Modern Mining

ASX-listed mineral sands producer Base Resources has announced that, following completion of the Definitive Feasibility Study (DFS), its board has approved implementation of the Kwale Phase 2 project (KP2) at its Kwale Mineral Sands Operations (Kwale Operations) in Kenya. The incremental capital to implement KP2 is – says Base – a modest US$13,1 million, which will be fully funded from operating cashflows.

Base Resources approves Kwale The hydraulic mining unit (HMU) in operation at Kwale Central Dune (photo: Base Resources).

The DFS has confirmed the opportunity for significant improvement in the financial returns for Kwale Operations through further optimisation of the remaining mine life. The DFS was completed internally by Base’s project development team, supported by several specialist consulting firms, and included an independent peer review process.

The objective of the KP2 project is to maximise the overall economic returns of the Kwale Operations by implementing a solution to maintain maximum concentrate feed to the Mineral Separation Plant (MSP), and therefore final production volumes, in the face of declining ore grades expected from mid-2018 onwards. The KP2 DFS has established that this objective can be effectively and efficiently achieved.

Mining at the Kwale Operations was originally based on a conventional dozer trap mining unit (DMU), using Caterpillar D11T dozers to feed the DMU. Historically, when mining the high-grade areas of the Kwale Central Dune, DMU mining rates of up to 1 400 tph have been required to ensure the wet concentrator plant (WCP) is fully utilised. To offset the declining ore grades expected from mid-2018, the KP1 mine plan assumed an increase in the mining rate to 1 800 tph. To achieve this higher mining rate with the DMU alone requires the addition of a third D11T dozer.

The KP2 pre-feasibility study determined that the optimal mining rate to maximise the economic returns of Kwale Operations was 2 400 tph. The KP2 pre-feasibility study identified hydraulic mining as the preferred method to complement the DMU to achieve the targeted 2 400 tph mining rate. Operating dual mining units has the additional benefit of allowing concurrent mining of both the high and low grade ore, which assists in smoothing the grade profile to create a more consistent feed to the WCP.

In August 2016, as part of the DFS, a 400 tph hydraulic mining unit (HMU) was commissioned to trial the concept. The HMU has proven to be extremely well suited to mining Kwale ore, achieving higher availabilities and at lower unit operating costs than the DMU. Following the success of the HMU trial, the DFS concluded that the optimal mining setup for Kwale Operations was three HMUs mining at an average rate of 800 tph each to give a combined total of 2 400 tph.

At the lower ore feed grades and higher mining rates anticipated from mid-2018, the WCP must be upgraded to maintain optimal heavy mineral recoveries. A comprehensive pilot plant programme and spiral modelling work undertaken by mineral sands industry specialist consultants, Mineral Technologies, was employed to determine the optimal equipment configuration for different mining rates and ore grades.

The modelling established that an increase in the number of spirals is required to accommodate the mining rates contemplated under the KP1 (15 % increase) and KP2 (69 % increase) mining plans. In addition, modifications and equipment upgrades are required to the primary screens, feed de-sliming circuit, tailings cyclones, various pumps and piping. Other than increasing the capacity of the overflow pipework, tests confirm the capability of the two existing thickeners to manage the increased solids loading at the higher KP2 mining rate.

Following finalisation of the front-end engineering design, a nine-month implementation period will see construction completed in the June quarter of 2018. Upgrading of the existing HMU from 400 tph to 800 tph and commissioning of two additional 800 tph HMUs will be undertaken in FY 2018, gradually ramping up to the target 2 400 tph mining rate through the course of the 2018 year with the DMU production slowly phased out over the same period. The transition of mining from the Central Dune to the South Dune is scheduled for the second half of 2019.

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Title: Editor
Name: Arthur Tassell
Email: mining@crown.co.za
Phone: +27 11 622-4770
Fax: +27 11 615-6108

Title: Advertising Manager
Name: Bennie Venter
Email: benniev@crown.co.za
Phone: +27 11 622-4770
Fax: +27 11 615-6108

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