Knowledge Update

Gold mineralization in Nigeria

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Introduction

The goldfields in Nigeria have undergone severe artisanal workings that target both of the primary quartz-gold reefs and their related occurrences of alluvial in the absence of any systematic exploration and development. Nigeria's officially documented gold production began in 1913 and reached its peak between 1933 and 1943, when roughly 1.4t of gold was produced. Due to abandoned of mines by largely colonial businesses, gold production dropped as the Second World War was ongoing and never recovered. The Nigerian Mining Corporation started prospecting for gold there in the early 1980s, but due to a lack of funding, it was unable to continue. Despite the vast potential, gold exploration received little attention due to petroleum's discovery and subsequent economic domination in Nigeria.

Occurrence, Geological setting and Mineralization

Gold is found in Nigeria in primary veins, alluvial and eluvial placer deposits, and in various locations along schist belts in the northwest and southwest of the nation. The schist belts in northwest and southwest Nigeria's Maru, Anka, Malele, Tsohon Birnin Gwari-Kwaga, Gurmana, Bin Yauri, and Iperindo regions are all connected, have the most significant occurrences (Beyond these big places, there are a number of smaller occurrences). The upper Proterozoic fine-grained clastic, politic schists, phyllites, banded iron formations, marble, and amphibolites with imprints of the Kibaran and Pan-African tectonic processes make up the lithologies of the contained schist belts. With fewer quantities of volcanic rocks, the metamorphism within the belt is characterised by green schist facies grading into amphibolite, particularly in the older gneiss-migmatite-quartzite complex. Primary gold mineralization frequently occurs in quartz veins of various lithologies in the schist belt; these veins can have a variety of morphologies, such as bedding concordant veins or discordant vein systems. It is typical to find mineralized wall rocks next to well-known veins, and these rocks could include fine-grained sulphide minerals.

The Maru schist belt has the most significant two historic gold mines. The schistosity planes are frequently exploited by the shear zone that spans a quartzite-schist series and hosts Duki Mine. Past miners reportedly mined the mineralization, which appears to consist of gold-quartz veins, with a striking length of more than 1 km, leaving behind a sequence of collapsed N-S-trending workings with no mineralization exposed on the surface. Recent drilling by the Nigerian Geological Survey Agency (NGSA) has demonstrated the persistence of the quartz-gold-sulfide veins beneath the historic workings. A two-subparallel quartz vein system makes up Maraba, the other historic gold mine in Maru. Because of the severity of past mining, there are no in situ exposures, the only remnants of mineralization are tourmaline and chlorite in altered wall rocks and quartz floats. The Malele area is in the Maru schist belt's most southern region. An N-E trending line of gold-quartz veins that cut through both chlorite schist and biotite-gneiss is where gold mineralization occurs (Garba 2013). Today, a number of sub-parallel surface workings represents the series of veins, with the vein exposures being infrequently seen.  The schists, quartzites and phyllites of the schist belt are the hosts of several historic gold mines in the Anka area. According to the extent of previous workings, individual veins or reefs rarely have a strike length more than 0.5 km and are consistent with the foliation of the host rock.

The Kushaka schist belt contains the Kwaga and Tsohon Birnin Gwari gold sites. Pyrite is primarily present there, with lesser amounts of galena, magnetite, pyrrhotite, sphalerite, and chalcopyrite. Gold-quartz reefs and their altered wall rocks have been sampled relatively recently through recent core drilling and mining exposures close to the surface. The Kushaka schist belt's furthest southernmost region contains the Gurmana area of gold mineralization. Quartz-sulfide veins and gneisses are the two main types of gold mineralization. The gold-quartz-sulphide veins rarely run deeper than a few tens of metres. At the intersection of a pan-African granodiorite batholith invading phyllites and tourmalinites of the Zuru schist belt in Bin Yauri, Northwestern Nigeria, a brittle fault zone is cutting through hornfels, produces a gold-sulphide-carbonate quartz vein. The schist belt of Egbe-Isanlu in southwest Nigeria contains the gold-mining region of Okolom-Dogondaji. N-S and N-E- shear zones that are trending and cut gneisses, schists, and amphibolites, are the host of a number of gold-quartz veins. Southwest Nigeria's Ilesha schist belt is home to the Old Gold Mine at Iperindo. The Iperindo mineralization is currently characterised by parallel old working that extends 900 metres or so in an N-E direction, and it consists of a succession comprises carbonate-quartz veins that are auriferous confined by a secondary fault within mica schist and biotite gneiss.

Refreences

Garba, I., (2003) Geochemical characteristics of mesothermal gold mineralisation in the Pan-African (600 ± 150 Ma) basement of Nigeria, Applied Earth Science, 112:3, 319-325, DOI: 10.1179/037174503225003143

Gbadebo, A.M., Ekwue, Y.A. (2014) Heavy metal contamination in tailings and rocksamples from an abandoned goldminein southwestern Nigeria. Environ Monit Assess 186, 165–174 (2014). https://doi.org/10.1007/s10661-013-3363-4

 

Mr. Aliyu Mohammed Lawan is a Lecturer II in the Department of Geology, Skyline University Nigeria. He holds a Master’s degree in Applied Geophysics from Ahmadu Bello University Zaria and a Bachelor’s degree in Geology from the University of Maiduguri.

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