, O. F. AND ADEKEYE, J. I. D. 25 \ Akpoku 30 Kama TudunWada 30 30 Endo NASARAWA 7°40’E7°35’E 8°30’E 3000 meters 0 3 6 Kilometers3 N Older granites Granodiorite tonalite gneiss Younger granites (afu complex) Mica schist Tourmalinite Basic dyke Pegmatite Strike and dip of foliation Geological boundary 30 Legend Roads 8°25’N 8°21’N 8°18’N 8°30’E 8°25’N 8°21’N 8°18’N 7°45’E 7°50’E GidanKwma Figure 2: Geological Map of Nasarawa Area. 219 MINERALIZATION POTENTIALS OF PEGMATITES IN THE NASARAWA AREA OF CENTRAL NIGERIA Table 1: Trace elements of the microline, microperthies (K-feldspars) of the pegmatites. Sample l3 l6 l7 l10a luz lu ls s2 k1 k3 w2a P (ppm) 2400 2461 2662 2579 2130 4774 5398 6642 2854 2138 3024 F 0 0 0 0 0 0 326 0 0 0 0 Ba 44 35 34 67 10 30 53 36 69 91 39 Bi 20 10 17 15 17 15 10 13 12 10 21 Cd 13 7 9 5 6 bdl bdl Bdl bdl bdl 16 Ce 40 32 32 12 52 21 0 19 35 0 69 Co 16 33 18 28 20 28 31 25 23 31 18 Cr 10 13 9 14 2 15 35 11 6 1 6 Cs 1722 1487 1540 1226 1482 602 111 160 844 692 3489 Cu 7 7 14 9 0 13 13 8 4 19 16 Ga 18 15 17 15 17 16 44 19 18 14 17 La 95 73 74 58 84 27 2 16 38 31 166 Nb 8 5 9 7 9 22 39 8 4 8 8 Ni 20 0 31 28 0 0 0 0 0 0 27 Pb 70 57 81 79 69 46 0 35 125 140 93 Pr 19 15 16 13 18 8 0 6 9 8 29 Rb 8546 6536 9534 8303 8420 5537 2593 3069 5440 4089 9474 Sn 21 13 187 15 14 28 24 28 9 8 24 Sr 38 144 58 44 51 22 30 183 64 70 32 Ta bdl 1 2 bdl bdl 9 6 Bdl bdl bdl bdl Tl 49 38 57 49 49 30 12 16 39 30 73 W 155 241 137 187 176 203 195 154 143 204 160 V 10 0 0 14 18 0 0 0 0 0 20 Y 30 18 20 0 19 24 12 11 0 14 24 Zn 44 0 0 0 0 0 40 0 0 0 0 K/Ba 2521 2906 3492 1694 11058 3628 1696 2841 1571 1165 2916 K/Rb 13 16 12 14 13 20 35 33 20 26 12 K/Cs 64 68 77 93 75 181 811 639 128 153 33 K/Tl 2264 2676 2083 2316 2257 3628 7493 6393 2780 3534 1558 Rb/Tl 174 172 167 169 172 185 216 192 139 136 130 0.26 average in the amblygonites. Obviously, both the secondary albite/mica and the amblygonites are in paragenesis with the tantalum minerals. This ob- servation is in agreement with the findings of Moller and Morteani (1987). A sample with a very high (8.8%) L. O. I. was also identified (by XRD and ICP-OES) to be cookeite – a hydrated lithium aluminum silicate. It has Na/K ratio slightly less than 1. Cookeite crystal- lizes from late stage hydrothermal fluids evolved from residual albitic melts on stabilization of tourma- line (and the loss of other fluxing components such as P, B, Li, F and H2O) from the pegmatite melts (Cerny, 1991b). Cookeite is known to occur with other low temperature minerals like adularia and zeolites in miarolitic cavities of the highly evolved complex rare metal pegmatites. White Micas (Muscovites) in the Pegmatites The average chemical composition of the muscovites is typical of rare element pegmatites with high, F, Cs, Rb and Li (Deer et al., 1966; Gordiyenko, 1971) (Ta- ble 3). The XRD diffractogram of selected samples of the micas show that the crystal structures of the muscovites are close to the ideal dioctahedral and R2+ - free composition typical of muscovites from the rare-element pegmatites class (Cerny and Burt, 1984). The muscovites have a wider range of Rb val- ues (2659-10182ppm) and lower K/Rb ratios (8-31) than the K-feldspars’ (2593-9534ppm) and (12-35) respectively (Table 4). A late generation mica Ð taken from an inner zone of Liberia pegmatite has very high Cs (2353ppm), Rb (9910ppm), Sn (647ppm) and Ta (103ppm) and correspondingly low K/Rb (8), Nb/Ta (0.66), and K/Tl (1600) ratios. These are comparable to average values of Cs (2294ppm), Rb (8978ppm), Sn (665ppm), and Ta (464ppm) and the correspondingly low average K/Rb (9), Nb/Ta (0.14), and K/Tl (1361) ratios in muscovites from highly mineralized pegmatites in the northern part of the area. Nb/Ta ratios for the pegmatitic muscovites range from 0.13 to 8.07 with a mean of 2.965. The K/Rb ratios for the micas range from 8 and 31 with a mean of 16.20. Ta has a very high positive correla- tion with Cs (0.756) but a very high negative corre- lation with Nb (-0.856). Linnen (1998) and Morteani and Gaupp (1989) have observed that the different behaviour of Ta and Nb during crystalliza- tion is due to differences in solubility of Nb and Ta in Li-rich pegmatitic melts. The Cs vs. K/Rb plots of pegmatite muscovites from the area (Figure 4) concentrate in the field typi- cal of rare-element class pegmatites as defined by Cerny and Burt (1984). Only one sample which was collected about 100meters south of the Liberia peg- matite plots in the muscovite class. The K/Rb ratios of the muscovites range between 7.58 and 30.94. These low ratios of K/Rb as well as the high negative correlation of K/Rb and Cs (-0.830) are typical of muscovites of the rare-metals class of pegmatites (Preinfalk et al., 2000) and have been used success- fully as exploration tools for the pegmatites. Correlation of the Trace Elements and Fractionation Trends K/Tl, K/Rb, K/Cs, Al/Ga, Zr/Hf and Nb/Ta ratios give fractionation indices in the granite-pegmatites suites. Some of these ratios are compared with the average values of the trace elements in the pegmatitic minerals (Table 4). The table also shows that the rare earth ele- ments (REEs) Ce, La, Pr, and Y are enriched in the 220 AKINTOLA, O. F. AND ADEKEYE, J. I. D. barren 10p Be Li, Be Li, Cs, Be, Ta Cs 100001000100101 1 10 100 1000 K/Rb Figure 3. Classification of the Pegmatites Using the Plots of K/Rb Versus Cs of Their K-Feldspars. Note: The lines discriminating between barren pegmatites and pegmatites with significant Be; Li-Be-, Li-Be- Ta-mineralization are given according to Trueman and Cerny (1982). 221 MINERALIZATION POTENTIALS OF PEGMATITES IN THE NASARAWA AREA OF CENTRAL NIGERIA Table 2: Trace element content of the albitic pegmatite phases Phosphates Albites Cookeite Fluorapatite Amblygonites Sample lb6a lb8 sj3 rNa lc19 kj2fsp lb9 lb10 ch1 P2O5 (%) 0.481 0.487 2.169 1.763 0.243 0.017 24.97 49.973 43.25 F(ppm) 1240 0 0 0 0 294 11637 13897 14203 As 0 0 7 8 6 1 0 0 0 Ba 19 51 37 26 102 56 31 33 61 Bi 14 11 11 16 12 12 38 1 8 Ce 14 12 22 14 0 0 443 0 7 Cd 7 bdl bdl bdl bdl bdl 27 bdl bdl Co 115 47 25 31 37 5 16 8 6 Cr 1 0 0 11 0 15 1 2 1 Cs 851 23 19 74 9 49 1 28 6 Cu 0 0 24 16 4 0 0 16 535 Ga 76 24 21 22 39 58 14 21 18 Hf 2 3 0 3 3 2 0 3 2 La 48 9 0 3 3 0 204 0 0 Mo 0 5 1 1 0 4 0 1 0 Nb 88 75 62 326 115 33 190 26 25 Nd 3 11 9 8 2 0 144 5 7 Ni 14 5 3 4 0 3 9 4 3 Pb 25 10 7 0 0 0 74 9 0 Pr 10 2 1 2 1 0 65 0 1 Rb 4829 69 347 252 31 444 46 290 62 Sc 0 0 9 0 4 0 0 0 5 Sm 1 3 2 2 1 1 66 1 1 Sn 565 659 14 174 35 54 28 231 67 Sr 263 52 1037 305 51 8 64 11 188 Ta 345 109 67 305 297 37 21 107 86 Th 0 0 0 0 0 3 2 1 4 Tl 23 bdl bdl bdl bdl 5 bdl bdl bdl U 0 3 0 10 0 1 216 0 7 K-bearing minerals, K-feldspars and muscovites, with the highest concentrations of the element in the K-feldspars. Because of their similar geochemical mi- gration patterns, K, Rb, Cs and Tl are concentrated, and have very high positive correlations in the K-feld- spars and muscovites (Table 6). The muscovites how- ever have higher fractionation indices compared with the K-feldspar as indicated by their low average K/Rb, K/Tl, and K/Cs ratios. The muscovites have high val- ues of Sn (383ppm average), Nb (155ppm average), Ta (96ppm average), Ga (196ppm average), F (2128ppm average), and Zn (379ppm average) and have higher Rb/Tl ratio than the K-feldspars. The muscovites have the highest values of Ga (with amean value of 161ppm) and lowest Al/Ga ratio of theminer- als. This corroborates the observations of Cerny et al (1985) that tourmaline and muscovites are the main concentrators of Ga in pegmatites. Ba, Sr, W, Zr and Ta are highest in the Na-feld- spars with the lowest Nb/Ta ratios, which is an indi- cation that these elements are enriched along with Ta in the late mineralizing fluids. The following groups of elements (Table 5) have high positive correlation indices in the Na-feldspars: Rb versus Cs (0.922), Cs versus Zn (0.866), Cs versus Co (0.802), Co versus W (0.974), Ga versus Co (0.890), Ga versus W (0.851), Nb versus Zr (0.941), Nb versus Bi (0.850), Ta versus Bi (0.769), Ta versus Ga (0.638), Ta versus Nb (0.629) and Ta versus W (0.538).The high posi- tive correlations of these elements reflect their asso- ciations in the formation of rare metal ores from the Na-rich late fluids. The pegmatitic K-feldspars have very high negative correlations of K/Tl and K/Rb with the rare lithophile elements such as Cs, Bi, Y, Rb, La, Pr, Pb (Table 7). Similarly, the muscovites have very high negative correlations of K/Tl and K/Rb with the rare lithophile elements as well as the ore elements Sn and Ta. Nb is negatively correlated with Rb, Cs, Tl, Ta, La, Pr and Sn but positively correlated with K and Ga in both the K-feldspars and muscovites (Table 7). Nb and Ga have positive correlations in both muscovites and K-feldspars (0.704 and 0.472) respectively. Obviously, the 222 AKINTOLA, O. F. AND ADEKEYE, J. I. D. Sample lb6a lb8 sj3 rNa lc19 kj2fsp lb9 lb10 ch1 V 5 1 4 15 6 5 16 4 8 W 502 346 201 247 298 64 46 89 124 Y 6 1 0 0 1 0 1391 1 0 Zn 229 63 26 187 12 39 62 26 119 Zr 17 12 17 68 18 5 17 54 7 H2O 2.42 0.43 1.1 0.82 0.36 8.8 0.51 5.27 7.54 SUM 98.71 98.24 97.67 99.4 99.79 98.01 98.12 102.94 86.53 K 33457 1577 11540 3321 1079 9132 1494 3487 664 K/Rb 7 23 33 13 35 21 32 12 11 Mg(hx) 13 139 7 23 Li(hx) 225 685 16400 20750 Li(fusion) 227 2900 13366 17882 Na/K 1.17 43.74 5.81 19.80 72.80 <1 21.80 4.23 n.d Nb/Ta 0.26 0.69 0.93 1.07 0.39 0.89 9.05 0.24 0.29 223 MINERALIZATION POTENTIALS OF PEGMATITES IN THE NASARAWA AREA OF CENTRAL NIGERIA T a b le 3 . T ra ce el em en ts in th e p eg m at it e m ic as S a m p le (p p m ) le 7 le 8 le 1 4 le 1 3 le 1 8 l4 l1 0 b l8 a l9 a lz lu a ls 7 L c1 9 lc 2 0 lc 2 0 a s1 k k a lc 2 3 lc 2 8 w w 2 R lc 3 0 lc 3 1 lc 3 2 lc 3 3 F 2 9 3 3 3 1 9 7 3 2 1 5 3 2 2 0 2 9 7 2 7 4 3 2 3 3 1 3 1 2 8 8 4 4 3 5 2 4 6 5 2 1 0 6 6 1 7 1 0 0 4 3 9 0 3 9 3 3 2 9 6 6 7 4 6 1 2 8 4 1 2 2 5 4 2 6 1 6 2 9 6 5 4 7 5 1 9 4 0 1 0 8 8 8 8 1 3 7 4 B a 1 5 6 0 3 1 2 7 2 4 1 2 3 0 3 5 2 0 3 1 2 3 5 3 7 6 9 3 5 1 9 1 3 2 8 1 5 4 2 2 5 1 0 0 7 4 3 3 1 6 2 3 4 4 1 8 B i 1 7 2 1 2 0 1 6 2 1 2 5 1 6 1 9 1 2 1 9 1 3 1 4 1 2 1 5 2 8 3 4 1 4 2 1 1 7 1 8 2 0 1 1 1 8 1 5 1 3 1 2 1 3 1 7 C e 1 2 2 9 5 2 0 2 6 1 3 0 1 1 0 0 0 0 9 3 2 3 9 3 7 1 8 2 6 1 4 1 2 9 0 2 7 0 2 2 0 2 3 C s 1 7 1 8 7 4 2 9 0 3 0 0 2 6 0 8 7 4 1 0 0 1 0 0 1 2 3 2 8 9 6 2 0 6 3 2 1 1 8 3 4 2 2 1 2 0 2 4 6 7 4 2 4 5 1 5 6 9 4 5 1 6 9 4 2 1 5 1 7 4 9 2 9 1 4 9 9 6 3 1 1 6 3 4 6 G a 1 6 7 1 6 3 1 6 3 1 5 3 1 6 7 1 6 8 1 5 8 1 6 4 1 6 2 1 7 4 1 5 5 2 0 3 2 0 0 1 6 6 1 5 6 1 6 4 1 5 9 1 4 1 1 7 6 1 7 4 1 9 7 1 5 4 1 4 5 1 6 2 9 7 1 4 7 1 6 1 1 3 8 La 0 5 7 1 5 2 0 2 3 5 4 4 4 4 5 1 0 3 6 9 0 0 4 7 9 8 1 0 8 1 7 1 4 3 6 0 4 0 3 2 0 4 9 7 1 0 2 1 5 N b 1 8 1 1 1 6 1 7 8 1 6 5 1 8 2 1 3 1 1 1 9 1 1 3 1 8 5 1 4 4 1 7 8 2 1 8 2 5 6 1 8 7 7 5 5 5 1 4 6 1 5 1 1 6 0 2 1 1 1 4 3 1 9 3 2 0 0 1 2 7 6 4 2 2 3 1 9 0 1 3 5 N d 9 1 7 4 1 4 1 0 6 0 7 2 0 2 0 1 9 1 2 7 7 1 3 2 1 7 0 1 1 0 9 4 5 7 N i 7 2 7 1 7 1 8 2 1 2 3 2 4 2 4 2 1 2 3 1 3 8 9 1 8 2 7 3 1 1 8 2 1 1 6 1 1 2 0 1 0 6 1 7 1 1 1 6 1 8 2 4 P b 1 8 4 7 2 3 2 1 3 0 4 6 4 5 4 5 1 9 4 4 1 7 6 4 2 5 4 7 6 4 1 8 2 6 2 2 7 3 3 1 0 9 3 3 2 7 9 1 8 1 9 P r 3 1 5 6 8 8 1 4 1 2 1 2 6 1 1 6 1 3 1 1 1 9 2 2 6 6 9 2 1 1 7 3 1 1 1 3 2 4 5 R b 4 8 0 3 9 4 1 0 5 0 9 3 5 5 7 8 5 8 3 9 1 3 9 1 5 8 8 0 3 5 2 8 9 8 8 7 4 7 5 1 3 1 3 3 2 6 5 9 5 6 3 8 7 7 7 4 1 0 1 8 4 5 0 4 4 9 4 1 5 5 2 7 3 4 7 1 7 7 4 9 3 2 8 4 2 8 7 0 6 8 0 3 4 5 8 1 3 6 4 5 4 3 2 4 4 2 4 8 S n 2 1 7 4 7 1 2 7 5 3 3 6 3 5 7 5 2 5 5 3 3 5 9 7 2 7 4 6 8 1 2 3 9 6 1 2 6 6 3 9 7 6 8 1 6 4 9 2 9 5 3 6 4 3 9 4 8 7 4 3 7 1 3 9 1 1 8 9 0 2 5 3 9 1 4 7 2 7 1 2 1 9 S r 1 5 5 0 4 1 1 8 1 9 2 4 2 7 2 5 1 7 2 4 1 6 1 1 1 3 1 8 2 5 3 2 1 6 1 8 1 9 1 1 2 3 1 5 1 2 2 1 1 5 1 7 1 7 1 6 T a 4 4 5 8 4 5 5 0 6 3 5 3 5 9 7 1 7 1 7 1 4 1 2 7 4 6 7 2 5 0 2 4 2 5 7 5 8 5 1 1 5 3 1 5 1 6 2 6 4 1 2 0 1 8 3 3 9 3 1 1 4 0 T l 2 2 4 3 2 4 2 7 2 6 4 0 3 9 3 9 2 5 4 0 2 1 1 7 1 5 3 1 5 2 6 4 2 4 2 9 2 8 1 6 3 5 1 8 1 7 3 6 3 3 1 8 2 1 2 5 W 7 1 5 1 6 5 7 1 2 3 7 3 9 3 3 2 8 3 8 7 7 2 5 8 4 6 5 4 0 8 6 8 9 3 4 3 6 4 8 5 6 5 2 4 0 4 9 9 1 5 6 1 1 4 3 2 6 1 Z n 4 2 1 1 0 0 0 4 5 2 4 3 5 4 7 2 9 6 1 3 9 1 1 4 1 6 8 0 0 3 7 9 2 3 1 1 3 1 2 1 7 1 1 1 1 2 3 1 4 2 2 4 2 1 4 2 1 8 7 3 4 1 2 4 9 1 6 3 4 5 3 4 7 1 6 1 1 7 7 1 1 2 K /R b 1 7 9 1 6 1 5 1 4 9 9 9 1 5 9 1 7 2 7 3 1 1 4 1 0 8 1 8 1 6 1 5 2 3 1 0 2 6 2 8 1 2 1 7 2 3 1 8 1 9 M g (h x) 6 1 2 0 6 9 6 9 7 6 2 2 2 8 2 2 5 2 2 1 7 4 8 1 1 2 9 7 5 7 0 6 6 2 0 5 0 3 1 8 9 6 6 9 1 1 0 7 8 5 6 6 8 3 3 6 4 4 N b /T a 4 .1 1 2 3 .9 6 3 .3 2 .8 9 2 .4 7 2 .0 2 1 .5 9 2 .6 1 2 .0 3 4 .3 4 8 .0 7 5 .5 7 2 .6 0 .1 5 0 .1 3 1 .9 5 1 .7 8 1 .3 9 6 .8 1 2 .8 3 .1 1 3 .1 3 1 .0 6 0 .3 5 5 .7 2 6 .1 3 0 .9 6 K /R b (h x) 1 0 .9 5 6 .0 1 1 0 .6 6 9 .4 5 9 .6 1 6 .2 4 6 .3 0 6 .4 3 9 .6 0 6 .8 6 1 0 .5 8 1 5 .5 4 1 8 .3 5 9 .2 6 6 .9 5 5 .5 4 1 1 .2 9 1 0 1 0 .0 1 1 3 .4 8 7 .2 5 1 4 .2 4 1 5 .8 9 8 .2 1 9 .9 1 1 4 .0 5 1 1 .6 9 1 1 .1 4 M g /L i( h x) 1 .3 0 .3 4 1 .3 5 1 .1 7 0 .8 4 0 .2 6 0 .1 7 0 .1 9 1 .2 4 0 .2 4 1 .5 7 1 6 .2 3 2 .2 5 2 .2 1 5 7 .3 3 1 0 1 .6 1 1 5 .5 1 1 .1 3 1 1 4 .5 5 4 .4 6 8 .5 2 2 5 .7 2 2 .2 5 1 1 Li -A A S (h x) 4 7 5 8 5 1 5 9 9 0 8 6 1 6 8 1 1 5 4 2 8 8 4 7 5 4 3 4 1 4 9 2 3 1 2 8 6 2 0 2 4 1 0 3 1 4 .5 1 6 4 Li -A A S (f u s. ) 1 5 4 2 8 3 2 0 1 1 9 8 2 7 2 3 9 5 4 6 8 3 0 3 1 7 4 3 2 4 2 3 1 3 0 4 0 2 0 4 7 3 6 1 1 2 1 5 8 1 0 4 3 3 1 7 6 1 1 1 6 0 2 9 5 4 7 2 3 0 K -A A S (h x) 5 8 0 5 4 1 8 0 5 9 1 8 4 6 8 0 0 0 7 2 2 5 4 2 2 5 4 8 1 5 5 0 5 0 2 8 4 5 4 0 7 5 4 3 1 0 3 5 1 5 5 3 0 5 4 2 5 0 7 4 5 5 5 0 5 5 4 9 3 0 4 1 3 0 5 1 6 5 4 5 5 5 3 8 1 5 5 9 7 0 6 0 8 0 4 2 9 0 R b -A A S (h x) 5 3 0 6 9 5 5 5 5 4 9 5 9 0 0 8 7 5 8 9 5 1 1 2 4 4 4 0 4 4 5 5 3 2 5 1 5 5 4 4 0 6 2 0 6 3 5 4 7 0 4 2 5 7 4 5 3 7 5 6 8 0 2 9 0 3 2 5 5 5 5 3 8 5 4 2 5 5 2 0 3 8 5 -A A S (f u s. ) 2 8 1 9 5 2 9 9 3 7 0 5 3 6 0 4 6 8 6 1 0 6 3 4 3 6 0 3 8 0 8 2 5 1 2 2 3 0 0 3 9 3 4 4 2 3 1 6 8 8 6 3 2 5 3 3 0 8 3 4 1 5 0 2 7 8 3 4 2 9 1 1 4 4 4 2 1 8 3 4 4 3 5 3 0 7 7 2 2 0 7 3 2 5 8 3 5 8 0 224 AKINTOLA, O. F. AND ADEKEYE, J. I. D. Table 4: Average contents of trace elements (range given in brackets) in the K-feldspars, Na-feldspars and micas of the pegmatites K-fedlspar(n=11) Muscovite(n=29) Albitesn=4(true albites) Ba 46ppm(10-91) 31ppm (3-100) 54ppm (26-102) Cs 1214ppm (111-3489) 664ppm (32-2467) 31ppm (9-74) Ga 19ppm (14-44) 161ppm (97-203) 27ppm (21-39) La 60ppm (2-166) 33ppm (1-109) Bdl Nb 12ppm (4-39) 155ppm (55-256) 145ppm (62-326) Pb 73ppm (10-140) 27ppm (4-64) Bdl Pr 13ppm (1-29) 9ppm (1-22) Bdl Rb 6504ppm (2593-9534) 5930ppm (2659-10182) 175ppm (31-347) Sn 34ppm (8-187) 383ppm (61-902) 221ppm (14-659) Sr 67ppm (22-183) 22ppm (11-64) 361ppm (51-1037) F Bdl 2128ppm (329-4751) Bdl Ni 9ppm (0-31) 18ppm (6-31) Bdl Ta 2ppm (0-9) 96ppm (27-502) 195ppm (67-305) Ce 28ppm (0-69) 15ppm (0-47) 12ppm (0-22) Zn 3.64 379ppm (47-1023) 72ppm (12-187) Tl 40ppm (12-73) 30ppm (15-64) Bdl W 178ppm (137-241) 62ppm (25-237) 273ppm (201-346) Y 16ppm (0-30) 15ppm (0-39) 0.5ppm (0-1) K/Tl 3362 (1558-7493) 3096 (1206-5485) - Rb/Tl 168 (130-216) 198 (139-235) - K/Rb 19 (12-35) 16 (8-31) 26 (13-35) K/Cs 211 (33-811) 121 140 K/Ba 3226 (1165-11058) 2575 81 Al/Ga 5359 1197 3680 Nb/Ta 7.04 2.89 (0.15-8.07) 0.77 Nb-dominant minerals crystallize earlier than Ta and the positive correlations of Nb, K and Ga indi- cate that Nb enters the silicate structure more easily than Ta. This agrees with the observations of Cerny and Burt (1989) that Nb/Ta ratios in silicates are rather high. Linnen (1998) has also observed that the different behaviour of Ta and Nb during crystallization is due to differences in solubility of Nb and Ta in Li-rich pegmatitic melts. Such behav- iour has also been observed in the Bruno and Xuxa pegmatites of the Aracuai pegmatite District of Brazil (Preinfalk et al., 2000). In the muscovites (Table 7), Ta has a very high positive correlation (0.756) with Cs but lower cor- relations with Rb in both muscovites and the albites (0.428 and 0.213 respectively). Ta and K/Rb however have better correlations in the mus- covites and albites (-0.441 and -0.592 respec- tively) when compared with Ta and Rb. The reason for this relationship between the elements may be explained by the fact that ideal positions for TaO 4 3- and TaO3- are lacking in the silicates. Therefore, Ta partitioning into mica will be small and TaO 4 3- which grow epitaxially at the mica faces account for much of the Ta contents in the micas (Moller and Morteani, 1987). Mg/Li has a high negative (-0.856) correlation with Zinc; the high positive correlations of Zn, Li and F (³0.759) in themicas are traceable to the fact that the three elements occupy the octahedral layer in the mica crystal structure. Li has negative correlation with Ta (-0.244), which shows that Li content of the early peg- matite micas are higher than the later ones; obviously increased concentration of Li through fractionation in the late fluids crystallized to form discrete Li-minerals such as amblygonite-montebrasite rather than enter mica phyllosilicate structure. This is in agreementwith the observation of Cerny et al (1985) that the buildup of Li concentration in a pegmatite melt that precedes the precipitation of Li minerals sensu stricto leads to increased contents of Li in early rock-forming mineral phases. Sn average value is highest in the muscovites; it also has much higher positive correlations with Cs (0.902), Rb (0.829), Tl (0.868), La (0.799) compared with the very low correlations it has with these ele- ments in the feldspars, which reflects the enrichment of tin with greisenization. Using K/Rb, K/Tl and Cs, it is therefore possible to recognize different generations of feldspars and micas within a complex-zoned mineralized pegma- tite (Table 8). E.g. early and late, which have signifi- cant differences in the range, and mean contents of the rare elements. Generally, the rare alkali (Rb and Cs) and Tl concentrations in the muscovites and K-feldspars give a good reflection of the concentra- tion of the rare elements in the pegmatites. The Liberia (lb) Pegmatite Deposit In this section, the trace element contents of the K-feldspars and muscovites of pegmatites in the Nasarawa area are compared with those of well-stud- ied pegmatites both within and outside Nigeria. The Liberia pegmatite in the study area is the most exposed of the studied pegmatites, because some blasting and drilling had been carried out on it. Twelve (12) muscovite samples of the pegmatite were analyzed. Extensive fractionation within the pegmatite is indicated by the wide range of K/Rb 225 MINERALIZATION POTENTIALS OF PEGMATITES IN THE NASARAWA AREA OF CENTRAL NIGERIA Rare-elements pegmatites’Class Muscovite Class Cs 10000 K/Rb 10001000 10 100 1000 Figure 4: Plots of K/Rb Versus Cs for The Pegmatites’ Muscovites. Note: The dash line represents the boundry between the muscovite and rare-metal classes (after Cerny and Burt, 1984). The solid lines represent the best fit lines for the LCT type pegmatites. 226 AKINTOLA, O. F. AND ADEKEYE, J. I. D. T a b le 5 . C o rr el at io n m at ri x o f so m e tr ac e el em en ts th at h av e si g n if ic an t B iv ar ia te C o rr el at io n s in th e N a- F el d sp ar s (n = 5 ) B a C s G a N b R b S n T a W Z n Z r K /R b N b /T a B a 1 .0 0 0 C s -0 .8 6 8 1 .0 0 0 G a -0 .2 3 7 0 .6 6 9 1 .0 0 0 N b -0 .1 8 3 0 .1 2 2 -0 .1 6 8 1 .0 0 0 R b -0 .9 0 0 0 .9 2 2 0 .5 6 5 -0 .0 8 7 1 .0 0 0 S n -0 .4 2 7 0 .6 1 3 0 .3 7 1 0 .1 3 2 0 .3 2 5 1 .0 0 0 T a -0 .1 4 9 0 .4 8 6 0 .6 3 8 0 .6 2 9 0 .2 1 3 0 .5 5 5 1 .0 0 0 W -0 .2 6 5 0 .6 7 7 0 .8 5 1 -0 .1 6 6 0 .4 6 5 0 .4 8 3 0 .5 3 8 1 .0 0 0 Z n -0 .8 9 1 0 .8 6 6 0 .2 7 4 0 .4 0 2 0 .7 1 8 0 .7 4 0 0 .3 9 3 0 .4 6 7 1 .0 0 0 Z r -0 .3 5 1 0 .1 6 0 -0 .2 7 5 0 .9 4 1 0 .0 6 9 0 .1 5 2 0 .4 5 1 -0 .3 5 5 0 .4 2 7 1 .0 0 0 K /R b 0 .8 3 4 -0 .9 7 3 -0 .6 0 8 -0 .3 0 1 -0 .4 7 6 -0 .8 1 8 -0 .5 9 2 -0 .6 8 5 -0 .9 2 8 -0 .2 9 0 1 .0 0 0 N b /T a -0 .0 1 6 -0 .4 6 1 -0 .9 6 1 -0 .3 1 5 -0 .1 3 1 -0 .3 5 4 -0 .5 4 1 -0 .8 3 6 -0 .0 4 5 -0 .3 9 6 0 .3 9 6 1 .0 0 0 227 MINERALIZATION POTENTIALS OF PEGMATITES IN THE NASARAWA AREA OF CENTRAL NIGERIA T a b le 6 . C o rr el at io n m at ri x o f tr ac e el em en ts th at h av e si g n if ic an t B iv ar ia te co rr el at io n s in th e K -F el d sp ar s (n = 1 1 ) C s G a L a N b P b P r R b S n T l W K /T l R b /T l K /R b K /C s C s 1 .0 0 0 G a -0 .6 6 7 1 .0 0 0 L a 0 .9 4 7 -0 .8 0 1 1 .0 0 0 N b -0 .5 6 6 0 .7 0 4 -0 .6 9 4 1 .0 0 0 P b 0 .7 3 8 -0 .8 5 2 0 .7 9 2 -0 .7 8 3 1 .0 0 0 P r 0 .9 2 3 -0 .8 1 2 0 .9 9 7 -0 .6 8 5 0 .7 7 7 1 .0 0 0 R b 0 .9 4 3 -0 .5 8 5 0 .9 0 3 -0 .4 5 4 0 .6 1 0 0 .8 8 8 1 .0 0 0 S n 0 .2 6 0 .1 4 7 0 .0 3 3 0 .2 9 2 -0 .2 1 6 0 .0 5 7 0 .2 3 6 1 .0 0 0 T l 0 .9 8 0 -0 .6 6 2 0 .9 4 0 -0 .5 6 4 0 .7 6 1 0 .9 2 1 0 .9 6 7 0 .1 1 4 1 .0 0 0 W -0 .1 3 3 -0 .0 3 3 -0 .2 1 9 0 .2 4 5 -0 .2 4 7 -0 .2 3 6 -0 .2 5 4 -0 .4 6 3 -0 .2 7 5 1 0 0 0 K /T l -0 .9 8 9 0 .6 3 6 -0 .9 3 4 0 .5 6 1 -0 .7 4 1 -0 .9 1 1 -0 .9 6 3 -0 .0 8 1 -0 .9 9 7 0 .2 3 8 1 .0 0 0 R b /T l -0 .6 5 0 0 .5 9 3 -0 .6 2 8 0 .6 3 7 -0 .8 6 7 -0 .6 0 2 -0 .4 3 2 0 .3 0 1 -0 .6 4 8 0 .2 1 5 0 .6 5 0 1 .0 0 0 K /R b -0 .9 3 8 0 .5 3 2 -0 .8 8 5 0 .4 2 8 -0 .5 6 1 -0 .8 6 8 -0 .9 9 6 -0 .2 4 3 -0 .9 5 4 0 .2 3 6 0 .9 5 5 0 .3 9 7 1 .0 0 0 K /C s -0 .9 9 9 0 .6 5 1 -0 .9 3 9 0 .5 6 3 -0 .7 2 3 -0 .9 1 3 -0 .9 3 3 -0 .0 0 3 -0 .9 7 1 0 .1 0 4 0 .9 8 3 0 .6 4 6 0 .9 3 1 1 .0 0 0 228 AKINTOLA, O. F. AND ADEKEYE, J. I. D. T a b le 7 . C o rr el at io n m at ri x o f tr ac e el em en ts th at h av e si g n if ic an t B iv ar ia te co rr el at io n s in th e P eg m at it es ’ M u sc o v it es F C s G a L a N b R b S n T a T l Z n L i( x) L i( fu s) R b (x ) R b (f u s ) K /R b N b /T a K /T l R b /T l M g /L i F 1 .0 0 0 C s -0 .1 1 6 1 .0 0 0 G a -0 .1 5 5 -0 .3 2 9 1 .0 0 0 La -0 .0 0 2 0 .9 1 3 -0 .3 2 7 1 .0 0 0 N b 0 .2 1 7 -0 .8 7 5 0 .4 7 2 -0 .7 5 3 1 .0 0 0 R b 0 .1 8 0 0 .8 2 1 0 .0 1 2 0 .7 7 1 -0 .6 9 6 1 .0 0 0 S n -0 .0 3 6 0 .9 0 2 -0 .1 8 5 0 .7 9 9 -0 .7 0 0 0 .8 2 9 1 .0 0 0 T a -0 .5 0 7 0 .7 5 6 -0 .3 9 4 0 .6 7 5 -0 .7 9 6 0 .4 2 8 0 .5 9 5 1 .0 0 0 T l -0 .0 4 8 0 .9 2 2 -0 .1 5 6 0 .8 5 1 -0 .8 5 8 0 .9 3 9 0 .8 6 8 0 .6 8 2 1 .0 0 0 Z n 0 .7 5 9 0 .1 6 0 0 .3 4 8 0 .1 9 3 0 .0 7 5 0 .5 5 9 0 .2 8 1 -0 .3 7 5 0 .2 8 7 1 .0 0 0 Li (x ) 0 .6 6 6 0 .1 2 7 0 .0 4 4 0 .1 8 3 0 .0 5 6 0 .4 5 2 0 .2 3 2 -0 .2 4 4 0 .2 5 0 0 .8 1 4 1 .0 0 0 Li (f u s) 0 .6 3 0 0 .1 6 7 0 .0 0 5 0 .2 1 4 0 .0 0 5 0 .4 5 5 0 .2 7 5 -0 .1 9 4 0 .2 8 4 0 .7 7 3 0 .9 8 0 1 .0 0 0 R b (x ) 0 .2 7 9 0 .5 8 3 0 .0 7 2 0 .5 5 8 -0 .4 3 1 0 .8 5 9 0 .6 1 9 0 .1 8 2 0 .7 0 9 0 .6 0 8 0 .5 1 8 0 .4 4 5 1 .0 0 0 R b (f u s) 0 .1 1 6 0 .6 9 6 0 .1 2 9 0 .6 2 3 -0 .5 6 8 0 .9 1 9 0 .7 6 2 0 .3 3 3 0 .8 3 3 0 .5 1 8 0 .4 0 8 0 .4 3 1 0 .8 3 9 1 .0 0 0 K /R b -0 .1 6 4 -0 .8 3 0 0 .0 0 6 -0 .7 7 2 0 .7 0 8 -0 .9 9 8 -0 .8 4 0 -0 .4 4 1 -0 .9 4 3 -0 .5 3 4 -0 .4 4 1 -0 .4 4 6 -0 .8 5 8 -0 .9 2 1 1 .0 0 0 (8.0-17), K/Cs (66-406), K/Tl (1600-3764), and Nb/Ta (1.59-4.11) ratios in the micas (Table 9). Rb and Cs contents and K/Rb, K/Cs as well as Nb/Ta ra- tios in the micas show that there are at least two gen- erations of primary muscovites in the pegmatite, the early and the late. Table 8. Some trace elements distribution in the different muscovite generations in the Liberia Pegmatite Deposit Element Early generation Late generation Rb(%): Range 0.48-0.58 0.88-0.99 Mean 0.52 0.92 Cs(ppm):Range 171-300 874-2353 Mean 243 1168 Tl(ppm):Range 21-27 39-47 Mean 24.16 41.33 Ta(ppm):Range 41-71 53-103 Mean 52.33 69.16 Nb(ppm):Range 165-185 68-144 Mean 178 115 Sn(ppm):Range 217-357 471-681 Mean 283 575.67 K/Rb:Range 13.8-17 8.0-9.3 Mean 15.58 8.77 K/Cs:Range 242-406 66-81 Mean 301 74.6 K/Tl:Range 3007-3764 1600-2058 Mean 3375 1941 Nb/Ta:Range 2.61-4.11 1.59-2.47 Mean 3.54 2.02 Number of Samples 6 6 The Rb, Cs and Tl contents show enrichment in late muscovites by factors of 1.77, 4.81 and 1.71 re- spectively with a corresponding enrichment in the ore elements Sn and Ta by factors of 2.03 and 1.32 re- spectively but a noticeable depletion of Nb by a fac- tor of 1.55 in the late muscovite. Thus, the enrich- ment of Ta and Sn in the late muscovites is accompanied by decrease in the K/Rb, K/Cs, K/Tl and Nb/Ta ratios. While there is also enrichment in Zn in the late muscovite, they are depleted in MgO and TiO2. Similar enrichments of the rare elements have been observed in the late primary muscovites of well-studied pegmatites like Tanco, Noumas, Tip-top and Harding. Such late generation primary muscovites are found in the middle and central zones of the pegmatites where they occur in paragenesis with ores of the rare elements. In Table 8, a comparison ismade of the Rb, Cs, Ta and Ga contents of muscovites of selected pegmatites in the study area, Wamba (100km north-east of the area), and some well studied pegmatites from other parts of the world. The micas have high Rb (0.8978%) and Cs (2294ppm) which are comparable to those of the higly mineralized Tanco pegmatite of Manitoba, Canada as shown in Table 9. Pegmatites in the area have a wide range of min- eralization potential from low Ta – pegmatites through medium Ta-pegmatites to high Ta-pegma- tite. From Table 9, it is evident that the Rb and Cs contents of the micas reflect Ta mineralization in pegmatites. Extremely low K/Rb (8.86 or less), and K/Cs (34 or less) characterize such highly mineral- ized pegmatites like Tanco and Liberia. The high Ta-mineralization potentials of the complex pegmatites in this area is corroborated by the high av- erage Ta2O5 content (406ppm) and Ta/Nb ratio (3) of eighteen concentrate samples taken from different mines in the area (Okunlola, 1998). Muscovites of the mineralized pegmatites from Wamba area have low Ta-potential with correspond- ingly low Cs (116ppm), Rb (0.3150%) and high K/Rb (25) and K/Cs (800) Nb/Ta (4.50) ratios. The Wamba pegmatites vary from barren, muscovite class to complex albitized, and Sn-mineralized pegmatites (Kuster, 1990). On the whole, it appears the pegmatities in Nasarawa, the study area, are more fractionated and therefore have higher Ta-mineral- ization potential than those of Wamba and the other 229 MINERALIZATION POTENTIALS OF PEGMATITES IN THE NASARAWA AREA OF CENTRAL NIGERIA studied pegmatites in Nigeria (Matheis and Kuster, 2001, personal communication). Discussion and conclusion The very low Ta contents in the K-feldspars may be attributed to the fact that TaO3 - cannot enter the fully polymerized (AlSi)O4 network of the K-feldspar (Moller and Morteani, 1987). Thus, the rare alkalis Rb and Cs are better indicators of the rare metalsmin- eralization potentials in the pegmatites’ K-feldspars than the ore elements Ta. The higher contents of the rare earth elements (REEs) Ce, La, Pr, and Y in the K-feldspar when compared with those of the other major pegmatite minerals shows that the REEs in the fluids from which the pegmatites crystallized were partitioned more into the K-feldspar than the other rock-forming minerals. This corroborates the obser- vations of Simmons and Heinrich (1980) that REE-bearing minerals occur in K-feldspar-rich parts of pegmatites. The high negative correlation of K/Rb versus Cs is characteristic of K-feldspars of rare metal pegmatites and has been used along with K/Rb versus Cs in the micas as reliable prospection aids for rare metal pegmatites (Preinfalk et al., 2000). High positive correlations between Cs, Rb and the REEs: Ce, La, and Pr are notable in the K-feld- spars, compared with the muscovites. This may be due to selective complexing of the REEs in the re- sidual melt by the framework silicate feldspar. The same process of selective complexing by P and F must have enriched the fluorapatite with high con- centrations of the REEs. The low average Nb/Ta ra- tio for the muscovites (2.965) is still lower than the (4±0.7) upper limit diagnostic of Ta-pegmatites (Cerny, 1989). Higher Nb/Ta ratios (9.5±1.5) and high Nb-concentrations (³200ppm) are diagnostic of the less specialized Nb-rich columbite pegmatites. Beus (1966) determined that ³20ppm Ta concentrations are characteristic of columbo- tantalite pegmatites and Gordiyenko (1971) also de- termined that 65-75ppm Ta concentrations are char- acteristic of the Ta-enriched pegmatite (Figure 5). Simultaneous enrichment of Rb, Cs along with Ta in the LCT granite pegmatite suites makes the alkalis reliable indicators of rare-metals mineralization in pegmatites. Thus K/Rb versus Cs, and Ta versus Cs plots of primary muscovites have been reliably used to determine the mineralization potentials of pegmatites. 230 AKINTOLA, O. F. AND ADEKEYE, J. I. D. Table 9. Geochemical characteristics of some well-studied pegmatites compared with Nasarawa Pegmatites K(%) Rb(%) Cs(ppm) Ta(ppm) Ga(ppm) K/Rb K/Cs No of Samples Liberia 8.0831 0.6972 556 57 163 12.6 198 11 Loc 20/20a 7.7997 0.8978 2294 464 160 8.86 30 2 K/Ka 8.2231 0.5234 605 100 159 15.75 119 2 W/W2 8.3145 0.3077 196 63 150 27.12 374 2 Tip Top, South Dakota (Low Ta) 8.52 0.355 222 56.0 175 24 384 13 Tanco, Manitoba (High Ta) 8.33 2.450 2420 240.9 433 3.4 34 19 Noumas, Namaqualand 8.21 0.357 566 74.2 92 23 145 2 Harding, New Mexico (Low Ta) 9.47 0.631 1917 64.0 123 15.0 49 21 Wamba, Central Nigeria n.d 0.3150 116 53 n.d 25 800 51 Matheis (1979) has earlier shown that mineral- ized pegmatites in Ijero and Egbe area of southwest- ern Nigeria are strongly depleted in Ba, Sr, and Zr but are enriched in Rb, Li, Y, Be, Sn, Nb, and Ta. Kuster (1990) has also observed similar geochemical evolu- tion in late Pan African tectonic granites and mineral- ized pegmatites in Wamba area. The relative enrichment of Ba, Sr, W, Zr and Ta in the Na-feld- spars indicate that pegmatites in Nasarawa area crys- tallize from a more fluid and rare metals-enriched melt than those of Ijero and Egbe, as well as Wamba areas. These results agree with observations of Cerny et al. (1985) who noted that these elements are en- riched in late hydrothermal stages of pegmatite for- mation. High activity of P during the primary pegma- tite crystallization in this area resulted in the for- mation of the amblygonite subtype (Burt and London, 1982; London and Burt, 1982b; Cerny, 1991b) of the complex pegmatites. The exhaustion of Li and F by the phosphates from pegmatitic melt may account for the Li-, and F-poor micas with the highest Ta contents which probably crystallized af- ter the crystallization of the amblygonites in the area. Tl, Rb, Cs and the REEs La, Ce, Pr fraction- ation in K-feldspars and white mica demonstrates congruent/similar trends. K/Rb, K/Tl and K/Cs ra- tios are lower in the white mica than the K-feld- spars. Ta and Cs have the highest positive correlation (0.756) in the micas, therefore low K/Rb (16), K/Tl (3096) and K/Cs (121) as found in the Nasarawa area indicate high rare metal Ta-Nb-Sn-Li-Be mineralization potentials as ob- served in the Nasarawa pegmatites. Acknowledgement Financial Assistance for the fieldwork by the Nige- rian Government through the Raw Materials Re- search and Development Council, RMRDC is gratefully acknowledged. The German Govern- ment through the German Academic Exchange Programme (DAAD) provided financial assistance for the rocks/minerals chemical analyses in the Technical University of Berlin (TUB) which is also gratefully acknowledged. The authors are grateful to Dr. G. Matheis of the Technical University of Berlin (TUB) for his as- sistance on the research. We are also grateful for the assistance of Professor Peter Moller and Dr. Peter Dulski of the Geoforshungs Zentrum (GFZ), Potsdam for their assistance in analyzing the Rare Earth and trace elements of some of the samples. References Ajibade, A. C. and Wright, J. B. (1989) The Togo-Benin-Nigeria Shield: evidence of crustal aggregation in the Pan African belt. Tectonophysics 165, 125-129. Akande, S. O. and Reynolds, P. H. (1990) 40Ar/39Ar spectrum ages of micas from the Sn-Nb-Ta bearing pegmatites in Nigeria. In: Proceeding, Volume 15, Colloquium of Afri- can Geology. Centre International Pour la For- mation Et les Echanges Geologiques (CIFEG) Occassional Publication 1990/20 p243. Ball, E. (1980) An example of very consistent brittle deformation over a wide intra-continental area: The late Pan-African Fracture system of the 231 MINERALIZATION POTENTIALS OF PEGMATITES IN THE NASARAWA AREA OF CENTRAL NIGERIA Gordiyenko (1971) Bcus (1966) 10000100010010 1 10 100 1000 Cs Ta Figure 5. Plot of Ta Versus Cs For The Muscovites of Nasarawa Pegmatites. Note: The limits of 20ppm Ta according to Beus (1966), and of 65-75ppm set by Gordiyenko (1971) for a Ta mineralization are also given. Tuareg and Nigerian Shield. Tectonophys 61, 363-379. Beus, A. A. (1966). Geochemical exploration for endogenic deposits of rare elements on the ex- ample of tantalum. Nedra, Moscow, Engl. Transl. GSE Libr, Ottawa. Black, R. (1984) The Pan African event in the geo- logical framework of Africa, Pangea 2, 6-16. Bowden, P. and Kinnaird, J. A. (1984) Geology and mineralization of the Nigerian anorogenic ring complexes. Geol. Jb. B56, 3-65. Burt, D. M. and London, D. (1982) Subsolidus equi- libria. In: Cerny, P. (ed). Granitic pegmatites in science and industry: Mineralogical Associa- tion of Canada, Short Course Handbook 22, 221-232. Cerny, P. (1989). Exploration strategy and methods for pegmatite deposits of tantalum. In: Moller, P., Cerny, P. and Saupe, F. (eds). Lanthanides, Tantalum and Niobium: Society for Geology Applied to Mineral Deposits, Special Publica- tion 7, Springer-Verlag, 271-299 pp. Cerny, P. (1991b) Rare-element pegmatites, Part 1: Anatomy and internal evolution of pegmatite de- posits: Geoscience Canada, 18(2), 49-67. Cerny, P. and Burt, D. M. (1984). Paragenesis, crystallochemical characteristics and geochemi- cal evolution of micas in granites pegmatites: In: Bailey, S.W. (Ed.), Mica.Minerological Society of America, Reviews in Mineralogy 13, 257-297. Cerny, P., Meintzer, R. E. and Anderson, A. J. (1985) Extreme-Fractionation in rare-element granitic pegmatites: selected examples of data and mech- anisms: Canadian Mineralogist 22, 381-421. Dada, S. S., Lancelot, J. R. and Briqueu, I. (1987) Age and origin of a Pan-African charnockitic complex: U-Pb and Rb-Sr evidence from the charnockitic complex at Toro, Nothern Nigeria. Abtr. Vol. 14 Coll. Afri. Geol. Berlin, 72-73. Deer, W. A., Howie, R. A. and Zussman, J. (1966) An introduction to the rock-forming minerals. Longman, London. 528pp Ekwueme, B. N. and Matheis, G. (1995) Geochemis- try and economic value of pegmatites in the Pre-cambrian basement of Southeast Nigeria. In: Magmatism in relation to diverse tectonic set- tings (Srivastava, R. K. and Chandra, R. eds) IBH Publishing Co., New Delhi, India, 375-392 pp. Garba, I. (1992) Geology, geochemistry and origin of gold mineralization at Bin Yauri, Nigeria. PhD Thesis, University of London, UK. 264 pp. Garba, I. (2002) Late Pan-African tectonics and ori- gin of gold mineralization and rare-metal pegmatites in the Kushaka Schist belt, North-Western Nigeria. J. Min. & Geol., 38(1), 1-12. Garba, I. (2003) Geochemical discrimination of newly discovered rare-metal bearing and barren pegmatites in the Pan-African (600±150Ma) basement of northern Nigeria. Applied Earth Science (Trans. Inst. Min. Metall.) 112; 287-292. Gordiyenko, V. V. (1971) Concentrations of Li, Rb and Cs in potash feldspar and muscovites as cri- teria for pegmatites. Int. Geol. Reviews 13, 134-142. Holt, R. W., Egbenuwe, I. G., Fitches, W. R. and Wright, J. B. (1978) The relationships between low-grade metasedimentary belts, calc-alkaline volcanism and the Pan-African orogeny in N.W. Nigeria. Geol. Rund. 67, 631-646. Jacobson, R. and Webb, J. S. (1949) The pegmatites of Central Nigeria. Geol. Surv. Nig. Bull. 17, 61p. Jahns, R. H. and Burnham, C. W. (1969) Experimen- tal studies of pegmatites genesis. Amodel for the derivation and crystallization of granitic pegmatites. Econ. Geol. 64, 843-864. 232 AKINTOLA, O. F. AND ADEKEYE, J. I. D. Jahns, R. H. and Tuttle, O. F. (1983) Layered pegma- tite-aplite intrusives. Mineralogical Soc. Amer. Spec. Paper 1, 78-92. Kinnaird, J. A. (1984) Contrasting styles of Sn-Nb-Ta-Zn mineralization in Nigeria. J. Afr. Ear. Sci., 2(2), 81-90. Kuster, D. (1990) Rare-metal pegmatites of Wamba, Central Nigeria-their formation in relationship to late Pan-African granites. Mineral Deposita 25, 25-33. Linnen, R. L. (1998) The solubility of Nb-Ta-Zr-Hf-W in granitic melts with Li and Li + F: Constraints for mineralization in rare-metal granites and pegmatites. Econ. Geol. 93, 1013-1025. London, D. and Burt, D. M. (1982b) Lithium miner- als in pegmatites. In: Cerny, P (ed). Granitic pegmatites in science and industry: Mineralogi- cal Association of Canada, Short Course Hand- book 8, 99-133. Matheis, G. (1979) Geochemical exploration around the pegmatitic Sn-Nb-Ta mineralization of SW-Nigeria. Geol. Soc. Malaysia Bull. 11, 33-351. Matheis, G. and Caen-Vachette, M. (1983). Rb-Sr isotopic study of rare-metal bearing and barren pegmatites in the Pan-African reactivation zone of Nigeria. J. Afr. Ear. Sci. 1, 35-40. McCurry, P. (1971). Pan-African orogeny in North- ern Nigeria. Geol. Soc. Amer. Bull. 82: 3251-3262. Moller, P. and Morteani, G. (1987) Geochemical ex- ploration guide for tantalum pegmatites. Econ. Geol. 42, 1888-1897. Morteani, G. and Gaupp, R. (1989) Geochemical evaluation of the tantalum potential of pegmatites. In: Lanthanides, Tantalum and Nio- bium. Moller, P., Cerny, P. and Saupe, F. (eds). 303-310. Nigerian Minerals Appraisal and Monetization Programme NIMAMOP stage I Report (1998). Publ. Ministry of Solid Minerals Development, Abuja. Okunlola, O. A. (1998). NIMAMOP Stages II/III batch I Final Report: Specialty metals explora- tion programme in the Udegi (Ogapa Oto) Area of Nasarawa State. Published by the Min- istry of Solid Minerals Development, Abuja, Nigeria. Oversby, V. M. (1975) Lead isotopic study of aplites from the Pre-cambrian basement rocks near Ibadan, Southwestern Nigeria. Earth Planet. Sci. Lett. 27, 177-180. Preinfalk, C., Morteani, G. and Huber, G. (2000) Geochemistry of the granites and pegmatites of the Aracuai, Minas Gerais (Brazil). Chem. Erde 60, 305-326. Rahaman,M. A., Emofurieta, W. D., Caen-Vachette, M. (1983) The potassic granites of the Igbeti area: Further evidence of the polycyclic evolu- tion of the Pan-African belt in South-Western Nigeria. Precamb. Res. 22, 27-92. Schuiling, R. D. (1967) Tin belts on the continents around the Atlantic Ocean. Econ. Geol. 62, 540-550. Simmons, W. B. and Heinrich, E. W. (1980) Rare-earth pegmatites of the South Pit District Colorado. Col. Geol. Surv., Denver, Resources Ser. 11, 131 pp. Trueman, D. L. and Cerny, P. (1982) Exploration for rare-element granitic pegmatites. In: Cerny, P (ed). Granitic pegmatites in Science and Indus- try. Minerological Association of Canada, Short Course Handbook 8, 463-494. Turner, D. C. (1983) Upper proterozoic schist belts in the Nigerian sector of the Pan-African prov- ince of West Africa. Precamb. Res. 21, 55-79. Umeji, A. C. and Caen-Vachette, M. (1984) Geo- chronology of Pan-Africa Nasarawa Eggon and Mkar Gboko granites, South East Nigeria. Precambr. Res. 23, 317-324. 233 MINERALIZATION POTENTIALS OF PEGMATITES IN THE NASARAWA AREA OF CENTRAL NIGERIA Van Breemen, O., Pidgeon, R. T. and Bowden, P. (1977) Age and isotopic studies of Pan-African granites from North-Central Nigeria Precambr. Res. 4, 307-319. Wright, J. B. (1970) Controls of mineralization in the Older and Younger Tin Fields of Nigeria. Econ. Geol. 65, 945-951. Wright, J. B. (1976) Fracture systems in Nigeria and initiation of fracture zones in the South Atlantic. Tectonophys. 34, 43-47. 234 AKINTOLA, O. F. AND ADEKEYE, J. I. D.