THE BISIE TIN PROJECT SUMMARY
The Bisie Tin Project is located within the Walikale District roughly 140 km west-northwest of the regional centre of Goma (Figure 1), in one of the world’s principal Precambrian orogenic-metallogenic provinces in the Democratic Republic of Congo.
Alphamin Resources Corp (Alphamin), through its wholly owned subsidiary, Mining and Processing Congo sprl (MPC) has full legal title (100% ownership) over 5 exploration permits which cover 1,470km2 of highly prospective ground in the North Kivu Province (Figure 1).
Figure 1: Location of the Alphamin tenures in DRC
No systematic exploration has been carried out in the area since independence in the early 1960’s where the only known deposits exploited by the Belgians in the area were the Umate alluvial/elluvial deposits on PR5267.
Tin was first discovered at Bisie in 2004 and was mined by artisanal miners from two main target areas, Mpama North and Mpama South. Both targets are located along 1.5km of a ridge which extends over more than 9km on PR 5266. Artisanal mining from Bisie in the past has dominated the DRC’s production by supplying up to 70% of the cassiterite exported from the country.
Alphamin completed a first 2400m drilling programme between June and December 2012 to test the true width and grades of tin mineralisation at both target areas. A second drill programme was completed in August 2013 which focused on resource drilling at the Mpama North prospect, with a further 28 holes drilled for 3809m; better tin intercepts from the initial programme included
- 25.85m @ 2.26% Sn from 47.65m including 5.8m @ 8.55% Sn
- 12m @ 3.15% Sn from 53m & 3m @ 6.14% Sn from 80m
- 18.5m @ 2.21% Sn from 53m including 2.9m @ 6.27% Sn
- 11m @ 1.48% Sn from 71m including 2.5m @ 5.76% Sn
The second drilling programme intercepted a second, deeper zone with exceptionally high grades:
- 29m @ 3.3% Sn from 165m including 11m @ 6.06% Sn
- 17m @ 6.78% Sn from 185m including 4.35m @ 18.62% Sn
- 15m @ 7.94% Sn from 171m & 7.65m @ 9.40% Sn from 192m
- 17m @ 3.27% Sn from 133m
Copper and rare earth element (Cerium and Lanthanum) mineralisation is commonly associated with the tin rich zone, along with elevated lead and zinc. Significant results included:
- 11.9m @ 0.81% Cu from 67m including 3.5m @ 2.15% Cu
- 35m @ 0.77% Cu from 53m including 10m @ 1.67% Cu
- 10.1m @ 1042g/t Ce from 162m
Drilling further identified a zone rich in silver, zinc and lead mineralisation in the Mpama South target area,. Best results included:
- 19m @ 197g/t Ag from 61m
- 17.7m @ 14.11% Zn from 61m including 13m @ 18.09% Zn
- 14.75m @ 10.82% Pb from 61m
The Bisie Project area is underlain in part by the Kibaran Belt lithologies, interpreted as an inter-cratonic collision zone with different periods of extension and compression. The lower Paleo-proterozoic unit comprises Rusizian and Ante-Rusizian units, composed mainly of poorly exposed dolomites, quartzites, amphibolites, mica schists and migmatite gneisses. The Meso-Proterozoic rocks that overly the Rusizian Basement in the eastern DRC, Rwanda and Burundi are loosely termed the “Burundian”. These are composed of micaceous schists and arenaceous phyllites with minor interbedded quartzites and amphibolites. Shales and conglomerates are also found in the upper parts of this sequence.
Granite intrusions started mid Proterozoic (1,375 Ma) and continued up until the last so-called “tin granite” intrusion at about 986 Ma (late Proterozoic). These intrusions are usually interpreted as being the source of the numerous tin occurrences in the region and the granites themselves show elevated levels of tin.
Figure 2 shows the location of the Bisie prospect, along the edge of a massive granitic intrusion.
Figure 2: Regional Geology Map showing Alphamin Tenement Boundaries
The metamorphic units in the region generally have a strong northwesterly trend, although the ridge housing Bisie has a north south orientation up to the Oso river in the north, after which it trends to the northwest (Figure 3). While satellite imagery clearly shows large scale folding in the area, it has not been ascertained whether the Bisie ridge lies on a tight fold. There is strong evidence of a fault/shear zone which runs along the western slope of the ridge that probably gives rise to the elevation of the Bisie ridge. Moreover, landsat imagery clearly shows the ridge following the curve of a massive granitic pluton. Mineralized and highly sheared and altered amphibolites, which constitutes the main host rock of the mineralisation is exposed in small cliffs in the Mpama South area and further to the south.
Figure 3: Landsat Image showing limits of the Granite Pluton adjacent to the Bisie Ridge
Structural interpretation from Landsat imagery shows numerous cross-cutting ENE-WSW faults with possible offset of the mineralized structure along the ridge (Figure 4) Several of these structures can be followed over several kilometers. The massive plutonic intrusion to the west of the ridge shown in Figure 3 is thought to be the source of the mineralizing fluids.
Slickenslides are particularly common in the ore mined by artisanal miners and the movement has resulted in partial brecciation of cassiterite veins. Timing of emplacement and proximity to later structures determines the extent of this brecciation and disaggregation. The intensity of the lead, zinc and silver mineralisation also seems to have a structural control where lead, zinc and silver have replaced iron in massive pyrite units. Massive pyrite units generally show more galena and sphalerite replacement in areas of intense deformation related to shearing and faulting.
Figure 4: Structural Interpretation over the Bisie Ridge
The mineralisation at Bisie is clearly multi-phased and appears to be very similar in character to the San Rafael tin deposit in Peru. Similar to San Rafael it appears that the cassiterite was emplaced first, followed by copper, in the form of chalcopyrite and bornite, followed by silver, lead and zinc mineralisation. Chlorite alteration is extensive in parts and thought to be a result of the last stage of fluids entering the system. Generally tin and copper mineralisation is found in zones dominated by chloritic alteration, although mineralized zones with no chlorite have also been intercepted.
The cassiterite was emplaced in massive veins ranging in thickness from 2mm to 0.64m (as seen in drill core), generally within high grade chutes with an apparent shallow plunge to the north.. The dominant host units are highly chlorite-altered amphibolite, chlorite schists and to a lesser extent the juxtaposing mica and quartz schists. The cassiterite is massive, pinkish brown in colour, fine grained and often botryoidal, and shows compositional layering likely due to variations in the iron content. Historically this form of cassiterite has been referred to as wood tin (Figure 5).
Figure 5: Photograph of drill core showing botryoidal texture of pink cassiterite and copper sulphides
Copper mineralisation is usually associated with cassiterite zones, which are likely a result of continued tectonic movement which allowed copper rich fluids to move along the same mineralized structures. It is common to find chalcopyrite and bornite filling fractures within the cassiterite; however the majority of the copper mineralisation is normally in the form of blebs, lenses and veins, with the latter two being parallel to schistosity. Chalcopyrite is also common in quartz veins together with pyrite and to a lesser extent arsenopyrite. Generally copper mineralisation is wide spread but good grades are somewhat sporadic. Good copper intercepts are usually adjacent to and overlap high grade tin intercepts, if not directly correlating to them.
The zinc and lead mineralisation is often present in small quantities together with the tin and copper mineralisation although the majority of these elements are hosted separately in a massive pyrite unit together with silver. Structure appears to control the intensity of the galena and sphalerite replacement of the pyrite. In drill hole BGH001 the pyrite unit was crosscut by a shear/fault zone and replacement was almost complete over an interval of 14m, with at least 6m of those being massive sulphides. The massive zinc and lead mineralisation is shown in Figure 6.
Figure 6: Photograph of Drill Core showing Massive Sphalerite (Zinc) and Galena (Lead)
Tin mineralisation is better developed at Mpama North with thicker and more numerous cassiterite veins and substantial copper mineralisation in parts. Mpama South has less cassiterite and veins are normally thinner, however the lead and zinc mineralisation is more prevalent, likely due to the presence of the massive pyrite unit.
Soil samples were collected on lines spaced 200m apart with samples collected every 50m along the Bisie ridge. All samples were dried and sieved to -2mm and then -180µm before being analysed on site using the Niton hand held XRF analyser.
The results indicate a significant zinc and lead in soil anomaly that extends north and south of the artisanal workings over a length of 6km, with the anomaly open to the South (Figure 7). Lead is one of the path finder elements consistently associated with the tin mineralisation, and is a good indicator of the true mineralised potential along the ridge. Copper in soil is more limited, and extends principally north of the Mpama North zone.
Figure 7: Lead in soil anomaly over the Bisie Ridge
Two drilling programmes have been completed on the Bisie prospect:
- An initial, exploratory programme focused on covering both the Mpama North and Mpama South prospects, (Figure 8) and
- A second, resource-based phase, concentrated on Mpama North prospect where the tin grades returned from phase 1 were much higher. Figure 9 shows the collar positions of the second drilling programme.
To date 37 drill holes for 4930.65m have been drilled at the Mpama North prospect, and a further 10 drill holes for 1657.2m have been drilled at the Mpama South prospect to the south. Drilling was focused on areas of artisanal mining and along strike from these workings to test the strike extent of shallow mineralisation. To date mineralisation is open along strike in both directions and at depth at both prospects.
Drilling at Mpama South has been exploratory in nature, to determine the extent and nature of the mineralisation. Two distinct mineralised zones have been intercepted, with an upper zone showing well-developed lead, zinc and silver mineralisation, and a lower zone rich in tin and copper. Figure 10 below shows holes BGH001, 007A & 006 crossing the two zones. Drilling to date at Mpama South has delineated 260m of strike returning tin equivalent grades in excess of 1%.
Drilling at Mpama North was completed during the second program, aimed at a first resource definition, with section spacing of 50m over the areas of best mineralisation with the southernmost section being at 25m due to the presence of a cross cutting fault. Mineralisation has been sporadic in some areas and very predictable in others but generally consistent with high grades in massive cassiterite veins hosting the majority of the tin. The structural data suggests a shallow northerly plunge at this stage. The last four holes drilled in the northeastern portion of the project aimed to intercept this plunge at depth, and all returned exceptional mineralisation.,intercepts that included 15m @ 7.94% Sn and 7.65m @ 9.4% Sn (BGC034), and 17m @ 6.78% Sn (BGC036), (see Table 1). The next drilling programme, which has been planned to explore down dip at depth and along strike to the north will also aim to further define this outstanding mineralisation.
Copper mineralisation at Mpama North is consistently associated with tin mineralisation, generally overlapping it. While copper grades are generally low, some holes returned relatively high grades. BGC035 reported 14.8m @ 1.03% Copper within an interval of 29m @ 3.3% tin. It is envisioned that the copper sulphides will be floated off from the tin concentrate during the beneficiation process.
The one exploration hole drilled as part of the phase two programme (BGC033) was drilled 150m to the south of the main Mpama North workings and intersected the host unit, returning an intercept of 9m @ 0.81% tin. This confirmed the continuity of the mineralized system south of the east west cross-cutting fault that was thought to truncate mineralisation and the reason for the barren hole BGC003. This confirms the potential to intercept significant mineralisation over the 650m zone separating the two prospects. Although the thickness and grade of mineralisation varies, the style of mineralisation for each of the Sn/Cu and the Ag/Zn/Pb zones remains consistent. The Sn/Cu zone is well developed at both the Mpama North and Mpama South target areas while the Ag/Zn/Pb zone is better developed to the south at Mpama South.
Figure 8: Phase 1 drill collars, with significant intersects
Figure 9: Gecomines schematic drill hole locality map showing best intercepts
Figure 10: Schematic section showing drill holes BGH001, BGC006, and BGH007 and 007A at Golgotha Target Area
Figure 11: Section 19885850N showing drill holes BGC0013, 002, 010, 027 & 037 at Gecomines Target Area
Half core samples for all drillholes were submitted to accredited ALS Chemex laboratory in Johannesburg where samples were analyzed using ME-XRF05 conducted on a pressed pellet with 10% precision and an upper limit of 10 000ppm. Over limit samples were sent to Vancouver for ME-XRF10 which uses a Lithium Borate 50:50 flux with an upper detection limit of 60% and precision of 5%. ME-ICP61, HF, HNO3, HCL04 and HCL leach with ICP-AES finish was used for 33 elements including base metals. ME-OG62 a four acid digestion was used on ore grade samples for Pb, Zn, Cu & Ag. Industry accepted QA/QC checks were applied including use of duplicates and standards.
METALLURGICAL / BENEFICIATION WORK
A sample weighing approximately 65kg, made up of quartered core coming from three drill holes, was sent to SGS laboratories in Johannesburg in South Africa for a deportment study to assess recovery rates.
Results of the studies were highly positive, confirming the dominant tin mineral is cassiterite. The tin (cassiterite) is deported evenly around the various feed size fractions and no significant upgrading is achieved by screening. The average cassiterite mineralisation is relatively coarse at 0.2-0.3 mm. Liberation is partially achieved by crushing and subsequent gravity concentration which would result in a 50 % yield. Rod milling and flotation of the gravity tails would increase the overall yield to 85 %.
Copper is present at around 0.2 % as chalcopyrite and needs to be removed from the final concentrate by flotation. Copper recovery would result in less than 3 % contribution to revenue based on the sample sent.
Both sulphide and magnetic mineral removal on the concentrate has been allowed for in the process design and no penalties are expected at this stage.
All indications are that the Bisie system is extensive and has the potential to host significant resources of very high grade tin and base metal mineralisation in conjunction with minor REE. Although the structural influences and immobility of tin in soils complicates the exploration somewhat, the arsenic, copper, lead & zinc path finder elements provide a good indicator of the polymetallic subsurface mineralisation and therefore allow geochemical targeting for the tin mineralisation by association. High grade chutes of cassiterite can be limited in strike extent but also house substantial amounts of tin as demonstrated by past artisanal mining. While almost impossible to target with drilling, they will provide a significant upside when mining. Copper is nearly always associated with the cassiterite and will be recovered in future exploitation.
The latest round of drilling has confirmed that very high grade mineralisation still exists at Bisie and is likely to extend to considerable depths. The higher grade deeper holes at Mpama North prospect infer that similar mineralisation is possible at depth at Mpama South as well as in other future targets. The latest results also confirm Bisie’s status as one of the highest grade tin prospects anywhere in the world.
Regional exploration has plenty of potential in numerous areas. Volcano-sedimentary rocks hosted in a favorable structural setting to the west, where artisanal miners are exploiting alluvial gold, will be targeted in 2014, and there are numerous other known tin occurrences on the tenements held by MPC as well as the potential for new finds among the granites yet to be explored. On PR 5267 the Umate gold prospect has proven to be a significant source of gold in both modern and Belgian times and will be a future drilling target in the already identified hard rock mineralisation. For future exploration, airborne geophysics will likely provide additional structural targets and a greater understanding of the local geology.
Table 1: Summary of Drill Holes and Significant Intersections Received, Bisie Prospect, DRC
|Hole ID||GPS Easting||GPS Northing||EOH||Azi-muth||Incl.||Element||From (m)||To (m)||Width (m)||Grade (%)|
NSR: No significant results
1 Mined-out cavities in the section
2 One sample lost
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