As with the bulk of the exploration activities conducted to date, the principle focus in this year has been directed towards defining the extent of the known and potentially diamondiferous alluvial gravel occurrences within the Company’s project tenements. A Small-scale Mining Licence (SML) was also awarded to the Company in June 2015 which saw the commencement of trial-mining of the Golu Lower Terrace gravel package and the recovery of a diamond parcel for size-frequency test-work and pricing purposes.
In addition to this, the Company has refined numerous interpreted kimberlite targets and it is expected to conduct a follow-up airborne magnetometry survey of c.46 high-interest targets in H1 2016. The quality of the data is expected to be of a high-enough resolution to provide drill-ready targets.
Figure 1. L Locality of Allotrope’s Exploration licences along the diamondiferous Sewa River, Bo District, Sierra Leone.
Exploration Licence – EL 15/2012: Baoma Alluvial Project
Exploration was confined to trenching and pitting on the Sandia-Tugbebu and Waima-Matugbe River Targets on the Sewa River south-bank and north-east bank areas and to the Gbinima and Sejeye Creek targets near Nyandehun village (Figure 2). Some exploration focus in the latter half of the year comprised the planning and preparation of a trial-mining phase to coincide with the granting of a Small-scale Mining Licence (SML) at the Golu Alluvial Project.
Exploration Licence EL 20/2014: Jomu-Maina-Tongie Alluvial Project:
During this reporting period, a large-scale pitting and planned mechanised trenching exercise was initiated within the Jomu-Maina-Tongie Project (Figure 3). A total of c.690 test pits have been completed from a planned 913 pits, the remainder not completed due to inaccessibility. The planning of bulk-sample sites has commenced on the back of the interpreted results of this campaign, which has utilised gravel (facies) types, distribution and a first-pass assessment of the heavy mineral content (+2mm; -2mm fractions of the gravels, as well as the immediate footwall bedrock), in order to optimally site the planned bulk-sample sites.
Figure 3. Location of planned and completed gravel test-pits on the Jomu-Maina-Tongie Alluvial Project (black dots inside black polygon). A heavy mineral concentrate (HMC) isopach plot (-2mm fraction from gravel source) is shown. Higher heavy mineral concentrations are indicated by warmer colours. A high incidence of ‘heavies’ appears to be associated within and adjacent to, the Bebeye River system, (thin blue line) a tributary of the Sewa River. Background comprises a TMI image.
Exploration Licence – EL 19/2014: Hima-Mano Alluvial Program
A total of 376 mini pits (1m x 1m) have been completed on the Hima-Mano Alluvial Target with the processing of gravels for their heavy mineral content (HMC) being on those pits along the western (true right-hand) bank of the Sewa River. However, as the wet-season has commenced, a high water table has resulted in some of the excavations being deferred to the dry season.
In addition, work on the Hima-Mano flats (eastern or left-hand bank of the Sewa River) has been completed with twenty (20) 4m x 4m pits being completed, all intersecting palaeo-channel gravel. In the dry season, access is expected to improve and this alluvial target remains a high-priority for bulk-sampling to test for mineralisation, in order to replicate the results of the previous operator, Cream Minerals Ltd (cf. section 1.1.3 of the Quarterly Report for the Period Ending March 2015 – NWF ASX Release 29 April, 2015*) who recovered grades ranging from 0.4-1.5 carats per cubic yard (29 cpht -109 cpht) (cited in Hall, 1972).
Figure 4. Alluvial exploration activities in EL 19/2014 (red diamonds indicate 2m x 2m pits, black squares indicate 1m x 1m exploration pits). (Back-ground image Total Magnetic Intensity).
Exploration Licence – EL 12/2014: Tissana-Yambama &Lake Fula and Pongola-Mokombo Alluvial Programs
Tissana-Yambama Alluvial Project: A preparatory ground-truthing exercise over other potential alluvial diamond occurrences has identified a wider ranging potential diamondiferous gravel distribution covering occurrences both adjacent to the Sewa River and inland from it, including the Yambama swamp (Figure 5). A total of 272 exploration test-pits have been completed in the period on the Tisana-Yambama Alluvial Project.
Lake Fula (or Tula) Alluvial Project: Over 292 test pits have been completed to date. In addition, trenching on the Lake Fula Target has been initiated, with 50kg composite samples from the entire 445m length of trenching completed to date. The exploration conducted to date supports a high-terrace, lacustrine deposit. In addition, the lake follows the ENE trend of the regional kimberlite dyke emplacement and two micaceous dykes have been intersected in the trenches. Follow up work is continuing to ascertain the nature of these features – a duricrust layer comprising coarse ilmenite, rutile and other mafic minerals, has also been exposed in the trenching.
Figure 5. Gravel thickness isopach and posting plot showing distribution of gravel test-pits for the Yambama, Makombo (Sumbuya) and Lake Fula Targets. The warmer colours indicate thicker gravel development. The distribution of 657 alluvial exploration test-pits is shown (black squares). Background is a Total Magnetic Intensity (TMI) image from a regional Airborne Magnetic Survey. (Note: each grid square is 2km x 2km).
Mokombo Alluvial Bulk-sampling Program: A total of fifteen (15) bulk-sample pits have been excavated to date in the Mokombo Target area of EL12/2014 (Figures 6 & 7), with a total extracted volume of 2278m2 amounting to some +4000 tonnes of gravel awaiting processing. The program covers both the Kise and Mafuri River drainage catchments. Of the completed test pits, nine test pits have coincided with low terrace gravels in a swamp environment, one pit on fluvial, three on middle terrace and two on high terraces.
An additional seven bulk-sample pits have been planned and will be excavated as access allows at the completion of the wet season.
The majority of these areas are marshy throughout the year, with the lowest water level encountered between January and March. This period allows local artisanal miners to conduct active mining of the area. Anecdotally, diamonds have been reported in all of the swamps sampled so far, and this is supported by the high HMC counts, on the basis of which the bulk samples were planned.
Pongolo Terrace Bulk-sampling Program: Trenching has commenced on the Pongolo Terrace on a middle-terrace flat, intersecting rounded pebbles and cobbles associated with nearby Pongolo Lake, a remnant circular feature adjacent to the terrace. The lateritic terrace area (170053E -844883N) at least 1 kilometre in length, has been moderately mined by artisanal miners over the years, but the recovery of rounded cobbles, lends credence to the theory of a remnant palaeo-channel system being preserved and subsequently lateritised.
Figure 7. Mokombo Bulk-sampling Program. Figure 7 (a) at left, (b/s MABS023) showing oxidised fluvial terrace environment, and Figure 7 (b) at right, (b/s MABS019), showing reducing, low-terrace, swamp environment.
Exploration Licence – EL 11/2014: Yawei Flat, Lake Fula and Lake Gambia Alluvial Projects.
Yawei Flat: The 8m x 8m dimension bulk-sample pit located on the Yawei Flat has been suspended and will be recommenced following the end of the wet season.
Lake Gambia: To date, 300 pits have been completed over the Lake Gambia Target. The field teams have also completed the identification of heavy mineral concentrates (HMC) in over 80% of the pits. These results, along with geological logs, have been utilised in the selection of priority bulk-sample localities. To date, twenty-one (21) bulk sample pits (c.15m x 15m dimension) and five (5) trenches have been planned (Figure 8 & Figure 8, inset). Any potential alluvial resource here is very much intact, with only sporadic artisanal mining having occurred in the area. During a field survey, field teams confirm the recovery of diamonds being won from all the artisanal workings.
Figure 8. Gravel Isopach plot of the Lake Fula-Lake Gambia Alluvial Project. The warm colours indicate thicker gravel development. Background image is TMI and southern limit of the legacy Airborne Magnetic Survey data. Inset, shows planned bulk-sample pits and trenches overlying heavy mineral content (HMC) isopach.
Kimberlite Exploration Activities
Exploration Licence – EL 20/2014: Jomu-Maina-Tongie
The Company-owned Dando Multitec 4000 drill rig has been commissioned and the crew has begun on-site training and familiarisation with the rig. The Company authorised the manufacture of the rig late last year, which has been specifically adapted to suit the operating environment in the Allotropes Project.
In preparation for the drilling activities, a target definition and ranking exercise involving the review of all the available historical geological, geophysical and geochemical datasets for the licence area, has been completed. In addition, a consulting geophysicist, with significant experience in diamond exploration, was also engaged by the Company to reprocess and interpret this historic airborne geophysical data-set. On the basis of the target definition exercise, the Company has defined a total 183 kimberlite targets within the Allotropes Project, of which 46 are considered to be high-priority targets.
As the legacy data is considered to be at a reconnaissance level of detail only, a second airborne magnetic survey, which will be aimed at completing high-resolution coverage over select target groupings, will commence in Q1 2016. In this way, the Company expects the airborne survey to produce drill-ready high-resolution aeromagnetic kimberlite targets. An initial drilling phase of high-priority kimberlite targets with the Company’s Dando drill rig, will be then be systematically tested during H1 2016.
The Company’s Dando drill rig during its field commissioning phase. The rig’s arrival on site, inset.
Exploration Licence – EL 11/2014: Lake Popei Kimberlite Project
No additional activity is reported for this period as bagged samples have been progressively transported to site to await batch treatment with other exploration bulk-samples. A further 40 tons is awaiting transport to the DMS plant at Golu in the Bo District, some 60 km distant – this is planned for the dry season 2015, when roads are more passable. An approximate total of 215m of trenching has been excavated to date.
Dense Media Separation Plant Commissioning Complete
Newfield successfully completed the on-site commissioning of its Dense Media Separation (DMS) plant in March 2015.
The DMS plant is sited at the Golu area (Photograph 2), within the Company’s Allotropes Diamond Project in Sierra Leone. The plant consists of four separate containerised sections, each which has now been successfully commissioned and formally signed-off by the plant manufacturer. A series of ex-factory commissioning tests of the DMS and X-Ray units confirm that the recovery rates on the DMS cyclone and X-Ray efficiency tests are consistent with design specifications.
The successful commissioning of the DMS plant is the culmination of a nine month campaign to position the Company for an effective resource definition program and subsequent diamond production. The DMS circuit has a design capacity of 10 tonnes per hour with head feed rate varying from 20 – 40 tonne per hour dependent on gravel facies type.
Allotrope’s Diamond Project, Sierra Leone – Exploration bulk sample stockpiles in foreground and DMS plant in background
Hall, P.K., 1972. The diamond fields of Sierra Leone. Geol. Surv. Sierra Leone Bull. 5 (1) (133 pp.).
Ikona, C. K. (2006). Technical Report on Alluvial Diamond Properties –EPL 1/94 & EPL 5/94, Sierra Leone, for Cream Minerals Ltd., 77pp.