Lake Mackay’s hydrogeological setting and favourable brine chemistry provide important attributes that support the development of a globally significant SOP operation. Lake Mackay hosts the largest SOP deposit in Australia and covers an area of approximately 3,500km2.

Lake Mackay is a brine-hosted potash deposit in a closed basin, salt lake setting. The Mineral Resource is based on the dimensions of the lakebed sediments, the variations in porosity (void space) and the potassium grade within the groundwater.

The drainable porosity (or specific yield) Mineral Resource contains 123Mt of SOP to a maximum depth of 211m. This drainable porosity Mineral Resource represents the static free-draining portion of the total porosity Mineral Resource prior to extraction.

There is a high level of confidence in the geological model for the project. The geology is simple, with brine-hosted in flat lying, relatively uniform, lakebed sediments.

Geology has been used to separate the deposit into different layers for the resource estimate. The upper sandy layer is more porous, beneath which there is a less porous unit overlying the lower clays that are again less porous, prior to reaching the coarser LZ3 sediments.

Within the upper zone (UZ) the lakebed sediments are further separated into top and bottom sub- horizons labelled as UZT and UZB.

The lower zone (LZ) sediments are separated into three sub-horizons labelled as LZ1, LZ2 and LZ3.

These sub-horizon divisions were introduced on account of subtle changes in lithostratigraphy with increasing depth from surface.

Lake sediments are saturated in brine below 0.5m depth from surface which represents the average brine level during the dry season across the lakebed.

A basement surface has been identified from drilling and geophysics, limiting the vertical extent of the lake sediments above. Lakebed sediments extend to a drilling depth of 150m where a basal paleochannel unit has been identified.

The paleochannel is incised into the basement to a maximum depth of 211m. Beyond the extents of the paleochannel the basement surface rises gently towards the east to a depth of between 11m and 25m below surface in the shallowest parts.

Islands are situated on the lakebed surface. These low relief islands (elevation from 362m to 370m) are interpreted to be aeolian in origin and are not included as part of the Mineral Resource estimate.

Sedimentary processes affect the continuity of geology, whereas the concentration of potassium and other elements in the brine is related to water inflows, evaporation and brine evolution in the salt lake.

The top of the resource is defined by the surface of the lakebed and extends below islands at the same elevation between 361m and 362m (AMSL). The base of the resource is defined by the basements surface that varies in depth from 211m maximum to between 11m and 25m below lakebed surface. The resource remains open laterally outside of the Company’s tenements off the lake (where it is covered by sand dunes) and at depth.

The mine plan has an average brine extraction volume of 86 gigalitres per annum (“GL/a”) with an average potassium grade of 2,820 milligrams per litre (“mg/L”). Throughout the life of mine, extraction and recharge processes are expected to gradually dilute the potassium grade from 3,280 to 2,560mg/L. This grade dilution will be offset by increasing the annual brine extraction rate from 74 to 94GL/a in order to maintain a constant feed rate of SOP into the evaporation ponds.

The mine plan is predicted to deliver a constant brine feed containing 540ktpa of SOP into the evaporation ponds for the 40 year life, totalling the extraction of 21.6Mt of SOP. The Ore Reserve is based on the 20.0Mt of SOP that is predicted to be extracted from the Measured and Indicated Mineral Resource categories under the mine plan. In addition, 1.6Mt of SOP will be extracted from the Inferred Mineral Resource category. Accordingly, the DFS mine plan and production target contains 93% Ore Reserve and 7% Inferred Mineral Resource

Between August 2017 and July 2019, Agrimin’s DFS fieldwork involved the excavation of 22 pilot trenches which were geographically spread across Lake Mackay.

The trench network has been optimised to be laterally extensive and shallow in order to minimise the volume of material excavated and allow the use of the most productive excavation equipment.

The trench network has been split into 17 brine mining units (“BMU”) which represent areas of the lakebed sediments that are similar in physical and chemical characteristics. The trench network has an average depth of 4.5m below ground surface, with a range of 3.0 to 6.0m, to allow sufficient volume and gradient for the brine to naturally flow via gravity along the trenches.

Brine extraction will include gravity drainage into east-west orientated infiltration trenches. The brine will then flow into larger north-south orientated second order trenches that will gravity feed into the main feed canal. Brine will be transferred along the main feed canal to the evaporation ponds with the assistance of six pumping stations.

The trenches will be progressively extended into new BMU areas over the project’s life as potassium is depleted from the lakebed due to ongoing brine extraction.

The trenches have been designed so that the material excavated will be placed and built up around the trench perimeter to form a 1.5m high external bund. This bunding is designed to act as a barrier to stop direct surface water ingress into the trenches following rainfall events. A detailed hydrological model was developed as part of the basin-wide surface water assessment conducted during the DFS. Several model simulations were run based on differing rainfall scenarios throughout the life of the operation, with the results showing that significant infrequent (up to 1 in 100-year probability) rainfall events would not overlap the trench perimeter bunding.

Solar Evaporation Ponds
The evaporation pond system has been designed to produce 3.0Mtpa of raw potash salts grading 14% K2O. These raw potash salts will be fed to the processing plant and refined into 450ktpa of finished SOP fertiliser grading 52% K2O. The concentration of potassium and other elements in the brine that enters the evaporation ponds is a critical factor in the pond design and has been based on the mine plan. As discussed above, the brine composition is predicted to change over time due to groundwater recharge by rainfall and runoff, and associated flow and transport processes. The evaporation rate is also a critical factor for the determination of the size and configuration of the evaporation ponds. Lake Mackay is ideally located within a region with a very high average evaporation rate of between 3,200 to 3,400mm per year based on Australian Bureau of Meteorology pan evaporation data.

The evaporation ponds will be located in the south-western area of La ........