Base metals (Pb, Ag, Zn)

Mississippi Valley Type (MVT) Pb-Zn Deposits spanning upper/middle/lower Benue trough

Study Areas: Plateau, Nasarawa, Ebonyi

Basin Development and Geology

The Benue Trough is an Intra-Cratonic rift basin that extends southwest-northeast from the northern boundary of the Niger Delta close to the Gulf of Guinea, up to the southern boundary of the Chad basin.

It is a linear trough with a strike length of approximately 800km and a width that reaches a maximum of 160km in the south west. It rests unconformably upon the Precambrian basement.

The Benue Trough originated as a failed rift during the early Cretaceous opening of the South Atlantic Ocean. Differential Rifting of Gondwana started in the South, exerted major strain on the Central African inflection point and created several crustal scale tectonic features in Africa and South America.

The Benue basin Evolution involves;

  • Extensional marine Sedimentation in Albian to Turonian times;
  • Left-lateral strike-slip shearing;
  • Compressional Inversion in the early-Santonian;
  • Post-inversion sedimentation; and
  • Mesozoic to Cenozoic magmatism.


Mineralisation in the Benue Trough follows the Clastic Dominated Pb-Zn-Ag depositional model. A heat source at depth during the sag phase of basin development caused upward migration of carbonate dominated mineralizing fluids along pre-existing extensional structures. Local boiling or mixing with meteoric waters produce epigenetic, structurally controlled vein and disseminated mineralisation with pervasive carbonate replacement. Mineralized structures are parallel, en-enchelon, N/S or NW/SE trending. A heat source for mineralizing fluids is considered to be mafic intrusives due to the common spatial association of deposits and mafic rock.

The Pb-Zn deposits primarily contain sphalerite, galena, pyrite and chalcopyrite associated with calcite and subordinate quartz veining.

Target 2

Field Work

The area was mapped, soil sampled, and a magnetic survey was performed. This resulted in a new discovery. Due to sparse outcrop, soil geo-chemistry was the tool of choice for the exploration of this target. Pb-Zn mineralization is hosted in limestone and shale. An anomalous zone of over 1km in strike length follows the lithological unit interpreted to be a Shaley-Limestone. Sr and Fe shows a strong correlation with mineralization.

Mapping was achieved by combining observations of float with a Lithological interpretation of the Soil Geochemical dataset and the Radiometric dataset. Geochemistry shows that river sediments mask most of the Geology to the West of the river. The ground magnetic survey shows a NW-SE striking body cut by possibly two faults. The northern fault appears to have a left lateral displacement and to extend parallel to the anomalous zone. This is considered to be an exciting new target.

EM Survey

FDEM was carried out on all this target area to further ascertain the attitude of the anomalies picked up from other surveys. The result came out positive, it furthermore highlighted the possibility of a new discovery. Interpretations for this survey was based on the 30Hz frequency signal.

Three survey lines were planned across the soil anomalous area of target 2, from which two responses were returned as indicated.

This resulting response appears to be slightly offset to the east of the soil anomaly as shown.

It is believed that the offset of the soil anomaly to the West is as a result of the river movement which has moved some of the in-situ soil containing the anomaly.

Target 3

Field Work

At Target 3, four anomalous zones were identified from soil Geochemistry. The major anomaly in the center and SW are located in the vicinity of mines. Much of it is probably surface contamination by mining activities. The zone to the East is dubious since it coincides with a village and river where artisanal recovery of ore prevails. A NNW-SSE line of smaller anomalies coinciding with a magnetic lineament is considered to be of significance and has been studied further with EM.

In the South West a Magnetic survey showed a zone of different magnetic character striking SW-NE. This is interpreted to be a lithological unit hosting the mineralization. This area is covered by a monotonous turbidite sequence that showed no recognizable chemical variation. Field work also did not reveal much about the Geology. The only clue to the geology could be found at mine sites.

EM Survey

EM survey was planned across the four (4) anomalous zones in three (3) areas, identified from soil geochemistry.


The first block which is the zone to the east with just one planned line close to the village produced a high EM response at the eastern end of the line, it was therefore concluded that the high anomaly from Geochem test was probably in-situ not transported as earlier thought hence it’s been earmarked for further work.


Five EM lines were surveyed at this zone lying at the centre of the target. The EM data as shown below shows no clear pattern, although EM responses align with Pb and Zn values on the second and fourth line with another significant response on the third though it doesn’t align with the soil values.

Frequency Domain EM and specifically using induction at 30 Hz responds very well to subsurface mineralisation. There is a strong unexplained response over Basalts on all EM induction frequencies. Evidence suggests that the 30 Hz line still responds primarily to mineralisation although some exceptions were noted near Basalts.

Target 9

Field Work

Preliminary studies of this region show that there are Pb-Zn mineralization controlled by a set of extensional shears sandwiched between two regional shears that forms the Keana anticline. From the mapping of this region and soil samples collected, it was proven these smaller shears are mineralized and they are located west of the Olivine rich basalts. It is proposed the mafic intrusive serves a source of heat for the mineralizing fluids. Anomalous Pb values maps out mineralization to the west of the basalt.

Ground magnetic survey was carried out over three target areas. The raw data generated contained numerous high frequencies, high amplitude spikes, due to numerous outcrops and subsurface boulders of Basalt in the target area which has a high magnetic susceptibility. This masked a lot of the low frequency low amplitude magnetic field information relevant to the Benue Trough mineralisation. The main structure being mined on the west of the basalt exposure does appear to not be visible on the raw magnetic data.

EM Survey

In target 9 the FDEM survey was mainly planned to the extreme ends of the target area mainly due to the large basalt exposure at the centre of the target. To the East of target area where minor Pb soil anomaly was picked up from soil Geochem, six lines of about 1.5km each were surveyed, we observed that there was significant interference from the basalt outcrop on all frequencies except 30 Hz.

Two lines on Target 9_6 aimed what was believed to be an eastward displaced block of the mined structure. Line 8385 indeed picked up a significant response over 3 stations that seem to align with the edge of the soil anomaly (red ellipse in the image below).

The anomaly is not repeated southwards limiting the size of a possible deposit. This information will however be of great interest to the adjacent mine owners. Drilling of this target is recommended.


Juggernaut has scheduled the commencement of the drilling program of the above targets in the first quarter of 2020.

Five drill targets have been defined of which four are very promising. These correspond to the following EM survey targets: Target 2_1, Target 3_1, Target 3_3 and 4, Target 9_6 and Target 3_2;

The drilling required to evaluate the drill Targets is likely to be substantially more than the allotted 1500m

© Copyright - NIMEP