Polyhalite is a relatively common mineral which occurs in marine evaporite systems and is usually found in accumulations several centimetres thick. In Yorkshire, Sirius has intersected high-grade seams of polyhalite up to 70 metres thick.

The polyhalite formed when an ancient sea, the Zechstein Sea, evaporated some 260 million years ago. The polyhalite seams that are the focus of the Company are located approximately 1,550 metres below surface level and have a mean reserve thickness of 25 metres.

Mining at the Woodsmith Mine will adopt simple and conventional bulk mining methods to enable maximum extraction and low-cost operations. From the base of the shafts we can mine in all directions, maximising our ability to optimise ramp up from initial production. Using a combination of room and pillar and drill and blast mining methods we can excavate the thicker areas of the seam up to a height of 40 metres.

The company is constructing a mine to realise the potential of our world-class deposit. The exceptional nature of our resource means that all mine development will be excavated entirely within the polyhalite seam. This will result in a 1:1 mining ratio ensuring that every tonne of ore mined becomes a tonne of POLY4.

At the Woodsmith Mine site, two deep shafts are being constructed to access the polyhalite in the centre of the mineral reserve: the production shaft reaching a depth of 1,594 metres and the service shaft reaching a depth of 1,565 metres. Once constructed the production shaft will be fitted out with two Blair multi-rope winders, each capable of hoisting 6.7 Mtpa of polyhalite ore for a combined capacity of 13 Mtpa. A third shaft, the Mineral Transport System (MTS) access shaft will also be constructed. The MTS access shaft is being constructed to facilitate construction of the MTS.

The polyhalite ore will undergo a simple process of crushing, grinding, granulation, screening and drying to produce the finished POLY4 (Sirius Minerals’ trademarked polyhalite
product) granular product.

- Crushing: Run of mine ore is nominally crushed to below 50mm.

- Grinding: Crushed ore ground to pass 0.2mm.

- Granulation: Binder and water added to polyhalite powder and granulated to form POLY4 granules.

- Screening: POLY4 granules screened. Oversize and undersize removed for reprocessing.

- Drying: POLY4 granules dried to final moisture content, ready for storage and delivery.