Stellar Diamonds’ wholly owned Tongo Diamond Project is located within the mining licence EXPL05/07, roughly 45km north-north-east (NNE) of the regional town of Kenema, Sierra Leone.
The conceptual economic scoping studies (CESS) for the project were completed in June 2013, whereas the preliminary economic assessment (PEA) was completed in August 2015.
The overall investment to bring the project into production is estimated to be $24.2m, while the production life is estimated to be 18 years.
Being the first large-scale mining project since the onset of the Ebola crisis, the diamond mine project marks an important milestone for the country, as it aids in attracting new private sector investments that could contribute to its post-Ebola economic recovery.
Tongo mine geology and reserves
The Tongo licence is located on the Ga Leonean Province of the Archaean Man Craton (between 2.5 billion and four billion years ago). It is comprised typical granite-greenstone terranes hosting tonalite-trondhjemite-granodiorite gneisses and amphibolites.
The rocks are intruded by Jurassic dolerite and Cretaceous kimberlite dykes, the latter hosting the four identified kimberlite-hosted diamond deposits at the project site. The current project involves the development of the Tongo Dyke-1 kimberlite, which has a strike length of more than 2.5km.
The JORC-complaint inferred mineral resource estimated for the project, based on a depth between 300m and 400m below surface, is 895,000t of ore graded at 120cpht (+1mm cut off) containing 1.074 million carats.
Mining and processing at the Tongo diamond mine
The mining method envisaged for the project is the surface slot mining using the bench stoping method. It is complemented by underground mining with access via a vertical shaft in the fourth year of operation.
The mine will feature three mining pits, where each pit will be advanced with six benches each in opposite directions simultaneously.
The processing steps in the ore treatment will include primary crushing, scrubbing and screening, closed-circuit secondary crushing, dense medium separation (DMS), closed-circuit recrush crushing, X-ray recovery and hand-sorting, and water, slimes and tailings disposal.
The project is expected to treat a total of 1.66Mt of ore and recover 955,930ct over its lifetime, with the surface mining in the first four anticipated to produce 117,806ct of diamond.
Infrastructure for the diamond mine in Sierra Leone
Major infrastructure for the project will include a mine shaft, a tailings dump site, a slimes dam, ventilation equipment, main offices and the accommodation camp, a 150m² enclosed explosives storage area, a mine access road, internal roads and fuel handling facilities.
The required water for the site will be supplied from the Woa River while a small reverse osmosis (RO) plant and a water reservoir will also be developed at the project site.
The required power for operations will be generated from a power station incorporating two 590kVA and five 220kVA diesel-powered gensets, as well as two auxiliary 1MVA gensets.
Key players involved with the Tongo mine
Paradigm Project Management (PPM) was appointed as the independent consultant for the project’s CESS and the PEA, whereas the surface slot mining and underground mine designs, mine scheduling and operating cost estimates were prepared by SRK Consulting.