The Ferensola gold project is located in northeast Sierra Leone, approximately 200 km east-northeast of the capital Freetown. The license, registered under ABM’s 100% owned subsidiary Blue Horizon, totals 153km² and is host to the both gold and iron ore.
Historically, the Ferensola gold project had been termed the Yanfaran Dalakuru Sende Zone (YDS) with previous operators completing extensive soil sampling, RAB drilling and 5,392m of diamond drilling at three prospects considered prospective for gold. In total, 34 diamond drillholes were completed by previous operators who intercepted significant quartz-sulphide breccias:
The YDS was interpreted as being a 5km long northwest-southeast trending structure with mineralisation being controlled by faulting.
Since ABM acquired the license, extensive exploration activities undertaken have included:
The field mapping, sampling and re-logging / re-sampling of the historic drill core led ABM to report a JORC compliant Exploration Target for the Ferensola gold project, being authored by independent consultants SRK Consulting (UK) Ltd (SRK). The Exploration Target covers a 2km portion of a fold belt with evidence for high grade mineralisation over a distance in excess of 10km. In defining the Exploration Target, SRK used the magnetic anomaly data to define a fold structure and to establish a trace length for the mineralisation which approximated to 2km and with a dip extent of 300m. Mineralisation was assumed to comprise discontinuous sheets of massive sulphide of between 2 and 5m in width, with nominal strike extents of between 100m and 300m. The most significant accumulations of mineralisation were assumed to be contained in fold-hosted shoots akin to ‘saddle reefs’.
SRK defined an Exploration Target for the Ferensola Project with a tonnage range of between 5 and 7 million tonnes (“Mt”) at a grade range of between 4 and 8 grammes per tonne (“g/t”). This equates to between 0.8 and 1.5 million ounces (“Moz”) Au.
|Tonnage range (Mt)||Au Grade Range (g/t)||Contained Gold Range (Moz)|
Table 1: Ferensola Gold JORC Compliant Exploration Target
The Exploration Target was generated after all data existing for the project was reinterpreted along with field observations and extensive sampling was undertaken on key locations and on the existing drill core. The results of the reinterpretation resulted in the identification of a regional fold structure trending northeast-southwest that is on a similar geological trend to the Ferensola iron project and the neighbouring Tonkolili iron ore project as well as the regional trend of the ABM Kangari greenstone belt. Significantly, the work completed advanced the geological understanding of the project and has advanced the project beyond the previous interpretation of the northwest-southeast trending YDS.
Location of the SRK defined Exploration Target (white oval) and regional fold trace interpreted through a review of the ground magnetic data and the collation of the historical and recent sampling programmes undertaken. (Click to zoom in)
The work programmes associated with the generation of the Exploration Target started to identify the various mineralisation styles observed in the area. Within the hard duricrust oxide cover, mineralisation is observed as being hosted within iron oxide nodules of hematite / goethite. Sampling of the trenches completed by ABM returned assay results of 2.3g/t over a 20m zone, including 4m at 3.4g/t and 8m at 4g/t from Trench number 2. Trench number 5 returned assay results of 1g/t over 24m including 4m at 1.3g/t and 4m at 3.9g/t. Trench 11, located outside of the current Exploration Target area returned assay results of 4m at 3.3g/t and 4m at 2.5g/t.
Other sampling from across the license identified samples termed as goldstone and sulphide stone, displaying varying degrees of oxidation. The goldstones represent material targeted by the artisanal miners in the area being similar to the iron oxide rich nodules observed in the trenches. The sulphide stones are believed to represent partially weathered derivatives of the underlying primary ore, with the goldstones representing the fully weathered derivative. The goldstones are targeted by the artisanal miners due to the fact that all gold has been liberated from the degraded sulphides, being predominantly pyrite as observed in the sulphide stones.
Samples collected to date range from ~0.5 g/t to up to 69.2 g/t Au.
|Sample No||X||Y||Z||Weight (kg)||Sample Type||Au (g/t)|
Mineralisation within the fresh, primary material, as observed in the various drilling campaigns has shown that the ore is hosted by a complex shear zone system within mafic volcanics. The shear zone consists of multiple, discrete, biotite-altered shears and a peripheral zones of veining, with several phases of overprinting deformation and sulphide deposition. Gold is primarily associated with massive pyrite breccias that form within the highly sheared intervals and within veining in the adjacent wall rock.
ABM completed an IP survey over a portion of the license in the first half of 2016. The IP survey highlighted the larger scale potential of the Ferensola Gold Project outside the Company’s currently defined Exploration Target. In total, 8.5km of strike length was recorded from the various high chargeability zones interpreted to be associated with potentially mineralised sulphides.
Drilling at the Ferensola gold project has to date focused on Sanama Hill and the TZ2 and TZ4 anomalies with drilling confirming the presence of significant shear zone related features and sulphide mineralisation.
At Sanama Hill, the majority of drillholes completed have intersected gold bearing structures corroborating the assumptions used in the generation of the Exploration Target, in that mineralisation is observed within a complex network of shear zones and veins. Highlights to date include drillhole FDD014 which intersected a zone of 32.6m in apparent thickness with a length weighted average grade of 3.65 g/t Au. A true thickness of 21m, being 64% of the apparent thickness has been calculated using the drilling angle and dip of the controlling shear zone in this area. Logging of the core within the mineralised zone of FDD014 shows a complex network of quartz-pyrite breccia with one sample assaying 37 g/t Au and being composed of up to 70% pyrite. This high-grade sample lies within a zone with a length weighted grade of 7.4 g/t Au over a true thickness of 8.1m.
Drilling at Sanama Hill continues to test the mineralisation extents in all directions with mineralisation currently observed by drilling over an approximate strike length of 500m. Multiple strands of mineralisation have been intersected with a true thickness of approximately 2m with a length weighted average grade of approximately 4 g/t Au.
At TZ4, the Southern Target, ABM has completed two drillholes with both FDD021 and FDD023 returning mineralised intervals. FDD021, the discovery hole, returned 5.2 g/t Au over 1.22m and FDD023, intersected two true thickness intervals of 0.8m grading 1.59g/t and 1.79g/t. These hits are 135m distant from the discovery hole FDD021 and so provide evidence of potential to establish lateral continuity of mineralisation. In addition to the drillholes completed by ABM, SDD013 completed by the previous licence holders returned an oxide sample of 1.72g/t over an apparent thickness of 6.45m. The true thickness of the historical intersection is unknown due to the oxide nature of the sample and the unknown dip of the mineralisation in this area.
At TZ2, eight drillholes have been completed. This includes a single hole (FDD024) that targeted a high resistivity zone below an area of intense artisanal workings and returning a fresh rock sample of 2.13 g/t Au over a 1m sample. No other significant intersections were returned from TZ2 although all holes showed evidence of shearing and sulphide mineralisation.
Drilling continues to de-risk the project with detailed structural logging being carried out that aids the geological interpretation.
ABM commissioned a review of all data collected to date by Tect Geological Consulting. Tect is a group of structural geologists who specialise on the link between structural geology and mineralisation. They have worked on gold mineralisation in Sierra Leone and several other West African countries for a number of companies. Tect focussed on the regional geology, geophysical data and structural data collected during the two drill campaigns completed by ABM along with the assay results and core photographs.
Based on the work completed, Tect identified 19 targets that are deemed suitable structural traps for gold mineralisation as well as creating an interpretation of the regional shear zone network within the licence.
Of the 19 targets identified, Target 1 corresponds with Sanama Hill and Targets 5 and 16 correspond with the TZ4 Southern Target. Several of the other targets are also corroborated by artisanal activity or soil geochemistry.
The work completed by Tect will be used to guide future exploration campaigns.