OVERVIEW OF LEAD-ZINC IN NIGERIA

Lead-Zinc occurrences in Nigeria are associated with saline water intrusion in the sedimentary basins or fractured / shear zones in crystalline rocks. The mineralisation is often associated with minor to significant amounts of copper and silver, occurring in lodes filing the fractures within the sedimentary rocks in the Benue Trough as well as in crystalline basement rocks as shown in recent studies by Nigerian Geological Survey Agency. The Trough, which is believed to have originated as a failed arm of an aulacogen at the time of the opening of the South Atlantic oceans during the separation of the African plate and the South American plate, is partitioned into the Lower, Middle and Upper region with Lead-Zinc mineralization occurring in almost the entire 800km Length. The Lead-Zinc are localized along the Northeast-Southwest trending belt of slightly deformed volcanic and sedimentary Cretaceous sequences (Albian Asu River Group) which is about 500m thick, and they occur in the form of veins and veinlets associated with the host rock. The Lead-Zinc is often associated with other gangue minerals such as marcasite, pyrite, quartz, barites e.t.c.

LOWER BENUE TROUGH LEAD-ZINC MINERALIZATION

The general geology of lower Benue Trough in Abakaliki area is made up of thick sequences (500m) of slightly deformed cretaceous sedimentary rocks made up of essentially of albian shales, subordinate siltstones of the Asu River Group. There is also the presence of Volcanic and Pyroclastic materials forming elongated conical hills in the cores of the anticlinal Structures. The Abakaliki Lead-Zinc is believed to be of hydrothermal origin emplaced at a low temperature of about 140°C and it is made up of primarily four lodes namely Ishiagu, Enyigba, Ameri and Ameka in the lower Benue Trough located in Ebonyi State.

MIDDLE BENUE TROUGH LEAD-ZINC MINERALIZATION

The middle Benue Trough veins are located mainly in Akwana and Arufu. This mineralization is hosted in silicified limestone sequence and also belongs to the Asu River Group. Dips of these veins are generally steep to vertical with a width of between 0.5m-10m and length of approximately 100m along the strike length of the bodies. Contacts with wall rocks are sharp and ore grades vary from 3% to 5% combined Lead and Zinc. Vein constituents include galena, sphalerite, tetrahedrite and occasionally native silver. At Azara, the veins are rich in barites with occasional cubic galena. Limestone wall rock at Arufu and Akwana is highly silicified, which appears to be related to the mineralization processes as the intensity of the silicification decreases away from the vein.

UPPER BENUE TROUGH LEAD-ZINC MINERALIZATION

The Upper Benue Trough is made up of sedimentary sequences represented by medium to fine grained sandstone which is divided into Bima sandstone (Upper Albian age) and Yolde sandstone (Cenomanian age), shales of Yolde formation which underlies the alluvium which is associated with the sandstones as intercalations .These mineralizations are located in and around Isamiya, Diji and Gidan Dari in Bauchi State.