Tin explorer and developer Alphamin Resources has announced a 34% increase in the measured and indicated mineral resources at the Mpama North prospect at its Bisie tin project, in North Kivu, in the Democratic Republic of Congo (DRC).

The 34% increase in these resources from those announced in October 2015, follows new results from infill and deep drilling at the Mpama North prospect. The inferred mineral resource, however, decreased by 41% contained tin with additional inferred resources being transferred to the measured and indicated categories through the results of infill drilling, a revised structural interpretation and additional borehole survey data.

“These new results support an increase in tin grade with depth as tin mineralisation continues down dip and is open along strike and at depth. The results underpin excellent potential to define significant additional tin resources to increase the life-of-mine at Mpama North, thus, unlocking exciting further investment potential of the Bisie tin project,” says Alphamin CEO Boris Kamstra.

The updated mineral resource was prepared by independent consulting firm The MSA Group of Johannesburg, South Africa, and was estimated using the Canadian Institute of Mining, Metallurgy and Petroleum (CIM) best practice guidelines. The updated mineral resource is reported in accordance with the 2014 CIM definition standards, which have been incorporated by reference into National Instrument 43-101, which deals with standards of disclosure for mineral projects.

The updated mineral resource estimate at Mpama North has increased the mineral resources over that used in the feasibility study (FS) to 4.6-million tonnes, grading at 4.52% tin, for 208 100 t contained tin (at 0.5% tin cutoff) in the measured and indicated categories, and 0.5-million tonnes, grading at 4.25% tin, for 22 800 t contained tin in the
inferred category.

The robust and high-grade nature of the orebody is further demonstrated in the grade tonnage, which indicates that, should the measured and indicated mineral resource be reported at a 2% tin cutoff grade, tonnages are 3.07-million tonnes, grading at 6.11% tin, for 187 700 t contained tin with 0.33-million tonnes, grading at 6.21% tin, for 20 200 t contained tin reported for the inferred category. The measured and indicated mineral resource has been tabulated using a number of cutoff grades.

The updated mineral resource estimate is based on tin, copper, lead, zinc and silver assays and density measurements obtained from the cores of 122 NQ (75.7 mm) sized diamond drill holes, which were completed by Alphamin between July 2012 and November 2015, inclusive. In addition to the exploration drill holes, the split cores from 21 PQ (122.6 mm) sized holes were used in the estimate. These holes were drilled in three clusters for the purpose of obtaining a metallurgical test sample.

The updated mineral resource includes results received from the final 13 holes for 4 433 m from the drilling programme at Mpama North, which was completed in November 2015. Holes were drilled to better delineate the up-dip limit and continuation of the high-grade mineralisation within the northerly plunging chute at depth and to close off mineralisation in the wedge target area adjoining Mpama North to the south.

A number of infill holes were also drilled to convert inferred mineral resources to the indicated category. The company has now stopped drilling to allow for the construction and development phase as follow-up to the positive FS.

Meanwhile, tin mineralisation is associated with a steeply dipping (65° east) north to south striking zone of intense chlorite alteration contained within micaceous schists. The main tin-bearing chloritised zone is on average about 9-m-thick and narrower subordinate zones occur several metres above and below the main zone in certain areas. The mineralisation occurs in the form of irregular high-grade veins of botryoidal cassiterite (‘wood tin’) several tens of centimetres thick and blebs and vein fragments of cassiterite irregularly disseminated in the chlorite schist.

The mineralised zone contains two parallel high-grade chutes separated by a zone of economic, lower-grade mineralisation that plunges about 35° to the north. The chutes appear to merge at depth with best grades reported from the deepest holes drilled to the north supporting a distinct increase in grade of mineralisation, which is open at depth. The mineral resource area extends over about 300 m in the plane of mineralisation perpendicular to the plunge direction.

The updated mineral resource was limited to deeper than about 50 m below surface in the area where artisanal mining has taken place, as the quantity of remaining mineralised material in the affected area cannot be stated within reasonable limits. The deepest mineral resources reported are about 550 m below surface and the mineral resource extends for 700 m in the down plunge direction.

Alphamin is confident of adding additional high-grade resources at depth at Mpama North and at Mpama South, located 750 m to the south along the ridge where mineralisation is potentially confined to a similar high-grade chute. The best results of 32 m at 2.46% of tin from 192.2 m and 6.7 m at 2.34% of tin from 146 m, were reported previously.

In addition, significant tin, copper, lead, zinc and arsenic anomalies have been identified within the same geophysical setting along the 15 km ridge at Bisie and will be followed up with a ground induced polarisation survey and drilling to identify areas of potential new discovery.

According to the Bisie FS published in February, the project is expected to have an operating cost of $8 450/t – landed in Malaysia – and, based on the prior indicated mineral resource of 3.94-million tonnes at 3.94% tin for 155 300 t of contained tin, announced in October 2015, and a tin price of $14 800/t, was expected to offer a rate of return of 36.4% after tax.

Since the publication of the FS, the spot tin price has increased to $17 476/t.

Kamstra explains that given that Taiwan’s nonprofit research and development organisation, the Industrial Technology Research Institute, is forecasting a significant shortage in the supply of tin from 2018 and that there are few other new industrial-scale tin mines outside the Asian countries of Myanmar and China which do not face significant technical, financing, permitting and other challenges, Bisie is one of the most advanced tin projects currently being developed.

“It has the significant advantages of being one of the highest-grade known undeveloped tin orebodies in the world with favourable metallurgical properties and an approved mining licence, and we expect it to become the next significant tin producer,” concludes Kamstra.