The target deposit type at Songwe Hill is a high-level, REE-enriched carbonatite intrusive complex. Carbonatites are traditionally defined as intrusive and extrusive igneous rocks that contain in excess of 50 % modal carbonate minerals (Woolley and Kempe, 1989). Mitchell (2005) defines carbonatites as “containing greater than an arbitrary 30 % by volume of primary igneous carbonate regardless of silica content”. Carbonatites can be named according to their carbonate mineralogy (e.g. calcite carbonatite, dolomite carbonatite and ankerite carbonatite), and chemically they can be divided into the three main varieties: calcio-, magnesio- and ferro-carbonatite.

Carbonatites usually occur as plugs or pipe-like bodies within zoned alkalic intrusive complexes, or as dykes, sills, breccias, and veins, and are almost exclusively associated with continental rift-related tectonic settings. They are characterised by an aureole of metasomatically altered country rocks which are usually referred to as fenites. Carbonatite magmas are typically low-viscosity and volatile-rich, and when intruded at a high crustal level, produce widespread intrusion- and explosion-breccias incorporating country rocks, carbonatites and associated fenites. Carbonatites are typically associated with silicate rocks of which the seven key carbonatite-silicate rock associations are, in decreasing order of abundance, 1) nephelinite-ijolite, 2) phonolite-feldspathoidal syenite, 3) trachyte-syenite, 4) melil ........

The mining method at Songwe Hill will be conventional open-pit mining, making use of relatively small-scale trucks and diesel-hydraulic excavators, selected to match the mining conditions and required production rates.

The pit design was structured around the strategy of Phase 1 accessing high-grade Type 1 ore for the first five years and stockpiling any medium-grade Type 1 ore to feed as run of mine (ROM) at a later stage. The high-grade pit shell from the pit optimisation was used as a guide for the design of the first five-year pit.

The final pit pushback Phase 2 was then designed to the final pit limits, and the final pit shell from the pit optimisation was used as a guide.

The final pit design is approximately 660 m north to south, 550 m east to west, and has a depth of 354 m from the pit rim on the south side (top of Songwe Hill) and 134 m on the north side (bottom of Songwe Hill).

A mining schedule was developed, targeting the design plant throughput of 1,0 Mt/a of ore.

Bench Height
Mining equipment used to drill and blast the rock determines the bench height. Currently, most large mining operations adopt 10 m to 15 m bench heights. For the Songwe Hill open pit, a maximum of 10 m bench heights were adopted based on the PFS mine design criteria.

Bench Face Angles
Based on the SWedge analysis results, a bench face angle of 70° is suggested for both transitional and trans-fresh domains.

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