Mesostructural and microstructural evidences for a two stage tectono-metallogenetic model for the uranium deposit at Mika, Northeastern Nigeria: A research note

Nonrenewable Resources, VoL 7, No. 1, 1998 Mesostructural and Microstructural Evidences for a Two Stage Tectono-Metallogenetic Model for the Uranium Deposit at Mika, Northeastern Nigeria: A Research Note C. E. Suh 1'2 and S. S. Dada ~ Received December 3, 1996; accepted January 30, 1997 The Mika uranium deposit is of the Central Massif vein-type. The deposit consists of a series of subparallel veins, similar to Lilljuthatten deposit (Sweden), with variable ore grade. Two main structural trends occur within the vicinity of Mika namely: (1) vertical N160E-N180E or N-S normal fault trend in which the brecciated granite has been permeated and cemented by silica ribbons; (2) N130E trend associated with reddish brown hematitized siliceous breccias filling open fractures. The N130E trend is younger, and it is a local, passive shear trend developed at the bends of the N-S faults. On a microscopic scale, samples from the N-S trend are rich in crude cubie-tetragonal prismatic crystals of uraninite and/or pitchblende ores occurring in association with a low-temperature greenschist mineral assemblage of chlorite, epidote, and mica. Conversely, samples from the N 130E trend show widespread kaolinitisation, goethite formation and layering reminiscent of groundwater activity at shallow depths near the earth's surface. The main uranium mineral in this zone is yellowish autunite. The model proposed here envisages that the mineralization was related to two separate processes. A first mineralization episode developed simultaneous with the greenschist mineral assemblage, and a second episode was related to remobilization and subsequent mineral concentration in the passive NI30E open fractures by groundwater to form autunite. Such a model has far reaching implications for exploration. Although the secondary minerals along the NI30E fractures are more obvious in the field, the potentially economic primary mineral concentrations may be concealed at greater depth in the N-S structures. KEY WORDS: Uranium; Nigeria; tectono-metallogeneticmodel. INTRODUCTION being mentioned in government circles. Finding eco- nomic uranium deposits in Nigeria is of prime impor- Energy requirements in Nigeria are on a constant tance if the ambition of running nuclear power plants increase. Electricity generated from hydroelectricity for peaceful purposes in the future is to be achieved. dams and thermal stations meet only about 40% of the Research into uranium deposits in Nigeria is on the nation's energy needs. The prospects of increasing this rise due to the creation of two centers for energy meager output by turning to nuclear energy are not research. These centers are: Center for Energy very optimistic at present, but are more frequently Research and Development (CERD), Obafemi Awo- lowo University, Ife, and Center for Energy Research and Training (CERT), Ahmadu Bello University, Zaria. Presently, uranium ore beneficiation studies on ura- ~Geology Programme, Abubakar Tafawa Balewa University, nium minerals from deposits in Nigeria including Mika P.M.B. 0248 Bauchi, Nigeria. are going on at CERT, but the results so far obtained 2 To whom correspondenceshould be sent. are not yet in the public domain. 75 0961-1444/9gt0300-0075515.00/1 9 1998 International Association for Mathematical Geology 76 Suh and D a d a Mika is located in Adamawa state, former Gongola Although so much has been said about their economic state, with Yola as its capital city (fig. 1A). The uranium potentials, these granite bodies have never been drilled, deposit at Mika is of the Central massif vein-type in and current knowledge among uranium explorationists France, (cited for example, in Poty and others, 1986; in Nigeria treat them as insignificant resource. Leveque and others 1988; and Valois, 1991). The The Mika deposit occurs within a regional and deposit comprises a series of subparallel veins, quite very extensive mineralized fault system which spans similar to the Lilljuthatten deposit in Sweden (Stuckless several hundred kilometers along the strike and is sev- and Troeng, 1984), with variable ore grade. Each miner- eral kilometers wide. This fault system in northeastern alized vein zone is over 100m along the strike and 20m Nigeria is widely documented in the literature (see wide and spans over an area 25 km2 wide. for example, Maurin and others, 1986: Benkhelil and Mika is one of the most significant deposits dis- Robineau, 1983). Several uranium deposits are known covered by the Nigerian Uranium Mining Company to occur within this regional fault system and they (NUMCO) in the early 1980s. Prior to its discovery, include the Mika deposit; Ghumchi deposit; Zona efforts in uranium exploration in Nigeria were geared deposit and Kanawa deposit (Okujeni and others, 1988; towards the Jos Plateau younger granites in north- Funtua and others, 1992; Ogunleye and Okujeni, 1993; central Nigeria (Bowden and others, 1981). These Funtua and Okujeni, 1996). Uranium minerals in this granites, especially in Lurui Hills (Kano state) and region are mainly concentrated at areas where fracture Kigom Hills (Plateau state) were found to have pyro- trends intersect. Several insignificant occurrences also chlore disseminations (Oshin and Rahaman, 1986). do exist in this region. In all, the Mika deposit which r 11"36" E +'~ 11" 39'E 9"00' I,i 12" ~N/ 4, ;It ' "" -.,d. /+ +, +{/f" Ar Y .iI / 'y/ II A ,y y ,lie 58'N 1 Nm. L , I Figure 1. (A) Sketch Map of Nigeria showing location of study area (shaded portion). (B) Geological sketch map of the area around Mika. (1) Porphyritic granite (2) Faults/fractures (3) Uranium deposits (4) Rivers (5) Settlement (6) Footpaths. (C) Rose diagram depicting three main structural trends: N-S; NI30E and N30E-N55E.