Tongo Mine Development

Newfield’s flagship asset is the highly endowed Tongo Mine Development in eastern Sierra Leone.  Recent completion of Front End Engineering and Design (FEED) work and commencement of underground portal excavation has laid the foundation for targeted FID and project build from 2H 2019.

The Tongo Mine Development combines kimberlite dyke hosted diamond resources on two adjacent mining licences that cover over 134 square kilometres and host 11 known kimberlites.  It is subject to a Tribute Mining Agreement between the two mining licence holders, being Newfield’s subsidiary company, Sierra Diamonds Limited, and Octea Mining’s subsidiary company, Tonguma Limited.



FEED Study highlights technically robust and highly economic project

A Front End Engineering and Design (FEED) Study on the Tongo Mine Development was commissioned by Newfield following its acquisition of Stellar Diamonds plc in early 2018.  The FEED Study was completed by leading mining consultant, PPM, in April 2019 and delineates a technically robust and highly economic project.

Based on the Reserves-only model from the FEED Study, the Tongo Mine Development is expected to deliver a diamond mining operation with:

  • 1 Mcts initial Ore Reserve
  • Initial 8-year life with peak annual diamond production of 260,000 carats forecast in Year 5
  • US$222/ct average realised price and US$115/ct forecast unit opex (real basis)
  • First carats expected within 12 months of initial decline blast

For full details of the Tongo FEED Study outcomes, view the ASX announcement here.




    Mine method and scheduling

    Mining is planned to be exclusively by underground methods with access to the Kundu and Lando kimberlites being from a single portal entrance located approximately midway between the two kimberlites.  The selected mining method is traditional shrinkage stoping.  This method has been commonly used in similar kimberlite dyke mining operations in South Africa.

    Summary mining schedule (Ore Reserves only)

    First production diamonds from Kundu and Lando are scheduled to be realised within 12 months of the decline development commencing.  The Reserves-only life-of-mine schedule sees a progressive build of annual diamond production volumes as increasing numbers of mining faces are opened along strike and at depth.

    Newfield plans to undertake significant further investment in infill drilling of the lower zones of Inferred Resources at both Kundu and Lando. This infill program is targeted at significantly expanding peak diamond production rates, and substantially extending the current operating life, of the Reserves-only life-of-mine schedule shown above.

      A Generational Asset

      Key upside opportunities from the FEED Study to be pursued by Newfield concurrently with planned mine development include:

      • Targeted realisation of long-life extension and expansion potential from infill drill program of Kundu, Lando and Tongo D-1 (6.3 Mcts total Resources sit outside of initial Ore Reserves)
      • Parallel development of optimisation strategy to increase mine development and production rates, and increase plant capacity
      • Targeted exploration across seven other kimberlites not currently at resource status
        Starting base and growth

        Reserves at +1.18mm and Resources at +1.00mm; Resources are inclusive of Reserves.

        Long-term potential

        The Exploration Target Ranges are conceptual in nature. There has been insufficient exploration to estimate a Mineral Resource in these areas and it is uncertain if further exploration will result in the estimation of a Mineral Resource.

        The road ahead

        Newfield’s plans for the Tongo Mine Development target the creation of a substantial diamond mining operation.  With strong support from local communities and government agencies, Newfield expects to forge an effective partnership amongst all stakeholders.  Our key objective is to deliver a long-life mining operation that will generate sustainable returns as well as provide significant economic benefits to Sierra Leone and its local communities.

        Newfield’s management team has over 150 years of combined experience in discovering and developing diamond mining operations. The core values and culture of Newfield drive application of the highest standards of technology, safety and environmental practices.  Above all, we believe in treating our host country, its people and its lands with the utmost respect.


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