Base metal exploration Benue trough final - Steffen Kalbskopf

BASE METAL
EXPLORATION
BENUE TROUGH,
NIGERIA
STEFFEN KALBSKOPF
HIDDEN TREASURE CONSULTING
DEON SCHEEPERS
MINUTOR MINING, JUGGERNAUT INDUSTRIES
GSSA AFRICAN EXPLORATION SHOWCASE NOVEMBER 2020

BENUE TROUGH BASE METALS
2
TO REDUCE ITS DEPENDENCE ON OIL, THE
GOVERNMENT HAS FUNDED AN INTEGRATED SOLID
MINERALS EXPLORATION PROGRAMME ADMINISTERED
VIA THE MMSD AND NGSA (Nigerian Geological Survey)
1. TARGETED MINERALS
 GOLD, PGE, Ni-Cr-Co -Proterozoic schist & granite-greenstone belts https://nimep.ngsa.gov.ng/projects/lot-1/
 CRITICAL METALS – Li, Sn, Ta-Nb, (REE) – Pegmatites and “younger” granites https://nimep.ngsa.gov.ng/projects/lot-2/
 BASE METALS Pb-Zn (Cu-Ag) – Benue Trough https://nimep.ngsa.gov.ng/projects/lot-3/
 BARITE - Benue Trough https://nimep.ngsa.gov.ng/projects/lot-4/
 IRON - Proterozoic schist and granite-greenstone belts https://nimep.ngsa.gov.ng/projects/lot-5/
2. TENDERS AWARDED LATE 2017
 CONTRACTORS WITH 2nd LAYER OF COLLABORATING CONSULTANTS – BOTH PARTIES HAVE EMBEDDED QP’S FOR
JORC / NI 43-101 STANDARDS
3. STAGED PROGRAMME
PHASE 1 - NGSA AIRBORNE SURVEY DATA INTERPRETATION, DESKTOP STUDY AND INTERPRETATION, TARGETING
PHASE 2 - GROUND RECONNAISSANCE, MAPPING, SOIL SAMPLING, GROUND MAGNETIC SURVEYS
PHASE 3 – TRENCHING AND DRILLING FOR TARGET POTENTIAL → JORC REPORTS FOR POTENTIAL INVESTORS

_______________________________________________________________
HISTORY- Pb-Ag-Zn EXPLOITATION
 Argentiferous galena known in the late 19thC with colonial production
commencing in 1925
 Production 1925-1937 & 1946-1974 = 18000t Pb and
1180t Zn ores (direct smelting material) mostly from Lower Benue lodes
but production declined after independence (1960)
 NMC estimated inferred “reserves” of 1.4M tonnes in 1956
 No data readily available 1974-2012
 Production after 2000 mostly from artisanal mining and post 2013 dominated by
Chinese companies - accurate data unavailable
 2013-2017 49900t Pb and 30800 Zn concentrates and “ore” exported
 MMSD estimated “reserves” (= target potential???) of 5M to 16Mt between 2013
and 2018
 Pb ore is argentiferous but Ag is not accounted for!
4
AUGUST 2018
AUGUST 2019!
IMPERIAL PROJECT

BENUETROUGHBASEMETALS
_______________________________________________________________
HISTORY- BARITE EXPLOITATION
 Tate in 1959 lists occurrences in the Middle Benue with a “reserve” of
400 000 tonnes to 20m at Azara
 NMC 1998 estimated resources of 730 000 tonnes to 30m depth from 5 out
18 veins around Azara with an average SG of 3,64
 Semi-formal production of barite commences in the late 1960’s as oil
exploration gathers pace
 Production almost all from artisanal mining and post 2015 involving local and
Chinese companies
Annual demand augmented for quality
and quantity by imports
 Most production trucked to mills in Cross River-Ebonyi-Port Harcourt region for
upgrading 4
API SPECIFICATIONS
Premium grade SG = 4,2
Cd and Hg both <3ppm
Lower Benue veins
generally higher SG

5
BENUE TROUGH GEOGRAPHY AND SUB-DIVISIONS
SAME SCALE
Lot A3 (Pb-Zn)
Boundary area
(left)
LotA4 (Ba) principal
blocks (right)

6
BARITE OCCURRENCES
Target = steep,
epithermal, fault-bound,
clastic sediment-hosted
Pb-Zn-Ag-Ba–Cu (F) veins
>>97% Pb-Zn-Cu-Ba-F
production derived from
the Benue Trough

7
FORMATION OF THE BENUE TROUGH
 Formed as an extension of early Cretaceous
proto-Atlantic transform faults → failed
third arm of a triple junction or alaucogen
 Not a typical graben!

8
SIMPLIFIED TROUGH STRUCTURES APTIAN-ALBIAN
 Major fracture system runs SW to NE along trough
axis associated with left-lateral wrench faults &
extensional tectonics.
 Series of probable NE-SW elongate pull-apart basins
with concordant fault bound horsts bound by
significant NNE-SSW sinistral shears & extensional
normal faults along the central axis

9
STRATIGRAPHY OF THE BENUE TROUGH
Mostly terrestrial sediments
but >marine in Lower Benue
Compressional phase,
deformation, mineralization
Terrestrial, lacustrine sediments
Upper Benue but marine-deltaic
cycles → Lower Benue; basal
oxidized arenites
Mixed marine & deltaic shales,
siltstone, sandstone >limestone
>coal; continental sandstones @
base Middle & Upper Benue
V
V
Mineralization
Igneous activityV

11
STRUCTURE
Ternary radiometrics
show trace of folds
parallel to the axis of the
trough and lithological
differences.
Lineaments derived
from magnetics, SPOT,
Aster and NigeriaSat-X
images
NE to ENE lineaments
dominate, also more
subtle NW-SE features,
from tilt derivative
magnetics – important!
Fault-bound intra-trough
grabens control local
sedimentation and
possible mineralization
Simplified structure - Benkhelil 1982

12
 Principal Deformation Zone ≈050°-060°
 Results in ENE to NE – trending, fault-bound depo-centres with
NNE-SSW tensional normal faults bounding ends of intra-basement
horsts
 Southern boundary often unconformity not fault
 Brittle >ductile cataclasis
1. INITIAL RIFTING AND SINSTRAL TRANSTENSION (D1)
3. SANTONIAN COMPRESSION (D3) Upper, Middle Lower B.T. lineaments
 Ϭ1 ≈145°- 170° (local variations)
 Asymmetric & open cylindrical & en-echelon folds
 Local thrusting
 Conjugate fault sets
 May locally re-activate D1 wrench faults
 Anticlinoria, v gently plunging folds
 Principle mineralization episode
Actual trough alignment
2. LATE-ALBIAN SYN-SED DEFORMATION & WEAK CONCORDANT FOLDING (D2)
Very limited in Lower Benue with volcanism (Abakaliki Anticlinorium) – minor Pb-Zn mineralization?

D
1
D
2
D
3
13
TILT DERIVATIVE LINEAMENTS
Tilt Derivative
product useful for
discerning smaller
features and
narrow zones of
magnetic contrast
TMI-AS image
more suitable to
show the overall
magnetic
configuration at
this scale than Tilt
Derivative.
Rectangles are
high potential Pb-
Zn areas
TMI - ANALYTICAL SIGNAL

14
BARITE EXPLORATION
PHASE 1
 Literature search and desktop study
revealed prospective zones with clusters of
significant Ba deposits within >64000km2
 Interpretation of satellite imagery &
delineation of structures from regional
magnetic & radiometrics surveys provided
the geological background
 Source Parameter Imaging technique
(magnetics & gravity) show depths to
basement – tendency for deposits to occur
marginal to local basins
 Targets were known to be narrow fault
veins with little alteration in mostly non-
magnetic sediments with little magnetic
contrast - PLUS
 No significant alteration halos so no large
scale anomalies from radiometrics =
CHALLENGE

15
PHASE 2 - FOLLOW UP
 Regional mapping 1:10 000 scale - blocks <200km2 ->1000 km2
 Visiting known pits
 Thin soils so most discoveries made from outcrops and during agricultural
activities etc support thriving small scale mining – local villagers guide
 No soil geochemical sampling!
1. Too large areas to sample within the limited time and budget
2. Significant Ba anomalies often below pXRF LDL
 Collation of field data and grab sample analysis

16
TARGETING WORKSHOP
Occurrences scored based on the following criteria:
1. Quality of the barite – high purity and SG >4.1
2. Alteration – type, intensity, how extensive and if multi-phase
3. If mined and pit dimensions
4. Secondary Pb-Zn-Cu mineralization – potential for by-products
5. Regional geophysical signature – assoc with lineaments, flanks of ENE +ve anomalies and intersections
6. Lithological setting - overwhelmingly in arenites but granites also favourable
7. Structural setting – major arrays? Favourable orientations? Association with fold axes or warped flanks
8. Degree of brecciation – potential multi-phase mineralization?
9. Trenching and drilling
10. Data quality- any historical accounts or production?
11. Vein dimensions
12. Concealment & extension potential
13. Infrastructure
14. Security & community support
Azara area - Middle Benue immediately stood out for follow up fieldwork.
Given the limited good quality exposures and need to discern behaviour of
veins downwards, we tried geophysics but the limited resistivity, gravity and
ground EM surveys proved ineffective………………………………………………………………ONLY ONE OPTION

17
MIDDLE BENUE and AZARA AREA

18
MIDDLE BENUE and KEANA ANTICLINE – TILT DERIVATIVE
 Shows volcanics and near
surface basement as sharp, high
contrast short wavelength
signature
 More subtle ENE-trending
lithological boundaries and
parallel discontinuities extending
beyond the fold closure
 Barite deposits clustered around
Keana Anticline nose in NE
 Aloshi Fault coincides with a
more subtle NW-SE break and
associated Ba (Pb) deposits

19
MIDDLE BENUE- AZARA AREA
Azara area, Keana Anticline– barite vein
orientations
1. Gossan veinlets
derived from
siderite next to
mined out barite
lodes
2. Brecciated barite
in limonite matrix
after siderite
3. Barite in siderite
1
2 32

20
Scout drilling along the 1km Vein 17
and Vein 18, Azara
1. Siderite-barite ±quartz ±carbonate
veining in coarse arkose DV1702
2. Barite vein with weathered siderite
alteration
3. Vein 17 and 18 drill positions
4. DV1701 start main barite lode –
stockwork barytes-siderite
1
4
2 3

21
PARAGENESIS
Barite only veins Hybrid Barite-Galena Veins
Variations among Ba only and hybrid Ba-Pb veins are locally caused by repetitions of siderite and Pb-Zn±Cu mineralizing
episodes and intermediate brecciation with late-stage siderite (rare quartz) and/or barite.
Occasional Cu rich veins around Azara-Akiri have a dominant early chalcopyrite with siderite vein composition
succeeded by quartz ± galena and calcite with minor late barite.
I I II II III III Iv v
WEATHERING
___
____
___
___
__ _ _____
_____
_____
? ? ? ?
ALTERATION
Silicification ____
Quartz
Siderite
Barite
Chalcopyrite
Pyrite
Calcite
Goethite
Marcasite
K mica?
Galena
Sphalerite
?-----
Limonite
Pyromorphite
Zn-Cu-Pb
secondaries
I I II II III III Iv v
BRECCIA WEATHERING
___ _____
____ ____
? ? ? ?K mica?
____
Barite
? ?
Pyrite
Calcite
ALTERATION
Limonite
XXXXX
Silicification
Siderite
Quartz
Chalcopyrite
Goethite
? ?

22
ENSIGNE MINE, LOWER BENUE
Solid high-grade barite but with 10->40% galena & sphalerite
1 metre-wide vein in
normal fault with no
obvious carbonate
alteration and no pyrite.
Locally brecciated barite
with fine galena and
sphalerite

23
Pb-Zn EXPLORATION – Focus on Low Cost and Efficiency
This is Nigeria – a country with significant but under
explored and under-utilised Resources – A country with
highly intelligent, well trained and hardworking, but
inexperienced geologists – A country without a modern
mining culture and infrastructure. In short, the type of
destination explorers dream about.
Our focus with this project is to:-
1)Harness and build on the skills available;
2)Establish low cost, efficient exploration techniques
relevant to exploring the Benue Trough base-metal
deposits;
3)Add to the knowledge base; and
4)Transfer skills to the Nigerian Geological Survey
personnel.
This part of the presentation will be focussed on practical
considerations of Benue Trough base metal exploration.

24
Pb-Zn EXPLORATION - Targeting Strategies
Several Targeting techniques were attempted - Processing ASTER
images for alteration signatures, extracting Lineaments from public
domain data etc.
Most successful – Areas of high basement heat flow derived from
magnetic data overlaid on a map of pre-Santonian lithologies as
digitised from existing maps and refined using radiometric data.
Inferred areas
of high heat
flow
corresponding
to magnetic
anomalies.
(Analytical Signal)

25
Middle Benue Trough – Magnetic Outline
Large scale, low amplitude, smooth magnetic
signature more typical of sediments and
reflects better developed basins.
Short wavelength and high amplitude sharply
contrasting features derive from volcanics and
near surface basement (shallow sediments
over horsts?) with more fractured, deformed
and dyke-veined basement along northern and
SE margins
3 high priority rectangles based on targets
from magnetics, lineament analysis,
radiometrics and known mineralization
All magnetic data in this presentation derived from country-wide
2002-2009 Fugro survey flown at 500m line spacing
ZURAK
AZARA

26
Pre-Santonian lithologies
are shown over a DTM of
the Benue Trough. Yellow
dots are mapped base
metal workings.
Major structures were
digitised from various
sources. It seems obvious
that most of the known
workings are located in
areas of high basement
heat flow and/or areas of
structural complexity.
Using this information, 3
exploration Targets were
chosen for this project using
score-based prioritising
AZARA
ZURAK

27
Information presented here is
derived from exploration
activities on 5 tenements, 3 of
which formed part of the NIMEP
project.
4 Targets are Pb-Zn-Ag
occurrences. Akiri, located in the
nose of the Keana Anticline is a
Cu-Barite occurrence. The Vinco
property is located within the
basement granitoids but exhibits
features very similar to the
Benue Trough Pb-Zn-Ag deposits.
Soil samples were taken over all
targets and focussed Ground
Magnetics and EM were
performed. 2 Targets have been
drilled to date (bright green).
Target 9
Akiri
Vinco

28
Pb-Zn EXPLORATION - Exploration Strategy
Soil Geochemistry -Significant Pb-Zn-Fe-Sr Anomalies
-Geology from litho-geochemistry
Ground magnetic survey -Limited signal dynamics
-Successfully defines major structures
Frequency Domain EM -Limited success at low Frequencies
Ca-Sr
Pb TMI

29
Vinco is a steep dipping, highly silicified alteration package within basement
granitoids to the north of the Benue Trough, hosting Pb-Zn-Ag mineralisation
up to 5m wide. Total strike length is 1.7km. It is truncated to the south by a
young granite intrusion. Soil geochemistry indicated previously unknown
mineralisation near the contact with the young Granite.
Pb-Zn EXPLORATION – A Soil-Geochem success story

30
Pb-Zn EXPLORATION – A Soil-Geochem success story
Four Trenches were dug over the soil geochemical anomaly within 400m of
the contact with the younger granite. Three of the trenches intersected good
mineralisation over 1-3m. It is planned to expose the contact during the next
field visit.

31
Pb-Zn EXPLORATION - Drilling and Sampling
Drilling started during lockdown with an inexperienced crew.
Pre- lockdown training was supplemented with a simple logging
app and open communication channels. This approach worked
well.
2000m were drilled at 3 localities, starting with the Tunga Pit.
The crew responded very well to the steep learning curve and
some excellent results were obtained. It was soon obvious that a
pXRF was needed at the drill so information guiding the daily
drill planning could be improved. Near real time communication
of info made this venture a success.

32
Target 3-3 Tunga Strike of 600m. Mineralisation hosted in -80⁰ West dipping structure.
Shale replaced by siderite in a halo
of 15-20m around the zone. An off-
shoot of the main body was
intersected in RCN3-3-1. Possibility of
several more mineralised zones to
the East, based on soil geo-chem.

33
Target 3-1 Gimbi
Infill sampling around the original discovery
defined a N-S anomaly with a 250m strike
length and values in excess of 300ppm Zn. A line
of boreholes were drilled near the southern
edge of the anomaly. A gently curved low angle
shear zone was found with good mineralisation
where it cuts the surface. This is interpreted to
be the root zone of a mineralised structure.

34
General observations Pb-Zn-Ag exploration
1. Carbonate dominated mineralising fluid - pervasive presence of siderite replacement of fine-grained sediments and
calcite in the matrix of mineralised sandstone.
2. Range of temperatures. Higher temperature – more wall rock silicification - Vinco and lesser extent Target 9.
3. Structurally controlled in steep dipping extensional shears. Possibly vertically limited with a local listric root zone.
4. Mineralised extensional structures commonly arranged in an en-echelon pattern.
5. Mineralisation occurs as galena or sphalerite dominated lenses. Lenses can be displaced vertically or along strike.
6. Copper often occurs strata bound in ferruginous sandstone. In at least one location, a later hydrothermal event
appears to have remobilised copper into a cross cutting barite vein.
7. As shown soil geochem is an effective way of locating mineralisation. This is however not true for barite. No sulphur or
barium could be detected in the vicinity of a known barite deposit on the Akiri tenement.
8. Soil grids of 100x400m will detect most significant Pb-Zn-Cu mineralisation on surface. Infill to 50x200 and 25x50m
over anomalies for drill planning.
9. Larger deposits at surface can relatively easily be found, as witnessed by the countless artisanal workings dotted over
the Pre-Santonian landscape. Very few of these have been systematically explored. Equally numerous deposits should
still be hidden under cover. We recognise that a low-cost method should be found to establish sub-surface sulphide
targets. IP is a possibility but relatively costly and slow. We intend investigating other possibilities based on highly
mobile chemical compounds related from this style of mineralisation such as CO₂ and fluorine.

35
CONCLUSIONS – GEOLOGY
1. MODEL AND CONTROLS WELL CONSTRAINED: CLASTIC-HOSTED RIFT-TYPE EPIGENETIC FRACTURE FILLINGS
2. HEATED CONNATE BRINES SCAVENGED METALS AS THEY CIRCULATED THROUGH THE SEDIMENTARY BASIN
3. Mineralogy and fluid inclusion work (TH 90°-250°, 16-22% NaCl) vaguely MVT affinities but only local replacement
4. Mineralized structures are parallel to sub-parallel en-echelon NW/SE or NE/SW trending, up to 2km length & +10m
width
5. Barite veins largely in sandstones whereas Pb-Zn mineralization dominates in argillaceous host rocks
6. Barite-dominated clusters and significant veins are spatially separate from major Pb-Zn-Cu-(F) centres
7. Many deposits are locally closely spatially associated with pre-Campanian igneous intrusions or volcanics but post-
date them – heat drivers for hydrothermal fluids?
8. Deposit clusters and/or major veins, often associated with NW or NNW faults and structures intersecting E to NE
striking magnetic anomalies and/or displacing NE-trending magnetic features
9. NW-SE and near N-S fractures are preferentially mineralised although ENE to ESE secondary vein directions are locally
very significant.
10. Wall-rock alteration is minimal to non-existent for Ba mineralization evidencing low temperature fluids with narrow
carbonate-rich aureoles for some Pb-Zn veins.
11. Significant Ba mineralization associated with saline springs (Middle Benue – fluid mixing?) with supporting isotopic
evidence for a metal derivation from the sedimentary pile

36
CONCLUSIONS – EXPLORATION GUIDES
STRATEGIES ADOPTED FOR BOTH Pb-Zn and Ba EXPLORATION WORK!
1. Targeting criteria chosen highlight prospective locations:
 Aeromagnetics critical for delineating regional structures and volcanics - high heat flow
 Shallow cover so ground truthing/mapping – known prospects (local knowledge) especially Ba
 Radiometrics shows essential lithological contrasts and some structures
2. Follow up first pass pXRF soil geochemistry works well for Pb-Zn - also Sr ±Fe pathfinder signature
3. Geophysical surveys IP, magnetics clearly delineates relevant Pb-Zn bearing structures but not for Ba
4. For barite, large poorly exposed areas, especially in Middle Benue Trough; discoveries continue due to
excavations for buildings and agriculture etc
5. Significant deposits can be predicted using subtle magnetic NE and ENE trending features with breaks or
shallow cross-cutting orthogonal structures coincide with mineralization, particularly barite
UNDER-EXPLORED AND ONLY SUPERFICIALLY EXPLOITED PLUS ENABLING GOVERNMENT INIATIVES

37
FUTURE WORK
Continue follow up drilling prospective barite clusters & other large veins
Scout drill established Pb-Zn anomalies and geophysical targets
Collate and index all known Pb-Zn-Cu-Ba-F indications combined with field checks
Assess position in relation to known potentially anomalous geophysical features and lithologies
Aeromagnetic survey on 200m line spacing (extend into adjacent basement) and combine with ongoing
government detailed gravity survey (2km2) and rank targets
Regional soil sampling, (including covered Middle Benue regions) for Ba, Pb-Zn-Cu and EM/IP
over potential Pb-Zn-Cu targets + stream sediment sampling in dissected Lower Benue
Soil gas surveys for CO2 and fluorine to test the effectiveness of these techniques in detecting sub-surface
mineralisation.

38
FUTURE WORK
Will a better understanding of
the Benue Trough architecture
& mineralization lead to
discovery of possible CACB-type
or related stratiform sediment
hosted Cu-Pb-Zn deposits?
Selley et al, 2010, AMIRA P872

39
THANK YOU
ACKNOWLEDGEMENTS
Dr Garba Riaan V D Westhuizen Deon Scheepers Kayode Olumedji Chuka Offodile
Director General & team General Manager MD, Geokooy MD, Mecon Geology &
NGSA Minutor Mining Minutor Mining Environmental Services Engineering Services
Hidden Treasure Consulting: Steffen Kalbskopf:- steffen@mweb.co.za; +27 73 370 6799 roaming; +27 84 514 0201 WhatsApp
www.minutor mining.com +1 973 722 7885 WhatsApp; +234 814 756 2034

40
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