Gold Mining in Nigeria
Gold is a valuable resource located within the subsurface and its mineralization is controlled by geology, structures and alterations within rocks. The search for gold is therefore the search within hydrothermally altered structures. In several areas of Nigeria, gold deposit is majorly found in the alluvial and eluvial placers, and primary veins within several lithology of the supracrustal schist belts in the north-western part of the country around Gwari, Yauri, Maru and Anka, and as well as the south-western part around Ife-Ilesha ( Iperindo ), Egbe and Isanlu – Dogondaji ( Okolom ). Smaller occurrences beyond the major areas also abound. The primary gold mineralization in the Nigeria Schist belts is commonly associated with several morphologic types such as veins, lenses, stringers, reefs and similar bodies of quartz, quartz – feldspar and quartz – tourmaline rocks.
The structural patterns responsible for the control of gold inclusion hydrothermal fluid responsible for the transportation and deposition gold in the Nigerian Pan-African basement consists essentially of transcurrent fault systems, subsidiary faults along with other penetrative structures within the Nigerian Schist belt.
Morphologically, the gold bearing veins range from several centimetres to a few metres in thickness, often exhibiting varying forms ranging from lenticular to pinch and swell (boudinage) structures, and invariably inclining and occurring as isolated bodies or as parallel or en-echelon vein systems. These veins are commonly associated with fractures or shear zones and are very often conformable with the general N–S to NNE–SSW structural grain of the basement and occur in a variety of geologic settings which suggests that there was more than one period of mineralization. The adjoining mineralized wall rocks are often rich in fine grain sulphide minerals, with galena and pyrite being the most common
Gold mining in Nigeria reached its peak in the period 1935–1941 but since 1950 has been
generally limited to very small scale alluvial workings. The major gold metallogenic provinces in Nigeria are; Maru, Anka, Bin Yauri and Tsohon Birnin Gwari in the north-western region, and Okolom-Dogondaji and Iperindo in the south-western region.
MARU SCHIST BELT
Maru Schist belt in Zamfara state is a harbour of two important old gold mines namely the Duki mine and the Mararaba mine. The Duki mine is hosted by a shear zone which traverses a quartzite-schist series often exploiting the S1 schistocity planes. The mineralization consisting of gold-quartz vein have been exploited by miners in the past for more than 1km length of strike, the aftermath of which is a series of collapsed N-S trending working, leaving no surface exposure of the gold mineralization. However, past exploration drillings by the Nigerian Mining Corporation have shown that the gold-quartz vein trend below the old exploitation workings.
The Mararaba gold mine is a two sub-parallel system of quartz-vein. The intensity of past mining has almost depleted all indicators of mineralization within the mine except for the altered wall rock and the presence of floating chlorite and tourmaline within the mine. There are also gold occurrences at Malele which is the extreme southern part of the Maru Schist belt.
ANKA SCHIST BELT
Gold-bearing veins have also been associated with the rock formations of the Anka Schist belt resulting in gold mineralization in areas such as Kwali, Jameson, Zuzzurfa and Kuba hosted by schist, phyllites and quartzite of the schist. Individual vein or reef intrudes the host rock and lies concordantly with the foliation hardly exceeding 0.5km of strike length. Gold mineralization occurs in this belt in association with lead-zinc-copper and sulphide mineralization in the form of quartz-sulphide vein.
BIN YAURI
Gold mineralization of Bin Yauri extends over 1.5km strike length as reported by past miners (1920s – 1940s). The gold-bearing veins are enclosed in a narrow zone of hydrothermal alterations in which a chlorite-tourmaline-pyrite-carbonates association overprints a dominantly sericitic fabric of the hornfel wall rocks. The Bin Yauri veins consist of quartz veins primarily in the mica schist. Recoinnaizance explorations and record from past mines have shown that the gold grade from 5 – 15 parts per million (ppm).
TSOHON BIRNIN GWARI
The Tsohon Birnin Gwari gold mine is located within the Kushaka Schist belt; a belt of about 50km wide and stretching from Minna up to the Tsohon Birin Gwari of north-western Nigeria. The Tsohon Birnin Gwari is an old gold mine which has produced over 600 ounces of gold in the 1930s. Its extension in recent times has led to the discovery of the Kwaga mine by artisinal miners. The Tsohon Birnin Gwari gold reef system stretches over a distance of about 7km in length, while the recently discovered Kwaga which is an extension of Tsohon Birnin Gwari is about 3km. The commonly associative mineral is mainly pyrite with some traces of of sphalerite, galena, pyrrhotite, magnetite and chalcopyrite.
The geochemical characteristics of the Tsohon Birnin Gwari mineralization has been studied from the relatively fresh samples of gold-quatz reefs and their altered wall rocks from core drilling samples obtained from recent exploration studies and near-surface mine exposures.
OKOLOM-DOGONDAJI
Okolom-Dogondaji in the Egbe-Isanlu Schist belt of south-western Nigeria lies within the southern part of the northerly trending Schist belt of Nigeria. Gold bearing veins at Okolom are hosted in many lithologies including biotie-gneiss, amphibolite and talc-tremolite schist of the Okolom area. Extensive mining of both alluvial/eluvial placers and the primary gold veins have taken place in the past between the 1930s and 1950s. The commonly associative minerals in this area are pyrrhotite, chalcopyrite, marcassite, argentite and galena with a gangue of quartz, tourmaline, sericite and chlorite.
IPERINDO
The Iperindo old gold mine in the Ife-Ilesha Schist belt of south-western Nigeria is one of the clusters of gold deposit around Ilesha. The gold mineralization consists of a series of auriferous quartz-carbonate veins hosted by a subsidiary fault within biotite gneiss and mica schist. Gold occurs in association with pyrrhotite, pyrite and minor galena, ilmenite, chalcopyrite, magnetite and sphalerite. The Iperindo gold deposit which covers a 1km2 area up to a depth of 100m has a proven reserve of one million ounces, with a grade range of 1 – 23.6g/ton.
