Imbo Licence – Prospects/Targets
Underground exploitation was carried out on the Adumbi Prospect by the Belgians from 1952 to 1959. Unverified historical records indicate approximately 0.2 Moz of gold was exploited from a high grade quartz vein, over a strike length of about 2 km, hosted within a shear zone. Wall rock mineralization was not exploited. The figure following, sourced from the archieves in the Royal Museum for Central Africa, illustrates a vertical longitudinal section and a level plan of the Belgian exploitation from the Main Vein, an auriferous quartz vein.
Kilo carried out 14 871.56 m of diamond drilling during 2010 and 2011. The Mineral Corporation, based in Sandton (Johannesburg), South Africa concluded 1.87 Moz in rock grading 1.67 g/t Au at a 0.50 g/t Au cut-off in an NI 43-101 compliant Inferred Resource Estimate dated April 2012. Preliminary metallurgical testwork on the Adumbi Prospect has achieved in excess of 90% gold recovery from the oxide mineralization and in two of three composite drill drill core samples, greater than 90% gold recovery in the sulphide mineralization.
Lithological and structural mapping over a strike length of 600 m and about 250 m across strike of the underground workings, accessible adits, cross-cuts and stopes, using compass, chain and GPS for portal co-ordinates, was carried out by Kilo geologists. An auriferous quartz vein, hosted in a shear zone trending northwest–southeast, is present on the southwestern flank of Adumbi Mountain. This shear zone and the associated quartz vein are collectively referenced herein as the ‘Adumbi Shear Zone’ (“ASZ”) and in the following discussion footwall and hangingwall are with respect to this structure. Gold was exploited underground by the Belgians from the quartz vein
The Adumbi Prospect is hosted within chemical metasedimentary rocks that dip steeply towards the northeast. The chemical metasedimentary rocks, is a mega unit comprised of well bedded magnetite and chert as well as a well bedded haematite and chert unit, or collectively referred to as banded iron formation (“BIF”). In addition chert, chert interbedded with fine clastic metasediments, chert interbedded with black shale, and minor thin intervals of black shale are included within the chemical metasedimentary mega unit. Field observations coupled with petrography, reveals that predominantly interbedded clastic metasedimentary rocks (field name – greywacke) and black shale flank the chemical metasedimentary rocks to the northeast and to the southwest. Lithologies proximal to the ASZ generally dip steeply towards the north-east, although in some localized areas the dip is steeply towards the south-west. Occasionally about 150 m southwest of the ASZ, moderate dips of 40° to 60° towards the northeast were noted. Dip steepening towards the ASZ may be a function of spatial distance from an axial plane of a large scale fold.
The ASZ together with other shear zones and quartz veins all predominantly within the chemical metasedimentary rocks, a mega unit comprised of well bedded magnetite and chert as well as a well bedded haematite and chert unit, or collectively referred to as banded iron formation (“BIF”), chert, chert interbedded with fine clastic metasediments, chert interbedded with black shale, and minor thin intervals of black shale hosts the majority of the gold mineralization. The thickness of the chemical metasedimentary rocks varies greatly, and although some of this may be due to sedimentary processes, the majority is considered likely due to intense folding. Furthest south-east underground mapping noted two narrow BIF horizons 6 m and 3 m wide separated by 12 m of shale and greywacke on the footwall of the ASZ. BIF about 150 m northwest, in the central sector, has a thickness of 40 to 50 m and can be found in both the hanging and footwall of the ASZ. Mapping underground some 400 m northwest of the southeast most mapping noted that the BIF is approximately 120 m wide, very strongly folded and occurs in the hanging wall of the ASZ. A felsic dyke with xenoliths of mineralized shear zone was observed cross-cutting the mineralized shear zone.
Ninety five samples were selected from one Adumbi Prospect diamond drill hole and submitted to Vancouver Petrographics, Canada, for petrograhic study. The objective is to determine the spactial relationship between gold, lithological host, sulphide assemblages and alteration minerals to guide further work.
The findings of this work will be reported as soon as the scope of work is concluded.
The banded iron formation (BIF) is strongly folded, with the majority of the folds being tight with fold axes parallel or sub-parallel to the ASZ at 300°-120° to 330°-150° and dipping steeply to the northeast, or less commonly to the southwest. Fold hinges are also generally steeply dipping, indicating that folding, in part at least may be associated with the shearing, as the foliations, cleavages and fold axes are all parallel. Immediately adjacent to the ASZ, the shearing is particularly intense and can also be seen in the shale and greywacke units. As the principal shear direction is parallel to the fold axes of the minor folds, it is a possibility that this shear zone is axial planar to a larger slightly overturned, towards the northeast, anticline that is only partially exposed in workings on Adumbi Hill.
Folds with low-angle fold axes were noted and possibly they represent an earlier folding event that has been mostly over-printed by the later shear-related folding. Minor folds with shallow-dipping fold hinges associated with small-scale reverse and normal faults occur in the foot wall some distance from the mineralized zone.
The ASZ varies in width from 1 to 5 m and often contains a fractured grey quartz vein which has been the principal target of Belgian and artisanal exploitation. The style of deformation is generally brittle-ductile, as there is often intense folding and shear foliation associated with the zone, and also brecciation and dilational vein development. The style of deformation is somewhat dependent on the lithology being transacted. ASZ displays a preference for lithological contacts, particularly that between shale and BIF, however it also transgresses across lithologies thus it varies from parallel to sub-parallel, or oblique, to bedding.
In the extreme southeast of Adumbi Mountain, the BIF is on the footwall side of the ASZ whereas in the central part of Adumbi Mountain it transects the BIF often on the BIF/Shale contact and in the extreme northwest of Adumbi Mountain, it trends 330°-150° entirely within shale interbedded with BIF and greywacke ASZ is in the hanging wall.
Within the central portion of Adumbi Mountain there are also at least two subsidiary shear zones that bifurcate and re-join the ASZ, indicative of a dilational jog within the central portion of the Adumbi hill. Dilational jogs tend to create boudins in competent lithologies, particularly BIF, that are less deformed and less mineralized. The pattern of dilation is compatible with a sinistral wrench fault system, and this is also demonstrated by the displacement of the BIF horizon across the shear zone.
Folded BIF observed in an adit between the extreme southeast and central portion of Adumbi Mountain, where ASZ crosses from the hanging wall to the foot wall, indicates dextral (right-lateral) movement, which may predate the mineralizing event.
Fractures, faults and quartz veins not related to the ASZ are most likely a later dip-slip reactivation, as some of the low angle white ‘bucky’ quartz veins and fractures cross-cut the ASZ foliation. This dip-slip movement, both reverse and normal, is observable along bedding parallel fractures and low-angle faults and fractures in the footwall sediments in several adits. This deformation event is not considered to be associated to the mineralizing event, given the lack of known mineralization far away from the ASZ, where these structures are most evident.
The primary control of Adumbi gold mineralization is ASZ with an average strike of 310°-130° and a steep average dip of 80° towards the northeast, hosted in steeply-dipping metamorphosed chemical metasedimentary rocks a mega-unit predominantly characterized by intervals of chert, banded iron formation (“BIF”) as well as minor intervals of chert banded with black shale and several narrow intervals of black shale. Quartz veins occur throughout the chemical metasedimentary rocks.
The gold bearing fluid pathway at Adumbi is associated with the late structurally controlled southeast northwest trending strike-slip ASZ that dips steeply towards the northeast, and exhibits sinistral (left-lateral) movement. ASZ is parallel to the axial planar cleavage of the widespread small scale folding, indicating it may be axial planar to a district scale fold. The ASZ is a narrow discrete gold bearing deformation zone until it intersects the structurally thickened chemical metasedimentary unit, whereupon the mineralized zone becomes wider due to dilational jogging and brittle fracturing.
The ASZ preferentially follows the footwall or close proximity thereto side of the chemical metasedimentary rocks, but in general is oblique to lithology. In addition, multiple sub-parallel shear zones, one of which is continuous over the strike length of the chemical metasedimentary rocks are present predominantly on the hangingwall side of the ASZ. There is potential for further dilationally or lithologically enhanced mineralized zones along strike as well as down dip of the shear zone.
Preliminary interpretation concludes that gold mineralization is associated quartz-carbonate-sulphide assemblages that were channelled through structurally controlled brittle fractures. Gold is associated with pyrrhotite±arsenopyrite±second generation pyrite.
Geological modelling of the gold bearing mineralization concludes three discrete zones of gold mineralization. Two of these are sub-parallel along strike and to depth, and occasionally are in contact one with the other.
High grade gold bearing shoots generally plunge steeply towards the northeast, parallel to the intersection of lineations, but locally may also dip towards the northwest. Adumbi remains open along strike and to depth, and preliminary interpretation from observations conclude that the Adumbi Prospect has potential for deep extensions of mineralization beneath the current extent of drilling as well as potential along strike for mineralized dilational jogs and similar geological settings analogous to those in the central portion of Adumbi Mountain.
Adumbi/Canal Prospect hosts an NI 43-101 inferred resource estimate of 1.87 Million ounces gold (Troy) grading 1.63 g/t Au at a 0.5 g/t Au cut-off (The Mineral Corporation, April 2012).
Interpretation of a series of vertical cross sections centred on the collars of the Adumbi/Canal Prospect diamond drill holes formed the basis for a structural model of the gold mineralization. Discrete gold bearing zones were then wire framed to generate a 3D block model. Two sub-parallel Adumbi linear gold zones, plus one linear zone on the Canal Prospect, possibly a splay off the Adumbi Prospect were wire framed. Following figures illustrate a vertical cross section through the wire frame model, and a level plan through the wire frame model.
Distinction between oxide, transition and sulphide mineralization was made on the basis of noted observations of the drill core, and modelled accordingly. The Adumbi historical mining impact has been volumetrically deleted by incorporating historical level plans into the wireframe model. An addition loss of 1.5% was applied to account for post-mineralization intrusive. The block model was constrained at a depth of 400 m above mean sea level (mamsl). Maximum vertical distance from surface ascribed to the inferred mineral resource is approximately 350 m and a maximum extrapolation of 50 m has been applied to the deepest mineralized zone intersection points.
Statistical and geostatistical analysis for the inferred resource estimate commenced with compositing the drill core sample intervals such that each composited sample represented 2.5 m true thickness of the mineralized zones. On the Adumbi Prospect the mean gold value determined on composite samples for the two parallel gold bearing zones, namely Zone 1 and Zone 2 is 2.12 g/t Au and 2.75 g/t Au respectively. Rock between Zones 1 and 2 was assigned Zone 0 and the calculated mean value is 0.22 g/t Au. Mean gold value for Zone 3, the Canal Prospect was determined as 1.16 g/t Au. The spatial distribution of the gold bearing zones at an elevation of 650 m above mean sea level (“amsl”).
|Adumbi Inferred Resource Estimate, The Mineral Corporation, March 2012|
|Oxide||11 976 239||3.07||1.61||0.62|
|Transition||4 766 819||3.07||1.67||0.26|
|Sulphide||18 912 221||3.07||1.63||0.99|
|Total||35 655 279||3.07||1.63||1.87|
|Adumbi Inferred Resource Estimate, The Mineral Corporation, March 2012|
|Cut-off gradeg/t of Au||Density
|% of resource retained
(0.5 g/t Au)
|0.5||3.05||35 655 279||1.63||100||1.87|
|0.75||3.06||28 919 158||1.86||81||1.73|
|1.0||3.07||24 604 478||2.04||69||1.61|
|1.25||3.08||19 772 499||2.26||55||1.44|
|1.50||3.08||15 507 916||2.50||43||1.25|
|2.0||3.08||9 552 755||2.99||27||0.92|
|2.5||3.09||6 193 606||3.41||17||0.68|
|3.0||3.09||3 805 154||3.83||11||0.47|
Classification of the mineralization as an Indicated Resource Estimate was considered by The Mineral Corporation as prohibitive based on a number of factors, one being that geostatistical analysis indicated the drill hole spacing to be excessive, both along strike and to depth. Given that the mean gold value for Zones 1 and 2 are 2.12 g/t Au and 2.75 g/t Au, respectively we are optimistic that infill drilling will also increase the overall grade of the Adumbi/Canal Prospects.